Journal articles: 'Unsteady Turbulent Flow'

1

Ge, Liang, Hwa-Liang Leo, Fotis Sotiropoulos, and Ajit P. Yoganathan. "Flow in a Mechanical Bileaflet Heart Valve at Laminar and Near-Peak Systole Flow Rates: CFD Simulations and Experiments." Journal of Biomechanical Engineering 127, no. 5 (March 31, 2005): 782–97. http://dx.doi.org/10.1115/1.1993665.

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Time-accurate, fully 3D numerical simulations and particle image velocity laboratory experiments are carried out for flow through a fully open bileaflet mechanical heart valve under steady (nonpulsatile) inflow conditions. Flows at two different Reynolds numbers, one in the laminar regime and the other turbulent (near-peak systole flow rate), are investigated. A direct numerical simulation is carried out for the laminar flow case while the turbulent flow is investigated with two different unsteady statistical turbulence modeling approaches, unsteady Reynolds-averaged Navier-Stokes (URANS) and detached-eddy simulation (DES) approach. For both the laminar and turbulent cases the computed mean velocity profiles are in good overall agreement with the measurements. For the turbulent simulations, however, the comparisons with the measurements demonstrate clearly the superiority of the DES approach and underscore its potential as a powerful modeling tool of cardiovascular flows at physiological conditions. The study reveals numerous previously unknown features of the flow.

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Mankbadi, Reda R., and Joseph T. C. Liu. "Near-wall response in turbulent shear flows subjected to imposed unsteadiness." Journal of Fluid Mechanics 238 (May 1992): 55–71. http://dx.doi.org/10.1017/s0022112092001630.

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Rapid-distortion theory is adapted to introduce a truly unsteady closure into a simple phenomenological turbulence model in order to describe the unsteady response of a turbulent wall layer exposed to a temporarily oscillating pressure gradient. The closure model is built by taking the ratio of turbulent shear stress to turbulent kinetic energy to be a function of the effective strain. The latter accounts for the history of the flow. The computed unsteady velocity fluctuations and modulated turbulent stresses compare favourably in the ‘non-quasi-steady’ frequency range, where quasi-steady assumptions would fail. This suggests that the concept of rapid distortion is especially appropriate for unsteady flows. This paper forms the basis for acoustical studies of the problem to be reported elsewhere.

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Brereton, G. J., and R. R. Mankbadi. "Review of Recent Advances in the Study of Unsteady Turbulent Internal Flows." Applied Mechanics Reviews 48, no. 4 (April 1, 1995): 189–212. http://dx.doi.org/10.1115/1.3005100.

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Turbulent flow which undergoes organized temporal unsteadiness is a subject of great importance to unsteady aerodynamic and thermodynamic devices. Of the many classes of unsteady flows, those bounded by rigid smooth walls are particularly amenable to fundamental studies of unsteady turbulence and its modeling. These flows are presently being given increased attention as interest grows in the prospect of predicting non-equilibrium turbulence and because of their relevance to turbulence–acoustics interactions, in addition to their importance as unsteady flows in their own right. It is therefore timely to present a review of recent advances in this area, with particular emphasis placed on physical understanding of the turbulent processes in these flows and the development of turbulence models to predict them. A number of earlier reviews have been published on unsteady turbulent flows, which have tended to focus on specific aspects of certain flows. This review is intended to draw together, from the diverse literature on the subject, information on fundamental aspects of these flows which are relevant to improved understanding and development of predictive models. Of particular relevance are issues of instability and transition to turbulence in reciprocating flows, the robustness of coherent structures in wall-bounded flows to forced perturbations (in contrast to the relative ease of manipulation in free shear flows), unsteady scalar transport, improved measurement technology, recent contributions to target data for model testing and the quasi-steady and non-steady rapid distortion approaches to turbulence modeling in these flows. The present article aims to summarize recent contributions to this research area, with a view to consolidating comprehension of the well-known basics of these flows, and drawing attention to critical gaps in information which restrict our understanding of unsteady turbulent flows.

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De Stefano, Giuliano, Oleg V. Vasilyev, and Eric Brown-Dymkoski. "Wavelet-based adaptive unsteady Reynolds-averaged turbulence modelling of external flows." Journal of Fluid Mechanics 837 (January 5, 2018): 765–87. http://dx.doi.org/10.1017/jfm.2017.798.

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The recent development of the adaptive-anisotropic wavelet-collocation method, which incorporates the use of coordinate transforms, opens new horizons for wavelet-based simulations of wall-bounded turbulent flows. The new wavelet-based adaptive unsteady Reynolds-averaged Navier–Stokes approach for computational modelling of turbulent flows is presented. The proposed methodology that is integrated with anisotropic wavelet-based mesh refinement is demonstrated for a two-equation eddy-viscosity turbulence model. The performance of the method is assessed by conducting numerical simulations of the turbulent flow past a circular cylinder at subcritical Reynolds number. The present study demonstrates both the feasibility and the effectiveness of the new wavelet-based adaptive unsteady Reynolds-averaged turbulence modelling procedure for external flows.

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Power, G. D., J. M. Verdon, and K. A. Kousen. "Analysis of Unsteady Compressible Viscous Layers." Journal of Turbomachinery 113, no. 4 (October 1, 1991): 644–53. http://dx.doi.org/10.1115/1.2929130.

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The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy–Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low-frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

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Bareš, V., J. Jirák, and J. Pollert. "Bottom shear stress in unsteady sewer flow." Water Science and Technology 54, no. 6-7 (September 1, 2006): 93–100. http://dx.doi.org/10.2166/wst.2006.588.

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The properties of unsteady open-channel turbulent flow were theoretically and experimentally investigated in a circular cross section channel with fixed sediment deposits. Velocity and turbulence distribution data were obtained using an ultrasonic velocity profiler (UVP). Different uniform flow conditions and triangular-shaped hydrographs were analysed. The hydrograph analysis revealed a dynamic wave behaviour, where the time lags of mean cross section velocity, friction velocity, discharge and flow depth were all evident. The bottom shear stress dynamic behaviour was estimated using four different approaches. Measurements of the velocity distribution in the inner region of the turbulent layer and of the Reynolds stress distribution in the turbulent flow provided the analysed data sets of the bottom shear stress. Furthermore, based on the Saint Venant equation, the bottom shear stress time behaviour was studied using both the kinematic and the dynamic flow principles. The dynamic values of the bottom shear stress were compared with those for the steady flow conditions. It is evident that bottom shear stress varies along the generated flood hydrograph and its variation is the function of the flow unsteadiness. Moreover, the kinematic flow principle is not an adequate type of approximation for presented flow conditions.

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Perot, J. Blair, Sasanka Are, and Xing Zhang. "Application of the Turbulent Potential Model to Unsteady Flows and Three-Dimensional Boundary Layers." International Journal of Rotating Machinery 9, no. 5 (2003): 375–84. http://dx.doi.org/10.1155/s1023621x03000356.

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The turbulent potential model is a Reynolds-averaged (RANS) turbulence model that is theoretically capable of capturing nonequilibrium turbulent flows at a computational cost and complexity comparable to two-equation models. The ability of the turbulent potential model to predict nonequilibrium turbulent flows accurately is evaluated in this work. The flow in a spanwise-driven channel flow and over a swept bump are used to evaluate the turbulent potential model's ability to predict complex three-dimensional boundary layers. Results of turbulent vortex shedding behind a triangular and a square cylinder are also presented in order to evaluate the model's ability to predict unsteady flows. Early indications suggest that models of this type may be capable of significantly enhancing current numerical predictions of turbomachinery components at little extra computational cost or additional code complexity.

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Liu, Zhong Qiu, Feng Sheng Qi, Bao Kuan Li, and Mao Fa Jiang. "Turbulent Flow of Molten Steel in Thin Slab Continuous Casting Mold." Advanced Materials Research 402 (November 2011): 432–35. http://dx.doi.org/10.4028/www.scientific.net/amr.402.432.

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The quality of continuously casting steel is greatly influenced by turbulent flow in the mold. Understanding the unsteady flow structures in this process is an important step in avoiding failures and decreasing defects. The cassette filter function is used to deal with unsteady Navier-Stokes equation, and then the turbulent flows in the thin slab continuous casting processes are simulated with the large eddy simulation (LES) method with the Smagorinsky sub-grid scale model. Characteristics of the unsteady turbulent flow in the thin slab continuous casting processes are exhibited. The turbulent asymmetric distribution was revealed even the nozzle in the centre position. And the vortices are located at the low velocity side adjacent to the nozzle.

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Fang, Fuh-Min, W. D. Hsieh, S. W. Jong, and J. J. She. "Unsteady Turbulent Flow Past Solid Fence." Journal of Hydraulic Engineering 123, no. 6 (June 1997): 560–65. http://dx.doi.org/10.1061/(asce)0733-9429(1997)123:6(560).

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10

Viola, John P., and Hans J. Leutheusser. "Experiments on Unsteady Turbulent Pipe Flow." Journal of Engineering Mechanics 130, no. 2 (February 2004): 240–44. http://dx.doi.org/10.1061/(asce)0733-9399(2004)130:2(240).

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11

KRAEV, Viacheslav. "Experimental research of incipient turbulent flow frequency spectra in hydrodynamic unsteadiness." INCAS BULLETIN 13, no. 2 (June 4, 2021): 91–102. http://dx.doi.org/10.13111/2066-8201.2021.13.2.10.

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Hydraulic and heat transfer processes play a very important role in the design and prototyping of aerospace technology. Unsteady conditions are the peculiarity of mostly aerospace systems. Flow acceleration and deceleration may significantly affect the heat transfer and hydrodynamic process in channels of aerospace systems. For unsteady process modeling, a fundamental research of unsteady hydrodynamic turbulent flow structure., Moscow Aviation Institute National Research University (MAI) has been building unsteady turbulent flow structures since 1989. An experimental facility was designed to provide gas flow acceleration and deceleration. Experimental data of a turbulent gas flow structure during flow acceleration and flow deceleration are presented. The frequency spectra of axial and radial velocity pulsations are based on experimental data. The results of experimental turbulent flow research demonstrate the fundamental hydrodynamic unsteadiness influence on the flow structure. The main results of the flow acceleration and deceleration experimental research show that there are tangible differences from the steady flow structure. The analysis of unsteady conditions influence on the turbulent pulsations generation and development mechanisms is presented. The results show the unsteady conditions influence onto turbulent vortexes disintegration tempo. The present paper describes a method of experimental research, methodology of data processing and turbulent accelerated and decelerated flow spectra results.

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12

Brereton, G. J., and A. Kodal. "A Frequency-Domain Filtering Technique for Triple Decomposition of Unsteady Turbulent Flow." Journal of Fluids Engineering 114, no. 1 (March 1, 1992): 45–51. http://dx.doi.org/10.1115/1.2909998.

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A new technique is presented for decomposing unsteady turbulent flow variables into their organized unsteady and turbulent components, which appears to offer some significant advantages over existing ones. The technique uses power-spectral estimates of data to deduce the optimal frequency-domain filter for determining the organized and turbulent components of a time series of data. When contrasted with the phase-averaging technique, this method can be thought of as replacing the assumption that the organized motion is identically reproduced in successive cycles of known periodicity by a more general condition: the cross-correlation of the organized and turbulent components is minimized for a time series of measurement data, given the expected shape of the turbulence power spectrum. The method is significantly more general than the phase average in its applicability and makes more efficient use of available data. Performance evaluations for time series of unsteady turbulent velocity measurements attest to the accuracy of the technique and illustrate the improved performance of this method over the phase-averaging technique when cycle-to-cycle variations in organized motion are present.

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13

Ekaterinaris, J. A., and M. F. Platzer. "Numerical Investigation of Stall Flutter." Journal of Turbomachinery 118, no. 2 (April 1, 1996): 197–203. http://dx.doi.org/10.1115/1.2836626.

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Unsteady, separated, high Reynolds number flow over an airfoil undergoing oscillatory motion is investigated numerically. The compressible form of the Reynolds-averaged governing equations is solved using a high-order, upwind biased numerical scheme. The turbulent flow region is computed using a one-equation turbulence model. The computed results show that the key to the accurate prediction of the unsteady loads at stall flutter conditions is the modeling of the transitional flow region at the leading edge. A simplified criterion for the transition onset is used. The transitional flow region is computed with a modified form of the turbulence model. The computed solution, where the transitional flow region is included, shows that the small laminar/transitional separation bubble forming during the pitch-up motion has a decisive effect on the near-wall flow and the development of the unsteady loads. Detailed comparisons of computed fully turbulent and transitional flow solutions with experimental data are presented.

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Bai, L., M. Fiebig, and N. K. Mitra. "Numerical Analysis of Turbulent Flow in Fluid Couplings." Journal of Fluids Engineering 119, no. 3 (September 1, 1997): 569–76. http://dx.doi.org/10.1115/1.2819282.

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Numerical simulation of three-dimensional unsteady turbulent flows in fluid couplings was carried out by numerically solving Navier-Stokes equations in a rotating coordinate system. The standard k-ε model was used to take turbulence into account. A finite volume scheme with colocated body-fitted grids was used to solve the basic equations. Computed flow structures show the vortex generation and its effect on the torque transmission. Computed local velocity and torque flow compare well with measurements.

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LESCHZINER, M. A., G. M. FISHPOOL, and S. LARDEAU. "TURBULENT SHEAR FLOW: A PARADIGMATIC MULTISCALE PHENOMENON." Journal of Multiscale Modelling 01, no. 02 (April 2009): 197–222. http://dx.doi.org/10.1142/s1756973709000104.

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The paper provides a broad discussion of multiscale and structural features of sheared turbulent flows. Basic phenomenological aspects of turbulence are first introduced, largely in descriptive terms with particular emphasis placed on the range of scales encountered in turbulent flows and in the identification of characteristic scale ranges. There follows a discussion of essential aspects of computational modeling and simulation of turbulence. Finally, the results of simulations for two groups of flows are discussed. These combine shear, separation, and periodicity, the last feature provoked by either a natural instability or by unsteady external forcing. The particular choice of examples is intended to illustrate the capabilities of such simulations to resolve the multiscale nature of complex turbulent flows, as well as the challenges encountered.

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Orth, U. "Unsteady Boundary-Layer Transition in Flow Periodically Disturbed by Wakes." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 707–13. http://dx.doi.org/10.1115/1.2929306.

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Boundary layers on turbomachinery blades develop in a flow that is periodically disturbed by the wakes of upstream blade cascades. These wakes have a significant effect upon laminar-turbulent boundary-layer transition. In order to study these effects, detailed velocity measurements using hot-wire probes were performed within the boundary-layer of a plate in flow periodically disturbed by wakes produced by bars moving transversely to the flow. The measurements were evaluated using the ensemble-averaging technique. The results show how the wake disturbance enters the boundary-layer and leads to a turbulent patch, which grows and is carried downstream. In favorable pressure gradients, transition due to wake turbulence occurred much earlier than predicted by linear stability theory. Between two wakes, laminar becalmed regions were observed far beyond the point at which the undisturbed boundary-layer was already turbulent.

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17

Kamran, Ahmad, Zhi Gang Wu, and Muhammad Amjad Sohail. "CFD Analysis of Oscillating Airfoil during Pitch Cycle." Applied Mechanics and Materials 152-154 (January 2012): 906–11. http://dx.doi.org/10.4028/www.scientific.net/amm.152-154.906.

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This research paper presents the CFD analysis of oscillating airfoil during pitch cycle. Unsteady subsonic flow is simulated for pitching airfoil at Mach number 0.283 and Reynolds number 3.45 millions. Turbulent effects are also considered for this study by using K-ω SST turbulent model. Two-dimensional unsteady compressible Navier-Stokes code including two-equation turbulence model and PISO pressure velocity coupling is used. Pressure based implicit solver with first order implicit unsteady formulation is used. The simulated pitch cycle results are compared with the available experimental data.

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NAGAO, Masatomo, Hiroto YAMAJI, and Masaki SAWAMOTO. "Devebpment of Animation for Unsteady Turbulent Flow." PROCEEDINGS OF HYDRAULIC ENGINEERING 34 (1990): 665–69. http://dx.doi.org/10.2208/prohe.34.665.

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19

Momen, Mostafa, and Elie Bou-Zeid. "Mean and turbulence dynamics in unsteady Ekman boundary layers." Journal of Fluid Mechanics 816 (March 7, 2017): 209–42. http://dx.doi.org/10.1017/jfm.2017.76.

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Unsteady pressure gradients in turbulent flows not only influence the mean, but also affect the higher statistical moments of turbulence. In these flows, it is important to understand if and when turbulence is in quasi-equilibrium with the mean in order to better capture the dynamics and develop effective closure models. Therefore, this study aims to elucidate how turbulence decays or develops relative to a time-varying mean flow, and how the turbulent kinetic energy (TKE) production, transport and dissipation respond to changes in the imposed pressure forcing. The focus is on the neutral unsteady Ekman boundary layer, where pressure-gradient, Coriolis and turbulent friction forces interact, and the analyses are based on a suite of large-eddy simulations with unsteady pressure forcing. The results indicate that the dynamics is primarily controlled by the relative magnitudes of three time scales: the inertial time scale (characterized by Coriolis frequency${\sim}12$ hours at mid-latitudes), the turbulent time scale (${\sim}2$ hours for the largest eddies in the present simulations) and the forcing variability time scale (which is varied to reflect different (sub)meso to synoptic scale dynamics). When the forcing time scale is comparable to the turbulence time scale, the quasi-equilibrium condition becomes invalid due to highly complex interactions between the mean and turbulence, the velocity profiles manifestly depart from the log-law and the normalized TKE budget terms vary strongly in time. However, for longer, and surprisingly for shorter, forcing times, quasi-equilibrium is reasonably maintained. The analyses elucidate the physical mechanisms that trigger these dynamics, and investigate the implications on turbulence closure models.

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Harada, Yuji, Kenji Uchida, Tatsuya Tanaka, Kiyotaka Sato, Qianjin Zhu, Hidefumi Fujimoto, Hiroyuki Yamashita, and Mamoru Tanahashi. "Wall heat transfer of unsteady near-wall flow in internal combustion engines." International Journal of Engine Research 20, no. 7 (June 10, 2019): 817–33. http://dx.doi.org/10.1177/1468087419853432.

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Although the near-wall turbulence is not fully developed in the engine combustion chamber, wall heat transfer models based on flow characteristics in fully developed near-wall turbulence are typically employed in engine simulations to predict heat transfer. Only few studies reported the wall heat transfer mechanism in near-wall flow where the near-wall turbulence was not fully developed as expected in the engine combustion chamber. In this study, the velocity distribution and wall heat flux in such a near-wall flow were evaluated using a rapid compression and expansion machine. In addition to the experimental approach, a numerical simulation with highly resolved calculation mesh was applied in various flow fields expected in the engine combustion chamber. As a result, the turbulent Reynolds number that represents the relationship between turbulent production and dissipation varied in the wall boundary layer according to the near-wall flow condition. This behavior affects the wall heat transfer. Considering this finding, a new model was formulated by introducing a ratio of turbulent Reynolds number in an intended near-wall flow to that in fully developed near-wall turbulence. It was confirmed that the proposed model could improve the prediction accuracy of wall heat flux even in near-wall flow where the near-wall turbulence was not fully developed. By applying the proposed model in engine computational fluid dynamics, it was found that the proposed model could predict the wall heat flux in a homogeneous charge compression ignition gasoline engine with acceptable accuracy.

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Kwon, O. Key, R. H. Pletcher, and R. A. Delaney. "Solution Procedure for Unsteady Two-Dimensional Boundary Layers." Journal of Fluids Engineering 110, no. 1 (March 1, 1988): 69–75. http://dx.doi.org/10.1115/1.3243513.

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An accurate and reliable solution procedure is presented for solving the two-dimensional, compressible, unsteady boundary layer equations. The procedure solves the governing equations in a coupled manner using a fully implicit finite-difference numerical algorithm. Several unsteady compressible and incompressible laminar flows are considered. Example results for two unsteady incompressible turbulent flows are also included. An algebraic mixing length closure model is used for the turbulent flow calculations. The computed results compare favorably with experimental data and available analytical/numerical solutions.

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Johnston, D. N. "Numerical modelling of unsteady turbulent flow in smooth-walled pipes." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, no. 7 (May 5, 2011): 1601–13. http://dx.doi.org/10.1177/0954406211400796.

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An efficient numerical model for turbulent friction has been developed for smooth-walled pipe flow. The aim was to develop a new approach to the numerical modelling, eliminating some important approximations and sources of error, such that the method can be applied reliably under a wide range of conditions. A simple two-region model of effective viscosity is used. For short timescales, the turbulence level and effective viscosity distribution are ‘frozen’ in time. The velocity profile is determined numerically for a range of frequencies and viscosity distributions, and this is used to determine the frequency-dependent friction. This is then approximated using simple weighing functions. This turbulence model can be implemented readily in several types of numerical model for pipe flow, including simple lumped parameter models, finite difference/finite element methods, and the method of characteristics.

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Javier García García, F., and Pablo Fariñas Alvariño. "On an analytical explanation of the phenomena observed in accelerated turbulent pipe flow." Journal of Fluid Mechanics 881 (October 24, 2019): 420–61. http://dx.doi.org/10.1017/jfm.2019.733.

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This research presents a new theory that explains analytically the behaviour of any fully developed incompressible turbulent pipe flow, steady or unsteady. We propose the name of theory of underlying laminar flow (TULF), because its main consequence is the description of any turbulent pipe flow as the sum of two components: the underlying laminar flow (ULF) and the purely turbulent component (PTC). We use the framework of the TULF to explain analytically most of the important and interesting phenomena reported in He & Jackson (J. Fluid Mech., vol. 408, 2000, pp. 1–38). To do so, we develop a simple model for the pressure gradient and Reynolds shear stress that could be applied to the linearly accelerated pipe flow described by He & Jackson (2000). The following features of the unsteady flow are explained: the deformation undergone by the mean velocity profiles during the transient, the velocity overshoot observed in the more rapid excursions, the dual deformation of mean velocity profiles when overshoots are present, the laminarisation effects described during acceleration, the rapid decrease of the Reynolds shear stress upon approaching the wall that brings forth the laminar sublayer, and some other minor effects. A new field is defined to characterise the degree of turbulence within the flow, directly calculable from the theory itself. Arguably, this new field would describe the degree of turbulence in a pipe flow more accurately than the familiar turbulence intensity parameter. Finally, a paradox is found in the deformation of the unsteady mean velocity profiles with respect to equal-Reynolds-number steady profiles, which is duly explained. The research also predicts the occurrence of mean velocity undershoots if the flow is decreased rapidly enough.

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Cataño-Lopera, Yovanni A., Blake J. Landy, and Marcelo H. García. "Unstable flow structure around partially buried objects on a simulated river bed." Journal of Hydroinformatics 19, no. 1 (September 17, 2016): 31–46. http://dx.doi.org/10.2166/hydro.2016.060.

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The unsteady flow characteristics around two partially buried objects, a short cylinder and a truncated cone, were examined with a three-dimensional, non-hydrostatic hydrodynamic model under similar steady unidirectional currents with flow Reynolds numbers, Re, of 86,061 and 76,209, respectively. Model simulations were conducted with the two objects partially buried in a simulated rippled river bed. A Reynolds-averaged Navier–Stokes (RANS) equation model coupled with a κ-ε turbulence closure was used to validate the experimental velocity measurements. A large eddy simulation (LES) turbulence model was subsequently used to characterize the unsteady flow structure around the objects. The LES closure allowed for the characterization of highly unsteady coherent turbulent structures such as the horse-shoe vortex, the arch-shaped vortex, as well as vortex shedding in the wake of the object.

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ZHANG, Yongxue. "IMPLICIT SMAC METHOD FOR UNSTEADY INCOMPRESSIBLE TURBULENT FLOW." Chinese Journal of Mechanical Engineering 42, no. 11 (2006): 54. http://dx.doi.org/10.3901/jme.2006.11.054.

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Bose, Sujit K., and Subhasish Dey. "Turbulent unsteady flow profiles over an adverse slope." Acta Geophysica 61, no. 1 (November 12, 2012): 84–97. http://dx.doi.org/10.2478/s11600-012-0080-2.

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Bukharkin, V. B., Guenrikh A. Dreitser, and V. M. Kraev. "Turbulent Gas Flow Structure under Unsteady Hydrodynamic Conditions." Heat Transfer Research 32, no. 7-8 (2001): 9. http://dx.doi.org/10.1615/heattransres.v32.i7-8.70.

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Guilmineau, E., J. Piquet, and P. Queutey. "UNSTEADY TWO-DIMENSIONAL TURBULENT VISCOUS FLOW PAST AEROFOILS." International Journal for Numerical Methods in Fluids 25, no. 3 (August 15, 1997): 315–66. http://dx.doi.org/10.1002/(sici)1097-0363(19970815)25:3<315::aid-fld555>3.0.co;2-l.

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Chung, Yongmann M. "Unsteady turbulent flow with sudden pressure gradient changes." International Journal for Numerical Methods in Fluids 47, no. 8-9 (2005): 925–30. http://dx.doi.org/10.1002/fld.917.

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Ahmed Hussein Hafez, Tamer Heshmat Mohamed Aly Kasem, Basman Elhadidi, and Mohamed Madbouly Abdelrahman. "Modelling Three Dimensional Unsteady Turbulent HVAC Induced Flow." Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 87, no. 1 (September 7, 2021): 76–90. http://dx.doi.org/10.37934/arfmts.87.1.7690.

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A three-dimensional numerical model for HVAC induced flow is presented. The nonlinear set of buoyancy driven incompressible flow equations, augmented with those of energy and turbulence model is solved. Various relevant are discussed. These challenges include avoiding expensive commercial packages, modeling complex boundaries, and capturing near wall gradients. Adaptive time stepping is employed to optimize computational effort. Three-dimensional simulation requirements are addressed using parallel computations. Two-dimensional and three-dimensional results are presented to clarify the model significance. Validation is done using full scale measurements. Good agreement with velocity and temperature profiles are illustrated.

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Karim, M. M., N. Mostafa, and M. M. A. Sarker. "Numerical study of unsteady flow around a cavitating hydrofoil." Journal of Naval Architecture and Marine Engineering 7, no. 2 (March 16, 2011): 51–60. http://dx.doi.org/10.3329/jname.v7i2.5270.

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This paper presents a numerical study of the non-cavitating and cavitating flow around CAV 2003 hydrofoil. The phenomenon of cavitation is modeled through a mixture model. For the numerical solution of cavitating flow a bubble dynamics cavitation model is used to describe the generation and evaporation of vapor phase. The non-cavitating study focuses on the influence of the turbulence model and different mesh sizes used in the computation. Three turbulence models such as Spalart-Allmaras, Shear Stress Turbulence (SST) k-? model, RNG k-? with enhanced wall treatment are used to capture turbulent boundary layer along the hydrofoil surface. The results predicted by these models are compared with each other. The cavitating study first presented an unsteady behavior of the partial cavity attached to the foil. Then, an analysis of a supercavitating condition is performed. The predicted results show good agreement with results published by other researchers.DOI: 10.3329/jname.v7i2.5270

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Brereton, G. J., W. C. Reynolds, and R. Jayaraman. "Response of a turbulent boundary layer to sinusoidal free-stream unsteadiness." Journal of Fluid Mechanics 221 (December 1990): 131–59. http://dx.doi.org/10.1017/s0022112090003512.

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In this paper, selected findings of a detailed experimental investigation are reported concerning the effects of forced free-stream unsteadiness on a turbulent boundary layer. The forced unsteadiness was sinusoidal and was superimposed locally on an otherwise-steady mainstream, beyond a turbulent boundary layer which had developed under constant-pressure conditions. Within the region over which free-stream unsteadiness was induced, the sinusoidal variation in pressure gradient was between extremes of zero and a positive value, with a positive average level. The local response of the boundary layer to these free-stream effects was studied through simultaneous measurements of the u- and v-components of the velocity fieldAlthough extensive studies of unsteady, turbulent, fully-developed pipe and channel flow have been carried out, the problem of a developing turbulent boundary layer and its response to forced free-stream unsteadiness has received comparatively little attention. The present study is intended to redress this imbalance and, when contrasted with other studies of unsteady turbulent boundary layers, is unique in that: (i) it features an appreciable amplitude of mainstream modulation at a large number of frequencies of forced unsteadiness, (ii) its measurements are both detailed and of high spatial resolution, so that the near-wall behaviour of the flow can be discerned, and (iii) it allows local modulation of the mainstream beyond a turbulent boundary layer which has developed under the well-known conditions of steady, two-dimensional, constant-pressure flowResults are reported which allow comparison of the behaviour of boundary layers under the same mean external conditions, but with different time dependence in their free-stream velocities. These time dependences correspond to: (i) steady flow, (ii) quasi-steadily varying flow, and (iii) unsteady flow at different frequencies of mainstream unsteadiness. Experimental results focus upon the time-averaged nature of the flow; they indicate that the mean structure of the turbulent boundary layer is sufficiently robust that the imposition of free-stream unsteadiness results only in minor differences relative to the mean character of the steady flow, even at frequencies for which the momentary condition of the flow departs substantially from its quasi-steady state. Mean levels of turbulence production are likewise unaffected by free-stream unsteadiness and temporal production of turbulence appears to result only from modulation of the motions which contribute to turbulence production as a time-averaged measure.

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33

Koppel, T., and L. Ainola. "Identification of Transition to Turbulence in a Highly Accelerated Start-Up Pipe Flow." Journal of Fluids Engineering 128, no. 4 (December 27, 2005): 680–86. http://dx.doi.org/10.1115/1.2201640.

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The transition from a laminar to a turbulent flow in highly accelerated start-up pipe flows is described. In these flows, turbulence springs up simultaneously over the entire length of the pipe near the wall. The unsteady boundary layer in the pipe was analyzed theoretically with the Laplace transformation method and the asymptotic method for small values of time. From the experimental results available, relationships between the flow parameters and the transition time were derived. These relationships are characterized by the analytical forms. A physical explanation for the regularities in the turbulence spring-up time is proposed.

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Li, Mingshui, Yang Yang, Ming Li, and Haili Liao. "Direct measurement of the Sears function in turbulent flow." Journal of Fluid Mechanics 847 (May 29, 2018): 768–85. http://dx.doi.org/10.1017/jfm.2018.351.

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The applicability of the strip assumption in the estimation of the unsteady lift response of a two-dimensional wing in turbulent flow is investigated. The ratio between the lift spectrum calculated from the two-wavenumber analysis and the lift spectrum calculated from the strip assumption is used to evaluate the accuracy of the strip assumption. It is shown that the accuracy of the strip assumption is controlled by the ratio of the turbulence integral scale to the chord and the aspect ratio. With an increase of these two parameters, the ratio for evaluating the accuracy of the strip assumption increases, the one-wavenumber transfer function obtained from the strip assumption approaches the Sears function gradually. When these two parameters take suitable values, the strip assumption could be applicable to the calculation of the unsteady lift on a wing in turbulent flow. Here, the term aspect ratio refers to the ratio of the specified span (an finite spanwise length of the two-dimensional wing) to the chord, the unsteady lift is calculated over this specified spanwise length. The theoretical analysis is verified by means of force measurement experiments conducted in a wind tunnel. In the experiment, a square passive grid is installed downstream of the entrance of the test section to generate approximately homogeneous and isotropic turbulence. Three rectangular wings with different aspect ratios ($\unicode[STIX]{x1D703}=3$, 5 and 7) are used. These wing models have an NACA 0015 profile cross-section and a fixed chord length $c=0.16~\text{m}$. The testing results show that, at a fixed ratio of turbulence integral scale to chord, the deviation between the experimental one-wavenumber transfer function obtained from the strip assumption and the Sears function is reduced with increasing aspect ratio, as expected by the theoretical predictions. However, due to the effect of thickness, the experimental values at high frequencies cannot be captured by the Sears function which is derived based on the flat plate assumption. In practical applications, the effect of thickness on the transfer function should be considered.

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Kim, S. W., K. B. M. Q. Zaman, and J. Panda. "Numerical Investigation of Unsteady Transitional Flow Over Oscillating Airfoil." Journal of Fluids Engineering 117, no. 1 (March 1, 1995): 10–16. http://dx.doi.org/10.1115/1.2816799.

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A numerical investigation of unsteady transitional flow over an oscillating NACA 0012 airfoil at a Reynolds number of 44,000 and reduced frequency of 0.2 is carried out and the results are compared with experimental data. The Navier-Stokes equations defined on arbitrary Lagrangian-Eulerian coordinates are solved by a time-accurate finite volume method that incorporates an incremental pressure equation for the conservation of mass. The transitional turbulence field is described by multiple-time-scale turbulence equations. The numerical method successfully predicts the large dynamic stall vortex (DSV) and the trailing edge vortex (TEV) that are periodically generated by the oscillating airfoil. The numerical results show that the transition from laminar to turbulent state and relaminarization occur widely in time and in space. The calculated streaklines and the ensemble-averaged velocity profiles are in good agreement with the measured data.

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Zeng, Zhuo Xiong, Zhang Jun Wang, and Yun Ni Yu. "Effect of Particle Finite Size on Gas Turbulent Flow." Advanced Materials Research 516-517 (May 2012): 752–57. http://dx.doi.org/10.4028/www.scientific.net/amr.516-517.752.

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Dynamic mesh and moving wall technique were employed to simulate the unsteady flow field of moving particle with finite size. For freely moving particle, it does not come into being particle wake. Middle particle can move straightforward outlet, but left and right particles move disorderly in a restricted region. Vortex location varies with the change of particle location. Turbulence energy and pressure is decreased gradually from inlet to outlet. But for moving particle with slip velocity between gas and particle, particle wake comes into being. Turbulence enhancement by particle wake effect is studied by numerical simulation of gas turbulent flows passing over particle under various particle sizes, inlet gas velocities, gas viscosity, gas density and the distance of particles.

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Schobeiri, M. T., K. Pappu, and J. John. "Theoretical and Experimental Study of Development of Two-Dimensional Steady and Unsteady Wakes Within Curved Channels." Journal of Fluids Engineering 117, no. 4 (December 1, 1995): 593–98. http://dx.doi.org/10.1115/1.2817308.

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Development of steady and periodic unsteady wake flows downstream of stationary and rotating cylindrical rods within a curved channel under zero longitudinal pressure gradient is theoretically and experimentally investigated. Wake quantities such as the mean velocity and turbulent fluctuations in longitudinal and lateral directions, as well as the turbulent shear stress, are measured. For the nondimensionalized velocity defect, affine profiles are observed throughout the flow regime. Based on these observations and using the transformed equations of motion and continuity, a theoretical frame work is established that generally describes the two-dimensional curvilinear wake flow. To confirm the theory, development of steady and periodic unsteady wakes in the above curved channel are experimentally investigated. The detailed comparison between the measurement and the theory indicates that the complex steady and unsteady wake flows are very well predicted.

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Zhou, Yu, Yuan Huang, and Zhongqiang Mu. "Large eddy simulation of the influence of synthetic inlet turbulence on a practical aeroengine combustor with counter-rotating swirler." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 3 (December 25, 2017): 978–90. http://dx.doi.org/10.1177/0954410017745900.

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To study the influence of inlet turbulence on the prediction of flow structure in practical aeroengine combustor, large eddy simulation with dynamic Smagorinsky subgrid model is used to explore the complex unsteady flow field in a single burner of a typical aeroengine combustor with two-stage counter-rotating swirler. The complex geometric configuration including all film cooling holes is fully simulated without any conventional simplification in order to reduce the modeling errors. First, unsteady process that flow developing from static to statistically stationary state is fully simulated under laminar inlet condition to obtain a fundamental understanding of flow characteristics in the combustor. Afterwards, synthetic eddy method is utilized to generate a turbulent inlet condition so that a perturbation with about 5% turbulence intensity is superimposed to the inlet plane. Simulation result shows that for the laminar inflow case, flow separation occurs in the near-wall region of the diffusion section, inducing a boundary layer transition and consequently introducing turbulence with nonuniformity in space before the swirler. In contrast, synthesized inflow generated under turbulent inlet condition by synthetic eddy method is more spatially homogeneous. Time-averaged flow field inside the swirler cup reveals that turbulent inflow ultimately causes the swirling flow with higher rotating speed in central region and more uniform distribution along the circumferential direction. It also enhances the transverse jet flow from primary holes and reverse flow in the central recirculation zone, and makes streamlines corresponding to the recirculation vortices more symmetrical on central profile. Maximum recirculating velocity predicted in central recirculation zone is −27.65 m/s and −17.86 m/s in turbulent and laminar case respectively, and corresponding total pressure recovery coefficient is 96.03% and 96.81%.

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Fan, S., and B. Lakshminarayana. "Computation and Simulation of Wake-Generated Unsteady Pressure and Boundary Layers in Cascades: Part 1—Description of the Approach and Validation." Journal of Turbomachinery 118, no. 1 (January 1, 1996): 96–108. http://dx.doi.org/10.1115/1.2836612.

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The unsteady pressure and boundary layers on a turbomachinery blade row arising from periodic wakes due to upstream blade rows are investigated in this paper. A time-accurate Euler solver has been developed using an explicit four-stage Runge–Kutta scheme. Two-dimensional unsteady nonreflecting boundary conditions are used at the inlet and the outlet of the computational domain. The unsteady Euler solver captures the wake propagation and the resulting unsteady pressure field, which is then used as the input for a two-dimensional unsteady boundary layer procedure to predict the unsteady response of blade boundary layers. The boundary layer code includes an advanced k–ε model developed for unsteady turbulent boundary layers. The present computational procedure has been validated against analytic solutions and experimental measurements. The validation cases include unsteady inviscid flows in a flat-plate cascade and a compressor exit guide vane (EGV) cascade, unsteady turbulent boundary layer on a flat plate subject to a traveling wave, unsteady transitional boundary layer due to wake passing, and unsteady flow at the midspan section of an axial compressor stator. The present numerical procedure is both efficient and accurate in predicting the unsteady flow physics resulting from wake/blade-row interaction, including wake-induced unsteady transition of blade boundary layers.

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HUANG, J. F., L. X. ZHANG, and Y. K. GUO. "NUMERICAL SIMULATION OF HIGH REYNOLDS NUMBER TURBULENT FLOW IN A VANE PASSAGE." International Journal of Modern Physics: Conference Series 19 (January 2012): 83–89. http://dx.doi.org/10.1142/s2010194512008616.

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The numerical simulations of two-dimensional high Reynolds number turbulent flow in a guide vane passage of a Francis hydro turbine are performed successfully by using the unstructured dynamic mesh model for moving body. The standard K – ε turbulence model is employed for the simulation of turbulence. The pressure-velocity coupling method is realized with the SIMPLEC algorithm. The temporal distributions of the pressure and turbulent viscosity in a passage were obtained in the closing of wicket gate on a platform of the software ANSYS FLUENT. The results show that the evolution of the flow field is unsteady with decrease of the geometrical opening of the gate. The details of the flow changes are obtained in the moving rigid body domain. The method can be used to simulate the high Reynolds number incompressible turbulent flow with moving boundary. The calculation provides some references for vortex-induced vibration of the structure in a complex turbulent flow.

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Wylie, E. B. "Frictional Effects in Unsteady Turbulent Pipe Flows." Applied Mechanics Reviews 50, no. 11S (November 1, 1997): S241—S244. http://dx.doi.org/10.1115/1.3101843.

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In the simulation of rapid transient events in fluid-filled pipelines, the method of characteristics is recognized to provide reliable results during the first pressure excursion. However, if a long term oscillatory response of a rapid event is needed, traditional methods of evaluating viscous losses are inadequate in low Reynolds number turbulent flow events. This paper looks at a method to implement frequency-dependent viscous losses in the method of characteristics for turbulent flow and provides comparisons with experimental records.

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Wang, Chun Lin, Tian Fang Zhang, Chun Lei Zhao, and Dong Liu. "3-D Numerical Simulation on Unsteady Turbulent Flow of Rotational Flow Self-Priming Pump." Advanced Materials Research 562-564 (August 2012): 899–902. http://dx.doi.org/10.4028/www.scientific.net/amr.562-564.899.

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The three-dimensional unsteady turbulent flow of rotational flow self-priming pump was simulated by using Reynolds time-averaged N-S equations and the standard k-ε turbulent model, sliding mesh model of static-dynamic coupled models and SIMPLE arithmetic. The static pressure distribution of the pump central rotative surface and relative velocity of the impeller central rotative surface in a complete application cycle were analyzed. The rule of instantaneous head in a impeller channel cycle was studied, and the positions of maximal head and minimal head were analyzed. It revealed that the unsteady method can truly simulate the changes of the rotational flow self-priming pump interior flow, and the unsteady characteristic of interior flow in rotational flow self-priming pump is obvious and it changes as the relative position of impeller and volute change. The change is periodical, and its frequency is relate to the impeller number and the rotate speed of the pump.

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43

Kasagi, N., A. Kuroda, and M. Hirata. "Numerical Investigation of Near-Wall Turbulent Heat Transfer Taking Into Account the Unsteady Heat Conduction in the Solid Wall." Journal of Heat Transfer 111, no. 2 (May 1, 1989): 385–92. http://dx.doi.org/10.1115/1.3250689.

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The deterministic near-wall turbulence model developed by Kasagi et al. (1984b) is used in a numerical analysis of turbulent heat transfer, in which the unsteady heat conduction inside the wall associated with the turbulent flow unsteadiness is taken into account. Unlike the typical methodology based on Reynolds decomposition, the algebraic expressions for the three fluctuating velocities given by the model are directly introduced into the governing energy equation. From the numerical results of the unsteady conjugate heat transfer, the statistical quantities, such as temperature variance, turbulent heat flux, and turbulent Prandtl number, are obtained for fluids of various Prandtl numbers. It is demonstrated that the near-wall behavior of these quantities is strongly influenced by the thermal properties and thickness of the wall. In addition, the budget of the temperature variance associated with coherent turbulence structure is calculated and, except for dissipation, each budget term is in qualitative agreement with the experiment.

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44

Hwang, C. J., and J. L. Liu. "Analysis of Steady and Unsteady Turbine Cascade Flows by a Locally Implicit Hybrid Algorithm." Journal of Turbomachinery 115, no. 4 (October 1, 1993): 699–706. http://dx.doi.org/10.1115/1.2929305.

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For the two-dimensional steady and unsteady turbine cascade flows, the Euler/Navier–Stokes equations with Baldwin-Lomax turbulence model are solved in the Cartesian coordinate system. A locally implicit hybrid algorithm on mixed meshes is employed, where the convection-dominated part in the flow field is studied by a TVD scheme to obtain high-resolution results on the triangular elements, and the second- and fourth-order dissipative model is introduced on the O-type quadrilateral grid in the viscous-dominated region to minimize the numerical dissipation. When the steady subsonic and transonic turbulent flows are investigated, the distributions of isentropic Mach number on the blade surface, exit flow angle, and loss coefficient are obtained. Comparing the present results with the experimental data, the accuracy and reliability of the current approach are confirmed. By giving a moving wake-type total pressure profile at the inlet plane in the rotor-relative frame of reference, the unsteady transonic inviscid and turbulent flows calculations are performed to study the interaction of the upstream wake with a moving blade row. The Mach number contours, perturbation component of the unsteady velocity vectors, shear stress, and pressure distributions on the blade surface are presented. The physical phenomena, which include periodic flow separation on the suction side, bowing, chopping and distortion of incoming wake, negative jet, convection of the vortices and wake segments, and vortex shedding at the trailing edge, are observed. It is concluded that the unsteady aerodynamic behavior is strongly dependent on the wake/shock/boundary layer interactions.

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Petit, Olivier, and Håkan Nilsson. "Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser." International Journal of Rotating Machinery 2013 (2013): 1–14. http://dx.doi.org/10.1155/2013/961580.

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Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.

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HSU, T. Y., H. ELORANTA, P. SAARENRINNE, and T. WEI. "Turbulent flow through a rectangular duct with a partially blocked exit." Journal of Fluid Mechanics 592 (November 14, 2007): 51–78. http://dx.doi.org/10.1017/s0022112007008300.

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This paper contains data on and insights into the origins of turbulence associated with a partial blockage at the exit of a two-dimensional, laminar, horizontal duct flow. In essence, this is the upstream approach region of the forward-facing step problem. This work was motivated by the need to identify and control unsteady streamwise vortices generated in the headbox (i.e. contraction section) of an industrial paper machine. The duct was 57.2 cm wide × 10.16 cm high, with up to a 50 % blockage. Experiments were scaled to match Reynolds numbers found in paper machines; exit velocities were as large as 200 cm s−1. The goal of the research was to map the flow at the exit and to examine the response of the flat-plate turbulent boundary layer on the opposing wall under the partial blockage. Laser-induced fluorescence (LIF) and digital particle image velocimetry (DPIV) were used to examine flow in three orthogonal planes at various stations upstream of the duct exit. Mean and instantaneous DPIV vector fields clearly show that an unsteady spanwise vortex forms in the corner formed by the top nozzle wall and partial blockage which, in turn, gives rise to turbulent streamwise vortices.A turbulent boundary layer was initiated on the duct wall opposite the blockage, upstream of a two-dimensional contraction. Results show that even though the acceleration parameter, K, exceeded the nominal critical level of 3.0 × 10−6 for relaminarization beneath the blockage, the flow did not reach a quasi-laminar state. In addition, there did not appear to be direct interaction between unsteady vortex formation at the partial blockage on the upper wall and bottom-wall turbulent boundary layer structures.

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He, S., C. Ariyaratne, and A. E. Vardy. "Wall shear stress in accelerating turbulent pipe flow." Journal of Fluid Mechanics 685 (September 21, 2011): 440–60. http://dx.doi.org/10.1017/jfm.2011.328.

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AbstractAn experimental study of wall shear stress in an accelerating flow of water in a pipe ramping between two steady turbulent flows has been undertaken in a large-scale experimental facility. Ensemble averaged mean and r.m.s. of the turbulent fluctuations of wall shear stresses have been derived from hot-film measurements from many repeated runs. The initial Reynolds number and the acceleration rate were varied systematically to give values of a non-dimensional acceleration parameter $k$ ranging from 0.16 to 14. The wall shear stress has been shown to follow a three-stage development. Stage 1 is associated with a period of minimal turbulence response; the measured turbulent wall shear stress remains largely unchanged except for a very slow increase which is readily associated with the stretching of existing turbulent eddies as a result of flow acceleration. In this condition of nearly ‘frozen’ turbulence, the unsteady wall shear stress is driven primarily by flow inertia, initially increasing rapidly and overshooting the pseudo-steady value, but then increasing more slowly and eventually falling below the pseudo-steady value. This variation is predicted by an analytical expression derived from a laminar flow formulation. The start of Stage 2 is marked by the generation of new turbulence causing both the mean and turbulent wall shear stress to increase rapidly, although there is a clear offset between the responses of these two quantities. The turbulent wall shear, reflecting local turbulent activities near the wall, responds first and the mean wall shear, reflecting conditions across the entire flow field, responds somewhat later. In Stage 3, the wall shear stress exhibits a quasi-steady variation. The duration of the initial period of nearly frozen turbulence response close to the wall increases with decreasing initial Reynolds number and with increasing acceleration. The latter is in contrast to the response of turbulence in the core of the flow, which previous measurements have shown to be independent of the rate of acceleration.

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Holman, Jiří. "Unsteady Flow past a Circular Cylinder Using Advanced Turbulence Models." Applied Mechanics and Materials 821 (January 2016): 23–30. http://dx.doi.org/10.4028/www.scientific.net/amm.821.23.

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This work deals with the numerical simulation of unsteady compressible turbulent flow past a circular cylinder. Turbulent flow is modeled by two different methods. The first method is based on the system of URANS equations closed by the two equation TNT model or modified EARSM model. Second method is based on the X-LES model, which is a hybrid RANS-LES method. Numerical solution is obtained by the finite volume method. Presented results are for the sub-critical turbulent flow characterized by Re=3900.

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Doorly, D. J. "Modeling the Unsteady Flow in a Turbine Rotor Passage." Journal of Turbomachinery 110, no. 1 (January 1, 1988): 27–37. http://dx.doi.org/10.1115/1.3262164.

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The effects of the wakes shed by an upstream blade row in forcing the transition of an otherwise laminar rotor blade boundary layer are well recognized. Previous experiments have demonstrated that the forced transition of the laminar boundary layer may greatly influence the surface heat flux. The effect of the wakes on the surface heat flux when the undisturbed boundary layer is already turbulent have been studied using an experimental simulation technique. The results have been analyzed with a view to establishing how well the effects of the wakes can be described by a model which treats only their turbulence content. The effects of wake passing at a reduced Reynolds number are also reported.

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García García, F. Javier, and Pablo Fariñas Alvariño. "On an analytic solution for general unsteady/transient turbulent pipe flow and starting turbulent flow." European Journal of Mechanics - B/Fluids 74 (March 2019): 200–210. http://dx.doi.org/10.1016/j.euromechflu.2018.11.014.

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Journal articles on the topic 'Unsteady Turbulent Flow'

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