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Ma, Libin, Chao Yan, and Jian Yu. "Suitability of an Artificial Viscosity Model for Compressible Under-Resolved Turbulence Using a Flux Reconstruction Method." Applied Sciences 12, no. 23 (2022): 12272. http://dx.doi.org/10.3390/app122312272.
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In the simulation of compressible turbulent flows via a high-order flux reconstruction framework, the artificial viscosity model plays an important role to ensure robustness in the strongly compressible region. However, the impact of the artificial viscosity model in under-resolved regions on dissipation features or resolving ability remains unclear. In this work, the performance of a dilation-based (DB) artificial viscosity model to simulate under-resolved turbulent flows in a high-order flux reconstruction (FR) framework is investigated. Comparison is conducted with results via several typical explicit subgrid scale (SGS) models as well as implicit large eddy simulation (iLES) and their impact on important diagnostic quantities including turbulent kinetic energy, total dissipation rate of kinetic energy, and energy spectra are discussed. The dissipation rate of kinetic energy is decomposed into several components including those resulting from explicit SGS models or Laplacian artificial viscosity model; thus, an explicit evaluation of the dissipation rate led by those modeling terms is presented. The test cases consist of the Taylor-Green vortex (TGV) problem at Re=1600, the freely decaying homogeneous isotropic turbulence (HIT) at Mat0=0.5 (the initial turbulent Mach number ), the compressible TGV at Mach number 1.25 and the compressible channel flow at Reb= 15,334 (the bulk Reynolds number based on bulk density, bulk velocity and half-height of the channel), Mach number 1.5. The first two cases show that the DB model behaves similarly to the SGS models in terms of dissipation and has the potential to improve the insufficient dissipation of iLES with the fourth-order-accurate FR method. The last two cases further demonstrate the ability of the DB method on compresssible under-resolved turbulence and/or wall-bounded turbulence. The results of this work suggest the general suitability of the DB model to simulate under-resolved compressible turbulence in the high order flux reconstruction framework and also suggest some future work on controlling the potential excessive dissipation caused by the dilation term.
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Salunkhe, Sanchit, Oumnia El Fajri, Shanti Bhushan, et al. "Validation of Tidal Stream Turbine Wake Predictions and Analysis of Wake Recovery Mechanism." Journal of Marine Science and Engineering 7, no. 10 (2019): 362. http://dx.doi.org/10.3390/jmse7100362.
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This paper documents the predictive capability of rotating blade-resolved unsteady Reynolds averaged Navier-Stokes (URANS) and Improved Delayed Detached Eddy Simulation (IDDES) computations for tidal stream turbine performance and intermediate wake characteristics. Ansys/Fluent and OpenFOAM simulations are performed using mixed-cell, unstructured grids consisting of up to 11 million cells. The thrust, power and intermediate wake predictions compare reasonably well within 10% of the experimental data. For the wake predictions, OpenFOAM performs better than Ansys/Fluent, and IDDES better than URANS when the resolved turbulence is triggered. The primary limitation of the simulations is under prediction of the wake diffusion towards the turbine axis, which in return is related to the prediction of turbulence in the tip-vortex shear layer. The shear-layer involves anisotropic turbulent structures; thus, hybrid RANS/LES models, such as IDDES, are preferred over URANS. Unfortunately, IDDES fails to accurately predict the resolved turbulence in the near-wake region due to the modeled stress depletion issue.
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Shi, Jingchang, and Hong Yan. "Turbulence amplification in the shock wave/turbulent boundary layer interaction over compression ramp by the flux reconstruction method." Physics of Fluids 35, no. 1 (2023): 016122. http://dx.doi.org/10.1063/5.0134222.
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Wall-resolved large eddy simulation on a supersonic turbulent boundary layer over a [Formula: see text] compression ramp is performed under the framework of high order discontinuous methods for a free-stream Mach number [Formula: see text] and Reynolds number [Formula: see text]. The turbulent flow is resolved by the high order flux reconstruction method, and the shock is captured by a high-resolution, but stable weighted essentially non-oscillation limiter. The solver used in this paper is validated by the double Mach reflection case and the Taylor–Green vortex case. The results of shock wave/turbulent boundary layer interaction at the ramp corner are validated by the numerical simulations and the experimental data in the literature. The analysis of the physics behind the turbulence amplification at around the ramp corner is presented. The shear effects and the flow deceleration/acceleration are the main reasons of the turbulence amplification.
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Connolly, Alex, Leendert van Veen, James Neher, Bernard J. Geurts, Jeff Mirocha, and Fotini Katopodes Chow. "Efficacy of the Cell Perturbation Method in Large-Eddy Simulations of Boundary Layer Flow over Complex Terrain." Atmosphere 12, no. 1 (2020): 55. http://dx.doi.org/10.3390/atmos12010055.
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A challenge to simulating turbulent flow in multiscale atmospheric applications is the efficient generation of resolved turbulence motions over an area of interest. One approach is to apply small perturbations to flow variables near the inflow planes of turbulence-resolving simulation domains nested within larger mesoscale domains. While this approach has been examined in numerous idealized and simple terrain cases, its efficacy in complex terrain environments has not yet been fully explored. Here, we examine the benefits of the stochastic cell perturbation method (CPM) over real complex terrain using data from the 2017 Perdigão field campaign, conducted in an approximately 2-km wide valley situated between two nearly parallel ridges. Following a typical configuration for multiscale simulation using nested domains within the Weather Research and Forecasting (WRF) model to downscale from the mesoscale to a large-eddy simulation (LES), we apply the CPM on a domain with horizontal grid spacing of 150 m. At this resolution, spurious coherent structures are often observed under unstable atmospheric conditions with moderate mean wind speeds. Results from such an intermediate resolution grid are often nested down for finer, more detailed LES, where these spurious structures adversely affect the development of turbulence on the subsequent finer grid nest. We therefore examine the impacts of the CPM on the representation of turbulence within the nested LES domain under moderate mean flow conditions in three different stability regimes: weakly convective, strongly convective, and weakly stable. In addition, two different resolutions of the underlying terrain are used to explore the role of the complex topography itself in generating turbulent structures. We demonstrate that the CPM improves the representation of turbulence within the LES domain, relative to the use of high-resolution complex terrain alone. During the convective conditions, the CPM improves the rate at which smaller-scales of turbulence form, while also accelerating the attenuation of the spurious numerically generated roll structures near the inflow boundary. During stable conditions, the coarse mesh spacing of the intermediate LES domain used herein was insufficient to maintain resolved turbulence using CPM as the flow develops downstream, highlighting the need for yet higher resolution under even weakly stable conditions, and the importance of accurate representation of flow on intermediate LES grids.
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Pinsky, Mark, and Alexander Khain. "Convective and Turbulent Motions in Nonprecipitating Cu. Part III: Characteristics of Turbulence Motions." Journal of the Atmospheric Sciences 80, no. 2 (2023): 457–71. http://dx.doi.org/10.1175/jas-d-21-0223.1.
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Abstract Velocity field in a nonprecipitating Cu under BOMEX conditions, simulated by SAM with 10-m resolution and spectral bin microphysics is separated into the convective part and the turbulent part, using a wavelet filtering. In Part II of the study properties of convective motions of this Cu were investigated. Here in Part III of the study, the parameters of cloud turbulence are calculated in the cloud updraft zone at different stages of cloud development. The main points of this study are (i) application of a fine-scale LES model of a single convective cloud allowed a direct estimation of turbulence parameters using the resolved flow in the cloud and (ii) the separation of the resolved flow into the turbulence flow and the nonturbulence flow allowed us to estimate different turbulent parameters with sufficient statistical accuracy. We calculated height and time dependences of the main turbulent parameters such as turbulence kinetic energy (TKE), spectra of TKE, dissipation rate, and the turbulent coefficient. It was found that the main source of turbulence in the cloud is buoyancy whose contribution is described by the buoyancy production term (BPT). The shear production term (SPT) increases with height and reaches its maximum near cloud top, and so does BPT. In agreement with the behavior of BPT and SPT, turbulence in the lower cloud part (below the inversion level) is weak and hardly affects the processes of mixing and entrainment. The fact that BPT is larger than SPT determines many properties of cloud turbulence. For instance, the turbulence is nonisotropic, so the vertical component of TKE is substantially larger than the horizontal components. Another consequence of the fact that BPT is larger than STP manifests itself in the finding that the turbulence spectrum largely obeys the −11/5 Bolgiano–Obukhov scaling. The classical Kolmogorov −5/3 scaling dominates for the low part of a cloud largely at the dissolving stage of cloud evolution. Using the spectra obtained we evaluated an “effective” dissipation rate which increases with height from nearly zero at cloud base up to 20 cm2 s−3 near cloud top. The coefficient of turbulent diffusion was found to increase with height and ranged from 5 m2 s−1 near cloud base to 25 m2 s−1 near cloud top. The possible role of turbulence in the process of lateral entrainment and mixing is discussed. Significance Statement 1) This study investigates the turbulent structure of Cu using a 10-m-resolution LES model with spectral bin microphysics, 2) the main source of turbulence is buoyancy, 3) turbulence in cumulus clouds (Cu) is nonisotropic, 4) turbulence reaches maximum intensity near cloud top, 5) turbulence spectrum obeys largely the −11/5 Bolgiano–Obukhov scaling, and 6) the main turbulent parameters are evaluated.
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Chen, Chang Hsin, and Diego A. Donzis. "Shock–turbulence interactions at high turbulence intensities." Journal of Fluid Mechanics 870 (May 14, 2019): 813–47. http://dx.doi.org/10.1017/jfm.2019.248.
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Shock–turbulence interactions are investigated using well-resolved direct numerical simulations (DNS) and analysis at a range of Reynolds, mean and turbulent Mach numbers ($R_{\unicode[STIX]{x1D706}}$, $M$ and $M_{t}$, respectively). The simulations are shock and turbulence resolving with $R_{\unicode[STIX]{x1D706}}$ up to 65, $M_{t}$ up to 0.54 and $M$ up to 1.4. The focus is on the effect of strong turbulence on the jumps of mean thermodynamic variables across the shock, the shock structure and the amplification of turbulence as it moves through the shock. Theoretical results under the so-called quasi-equilibrium (QE) assumption provide explicit laws for a number of statistics of interests which are in agreement with the new DNS data presented here as well as all the data available in the literature. While in previous studies turbulence was found to weaken jumps, it is shown here that stronger jumps are also observed depending on the regime of the interaction. Statistics of the dilatation at the shock are also investigated and found to be well represented by QE for weak turbulence but saturate at high turbulence intensities with a Reynolds number dependence also captured by the analysis. Finally, amplification factors are found to present a universal behaviour with two limiting asymptotic regimes governed by $(M-1)$ and $K=M_{t}/R_{\unicode[STIX]{x1D706}}^{1/2}(M-1)$, for weak and strong turbulence, respectively. Effect of anisotropy in the incoming flow is also assessed by utilizing two different forcing mechanisms to generate turbulence.
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Blake, Joshua D., Adrian Sescu, David Thompson, and Yuji Hattori. "A Coupled LES-Synthetic Turbulence Method for Jet Noise Prediction." Aerospace 9, no. 3 (2022): 171. http://dx.doi.org/10.3390/aerospace9030171.
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Large-eddy simulation (LES)-based jet noise predictions do not resolve the entire broadband noise spectra, often under-predicting high frequencies that correspond to un-resolved small-scale turbulence. The coupled LES-synthetic turbulence (CLST) model is presented which aims to model the missing high frequencies. The CLST method resolves large-scale turbulent fluctuations from coarse-grid large-eddy simulations (CLES) and models small-scale fluctuations generated by a synthetic eddy method (SEM). Noise is predicted using a formulation of the linearized Euler equations (LEE), where the acoustic waves are generated by source terms from the combined fluctuations of the CLES and the stochastic fields. Sweeping and straining of the synthetic eddies are accounted for by convecting eddies with the large turbulent scales from the CLES flow field. The near-field noise of a Mach 0.9 jet at a Reynolds number of 100,000 is predicted with LES. A high-order numerical algorithm, involving a dispersion relation preserving scheme for spatial discretization and an Adams–Bashforth scheme for time marching, is used for both LES and LEE solvers. Near-field noise spectra from the LES solver are compared to published results. Filtering is applied to the LES flow field to produce an under-resolved CLES flow field, and a comparison to the un-filtered LES spectra reveals the missing noise for this case. The CLST method recovers the filtered high-frequency content, agreeing well with the spectra from LES and showing promise at modeling the high-frequency range in the acoustic noise spectrum at a reasonable expense.
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Løken, Trygve K., David Lande-Sudall, Atle Jensen, and Jean Rabault. "Grid Turbulence Measurements with an Acoustic Doppler Current Profiler." Fluids 9, no. 3 (2024): 60. http://dx.doi.org/10.3390/fluids9030060.
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The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and it is desirable to exploit this property in laboratory and field applications. The ADCP was tested in a towing tank, where turbulence was generated from a grid towed under controlled conditions. Grid-induced turbulence is a well-studied phenomenon and a good approximation for isotropic turbulence. Several previous experiments are available for comparison and there are developed theories within the topic. In the present experiments, a Nortek Vectrino acoustic Doppler velocimeter (ADV), which is an established instrument for turbulence measurements, was applied to validate the ADCP. It was found that the mean flow measured with the ADCP was accurate within 4% of the ADV. The turbulent variance was reasonably well resolved by the ADCP when large grid bars were towed at a high speed, but largely overestimated for lower towing speed and smaller grid bars. The effective cutoff frequency and turbulent eddy size were characterized experimentally, which provides detailed guidelines for when the ADCP data can be trusted and will allow future experimentalists to decide a priori if the Nortek Signature can be used in their setup. We conclude that the ADCP is not suitable for resolving turbulent spectra in a small-scale grid-induced flow due to the intrinsic Doppler noise and the low spatial and temporal sample resolution relative to the turbulent scales.
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Mirocha, Jeff, Branko Kosović, and Gokhan Kirkil. "Resolved Turbulence Characteristics in Large-Eddy Simulations Nested within Mesoscale Simulations Using the Weather Research and Forecasting Model." Monthly Weather Review 142, no. 2 (2014): 806–31. http://dx.doi.org/10.1175/mwr-d-13-00064.1.
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Abstract One-way concurrent nesting within the Weather Research and Forecasting Model (WRF) is examined for conducting large-eddy simulations (LES) nested within mesoscale simulations. Wind speed, spectra, and resolved turbulent stresses and turbulence kinetic energy from the nested LES are compared with data from nonnested simulations using periodic lateral boundary conditions. Six different subfilter-scale (SFS) stress models are evaluated using two different nesting strategies under geostrophically forced flow over both flat and hilly terrain. Neutral and weakly convective conditions are examined. For neutral flow over flat terrain, turbulence appears on the nested LES domains only when using the two dynamic SFS stress models. The addition of small hills and valleys (wavelengths of 2.4 km and maximum slopes of ± 10°) yields small improvements, with all six models producing some turbulence on nested domains. Weak convection (surface heat fluxes of 10 W m−2) further accelerates the development of turbulence on all nested domains. However, considerable differences in key parameters are observed between the nested LES domains and their nonnested counterparts. Nesting of a finer LES within a coarser LES provides superior results to using only one nested LES domain. Adding temperature and velocity perturbations near the inlet planes of nested domains shows promise as an easy-to-implement method to accelerate turbulence generation and improve its accuracy on nested domains.
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Zhou, Bowen, and Fotini Katopodes Chow. "Large-Eddy Simulation of the Stable Boundary Layer with Explicit Filtering and Reconstruction Turbulence Modeling." Journal of the Atmospheric Sciences 68, no. 9 (2011): 2142–55. http://dx.doi.org/10.1175/2011jas3693.1.
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Abstract Large-eddy simulation (LES) of the stably stratified atmospheric boundary layer is performed using an explicit filtering and reconstruction approach with a finite difference method. Turbulent stresses are split into the resolvable subfilter-scale and subgrid-scale stresses. The former are recovered from a reconstruction approach, and the latter are represented by a dynamic eddy-viscosity model. The resulting dynamic reconstruction model (DRM) can sustain resolved turbulence with less stringent resolution requirements than conventional closure models, even under strong atmospheric stability. This is achieved by proper representation of subfilter-scale (SFS) backscatter of turbulent kinetic energy (TKE). The flow structure and turbulence statistics for the moderately stable boundary layer (SBL) are analyzed with high-resolution simulations. The DRM simulations show good agreement with established empirical formulations such as flux and gradient-based surface similarity, even at relatively coarse resolution. Similar results can be obtained with traditional closure models at the cost of higher resolution. SBL turbulence under strong stability is also explored. Simulations show an intermittent presence of elevated TKE below the low-level jet. Overall, the explicit filtering and reconstruction approach is advantageous for simulations of the SBL. At coarse resolution, it can extend the working range of LES to stronger stability, while maintaining agreement to similarity theory; at fine resolution, good agreement with theoretical formulations provides confidence in the results and allows for detailed investigation of the flow structure under moderate to strong stability conditions.
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Savelyev, Ivan, William Miller, Mark Sletten, et al. "Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East." Remote Sensing 10, no. 8 (2018): 1224. http://dx.doi.org/10.3390/rs10081224.
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This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1–14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.
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Nadarajah, S., S. Balabani, M. J. Tindal, and M. Yianneskis. "The turbulence structure of the annular non-swirling flow past an axisymmetric poppet valve." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 212, no. 6 (1998): 455–71. http://dx.doi.org/10.1243/0954406981521367.
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This paper describes an experimental investigation of the non-swirling flow through an axisymmetric port and poppet valve assembly under steady flow conditions using laser Doppler anemometry. The three velocity components and the associated Reynolds stresses were measured by ensemble-averaged techniques and the turbulence kinetic energy and its production rate were determined. Time-resolved measurements were also taken in order to determine turbulence time and length scales and the dissipation rate of the turbulence kinetic energy. The Reynolds number, based on the minimum cross-sectional area of the port, was 25000. The flow is characterized by an annular jet which forms two vortices, one on either side of the jet. A jet flapping instability is also evident since the skewness and kurtosis of the velocity probability distribution function depart from the Gaussian form. This instability causes an intermittent mixing between eddies in the jet region and the vortices which introduces a non-turbulent contribution to the measured quantities. The production rates of the turbulence kinetic energy were found to be negative in some regions of the flow, indicating counter-gradient transport of momentum by turbulence; according to the coherent structures approach, the distribution of the Reynolds shear stresses and the length scales in these regions imply possible changes in the orientation of eddies.
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Jovičić, N., M. Breuer, and J. Jovanović. "Anisotropy-Invariant Mapping of Turbulence in a Flow Past an Unswept Airfoil at High Angle of Attack." Journal of Fluids Engineering 128, no. 3 (2005): 559–67. http://dx.doi.org/10.1115/1.2175162.
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Turbulence investigations of the flow past an unswept wing at a high angle of attack are reported. Detailed predictions were carried out using large-eddy simulations (LES) with very fine grids in the vicinity of the wall in order to resolve the near-wall structures. Since only a well-resolved LES ensures reliable results and hence allows a detailed analysis of turbulence, the Reynolds number investigated was restricted to Rec=105 based on the chord length c. Admittedly, under real flight conditions Rec is considerably higher (about (35-40)∙106). However, in combination with the inclination angle of attack α=18 deg this Rec value guarantees a practically relevant flow behavior, i.e., the flow exhibits a trailing-edge separation including some interesting flow phenomena such as a thin separation bubble, transition, separation of the turbulent boundary layer, and large-scale vortical structures in the wake. Due to the fine grid resolution applied, the aforementioned flow features are predicted in detail. Thus, reliable results are obtained which form the basis for advanced turbulence analysis. In order to provide a deeper insight into the nature of turbulence, the flow was analyzed using the invariant theory of turbulence by Lumley and Newman (J. Fluid Mech., 82, 161–178, 1977). Therefore, the anisotropy of various portions of the flow was extracted and displayed in the invariant map. This allowed us to examine the state of turbulence in distinct regions and provided an improved illustration of what happens in the turbulent flow. Thus, turbulence itself and the way in which it develops were extensively investigated, leading to an improved understanding of the physical mechanisms involved, not restricted to a standard test case such as channel flow but for a realistic, practically relevant flow problem at a moderate Reynolds number.
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Spessa, E. "A Contribution to the Analysis of Turbulence Anisotropy and Nonhomogeneity in an Open-Chamber Diesel Engine." Journal of Engineering for Gas Turbines and Power 121, no. 2 (1999): 226–34. http://dx.doi.org/10.1115/1.2817110.
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Further investigation of the turbulence time-frequency spectral structure and its anisotropy and nonhomogeneity has been carried out in the combustion chamber of an automotive diesel engine with a high-squish reentrant in-piston-bowl and a helical intake port. An advanced HWA technique was applied for turbulence measurements along the injector axis, under motored engine conditions in the speed range of 600–3000 rpm. Autospectral density functions of each fluctuating velocity component, as was determined by a specific sensor-wire orientation, were evaluated in consecutive crank-angle correlation intervals during the induction, compression, and early expansion strokes. In order to study the speed dependence of the turbulence-structure anisotropy and nonhomogeneity in different portions of the engine cycle, time-scales of cycle-resolved and conventional turbulent fluctuations were analyzed as functions of the engine speed for different wire orientations, measurement locations, and correlation intervals. Anisotropy and nonhomogeneity were generally significant at low engine speeds, whereas a tendency towards isotropy and homogeneity was found by increasing the speed. With specific reference to the bowl-generated turbulence, spectral anisotropy was remarkable at all speeds in the reverse-squish flow, close to the cylinder-head wall. However, spectral nonhomogeneity was the main feature of the direct-squish flow at low engine speeds.
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Moura, Rodrigo C., Andrea Cassinelli, André F. C. da Silva, Erik Burman, and Spencer J. Sherwin. "Gradient jump penalty stabilisation of spectral/hp element discretisation for under-resolved turbulence simulations." Computer Methods in Applied Mechanics and Engineering 388 (January 2022): 114200. http://dx.doi.org/10.1016/j.cma.2021.114200.
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Zhou, Yong, James G. Brasseur, and Anurag Juneja. "A resolvable subfilter-scale model specific to large-eddy simulation of under-resolved turbulence." Physics of Fluids 13, no. 9 (2001): 2602–10. http://dx.doi.org/10.1063/1.1388053.
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Shi, Xiaoming, Hannah L. Hagen, Fotini Katopodes Chow, George H. Bryan, and Robert L. Street. "Large-Eddy Simulation of the Stratocumulus-Capped Boundary Layer with Explicit Filtering and Reconstruction Turbulence Modeling." Journal of the Atmospheric Sciences 75, no. 2 (2018): 611–37. http://dx.doi.org/10.1175/jas-d-17-0162.1.
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Abstract Large-eddy simulation (LES) has been an essential tool in the development of theory and parameterizations for clouds, but when applied to stratocumulus clouds under sharp temperature inversions, many LES models produce an unrealistically thin cloud layer and a decoupled boundary layer structure. Here, explicit filtering and reconstruction are used for simulation of stratocumulus clouds observed during the first research flight (RF01) of the Second Dynamics and Chemistry of the Marine Stratocumulus field study (DYCOMS II). The dynamic reconstruction model (DRM) is used within an explicit filtering and reconstruction framework, partitioning subfilter-scale motions into resolvable subfilter scales (RSFSs) and unresolvable subgrid scales (SGSs). The former are reconstructed, and the latter are modeled. Differing from traditional turbulence models, the reconstructed RSFS stress/fluxes can produce backscatter of turbulence kinetic energy (TKE) and, importantly, turbulence potential energy (TPE). The modeled backscatter reduces entrainment at the cloud top and, meanwhile, strengthens resolved turbulence through preserving TKE and TPE, resulting in a realistic boundary layer with an adequate amount of cloud water and vertically coupled turbulent eddies. Additional simulations are performed in the terra incognita, when the grid spacing of a simulation becomes comparable to the size of the most energetic eddies. With 20-m vertical and 1-km horizontal grid spacings, simulations using DRM provide a reasonable representation of bulk properties of the stratocumulus-capped boundary layer.
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BOU-ZEID, ELIE, CHAD HIGGINS, HENDRIK HUWALD, CHARLES MENEVEAU, and MARC B. PARLANGE. "Field study of the dynamics and modelling of subgrid-scale turbulence in a stable atmospheric surface layer over a glacier." Journal of Fluid Mechanics 665 (November 10, 2010): 480–515. http://dx.doi.org/10.1017/s0022112010004015.
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A field experiment – the Snow Horizontal Array Turbulence Study (SnoHATS) – has been performed over an extensive glacier in Switzerland in order to study small-scale turbulence in the stable atmospheric surface layer, and to investigate the role, dynamics and modelling of the subgrid scales (SGSs) in the context of large-eddy simulations. Thea prioridata analysis aims at comparing the role and behaviour of the SGSs under stable conditions with previous studies under neutral or unstable conditions. It is found that the SGSs in a stable surface layer remain an important sink of temperature variance and turbulent kinetic energy from the resolved scales and carry a significant portion of the fluxes when the filter scale is larger than the distance to the wall. The fraction of SGS fluxes (out of the total fluxes) is found to be independent of stability. In addition, the stress–strain alignment is similar to the alignment under neutral and unstable conditions. The model coefficients vary considerably with stability but in a manner consistent with previous findings, which also showed that scale-dependent dynamic models can capture this variation. Furthermore, the variation of the coefficients for both momentum and heat SGS fluxes can be shown to be better explained by stability parameters based on vertical gradients, rather than vertical fluxes. These findings suggest that small-scale turbulence dynamics and SGS modelling under stable conditions share many important properties with neutral and convective conditions, and that a unified approach is thus possible. This paper concludes with a discussion of some other challenges for stable boundary-layer simulations that are not encountered in the neutral or unstable cases.
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Wilson, Richard, Clara Pitois, Aurélien Podglajen, Albert Hertzog, Milena Corcos, and Riwal Plougonven. "Detection of turbulence occurrences from temperature, pressure, and position measurements under superpressure balloons." Atmospheric Measurement Techniques 16, no. 2 (2023): 311–30. http://dx.doi.org/10.5194/amt-16-311-2023.
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Abstract. This article deals with the detection of small-scale turbulence from in situ meteorological measurements performed under superpressure balloons (SPBs). These balloons allow long-duration flights (several months) at a prerequisite height level. The data set is gathered from the Strateole-2 probationary campaign during which eights SPBs flew in the tropical tropopause layer at altitudes of around 19 and 20.5 km from November 2019 to March 2020. Turbulence is not directly measured by the instrument set onboard the SPBs. Nonetheless, there is the potential to derive information about the occurrence of turbulence from the temporally well-resolved measurements of pressure, temperature, and position. It constitutes a challenge to extract the aforementioned information from a measurement set that was not designed for quantifying turbulence, and the paper explains the methodology developed to overcome this difficulty. It is observed that SPBs oscillate quasi-periodically around their equilibrium positions. The oscillation periods, which are 220 s on average with a range of 130 to 500 s, are close to but noticeably smaller than the Brunt–Väisälä period (∼300 s). The amplitude of these vertical motions is ∼±15 m, inducing large fluctuations in all quantities, whether measured (e.g., pressure, temperature and position) or inferred (e.g., density and potential temperature). The relationships between the changes in these quantities and the vertical displacements of the balloons are used to infer properties of the flow in which the SPBs drift. In the case of active turbulence, the vertical stratification as well as the wind shear are likely to be reduced by mixing. Hence, the increments of potential temperature, δθ, and of the vertical displacements of the balloon, δzB, are expected to be uncorrelated because ∂θ/∂z→0. Moreover, the local vertical gradients of measured quantities, temperature (T) and horizontal velocities (u and v), are estimated from the covariance of the increments of the considered quantity with δzB. The Richardson number of the flow is deduced. Several binary indexes (true or false) to describe the state of the flow, laminar or turbulent, are evaluated. These turbulence indexes, based either on correlations between δθ and δzB or on estimates of the local Richardson number, are found to be consistent, as they differ in less than 3 % of cases. The flow is observed to be turbulent for about 5 % of the time, with strong inhomogeneities along the longitude.
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FURUKAWA, JUNICHI, YOSHIKI NOGUCHI, TOSHISUKE HIRANO, and FORMAN A. WILLIAMS. "Anisotropic enhancement of turbulence in large-scale, low-intensity turbulent premixed propane–air flames." Journal of Fluid Mechanics 462 (July 10, 2002): 209–43. http://dx.doi.org/10.1017/s0022112002008650.
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The density change across premixed flames propagating in turbulent flows modifies the turbulence. The nature of that modification depends on the regime of turbulent combustion, the burner design, the orientation of the turbulent flame and the position within the flame. The present study addresses statistically stationary turbulent combustion in the flame-sheet regime, in which the laminar-flame thickness is less than the Kolmogorov scale, for flames stabilized on a vertically oriented cylindrical burner having fully developed upward turbulent pipe flow upstream from the exit. Under these conditions, rapidly moving wrinkled laminar flamelets form the axisymmetric turbulent flame brush that is attached to the burner exit. Predictions have been made of changes in turbulence properties across laminar flamelets in such situations, but very few measurements have been performed to test the predictions. The present work measures individual velocity changes and changes in turbulence across flamelets at different positions in the turbulent flame brush for three different equivalence ratios, for comparison with theory.The measurements employ a three-element electrostatic probe (EP) and a two-component laser-Doppler velocimeter (LDV). The LDV measures axial and radial components of the local gas velocity, while the EP, whose three sensors are located in a vertical plane that passes through the burner axis, containing the plane of the LDV velocity components, measures arrival times of flamelets at three points in that plane. From the arrival times, the projection of flamelet orientation and velocity on the plane are obtained. All of the EP and LDV sensors are located within a fixed volume element of about 1 mm diameter to provide local, time-resolved information. The technique has the EP advantages of rapid response and good sensitivity and the EP disadvantages of intrusiveness and complexity of interpretation, but it is well suited to the type of data sought here.Theory predicts that the component of velocity tangent to the surface of a locally planar flamelet remains constant in passing through the flamelet. The data are consistent with this prediction, within the accuracy of the measurement. The data also indicate that the component of velocity normal to the flamelet, measured with respect to the flamelet, tends to increase in passing through the flamelet, as expected. The flamelets thereby can generate anisotropy in initially isotropic turbulence. They also produce differences in turbulent spectra conditioned on unburnt or burnt gas. Local modifications of turbulence by flamelets thus are demonstrated experimentally. The modifications are quantitatively different at different locations in the turbulent flame brush but qualitatively similar in that the turbulence is enhanced more strongly in the radial direction than in the axial direction at all positions in these flames.
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Kadasch, Eckhard, Matthias Sühring, Tobias Gronemeier, and Siegfried Raasch. "Mesoscale nesting interface of the PALM model system 6.0." Geoscientific Model Development 14, no. 9 (2021): 5435–65. http://dx.doi.org/10.5194/gmd-14-5435-2021.
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Abstract. In this paper, we present a newly developed mesoscale nesting interface for the PALM model system 6.0, which enables PALM to simulate the atmospheric boundary layer under spatially heterogeneous and non-stationary synoptic conditions. The implemented nesting interface, which is currently tailored to the mesoscale model COSMO, consists of two major parts: (i) the preprocessor INIFOR (initialization and forcing), which provides initial and time-dependent boundary conditions from mesoscale model output, and (ii) PALM's internal routines for reading the provided forcing data and superimposing synthetic turbulence to accelerate the transition to a fully developed turbulent atmospheric boundary layer. We describe in detail the conversion between the sets of prognostic variables, transformations between model coordinate systems, as well as data interpolation onto PALM's grid, which are carried out by INIFOR. Furthermore, we describe PALM's internal usage of the provided forcing data, which, besides the temporal interpolation of boundary conditions and removal of any residual divergence, includes the generation of stability-dependent synthetic turbulence at the inflow boundaries in order to accelerate the transition from the turbulence-free mesoscale solution to a resolved turbulent flow. We demonstrate and evaluate the nesting interface by means of a semi-idealized benchmark case. We carried out a large-eddy simulation (LES) of an evolving convective boundary layer on a clear-sky spring day. Besides verifying that changes in the inflow conditions enter into and successively propagate through the PALM domain, we focus our analysis on the effectiveness of the synthetic turbulence generation. By analysing various turbulence statistics, we show that the inflow in the present case is fully adjusted after having propagated for about two to three eddy-turnover times downstream, which corresponds well to other state-of-the-art methods for turbulence generation. Furthermore, we observe that numerical artefacts in the form of grid-scale convective structures in the mesoscale model enter the PALM domain, biasing the location of the turbulent up- and downdrafts in the LES. With these findings presented, we aim to verify the mesoscale nesting approach implemented in PALM, point out specific shortcomings, and build a baseline for future improvements and developments.
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Ding, Aoshuang, Xiaodong Ren, Xuesong Li, and Chunwei Gu. "Numerical Investigation of Turbulence Models for a Superlaminar Journal Bearing." Advances in Tribology 2018 (2018): 1–14. http://dx.doi.org/10.1155/2018/2841303.
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With rotating machineries working at high speeds, oil flow in bearings becomes superlaminar. Under superlaminar conditions, flow exhibits between laminar and fully developed turbulence. In this study, superlaminar oil flow in an oil-lubricated tilting-pad journal bearing is analyzed through computational fluid dynamics (CFD). A three-dimensional bearing model is established. CFD results from the laminar model and 14 turbulence models are compared with experimental findings. The laminar simulation results of pad-side pressure are inconsistent with the experimental data. Thus, the turbulence effects on superlaminar flow should be considered. The simulated temperature and pressure distributions from the classical fully developed turbulence models cannot correctly fit the experimental data. As such, turbulence models should be corrected for superlaminar flow. However, several corrections, such as transition correction, are unsuitable. Among all the flow models, the SST model with low-Re correction exhibits the best pressure distribution and turbulence viscosity ratio. Velocity profile analysis confirms that a buffer layer plays an important role in the superlaminar boundary layer. Classical fully developed turbulence models cannot accurately predict the buffer layer, but this problem can be resolved by initiating an appropriate low-Re correction. Therefore, the SST model with low-Re correction yields suitable results for superlaminar flows in bearings.
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Peng, Cheng, Orlando M. Ayala, and Lian-Ping Wang. "A direct numerical investigation of two-way interactions in a particle-laden turbulent channel flow." Journal of Fluid Mechanics 875 (July 26, 2019): 1096–144. http://dx.doi.org/10.1017/jfm.2019.509.
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Understanding the two-way interactions between finite-size solid particles and a wall-bounded turbulent flow is crucial in a variety of natural and engineering applications. Previous experimental measurements and particle-resolved direct numerical simulations revealed some interesting phenomena related to particle distribution and turbulence modulation, but their in-depth analyses are largely missing. In this study, turbulent channel flows laden with neutrally buoyant finite-size spherical particles are simulated using the lattice Boltzmann method. Two particle sizes are considered, with diameters equal to 14.45 and 28.9 wall units. To understand the roles played by the particle rotation, two additional simulations with the same particle sizes but no particle rotation are also presented for comparison. Particles of both sizes are found to form clusters. Under the Stokes lubrication corrections, small particles are found to have a stronger preference to form clusters, and their clusters orientate more in the streamwise direction. As a result, small particles reduce the mean flow velocity less than large particles. Particles are also found to result in a more homogeneous distribution of turbulent kinetic energy (TKE) in the wall-normal direction, as well as a more isotropic distribution of TKE among different spatial directions. To understand these turbulence modulation phenomena, we analyse in detail the total and component-wise volume-averaged budget equations of TKE with the simulation data. This budget analysis reveals several mechanisms through which the particles modulate local and global TKE in the particle-laden turbulent channel flow.
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Fukami, Kai, Koji Fukagata, and Kunihiko Taira. "Super-resolution reconstruction of turbulent flows with machine learning." Journal of Fluid Mechanics 870 (May 7, 2019): 106–20. http://dx.doi.org/10.1017/jfm.2019.238.
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We use machine learning to perform super-resolution analysis of grossly under-resolved turbulent flow field data to reconstruct the high-resolution flow field. Two machine learning models are developed, namely, the convolutional neural network (CNN) and the hybrid downsampled skip-connection/multi-scale (DSC/MS) models. These machine learning models are applied to a two-dimensional cylinder wake as a preliminary test and show remarkable ability to reconstruct laminar flow from low-resolution flow field data. We further assess the performance of these models for two-dimensional homogeneous turbulence. The CNN and DSC/MS models are found to reconstruct turbulent flows from extremely coarse flow field images with remarkable accuracy. For the turbulent flow problem, the machine-leaning-based super-resolution analysis can greatly enhance the spatial resolution with as little as 50 training snapshot data, holding great potential to reveal subgrid-scale physics of complex turbulent flows. With the growing availability of flow field data from high-fidelity simulations and experiments, the present approach motivates the development of effective super-resolution models for a variety of fluid flows.
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Casper, Katya M., Steven J. Beresh, and Steven P. Schneider. "Pressure fluctuations beneath instability wavepackets and turbulent spots in a hypersonic boundary layer." Journal of Fluid Mechanics 756 (September 9, 2014): 1058–91. http://dx.doi.org/10.1017/jfm.2014.475.
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AbstractTo investigate the pressure-fluctuation field beneath turbulent spots in a hypersonic boundary layer, a study was conducted on the nozzle wall of the Boeing/AFOSR Mach-6 Quiet Tunnel. Controlled disturbances were created by pulsed-glow perturbations based on the electrical breakdown of air. Under quiet-flow conditions, the nozzle-wall boundary layer remains laminar and grows very thick over the long nozzle length. This allows the development of large disturbances that can be well-resolved with high-frequency pressure transducers. A disturbance first grows into a second-mode instability wavepacket that is concentrated near its own centreline. Weaker disturbances are seen spreading from the centre. The waves grow and become nonlinear before breaking down to turbulence. The breakdown begins in the core of the packets where the wave amplitudes are largest. Second-mode waves are still evident in front of and behind the breakdown point and can be seen propagating in the spanwise direction. The turbulent core grows downstream, resulting in a spot with a classical arrowhead shape. Behind the spot, a low-pressure calmed region develops. However, the spot is not merely a localized patch of turbulence; instability waves remain an integral part. Limited measurements of naturally occurring disturbances show many similar characteristics. From the controlled disturbance measurements, the convection velocity, spanwise spreading angle, and typical pressure-fluctuation field were obtained.
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Wu 吴, Yinhao 寅昊. "Asymmetry, Gap Opening, and a High Accretion Rate on DM Tau: A Hypothesis Based on the Interaction of Magnetized Disk Wind with Planets." Astrophysical Journal 970, no. 1 (2024): 25. http://dx.doi.org/10.3847/1538-4357/ad5553.
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Abstract Over 200 protoplanetary disk systems have been resolved by the Atacama Large Millimeter/submillimeter Array (ALMA), and the vast majority suggest the presence of planets. The dust gaps in transition disks are considered evidence of giant planets sculpting gas and dust under appropriate disk viscosity. However, the unusually high accretion rates in many T Tauri stars hosting transition disks challenge this theory. As the only disk currently observed with high turbulence, the high accretion rate (∼10−8.3 M ⊙ yr−1) observed in DM Tau indicates the presence of strong turbulence within the system. Considering the recent theoretical advancements in magnetized disk winds are challenging the traditional gap-opening theories and viscosity-driven accretion models, our study presents a pioneering simulation incorporating a simplified magnetized disk wind model to explain the observed features in DM Tau. Employing multifluid simulations with an embedded medium mass planet, we successfully replicate the gap formation and asymmetric structures evident in ALMA Band 6 and the recent Karl G. Jansky Very Large Array 7 mm observations. Our results suggest that when magnetized disk wind dominates the accretion mode of the system, it is entirely possible for a planet with a medium mass to exist within the gap inside 20 au of DM Tau. This means that DM Tau may not be as turbulent as imagined. However, viscosity within the disk should also contribute a little turbulence to maintain disk stability.
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Jordan, Stephen A. "Dynamic Subgrid-Scale Modeling for Large-Eddy Simulations in Complex Topologies." Journal of Fluids Engineering 123, no. 3 (2001): 619–27. http://dx.doi.org/10.1115/1.1374215.
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The dynamic eddy-viscosity relationship is a suitable choice for modeling the subgrid-scales (SGS) in a large-eddy simulation (LES) of complex turbulent flows in irregular domains. This algebraic relationship is easy to implement and its dynamic coefficient will give negligible turbulent viscosity contributions in the flow regions that are irrotational or laminar. Its fine-scale turbulence predictions can be qualitatively reasonable if the local grid resolution maintains the SGS field predominantly within the equilibrium range of turbulent energy spectra. This performance is given herein by two curvilinear coordinate forms of the dynamic Smagorinsky model that are formally derived and a-priori tested using the resolved physics of the cylinder wake. The conservative form evaluates the dynamic coefficient in the computational (transformed) space whereas its non-conservative counterpart operates in the physical domain. Although both forms equally captured the real normal SGS stress reasonably well, the real shear stress and dissipation rates were severely under-predicted. Mixing the eddy-viscosity choice with a scale-similarity model can ease this latter deficiency.
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Catania, A. E., and A. Mittica. "Induction System Effects on Small-Scale Turbulence in a High-Speed Diesel Engine." Journal of Engineering for Gas Turbines and Power 109, no. 4 (1987): 491–502. http://dx.doi.org/10.1115/1.3240069.
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The influence of the induction system on small-scale turbulence in a high-speed, automotive diesel engine was investigated under variable swirl conditions. The induction system was made up of two equiverse swirl tangential ducts, and valves of the same size and lift. Variable swirl conditions were obtained by keeping one of the inlet valves either closed or functioning, and by changing engine speed. The investigation was carried out for two induction system configurations: with both ducts operating and with only one of them operating. Two different engine speeds were considered, one relatively low (1600 rpm) and the other quite high (3000 rpm), the latter being the highest speed at which engine turbulence has been measured up to now. Cycle-resolved hot-wire anemometry measurements of air velocity were performed throughout the induction and compression strokes, under motored conditions, along a radial direction at an axial level that was virtually in the middle of the combustion chamber at top dead center. The velocity data were analyzed using the nonstationary time-averaging procedure previously developed by the authors. Correlation and spectral analysis of the small-scale turbulence so determined was also performed. The turbulence intensity and its degree of nonhomogeneity and anisotropy were sensibly influenced by the variable swirl conditions, depending on both the intake system configuration and engine speed; they generally showed an increase with increasing swirl intensity, at the end of the compression stroke. A similar trend was observed in the cyclic fluctuation of both the mean velocity and turbulence intensity. The micro time scale of turbulence was found to be almost uniform during induction and compression, showing a slight dependence on the measurement point and on the intake system configuration, but a more sensible dependence on the engine speed. No effect of the cylinder wall on turbulence was apparent.
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Jordan, Stephen A. "A Priori Assessments of Numerical Uncertainty in Large-Eddy Simulations." Journal of Fluids Engineering 127, no. 6 (2005): 1171–82. http://dx.doi.org/10.1115/1.2060735.
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Current suggestions for estimating the numerical uncertainty in solutions by the Large-Eddy Simulation (LES) methodology require either a posteriori input or reflect global assessments. In most practical applications, this approach is rather costly for the user and especially time consuming due to the CPU effort needed to reach the statistical steady state. Herein, we demonstrate two alternate a priori graphical exercises. An evaluation of the numerical uncertainty uses the turbulent quantities given by the area under the wave number spectra profiles. These profiles are easily constructed along any grid line in the flow domain prior to the collection of the turbulent statistics. One exercise involves a completion of the spectrum profile beyond the cutoff wave number to the inverse of Kolmorgorov’s length scale by a model of isotropic turbulence. The other extends Richardson Extrapolation acting on multiple solutions. Sample test cases of both LES solutions and direct numerical simulations as well as published experimental data show excellent agreement between the integrated matched spectra and the respective turbulent statistics. Thus, the resultant uncertainties themselves provide a useful measure of accumulated statistical error in the resolved turbulent properties.
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Winters, Andrew R., Rodrigo C. Moura, Gianmarco Mengaldo, et al. "A comparative study on polynomial dealiasing and split form discontinuous Galerkin schemes for under-resolved turbulence computations." Journal of Computational Physics 372 (November 2018): 1–21. http://dx.doi.org/10.1016/j.jcp.2018.06.016.
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Wang, X., L. Zhang, and M. D. Moran. "On the discrepancies between theoretical and measured below-cloud particle scavenging coefficients for rain – a numerical study." Atmospheric Chemistry and Physics Discussions 11, no. 7 (2011): 20375–87. http://dx.doi.org/10.5194/acpd-11-20375-2011.
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Abstract. Existing theoretical formulations for size-resolved scavenging coefficient Λ (r) for atmospheric aerosol particles scavenged by rain predict values lower by one to two orders of magnitude than those estimated from field measurements of particle-concentration changes for particles smaller than 3 μm in diameter. Vertical turbulence does not influence the theoretical formulation of Λ (r), but contributed to the field-generated Λ (r) due to its influence on the overall concentration changes of aerosol particles in the layers undergoing impaction scavenging. A detailed one-dimensional cloud microphysics model is used to simulate rain production and below-cloud particle scavenging, and to quantify the contribution of turbulent diffusion to the overall Λ (r) generated from concentration changes. The relative contribution of vertical diffusion to below-cloud scavenging is found to be largest for submicron particles under weak precipitation conditions. The discrepancies between theoretical and field Λ (r) values can largely be explained by the contribution of vertical diffusion for all particles larger than 0.01 μm in diameter for which field data were available. The results presented here suggest that the current theoretical framework for Λ (r) can provide a reasonable approximation of below-cloud aerosol particle scavenging by rain in size-resolved aerosol transport models if vertical diffusion is also considered.
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Kumar, Praveen, and Krishnan Mahesh. "Large-eddy simulation of flow over an axisymmetric body of revolution." Journal of Fluid Mechanics 853 (August 23, 2018): 537–63. http://dx.doi.org/10.1017/jfm.2018.585.
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Wall-resolved large-eddy simulation (LES) is used to simulate flow over an axisymmetric body of revolution at a Reynolds number, $Re=1.1\times 10^{6}$, based on the free-stream velocity and the length of the body. The geometry used in the present work is an idealized submarine hull (DARPA SUBOFF without appendages) at zero angle of pitch and yaw. The computational domain is chosen to avoid confinement effects and capture the wake up to fifteen diameters downstream of the body. The unstructured computational grid is designed to capture the fine near-wall flow structures as well as the wake evolution. LES results show good agreement with the available experimental data. The axisymmetric turbulent boundary layer has higher skin friction and higher radial decay of turbulence away from the wall, compared to a planar turbulent boundary layer under similar conditions. The mean streamwise velocity exhibits self-similarity, but the turbulent intensities are not self-similar over the length of the simulated wake, consistent with previous studies reported in the literature. The axisymmetric wake shifts from high-$Re$ to low-$Re$ equilibrium self-similar solutions, which were only observed for axisymmetric wakes of bluff bodies in the past.
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Xiao, Heng, Jian-Xun Wang, and Patrick Jenny. "An Implicitly Consistent Formulation of a Dual-Mesh Hybrid LES/RANS Method." Communications in Computational Physics 21, no. 2 (2017): 570–99. http://dx.doi.org/10.4208/cicp.220715.150416a.
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AbstractA consistent dual-mesh hybrid LES/RANS framework for turbulence modeling has been proposed recently (H. Xiao, P. Jenny, A consistent dual-mesh framework for hybrid LES/RANS modeling, J. Comput. Phys. 231 (4) (2012)). To better enforce componentwise Reynolds stress consistency between the LES and the RANS simulations, in the present work the original hybrid framework is modified to better exploit the advantage of more advanced RANS turbulence models. In the new formulation, the turbulent stresses in the filtered equations in the under-resolved regions are directly corrected based on the Reynolds stresses provided by the RANS simulation. More precisely, the new strategy leads to implicit LES/RANS consistency, where the velocity consistency is achieved indirectly via imposing consistency on the Reynolds stresses. This is in contrast to the explicit consistency enforcement in the original formulation, where forcing terms are added to the filtered momentum equations to achieve directly the desired average velocity and velocity fluctuations. The new formulation keeps the averaging procedure for the filtered quantities and at the same time preserves the ability of the original formulation to conform with the physical differences between LES and RANS quantities. The modified formulation is presented, analyzed, and then evaluated for plane channel flow and flow over periodic hills. Improved predictions are obtained compared with the results obtained using the original formulation.
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Solán-Fustero, P., A. Navas-Montilla, E. Ferrer, J. Manzanero, and P. García-Navarro. "Application of approximate dispersion-diffusion analyses to under-resolved Burgers turbulence using high resolution WENO and UWC schemes." Journal of Computational Physics 435 (June 2021): 110246. http://dx.doi.org/10.1016/j.jcp.2021.110246.
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Kim, Yusik, Helge Aa Madsen, Maria Aparicio-Sanchez, Georg Pirrung, and Thorsten Lutz. "Assessment of blade element momentum codes under varying turbulence levels by comparing with blade resolved computational fluid dynamics." Renewable Energy 160 (November 2020): 788–802. http://dx.doi.org/10.1016/j.renene.2020.06.006.
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Wang, Lai, Matthias K. Gobbert, and Meilin Yu. "A dynamically load-balanced parallel p-adaptive implicit high-order flux reconstruction method for under-resolved turbulence simulation." Journal of Computational Physics 417 (September 2020): 109581. http://dx.doi.org/10.1016/j.jcp.2020.109581.
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Moura, R. C., S. J. Sherwin, and J. Peiró. "Linear dispersion–diffusion analysis and its application to under-resolved turbulence simulations using discontinuous Galerkin spectral/hp methods." Journal of Computational Physics 298 (October 2015): 695–710. http://dx.doi.org/10.1016/j.jcp.2015.06.020.
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Deng, Bing-Qing, Zixuan Yang, Anqing Xuan, and Lian Shen. "Influence of Langmuir circulations on turbulence in the bottom boundary layer of shallow water." Journal of Fluid Mechanics 861 (December 19, 2018): 275–308. http://dx.doi.org/10.1017/jfm.2018.883.
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Langmuir circulations (LCs) generated by the interaction between wind-driven currents and surface waves can engulf the whole water column in neutrally stratified shallow water and interact with the turbulence in the bottom boundary layer. In this study, we perform a mechanistic study using wall-resolved large-eddy simulations (LES) based on the Craik–Leibovich equations to investigate the effects of LCs on turbulence statistics in the bottom half of shallow water. The highest Reynolds number considered in this paper, $Re_{\unicode[STIX]{x1D70F}}=1000$, is larger than the values considered in wall-resolved LES studies of shallow-water Langmuir turbulence reported in literature. The logarithmic layer is diagnosed based on a plateau region in the profile of a diagnostic function. It is found that the logarithmic layer disrupted at $Re_{\unicode[STIX]{x1D70F}}=395$ reappears at $Re_{\unicode[STIX]{x1D70F}}=1000$, but the von Kármán constant is slightly different from the traditional value $0.41$. To study the effects of LCs on turbulence statistics, LCs are extracted using streamwise averaging. The velocity fluctuations $u_{i}^{\prime }$ are decomposed into a LC-coherent part $u_{i}^{L}$ and a residual turbulence part $u_{i}^{T}$. It is found that the profiles of LC-coherent Reynolds shear stress $-\langle u^{L}v^{L}\rangle$ obtained at various Reynolds numbers are close to each other in the water-column coordinate $y/h$, with $h$ being the half-water depth. As the Reynolds number (or, by definition, the ratio between the outer and inner length scales) increases, the influence of LCs on the near-bottom momentum transfer is reduced, which is responsible for the reappearance of the logarithmic layer. At all of the Reynolds numbers under investigation, the peaks of $\langle u^{L}u^{L}\rangle$ are collocated in the water-column coordinate $y/h$, while those of $\langle u^{T}u^{T}\rangle$ are collocated in the inner-scale coordinate $y/(\unicode[STIX]{x1D708}/u_{\unicode[STIX]{x1D70F}})$. Due to the increase in the distance between the peaks of $\langle u^{L}u^{L}\rangle$ and $\langle u^{T}u^{T}\rangle$ with the Reynolds number, the profile of $\langle u^{\prime }u^{\prime }\rangle$ forms a bimodal shape at $Re_{\unicode[STIX]{x1D70F}}=700$ and $1000$.
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Mehrabadi, M., J. A. K. Horwitz, S. Subramaniam, and A. Mani. "A direct comparison of particle-resolved and point-particle methods in decaying turbulence." Journal of Fluid Mechanics 850 (July 4, 2018): 336–69. http://dx.doi.org/10.1017/jfm.2018.442.
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We use particle-resolved direct numerical simulation (PR-DNS) as a model-free physics-based numerical approach to validate particle acceleration modelling in gas-solid suspensions. To isolate the effect of the particle acceleration model, we focus on point-particle direct numerical simulation (PP-DNS) of a collision-free dilute suspension with solid-phase volume fraction $\unicode[STIX]{x1D719}=0.001$ in a decaying isotropic turbulent particle-laden flow. The particle diameter $d_{p}$ in the suspension is chosen to be the same as the initial Kolmogorov length scale $\unicode[STIX]{x1D702}_{0}$ ($d_{p}/\unicode[STIX]{x1D702}_{0}=1$) in order to overlap with the regime where PP-DNS is valid. We assess the point-particle acceleration model for two different particle Stokes numbers, $St_{\unicode[STIX]{x1D702}}=1$ and 100. For the high Stokes number case, the Stokes drag model for particle acceleration under-predicts the true particle acceleration. In addition, second moment quantities which play key roles in the physical evolution of the gas–solid suspension are not correctly captured. Considering finite Reynolds number corrections to the acceleration model improves the prediction of the particle acceleration probability density function and second moment statistics of the point-particle model compared with the particle-resolved simulation. We also find that accounting for the undisturbed fluid velocity in the acceleration model can be of greater importance than using the most appropriate acceleration model for a given physical problem.
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Wang, X., L. Zhang, and M. D. Moran. "On the discrepancies between theoretical and measured below-cloud particle scavenging coefficients for rain – a numerical investigation using a detailed one-dimensional cloud microphysics model." Atmospheric Chemistry and Physics 11, no. 22 (2011): 11859–66. http://dx.doi.org/10.5194/acp-11-11859-2011.
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Abstract. Existing theoretical formulations for the size-resolved scavenging coefficient Λ(d) for atmospheric aerosol particles scavenged by rain predict values lower by one to two orders of magnitude than those estimated from field measurements of particle-concentration changes for particles smaller than 3 μm in diameter. Vertical turbulence is not accounted for in the theoretical formulations of Λ(d) but does contribute to the field-derived estimates of Λ(d) due to its influence on the overall concentration changes of aerosol particles in the layers undergoing impaction scavenging. A detailed one-dimensional cloud microphysics model has been used to simulate rain production and below-cloud particle scavenging, and to quantify the contribution of turbulent diffusion to the overall Λ(d) values calculated from particle concentration changes. The relative contribution of vertical diffusion to below-cloud scavenging is found to be largest for submicron particles under weak precipitation conditions. The discrepancies between theoretical and field-derived Λ(d) values can largely be explained by the contribution of vertical diffusion to below-cloud particle scavenging for all particles larger than 0.01 μm in diameter for which field data are available. The results presented here suggest that the current theoretical framework for Λ(d) can provide a reasonable approximation of below-cloud aerosol particle scavenging by rain in size-resolved aerosol transport models if vertical diffusion is also considered by the models.
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Go¨ttlich, E., F. Neumayer, J. Woisetschla¨ger, W. Sanz, and F. Heitmeir. "Investigation of Stator-Rotor Interaction in a Transonic Turbine Stage Using Laser Doppler Velocimetry and Pneumatic Probes." Journal of Turbomachinery 126, no. 2 (2004): 297–305. http://dx.doi.org/10.1115/1.1649745.
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The current paper presents steady and unsteady flow data of a transonic test turbine stage operating under flow conditions similar to modern highly loaded gas turbines. Measurements were performed between stator and rotor as well as downstream of the rotor in planes perpendicular to the rotor axis. Time-resolved axial and tangential velocities were measured by a two-component laser doppler velocimeter (LDV) to investigate unsteady phenomena, while time-averaged flow properties were measured by means of a pneumatic seven-hole probe for all three spatial directions. The time-resolved investigation done by LDV allows to present velocity fields, flow angles and turbulence data at different stator-rotor positions during one blade passing period. Averaging these results enabled comparison with the pneumatic multihole probe measurement. LDV data and stage geometry can be obtained per email request and used for computational fluid dynamics (CFD) code verification.
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Panayotova, Iordanka N. "A New Surface Model for β-Plane Turbulence". Journal of the Atmospheric Sciences 64, № 7 (2007): 2717–25. http://dx.doi.org/10.1175/jas3970.1.
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Abstract This paper introduces a new numerical model for studying wave–turbulence interactions in a continuously stratified rotating flow, having a uniform potential vorticity and a rigid boundary. The meridional variation in the Coriolis parameter (β effect), a channel geometry, and the first-order nonlinear terms in a small Rossby number expansion are included into the surface quasigeostrophic dynamics. The model contains important dynamical characteristics of three-dimensional flows such as advection by ageostrophic winds, and stretching and tilting of relative vorticity. Nevertheless, it has the computational economy of two-dimensional flows. Long-term direct numerical simulations are performed for decaying turbulence arising from random initial conditions. In addition to the formation of steady zonal jets, frequently reported as a possible end state under the β effect, this model exhibits several other realistic physical effects that were lacking in the previously studied β-plane models for wave–turbulence interactions. There is a significant contrast in the spatial and time scales of the formed eddies, resulting in high meridional asymmetry of the flow. Mean surface cooling and persistent large-scale blocking eddies are observed as well. The surface potential temperature variance spectrum exhibits a well-resolved k−5/3 inertial range.
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Lobo, Brandon Arthur, Alois Peter Schaffarczyk, and Michael Breuer. "Investigation into boundary layer transition using wall-resolved large-eddy simulations and modeled inflow turbulence." Wind Energy Science 7, no. 3 (2022): 967–90. http://dx.doi.org/10.5194/wes-7-967-2022.
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Abstract. The objective of the present paper is to investigate the transition scenario of the flow around a typical section of a wind turbine blade exposed to different levels of inflow turbulence. A rather low Reynolds number of Rec=105 is studied at a fixed angle of attack but under five different turbulence intensities (TIs) up to TI = 11.2 %. Using wall-resolved large-eddy simulations combined with an inflow procedure relying on synthetically generated turbulence and a source-term formulation for its injection within the computational domain, relevant flow features such as the separation bubble, inflectional instabilities and streaks can be investigated. The study shows that the transition scenario significantly changes with rising TI, where the influence of inflectional instabilities due to an adverse pressure gradient decreases, while the influence of streaks increases, resulting in a shift from the classical scenario of natural transition to bypass transition. The primary instability mechanism in the separation bubble is found to be inflectional, and its origin is traced back to the region upstream of the separation. Thus, the inviscid inflectional instability of the separated shear layer is an extension of the instability of the attached adverse pressure gradient boundary layer observed upstream. The boundary layer is evaluated to be receptive to external disturbances such that the initial energy within the boundary layer is proportional to the square of the turbulence intensity. Boundary layer streaks were found to influence the instantaneous separation location depending on their orientation. A varicose mode of instability is observed on the overlap of the leading edge of a high-speed streak with the trailing edge of a low-speed streak. The critical amplitude of this instability was analyzed to be about 32 % of the free-stream velocity.
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Li, Cruz Y., Zengshun Chen, Tim K. T. Tse, et al. "A parametric and feasibility study for data sampling of the dynamic mode decomposition: Spectral insights and further explorations." Physics of Fluids 34, no. 3 (2022): 035102. http://dx.doi.org/10.1063/5.0082640.
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The present work extends the parametric investigation on the sampling nuances of dynamic mode decomposition (DMD) under Koopman analysis. Through turbulent wakes, the study corroborated the generality of universal convergence states for all DMD implementations. It discovered implications of sampling range and resolution—determinants of spectral discretization by discrete bins and the highest resolved frequency range, respectively. The work reaffirmed the necessity of the convergence state for sampling independence, too. Results also suggested that the observables derived from the same flow may contain dynamically distinct information, thus altering the DMD output. Surface pressure and vortex fields are optimal for characterizing the structure and the flow field, respectively. Pressure, velocity magnitude, and turbulence kinetic energy also suffice for general applications, but Reynolds stresses and velocity components shall be avoided. Mean-subtraction is recommended for the best approximations of Koopman eigen tuples. Furthermore, the parametric investigation on truncation discovered some low-energy states that dictate a system's temporal integrity. The best practice for order reduction is to avoid truncation and employ dominant mode selection on a full-state subspace, though large-degree truncation supports fair data reconstruction with low computational cost. Finally, this work demonstrated synthetic noise resulting from pre-decomposition interpolation. In unavoidable interpolations to increase the spatial dimension n, high-order schemes are recommended for better retention of original dynamics. Finally, the observations herein, derived from inhomogeneous anisotropic turbulence, offer constructive references for DMD on fluid systems, if not also for others beyond fluid mechanics.
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Conti, Davide, Nikolay Dimitrov, Alfredo Peña, and Thomas Herges. "Probabilistic estimation of the Dynamic Wake Meandering model parameters using SpinnerLidar-derived wake characteristics." Wind Energy Science 6, no. 5 (2021): 1117–42. http://dx.doi.org/10.5194/wes-6-1117-2021.
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Abstract. We study the calibration of the Dynamic Wake Meandering (DWM) model using high-spatial- and high-temporal-resolution SpinnerLidar measurements of the wake field collected at the Scaled Wind Farm Technology (SWiFT) facility located in Lubbock, Texas, USA. We derive two-dimensional wake flow characteristics including wake deficit, wake turbulence, and wake meandering from the lidar observations under different atmospheric stability conditions, inflow wind speeds, and downstream distances up to five rotor diameters. We then apply Bayesian inference to obtain a probabilistic calibration of the DWM model, where the resulting joint distribution of parameters allows for both model implementation and uncertainty assessment. We validate the resulting fully resolved wake field predictions against the lidar measurements and discuss the most critical sources of uncertainty. The results indicate that the DWM model can accurately predict the mean wind velocity and turbulence fields in the far-wake region beyond four rotor diameters as long as properly calibrated parameters are used, and wake meandering time series are accurately replicated. We show that the current DWM model parameters in the IEC standard lead to conservative wake deficit predictions for ambient turbulence intensities above 12 % at the SWiFT site. Finally, we provide practical recommendations for reliable calibration procedures.
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Schanderl, Wolfgang, Ulrich Jenssen, Claudia Strobl, and Michael Manhart. "The structure and budget of turbulent kinetic energy in front of a wall-mounted cylinder." Journal of Fluid Mechanics 827 (August 22, 2017): 285–321. http://dx.doi.org/10.1017/jfm.2017.486.
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We investigate the flow and turbulence structure in front of a cylinder mounted on a flat plate by a combined study using highly resolved large-eddy simulation and particle image velocimetry. The Reynolds number based on the bulk velocity and cylinder diameter is $Re_{D}=39\,000$. As the cylinder is placed in an open channel, we take special care to simulate open-channel flow as the inflow condition, including secondary flows that match the inflow in the experiment. Due to the high numerical resolution, subgrid contributions to the Reynolds stresses are negligible and the modelled dissipation plays a minor role in major parts of the flow field. The accordance of the experimental and numerical results is good. The shear in the approach flow creates a vertical pressure gradient, inducing a downflow in the cylinder front. This downflow, when deflected in the upstream direction at the bottom plate, gives rise to a so-called horseshoe vortex system. The most upstream point of flow reversal at the wall is found to be a stagnation point which appears as a sink instead of a separation point in the symmetry plane in front of the cylinder. The wall shear stress is largest between the main (horseshoe) vortex and the cylinder, and seems to be mainly governed by the strong downflow in front of the cylinder as turbulent stresses are small in this region. Due to a strong acceleration along the streamlines, a region of relatively small turbulent kinetic energy is found between the horseshoe vortex and the cylinder. When passing under the horseshoe vortex, the upstream-directed jet formed by the deflected downflow undergoes a deceleration which gives rise to a strong production of turbulent kinetic energy. We find that pressure transport of turbulent kinetic energy is important for the initiation of the large production rates by increasing the turbulence level in the upstream jet near the wall. The distribution of the dissipation of turbulent kinetic energy is similar to that of the turbulent kinetic energy. Large values of dissipation occur around the centre of the horseshoe vortex and near the wall in the region where the jet decelerates. While the small scales are nearly isotropic in the horseshoe vortex centre, they are anistotropic near the wall. This can be explained by a vertical flapping of the upstream-directed jet. The distribution and level of dissipation, turbulent and pressure transport of turbulent kinetic energy are of crucial interest to turbulence modelling in the Reynolds-averaged context. To the best of our knowledge, this is the first time that these terms have been documented in this kind of flow.
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Hamzeloo, S., A. Peña, X. G. Larsén, and A. N. Hahmann. "Atmospheric flow simulation over stationary waves with various steepness using WRF-LES." Journal of Physics: Conference Series 2767, no. 6 (2024): 062015. http://dx.doi.org/10.1088/1742-6596/2767/6/062015.
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Abstract We investigated the capability of the Weather Research and Forecasting (WRF) model to perform large-eddy simulations (LESs) of the structure of the marine atmospheric boundary layer and turbulence exchange between the sea surface and the atmosphere. The WRF-LES model results were compared to results from Sullivan (2008) [1] for two cases: flow over a flat surface and over an idealized stationary sinusoidal surface. We also investigated the sensitivity of the WRF-LES model in simulating turbulence through the marine atmosphere under a range of horizontal grid spacings and wave steepnesses. All simulations were performed in a conventionally neutral atmosphere with a geostrophic wind of 5 m s−1, aligned with the direction of wave propagation. The simulated wind vertical profiles from the WRF-LES model exhibit similar behavior to those of Sullivan (2008) over both wavy and flat surfaces, but the differences in Sullivan’s vertical wind profiles for the two cases are considerably larger in comparison to those derived from WRF-LES. Furthermore, spectral analysis clearly shows the effect of horizontal grid spacing. The impact of wave steepness on turbulence distribution is clearly noticeable in the vertical profiles of resolved velocity variances and covariances. The impact is largest close to the surface, but it is important throughout the bulk of the boundary layer.
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Miniati, Francesco, and Andrey Beresnyak. "Self-similar hierarchical energetics in the ICM of massive galaxy clusters." Proceedings of the International Astronomical Union 11, A29B (2015): 700. http://dx.doi.org/10.1017/s1743921316006402.
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AbstractMassive galaxy clusters (GC) are filled with a hot, turbulent and magnetised intra-cluster medium (ICM). They are still forming under the action of gravitational instability, which drives supersonic mass accretion flows. These partially dissipate into heat through a complex network of large scale shocks, and partly excite giant turbulent eddies and cascade. Turbulence dissipation not only contributes to heating of the ICM but also amplifies magnetic energy by way of dynamo action. The pattern of gravitational energy turning into kinetic, thermal, turbulent and magnetic is a fundamental feature of GC hydrodynamics but quantitative modelling has remained a challenge. In this contribution we present results from a recent high resolution, fully cosmological numerical simulation of a massive Coma-like galaxy cluster in which the time dependent turbulent motions of the ICM are resolved (Miniati 2014) and their statistical properties are quantified for the first time (Miniati 2015, Beresnyak & Miniati 2015). We combine these results with independent state-of-the art numerical simulations of MHD turbulence (Beresnyak 2012), which shows that in the nonlinear regime of turbulent dynamo (for magnetic Prandtl numbers≳ 1) the growth rate of the magnetic energy corresponds to a fraction CE ≃ 4 − 5 × 10−2 of the turbulent dissipation rate. We thus determine without adjustable parameters the thermal, turbulent and magnetic history of giant GC (Miniati & Beresnyak 2015). We find that the energy components of the ICM are ordered according to a permanent hierarchy, in which the sonic Mach number at the turbulent injection scale is of order unity, the beta of the plasma of order forty and the ratio of turbulent injection scale to Alfvén scale is of order one hundred. These dimensionless numbers remain virtually unaltered throughout the cluster's history, despite evolution of each individual component and the drive towards equipartition of the turbulent dynamo, thus revealing a new type of self-similarity in cosmology. Their specific values, while consistent with current data, indicate that thermal energy dominates the ICM energetics and the turbulent dynamo is always far from saturation, unlike the condition in other familiar astrophysical fluids (stars, interstellar medium of galaxies, compact objects, etc.). In addition, they have important physical meaning as their specific values encodes information about the efficiency of turbulent heating (the fraction of ICM thermal energy produced by turbulent dissipation) and the efficiency of dynamo action in the ICM (CE).
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Peña, Alfredo, Branko Kosović, and Jeffrey D. Mirocha. "Evaluation of idealized large-eddy simulations performed with the Weather Research and Forecasting model using turbulence measurements from a 250 m meteorological mast." Wind Energy Science 6, no. 3 (2021): 645–61. http://dx.doi.org/10.5194/wes-6-645-2021.
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Abstract. We investigate the ability of the Weather Research and Forecasting model to perform large-eddy simulation of canonical flows. This is achieved through comparison of the simulation outputs with measurements from sonic anemometers on a 250 m meteorological mast located at Østerild, in northern Denmark. Østerild is on a flat and rough area, and for the predominant wind directions, the atmospheric flow can be considered to be close to homogeneous. The idealized simulated flows aim at representing atmospheric boundary layer turbulence under unstable, neutral, and stable stability conditions at the surface, which are statistically significant conditions observed at Østerild. We found that the resolved fields from the simulations appear to have the characteristics of the three stability regimes. Vertical profiles of observed mean wind speeds and direction are well reproduced by the simulations, with the largest differences under near-neutral conditions, where the effect of the subgrid-scale model is evident on the vertical wind shear close to the surface. Vertical profiles of observed eddy fluxes are also well reproduced by the simulations, with the largest differences for the three velocity component variances under stable stability conditions, although nearly always within the observed variability. With regards to turbulent kinetic energy, we find good agreement between observations and simulations at all vertical levels. Simulated and observed velocity spectra match very well and show very similar behavior with height and with atmospheric stability within the low-frequency interval; at the effective resolution, the simulated spectra show the typical drop-off of finite differences. Our findings demonstrate that these idealized simulations reproduce the characteristics of atmospheric stability regimes often observed at a high turbulent and flat site within a direction sector, where the air flows over nearly homogeneous land.
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Moura, R. C., G. Mengaldo, J. Peiró, and S. J. Sherwin. "On the eddy-resolving capability of high-order discontinuous Galerkin approaches to implicit LES / under-resolved DNS of Euler turbulence." Journal of Computational Physics 330 (February 2017): 615–23. http://dx.doi.org/10.1016/j.jcp.2016.10.056.
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