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Naveen, Janjanam, A. Eswara Kumar, and M. Nagaraju. "Analysis of Fluid Structure Interaction in High Pressure Elbow Pipe Connections." Applied Mechanics and Materials 813-814 (November 2015): 1075–79. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.1075.
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Pipes in power plants generally subjected to high pressures and temperatures. These are connected by elbow, T-joints to get the continuity between different stages. Due to excessive joints the outlet velocity and pressure will drops by considerable amount. Stresses will be produced due to high pressure and temperature of fluid flow, which in turn creates the failure of the pipes. The turbulence of the fluid passing through the pipes will also plays a vital role to decide the outlet pressure and velocity. In this present study pipes are connected by the elbow joint are considered and observed the effect of pipe thickness, turbulence intensity and length of elbow on outlet pressure, velocity, von mises stress and turbulence kinetic energy. It results that with increase in pipe thickness and length of elbow, the velocity, von mises stress and turbulence kinetic energy are decreases but with increase in turbulence intensity, the velocity and turbulence kinetic energy are increases.
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Tian, Yifeng, Farhad A. Jaberi, and Daniel Livescu. "Density effects on post-shock turbulence structure and dynamics." Journal of Fluid Mechanics 880 (October 18, 2019): 935–68. http://dx.doi.org/10.1017/jfm.2019.707.
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Turbulence structure resulting from multi-fluid or multi-species, variable-density isotropic turbulence interaction with a Mach 2 shock is studied using turbulence-resolving shock-capturing simulations and Eulerian (grid) and Lagrangian (particle) methods. The complex roles that density plays in the modification of turbulence by the shock wave are identified. Statistical analyses of the velocity gradient tensor (VGT) show that density variations significantly change the turbulence structure and flow topology. Specifically, a stronger symmetrization of the joint probability density function (PDF) of second and third invariants of the anisotropic VGT, PDF$(Q^{\ast },R^{\ast })$, as well as the PDF of the vortex stretching contribution to the enstrophy equation, are observed in the multi-species case. Furthermore, subsequent to the interaction with the shock, turbulent statistics also acquire a differential distribution in regions having different densities. This results in a nearly symmetric PDF$(Q^{\ast },R^{\ast })$ in heavy-fluid regions, while the light-fluid regions retain the characteristic tear-drop shape. To understand this behaviour and the return to ‘standard’ turbulence structure as the flow evolves away from the shock, Lagrangian dynamics of the VGT and its invariants is studied by considering particle residence times and conditional particle variables in different flow regions. The pressure Hessian contributions to the VGT invariants transport equations are shown to be not only affected by the shock wave, but also by the density in the multi-fluid case, making them critically important to the flow dynamics and turbulence structure.
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TAKIZAWA, KENJI, and TAYFUN E. TEZDUYAR. "SPACE–TIME FLUID–STRUCTURE INTERACTION METHODS." Mathematical Models and Methods in Applied Sciences 22, supp02 (July 25, 2012): 1230001. http://dx.doi.org/10.1142/s0218202512300013.
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Since its introduction in 1991 for computation of flow problems with moving boundaries and interfaces, the Deforming-Spatial-Domain/Stabilized Space–Time (DSD/SST) formulation has been applied to a diverse set of challenging problems. The classes of problems computed include free-surface and two-fluid flows, fluid–object, fluid–particle and fluid–structure interaction (FSI), and flows with mechanical components in fast, linear or rotational relative motion. The DSD/SST formulation, as a core technology, is being used for some of the most challenging FSI problems, including parachute modeling and arterial FSI. Versions of the DSD/SST formulation introduced in recent years serve as lower-cost alternatives. More recent variational multiscale (VMS) version, which is called DSD/SST-VMST (and also ST-VMS), has brought better computational accuracy and serves as a reliable turbulence model. Special space–time FSI techniques introduced for specific classes of problems, such as parachute modeling and arterial FSI, have increased the scope and accuracy of the FSI modeling in those classes of computations. This paper provides an overview of the core space–time FSI technique, its recent versions, and the special space–time FSI techniques. The paper includes test computations with the DSD/SST-VMST technique.
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Perera, M. J. A. M., H. J. S. Fernando, and D. L. Boyer. "Turbulent mixing at an inversion layer." Journal of Fluid Mechanics 267 (May 25, 1994): 275–98. http://dx.doi.org/10.1017/s0022112094001187.
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A series of laboratory experiments was carried out to examine the interaction between stratification and turbulence at an inversion layer, with the objective of gaining insight into certain wave–turbulence encounters in the atmosphere. A three-layer stratified fluid system, consisting of a (thick) strongly stratified inversion layer, sandwiched between an upper turbulent layer and a lower non-turbulent weakly stratified layer, was employed. Oscillating-grid-induced shear-free turbulence was used in the upper layer. During the experiments, a fourth (interfacial) layer developed in the region between the inversion and the turbulent layer, and most of the wave–turbulence interactions were confined to this layer. Detailed measurements of the vertical velocity structure, internal-wave parameters and mixing characteristics were made in the stratified layers and, whenever possible, the results were compared to available theoretical predictions.
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Tian, Yifeng, Farhad A. Jaberi, Zhaorui Li, and Daniel Livescu. "Numerical study of variable density turbulence interaction with a normal shock wave." Journal of Fluid Mechanics 829 (September 22, 2017): 551–88. http://dx.doi.org/10.1017/jfm.2017.542.
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Accurate numerical simulations of shock–turbulence interaction (STI) are conducted with a hybrid monotonicity-preserving–compact-finite-difference scheme for a detailed study of STI in variable density flows. Theoretical and numerical assessments of data confirm that all turbulence scales as well as the STI are well captured by the computational method. Linear interaction approximation (LIA) convergence tests conducted with the shock-capturing simulations exhibit a similar trend of converging to LIA predictions to shock-resolving direct numerical simulations (DNS). The effects of density variations on STI are studied by comparing the results corresponding to an upstream multi-fluid mixture with the single-fluid case. The results show that for the current parameter ranges, the turbulence amplification by the normal shock wave is much higher and the reduction in turbulence length scales is more significant when strong density variations exist. Turbulent mixing enhancement by the shock is also increased and stronger mixing asymmetry in the postshock region is observed when there is significant density variation. The turbulence structure is strongly modified by the shock wave, with a differential distribution of turbulent statistics in regions having different densities. The dominant mechanisms behind the variable density STI are identified by analysing the transport equations for the Reynolds stresses, vorticity, normalized mass flux and density specific volume covariance.
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Carbone, M., A. D. Bragg, and M. Iovieno. "Multiscale fluid–particle thermal interaction in isotropic turbulence." Journal of Fluid Mechanics 881 (October 25, 2019): 679–721. http://dx.doi.org/10.1017/jfm.2019.773.
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We use direct numerical simulations to investigate the interaction between the temperature field of a fluid and the temperature of small particles suspended in the flow, employing both one- and two-way thermal coupling, in a statistically stationary, isotropic turbulent flow. Using statistical analysis, we investigate this variegated interaction at the different scales of the flow. We find that the variance of the carrier flow temperature gradients decreases as the thermal response time of the suspended particles is increased. The probability density function (PDF) of the carrier flow temperature gradients scales with its variance, while the PDF of the rate of change of the particle temperature, whose variance is associated with the thermal dissipation due to the particles, does not scale in such a self-similar way. The modification of the fluid temperature field due to the particles is examined by computing the particle concentration and particle heat fluxes conditioned on the magnitude of the local fluid temperature gradient. These statistics highlight that the particles cluster on the fluid temperature fronts, and the important role played by the alignments of the particle velocity and the local fluid temperature gradient. The temperature structure functions, which characterize the temperature fluctuations across the scales of the flow, clearly show that the fluctuations of the carrier flow temperature increments are monotonically suppressed in the two-way coupled regime as the particle thermal response time is increased. Thermal caustics dominate the particle temperature increments at small scales, that is, particles that come into contact are likely to have very large differences in their temperatures. This is caused by the non-local thermal dynamics of the particles: the scaling exponents of the inertial particle temperature structure functions in the dissipation range reveal very strong multifractal behaviour. Further insight is provided by the flux of temperature increments across the scales. Altogether, these results reveal a number of non-trivial effects, with a number of important practical consequences.
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Sharma, A. S., and B. J. McKeon. "On coherent structure in wall turbulence." Journal of Fluid Mechanics 728 (July 8, 2013): 196–238. http://dx.doi.org/10.1017/jfm.2013.286.
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AbstractA new theory of coherent structure in wall turbulence is presented. The theory is the first to predict packets of hairpin vortices and other structure in turbulence, and their dynamics, based on an analysis of the Navier–Stokes equations, under an assumption of a turbulent mean profile. The assumption of the turbulent mean acts as a restriction on the class of possible structures. It is shown that the coherent structure is a manifestation of essentially low-dimensional flow dynamics, arising from a critical-layer mechanism. Using the decomposition presented in McKeon & Sharma (J. Fluid Mech., vol. 658, 2010, pp. 336–382), complex coherent structure is recreated from minimal superpositions of response modes predicted by the analysis, which take the form of radially varying travelling waves. The leading modes effectively constitute a low-dimensional description of the turbulent flow, which is optimal in the sense of describing the resonant effects around the critical layer and which minimally predicts all types of structure. The approach is general for the full range of scales. By way of example, simple combinations of these modes are offered that predict hairpins and modulated hairpin packets. The example combinations are chosen to represent observed structure, consistent with the nonlinear triadic interaction for wavenumbers that is required for self-interaction of structures. The combination of the three leading response modes at streamwise wavenumbers $6, ~1, ~7$ and spanwise wavenumbers $\pm 6, ~\pm 6, ~\pm 12$, respectively, with phase velocity $2/ 3$, is understood to represent a turbulence ‘kernel’, which, it is proposed, constitutes a self-exciting process analogous to the near-wall cycle. Together, these interactions explain how the mode combinations may self-organize and self-sustain to produce experimentally observed structure. The phase interaction also leads to insight into skewness and correlation results known in the literature. It is also shown that the very large-scale motions act to organize hairpin-like structures such that they co-locate with areas of low streamwise momentum, by a mechanism of locally altering the shear profile. These energetic streamwise structures arise naturally from the resolvent analysis, rather than by a summation of hairpin packets. In addition, these packets are modulated through a ‘beat’ effect. The relationship between Taylor’s hypothesis and coherence is discussed, and both are shown to be the consequence of the localization of the response modes around the critical layer. A pleasing link is made to the classical laminar inviscid theory, whereby the essential mechanism underlying the hairpin vortex is captured by two obliquely interacting Kelvin–Stuart (cat’s eye) vortices. Evidence for the theory is presented based on comparison with observations of structure in turbulent flow reported in the experimental and numerical simulation literature and with exact solutions reported in the transitional literature.
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Miyanawala, T. P., and R. K. Jaiman. "Decomposition of wake dynamics in fluid–structure interaction via low-dimensional models." Journal of Fluid Mechanics 867 (March 28, 2019): 723–64. http://dx.doi.org/10.1017/jfm.2019.140.
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We present a dynamic decomposition analysis of the wake flow in fluid–structure interaction (FSI) systems under both laminar and turbulent flow conditions. Of particular interest is to provide the significance of low-dimensional wake flow features and their interaction dynamics to sustain the free vibration of a square cylinder at a relatively low mass ratio. To obtain the high-dimensional data, we employ a body-conforming variational FSI solver based on the recently developed partitioned iterative scheme and the dynamic subgrid-scale turbulence model for a moderate Reynolds number ($Re$). The snapshot data from high-dimensional FSI simulations are projected to a low-dimensional subspace using the proper orthogonal decomposition (POD). We utilize each corresponding POD mode to detect features of the organized motions, namely, the vortex street, the shear layer and the near-wake bubble. We find that the vortex shedding modes contribute solely to the lift force, while the near-wake and shear layer modes play a dominant role in the drag force. We further examine the fundamental mechanism of this dynamical behaviour and propose a force decomposition technique via low-dimensional approximation. To elucidate the frequency lock-in, we systematically analyse the decomposed modes and their dynamical contributions to the force fluctuations for a range of reduced velocity at low Reynolds number laminar flow. These quantitative mode energy contributions demonstrate that the shear layer feeds the vorticity flux to the wake vortices and the near-wake bubble during the wake–body synchronization. Based on the decomposition of wake dynamics, we suggest an interaction cycle for the frequency lock-in during the wake–body interaction, which provides the interrelationship between the high-amplitude motion and the dominating wake features. Through our investigation of wake–body synchronization below critical $Re$ range, we discover that the bluff body can undergo a synchronized high-amplitude vibration due to flexibility-induced unsteadiness. Owing to the wake turbulence at a moderate Reynolds number of $Re=22\,000$, a distorted set of POD modes and the broadband energy distribution are observed, while the interaction cycle for the wake synchronization is found to be valid for the turbulent wake flow.
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TAN, F. P. P., R. TORII, A. BORGHI, R. H. MOHIADDIN, N. B. WOOD, and X. Y. XU. "FLUID-STRUCTURE INTERACTION ANALYSIS OF WALL STRESS AND FLOW PATTERNS IN A THORACIC AORTIC ANEURYSM." International Journal of Applied Mechanics 01, no. 01 (March 2009): 179–99. http://dx.doi.org/10.1142/s1758825109000095.
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In this study, fluid-structure interaction (FSI) simulation was carried out to predict wall shear stress (WSS) and blood flow patterns in a thoracic aortic aneurysm (TAA) where haemodynamic stresses on the diseased aortic wall are thought to lead to the growth, progression and rupture of the aneurysm. Based on MR images, a patient-specific TAA model was reconstructed. A newly developed two-equation laminar-turbulent transitional model was employed and realistic velocity and pressure waveforms were used as boundary conditions. Analysis of results include turbulence intensity, wall displacement, WSS, wall tensile stress and comparison of velocity profiles between MRI data, rigid and FSI simulations. Velocity profiles demonstrated that the FSI simulation gave better agreement with the MRI data while results for the time-averaged WSS (TAWSS) and oscillatory shear index (OSI) distributions showed no qualitative differences between the simulations. With the FSI model, the maximum TAWSS value was 13% lower, whereas the turbulence intensity was significantly higher than the rigid model. The FSI simulation also provided results for wall mechanical stress in terms of von Mises stress, allowing regions of high wall stress to be identified.
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Zhang, Liaojun, Shuo Wang, Guojiang Yin, and Chaonian Guan. "Fluid–structure interaction analysis of fluid pressure pulsation and structural vibration features in a vertical axial pump." Advances in Mechanical Engineering 11, no. 3 (March 2019): 168781401982858. http://dx.doi.org/10.1177/1687814019828585.
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Current studies on the operation of the axial pump mainly focus on hydraulic performances, while the coupled interaction between the fluid and structure attracts little attention. This study aims to provide numerical investigation into the vibration features in a vertical axial pump based on two-way iterative fluid–structure interaction method. Three-dimensional coupling model was established with high-quality structured grids of ADINA software. Turbulent flow features were studied under design condition, using shear–stress transport k-ω turbulence model and sliding mesh approach. Typical measure points along and perpendicular to flow direction in fluid domain were selected to analyze pressure pulsation features of the impeller and fixed guide vane. By contrast, vibration features of equivalent stress in corresponding structural positions were investigated and compared based on fluid–structure interaction method. In order to explore fluid–structure interaction vibration mechanism, distribution of main frequencies and amplitudes of the measure points was presented based on the Fast Fourier Transformation method. The results reveal the time and frequency law of fluid pressure pulsation and structural vibration at the same position in the vertical axial pump while additionally provide important theoretical guidance for optimization design and safe operation of the vertical axial pump.
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ZHANG, LIXIANG, WENQUAN WANG, and YAKUN GUO. "NUMERICAL SIMULATION OF FLOW FEATURES AND ENERGY EXCHANGE PHYSICS IN NEAR-WALL REGION WITH FLUID-STRUCTURE INTERACTION." International Journal of Modern Physics B 22, no. 06 (March 10, 2008): 651–69. http://dx.doi.org/10.1142/s0217979208038806.
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Large eddy simulation is used to explore flow features and energy exchange physics between turbulent flow and structure vibration in the near-wall region with fluid–structure interaction (FSI). The statistical turbulence characteristics in the near-wall region of a vibrating wall, such as the skin frictional coefficient, velocity, pressure, vortices, and the coherent structures have been studied for an aerofoil blade passage of a true three-dimensional hydroturbine. The results show that (i) FSI greatly strengthens the turbulence in the inner region of y+ < 25; and (ii) the energy exchange mechanism between the flow and the vibration depends strongly on the vibration-induced vorticity in the inner region. The structural vibration provokes a frequent action between the low- and high-speed streaks to balance the energy deficit caused by the vibration. The velocity profile in the inner layer near the vibrating wall has a significant distinctness, and the viscosity effect of the fluid in the inner region decreases due to the vibration. The flow features in the inner layer are altered by a suitable wall vibration.
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Grinderslev, Christian, Niels Nørmark Sørensen, Sergio González Horcas, Niels Troldborg, and Frederik Zahle. "Wind turbines in atmospheric flow: fluid–structure interaction simulations with hybrid turbulence modeling." Wind Energy Science 6, no. 3 (May 6, 2021): 627–43. http://dx.doi.org/10.5194/wes-6-627-2021.
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Abstract. In order to design future large wind turbines, knowledge is needed about the impact of aero-elasticity on the rotor loads and performance and about the physics of the atmospheric flow surrounding the turbines. The objective of the present work is to study both effects by means of high-fidelity rotor-resolved numerical simulations. In particular, unsteady computational fluid dynamics (CFD) simulations of a 2.3 MW wind turbine are conducted, this rotor being the largest design with relevant experimental data available to the authors. Turbulence is modeled with two different approaches. On one hand, a model using the well-established technique of improved delayed detached eddy simulation (IDDES) is employed. An additional set of simulations relies on a novel hybrid turbulence model, developed within the framework of the present work. It consists of a blend of a large-eddy simulation (LES) model by Deardorff for atmospheric flow and an IDDES model for the separated flow near the rotor geometry. In the same way, the assessment of the influence of the blade flexibility is performed by comparing two different sets of computations. The first group accounts for a structural multi-body dynamics (MBD) model of the blades. The MBD solver was coupled to the CFD solver during run time with a staggered fluid–structure interaction (FSI) scheme. The second set of simulations uses the original rotor geometry, without accounting for any structural deflection. The results of the present work show no significant difference between the IDDES and the hybrid turbulence model. In a similar manner, and due to the fact that the considered rotor was relatively stiff, the loading variation introduced by the blade flexibility was found to be negligible when compared to the influence of inflow turbulence. The simulation method validated here is considered highly relevant for future turbine designs, where the impact of blade elasticity will be significant and the detailed structure of the atmospheric inflow will be important.
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Bao, Wen Bo, Yu Yong Hu, and Yang Cui. "Wind Loads Simulation of Tall Building Structure Subjected to Wind-Structure Interaction." Advanced Materials Research 163-167 (December 2010): 4286–89. http://dx.doi.org/10.4028/www.scientific.net/amr.163-167.4286.
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Wind is an important and complex load and an important basis in the structural analysis and the design of high-rise structure. Based on Davenport wind spectrum, multi-dimensional fluctuating wind and random wind load of tall building structure are simulated by using harmonic wave superposition method. To investigate the coupling effect of wind loads, wind-structure system is solved with Wilson-θ step-by-step numerical integration method, and the wind load of Tall building structure subjected to fluid-structure interaction. Turbulence intensity and its variation are presented in this paper.
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Shen, Bin Xian, and Wei Qiang Liu. "Numerical Simulation of Turbulence-Chemical Interaction Models on Combustible Particle MILD Combustion." Advanced Materials Research 1070-1072 (December 2014): 1752–57. http://dx.doi.org/10.4028/www.scientific.net/amr.1070-1072.1752.
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Typical combustible particle coal has been analyzed by using turbulence-chemistry interaction models to realize which models are more accurate and reasonable on pulverized coal MILD combustion. Three turbulence-chemistry interaction models are examined: the Equilibrium Mixture Fraction/PDF (PDF), the Eddy Break Up (EBU), the Eddy Dissipation Concept (EDC). All of three models can give a suitable prediction of axial velocity on combustible particle coal MILD combustion because turbulence-chemistry interaction models have little influence on flow field and flow structure. The Eddy Dissipation Concept model (EDC), based on advanced turbulence-chemistry interaction with global and detailed kinetic mechanisms can produce satisfactory results on chemical and fluid dynamic behavior of combustible particle coal MILD combustion, especially on temperature and species concentrations.
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Zhang, Hong Ming, and Li Xiang Zhang. "Numerical Simulation of Fluid-Structure Interaction with Water Hammer in a Vertical Penstock Subjected to High Water Head." Advanced Materials Research 860-863 (December 2013): 1530–34. http://dx.doi.org/10.4028/www.scientific.net/amr.860-863.1530.
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The theoretical model of weakly compressible coupling water hammer was established and a FSI program code was developed for coupled weakly compressible water with penstock movement. It combines the weakly compressible water source CFD code and FEM shell element code. The shell element based on orthogonal curvilinear coordinates was completed in FEAP. Meanwhile, the turbulence model in OpenFoam class library was called by using object-oriented technology. This code takes into account both the weak compressibility of water and fluid turbulence characteristics. Using this code, a fluid structure interaction analysis with water hammer was completed. The numerical results agree well with the field test results.
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Cheng, Han, Li Yu, Wei Rong, and He Jia. "A NUMERICAL STUDY OF PARACHUTE INFLATION BASED ON A MIXED METHOD." Aviation 16, no. 4 (December 24, 2012): 115–23. http://dx.doi.org/10.3846/16487788.2012.753676.
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ἀ e C9 parachute was the research object in this work and was studied by using a fluid-structure interaction method and CFD method. An arbitrary Lagrangian-Eulerian method, a kind of fluid-structure interaction method, was used to simulate the inflation process. ἀ e dynamic relationship between canopy shape and flow field was obtained. ἀ e canopy shape in a stable phase was exported and was transformed into the porous media domain. ἀ en the flow around the canopy shape was simulated by the CFD method we used based on the k-ε turbulence model. ἀ e experiments verified the accuracy of structural change and the feasibility of the porous media model. ἀ e arbitrary Lagrangian-Eulerian method not only can obtain the dynamic results of structure and flow field but also can provide a more accurate bluff body for further CFD analysis. ἀ e CFD method based on porous media and the turbulence model can obtain more detailed and accurate flow field results, which can be used as a complement to fluid-structure interaction analysis. ἀi s mixed method can improve the accuracy of analysis and be useful for other permeable fabric research.
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Formato, Gaetano, Raffaele Romano, Andrea Formato, Joonas Sorvari, Tuomas Koiranen, Arcangelo Pellegrino, and Francesco Villecco. "Fluid–Structure Interaction Modeling Applied to Peristaltic Pump Flow Simulations." Machines 7, no. 3 (July 9, 2019): 50. http://dx.doi.org/10.3390/machines7030050.
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In this study, fluid–structure interaction (FSI) modeling was applied for predicting the fluid flow in a specific peristaltic pump, composed of one metallic roller and a hyperelastic tube pumping a viscous Newtonian fluid. Hyperelastic material dynamics and turbulence flow dynamics were coupled in order to describe all the physics of the pump. The commercial finite element software ABAQUS 6.14 was used to investigate the performance of the pump with a 3D transient model. By using this model, it was possible to predict the von Mises stresses in the tube and flow fluctuations. The peristaltic pump generated high pressure and flow pulses due to the interaction between the roller and the tube. The squeezing and relaxing of the tube during the operative phase allowed the liquid to have a pulsatile behavior. Numerical simulation data results were compared with one cycle pressure measurement obtained from pump test loop data, and the maximum difference between real and simulated data was less than 5%. The applicability of FSI modeling for geometric optimization of pump housing was also discussed in order to prevent roller and hose parts pressure peaks. The model allowed to investigate the effect of pump design variations such as tube occlusion, tube diameter, and roller speed on the flow rate, flow fluctuations, and stress state in the tube.
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Noguchi, K., I. Nezu, and M. Sanjou. "Turbulence structure and fluid–particle interaction in sediment-laden flows over developing sand dunes." Environmental Fluid Mechanics 8, no. 5-6 (November 7, 2008): 569–78. http://dx.doi.org/10.1007/s10652-008-9114-3.
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Lund, E., H. Møller, and L. A. Jakobsen. "Shape design optimization of stationary fluid-structure interaction problems with large displacements and turbulence." Structural and Multidisciplinary Optimization 25, no. 5-6 (December 2003): 383–92. http://dx.doi.org/10.1007/s00158-003-0288-5.
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Yang, P., J. Xiang, F. Fang, and C. C. Pain. "A fidelity fluid-structure interaction model for vertical axis tidal turbines in turbulence flows." Applied Energy 236 (February 2019): 465–77. http://dx.doi.org/10.1016/j.apenergy.2018.11.070.
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Sakthivel, R., S. Vengadesan, and S. K. Bhattacharyya. "Application of non-linear k-e turbulence model in flow simulation over underwater axisymmetric hull at higher angle of attack." Journal of Naval Architecture and Marine Engineering 8, no. 2 (November 22, 2011): 149–63. http://dx.doi.org/10.3329/jname.v8i2.6984.
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This paper addresses the Computational Fluid Dynamics Approach (CFD) to simulate the flow over underwater axisymmetric bodies at higher angle of attacks. Three Dimensional (3D) flow simulation is carried out over MAYA Autonomous Underwater Vehicle (AUV) at a Reynolds number (Re) of 2.09×106. These 3D flows are complex due to cross flow interaction with hull which produces nonlinearity in the flow. Cross flow interaction between pressure side and suction side is studied in the presence of angle of attack. For the present study standard k-ε model, non-linear k-ε model models of turbulence are used for solving the Reynolds Averaged Navier-Stokes Equation (RANS). The non-linear k-ε turbulence model is validated against DARPA Suboff axisymmetric hull and its applicability for flow simulation over underwater axisymmetric hull is examined. The non-linear k-ε model performs well in 3D complex turbulent flows with flow separation and flow reattachment. The effect of angle of attack over flow structure, force coefficients and wall related flow variables are discussed in detail. Keywords: Computational Fluid Dynamics (CFD); Autonomous Underwater Vehicle (AUV); Reynolds averaged Navier-Stokes Equation (RANS); non-linear k-ε turbulence modeldoi: http://dx.doi.org/10.3329/jname.v8i2.6984 Journal of Naval Architecture and Marine Engineering 8(2011) 149-163
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Banerjee, Sanjoy. "Upwellings, Downdrafts, and Whirlpools: Dominant Structures in Free Surface Turbulence." Applied Mechanics Reviews 47, no. 6S (June 1, 1994): S166—S172. http://dx.doi.org/10.1115/1.3124398.
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Fluid motion at flat, unsheared interfaces develops primarily due to impingement of coherent turbulent structures from the far field. On the other hand, when shear is imposed, alternating low-speed/high-speed regions are formed with ejection-sweep cycles qualitatively similar to those seen in wall turbulence. The transition to this “active” state depends on a shear rate non-dimensionalized by the Reynolds stress and dissipation rate. Turning back to the unsheared (or free) surface case, the bulk turbulence structures cause “upwellings” when they approach the interface. The regions between upwellings appear as stagnation lines on the surface plane—the surface-normal velocity being downwards. Whirlpool-like attached vortices also form at the edges of the upwellings. These attached vortices are remarkably persistent—the main annihilation mechanism being interaction with a subsequent upwelling. For situations where the surface patterns convect away from a region of turbulence generation, i.e. a decaying pattern, the attached vortices become the dominant structure since new upwellings and downdrafts are not formed. The attached vortices pair and decay in a manner such that the near-surface turbulence structure is essentially two-dimensional. Even in situations where turbulence generation occurs quite close to the free-surface, measures such as energy spectra indicate a quasi two-dimensional near-surface structure.
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Priambudi Setyo Pratomo, Hariyo, Fandi Dwiputra Suprianto, and Teng Sutrisno. "Preliminary Study on Mesh Stiffness Models for Fluid-structure Interaction Problems." E3S Web of Conferences 130 (2019): 01014. http://dx.doi.org/10.1051/e3sconf/201913001014.
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One of the challenges in modern computational engineering is the simulation of fluid-structure interaction (FSI) phenomena where one of the crucial issues in the multi-physics simulation is the choice of stiffness model for mesh deformation. This paper focuses on the application of iteratively implicit coupling procedure on two transient FSI cases of vortex induced-vibration (VIV) that manifest oscillating flexible structures. The aim is to study various mesh stiffness models in the Laplace equation of diffusion employed within the arbitrary Lagrangian-Eulerian (ALE) methodology to handle the moving mesh. In the first case where a laminar flow interacted with a flexible splitter, it was demonstrated that a near FSI boundaries increased-stiffness model prevails to manage a large deformation of the moving structure as compared to a near volume increased-stiffness model. However, the potential technique could not be exploited to the second FSI configuration, where the effect of the turbulence of flow was included. It was found that the mesh topology near the FSI interface was collapsed. Instead of utilizing the same approach, a mesh stiffness based on a wall distance was found to be auspicious. Thus, the mesh stiffness model in the FSI simulation is case-dependent.
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Roul, Rajendra, and Awadhesh Kumar. "Fluid-Structure Interaction of Wind Turbine Blade Using Four Different Materials: Numerical Investigation." Symmetry 12, no. 9 (September 7, 2020): 1467. http://dx.doi.org/10.3390/sym12091467.
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The interaction of a flexible system with a moving fluid gives rise to a wide variety of physical phenomena with applications in various engineering fields, such as aircraft wing stability, arterial blood progression, high structure reaction to winds, and turbine blade vibration. Both the structure and fluid need to be modeled to understand these physical phenomena. However, in line with the overall theme of this strength, the focus here is to investigate wind turbine aerodynamic and structural analysis by combining computational fluid dynamics (CFD) and finite element analysis (FEA). One-way coupling is chosen for the fluid-structure interaction (FSI) modeling. The investigation is carried out with the use of commercialized ANSYS applications. A total of eight different wind velocities and five different angles of pitch are considered in this analysis. The effect of pitch angles on the output of a wind turbine is also highlighted. The SST k-ω turbulence model has been used. A structural analysis investigation was also carried out and is carried out after importing the pressure load exerted from the aerodynamic analysis and subsequently finding performance parameters such as deformation and Von-Mises stress.
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Wang, Zhikai, Xiongliang Yao, Nana Yang, and Zhenhuan Xu. "Simulation of Fluid and Structure Interface with Immersed Boundary–Lattice Boltzmann Method Involving Turbulence Models." Mathematical Problems in Engineering 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/4072758.
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The multiple-relaxation-time (MRT) version of the immersed boundary–lattice Boltzmann (IB-LB) method is developed to simulate fluid-structure interfaces. The innovations include the implicit velocity correction to ensure no-slip boundary conditions and the incorporated Smagorinsky’s algebraic eddy viscosity for simulating turbulent flows. Both straight and curved interfaces are investigated. The streamlines penetration can be well prevented, which means the no-slip boundary condition can be guaranteed. Due to the existence of two coordinate systems: the Lagrangian coordinate system and the Eulerian coordinate system, the velocity and force properties on the structure can be easily calculated. Several benchmark simulation cases are carried out to verify the correctness of the model, including flow around circular cylinder at Re = 20, 150, and 3900 and flow around square cylinder at Re = 150 and 1000. The results agree well with previous studies, especially in the events of lower Reynolds numbers. Due to the three-dimensional turbulence vortex effects, the discrepancy increases are associated with higher Reynolds numbers. In addition, the effect of rotating velocity on the interaction process of the square cylinder in flows is researched, coupled with the capability of dealing with the moving boundaries.
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Yang, Jing, Zhen Lu, Ke Li, and Yi Wang. "Heat Transfer Analysis of Exhaust Manifold with Water Jacket of a High Speed Gasoline Based on FSI." Applied Mechanics and Materials 532 (February 2014): 439–42. http://dx.doi.org/10.4028/www.scientific.net/amm.532.439.
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The fluid-structure interaction (FSI) method is employed to analyze heat transfer of a exhaust manifold with a water jacket. Three different turbulence models are valued to predict their spheres of application. The mutual effect on complex flow distribution and heat transfer with and without transition is also considered respectively. The results show that reasonable turbulence model and transition will contribute to a better numerical precision of temperature distribution. Considering transition will have a impact on the design of novel exhaust manifold of high speed gasoline engine. In addition, numerical results can be referred to improve the structure.
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Guma, Giorgia, Galih Bangga, Thorsten Lutz, and Ewald Krämer. "Aeroelastic analysis of wind turbines under turbulent inflow conditions." Wind Energy Science 6, no. 1 (January 14, 2021): 93–110. http://dx.doi.org/10.5194/wes-6-93-2021.
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Abstract. The aeroelastic response of a 2 MW NM80 turbine with a rotor diameter of 80 m and interaction phenomena are investigated by the use of a high-fidelity model. A time-accurate unsteady fluid–structure interaction (FSI) coupling is used between a computational fluid dynamics (CFD) code for the aerodynamic response and a multi-body simulation (MBS) code for the structural response. Different CFD models of the same turbine with increasing complexity and technical details are coupled to the same MBS model in order to identify the impact of the different modeling approaches. The influence of the blade and tower flexibility and of the inflow turbulence is analyzed starting from a specific case of the DANAERO experiment, where a comparison with experimental data is given. A wider range of uniform inflow velocities are investigated by the use of a blade element momentum (BEM) aerodynamic model. Lastly a fatigue analysis is performed from load signals in order to identify the most damaging load cycles and the fatigue ratio between the different models, showing that a highly turbulent inflow has a larger impact than flexibility, when low inflow velocities are considered. The results without the injection of turbulence are also discussed and compared to the ones provided by the BEM code AeroDyn.
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Goh, Michael Joon Seng, Yeong Shiong Chiew, and Ji Jinn Foo. "A Method for 3D Reconstruction of Net Undulation for Fluid Structure Interaction of Fractal Induced Turbulence." IEEE Sensors Journal 20, no. 20 (October 15, 2020): 12013–23. http://dx.doi.org/10.1109/jsen.2020.2987643.
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Voermans, J. J., M. Ghisalberti, and G. N. Ivey. "The variation of flow and turbulence across the sediment–water interface." Journal of Fluid Mechanics 824 (July 6, 2017): 413–37. http://dx.doi.org/10.1017/jfm.2017.345.
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A basic framework characterising the interaction between aquatic flows and permeable sediment beds is presented here. Through the permeability Reynolds number ($Re_{K}=\sqrt{K}u_{\ast }/\unicode[STIX]{x1D708}$, where$K$is the sediment permeability,$u_{\ast }$is the shear velocity and$\unicode[STIX]{x1D708}$is the fluid viscosity), the framework unifies two classical flow typologies, namely impermeable boundary layer flows ($Re_{K}\ll 1$) and highly permeable canopy flows ($Re_{K}\gg 1$). Within this range, the sediment–water interface (SWI) is identified as a transitional region, with$Re_{K}$in aquatic systems typically$O(0.001{-}10)$. As the sediments obstruct conventional measurement techniques, experimental observations of interfacial hydrodynamics remain extremely rare. The use of refractive index matching here allows measurement of the mean and turbulent flow across the SWI and thus direct validation of the proposed framework. This study demonstrates a strong relationship between the structure of the mean and turbulent flow at the SWI and$Re_{K}$. Hydrodynamic characteristics, such as the interfacial turbulent shear stress, velocity, turbulence intensities and turbulence anisotropy tend towards those observed in flows over impermeable boundaries as$Re_{K}\rightarrow 0$and towards those seen in flows over highly permeable boundaries as$Re_{K}\rightarrow \infty$. A value of$Re_{K}\approx 1{-}2$is seen to be an important threshold, above which the turbulent stress starts to dominate the fluid shear stress at the SWI, the penetration depths of turbulence and the mean flow into the sediment bed are comparable and similarity relationships developed for highly permeable boundaries hold. These results are used to provide a new perspective on the development of interfacial transport models at the SWI.
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Yim, Solomon C., and Wenbin Zhang. "A Multiphysics Multiscale 3-D Computational Wave Basin Model for Wave Impact Load on a Cylindrical Structure." Journal of Disaster Research 4, no. 6 (December 1, 2009): 450–61. http://dx.doi.org/10.20965/jdr.2009.p0450.
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A multiphysics multiscale finite-element based nonlinear computational wave basin (CWB) model is developed using LS-DYNA. Its predictive capability is calibrated using a large-scale fluid-structure interaction experiment conducted in a 3-dimensional wave basin to determine wave impact on a cylindrical structure. This study focuses on evaluating CWB accuracy using two wave excitation conditions — plane and focused solitary waves — and two cylinder arrangements — single and multiple cylinders. Water surface elevation and water particle velocity are predicted numerically for the fluid domain, obtaining horizontal force, overturning moment, and dynamic pressure on the cylindrical structure and calibrated against experimental measurement. The CWB model predicts wave motion characteristics — water surface elevation and velocity, and integrated structural response — horizontal force and overturning moment, for the given wave conditions well. Computation time increases and the predictive accuracy decreases as nonlinear fluid-structure interaction becomes increasingly complex. A study of computation settings for improving computation performance showed that a high-performance parallel-computing hardware platform is needed to model details of highly nonlinear physics of fluid flow including wave breaking and turbulence.
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ZIKANOV, OLEG, and ANDRE THESS. "Direct numerical simulation of forced MHD turbulence at low magnetic Reynolds number." Journal of Fluid Mechanics 358 (March 10, 1998): 299–333. http://dx.doi.org/10.1017/s0022112097008239.
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The transformation of initially isotropic turbulent flow of electrically conducting incompressible viscous fluid under the influence of an imposed homogeneous magnetic field is investigated using direct numerical simulation. Under the assumption of large kinetic and small magnetic Reynolds numbers (magnetic Prandtl number Pm[Lt ]1) the quasi-static approximation is applied for the computation of the magnetic field fluctuations. The flow is assumed to be homogeneous and contained in a three-dimensional cubic box with periodic boundary conditions. Large-scale forcing is applied to maintain a statistically steady level of the flow energy. It is found that the pathway traversed by the flow transformation depends decisively on the magnetic interaction parameter (Stuart number). If the magnetic interaction number is small the flow remains three-dimensional and turbulent and no detectable deviation from isotropy is observed. In the case of a strong magnetic field (large magnetic interaction parameter) a rapid transformation to a purely two-dimensional steady state is obtained in agreement with earlier analytical and numerical results for decaying MHD turbulence. At intermediate values of the magnetic interaction parameter the system exhibits intermittent behaviour, characterized by organized quasi-two-dimensional evolution lasting several eddy-turnover times, which is interrupted by strong three-dimensional turbulent bursts. This result implies that the conventional picture of steady angular energy transfer in MHD turbulence must be refined. The spatial structure of the steady two-dimensional final flow obtained in the case of large magnetic interaction parameter is examined. It is found that due to the type of forcing and boundary conditions applied, this state always occurs in the form of a square periodic lattice of alternating vortices occupying the largest possible scale. The stability of this flow to three-dimensional perturbations is analysed using the energy stability method.
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CAO, YIHUA, QIANFU SONG, ZHUO WU, and JOHN SHERIDAN. "FLOW FIELD AND TOPOLOGICAL ANALYSIS OF HEMISPHERICAL PARACHUTE IN LOW ANGLES OF ATTACK." Modern Physics Letters B 24, no. 15 (June 20, 2010): 1707–25. http://dx.doi.org/10.1142/s0217984910023323.
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For analyzing the flow field and topological structure of hemispherical parachute in low angles of attack, a fluid-structure interaction (FSI) simulation technique is established to decide the shape of the hemispherical parachute during terminal descent. In the fluid simulation, the semi-implicit method for pressure-linked equations consistent (SIMPLEC) algorithm is introduced to solve shear stress transport (SST) k–ω turbulence Navier–Stokes (N–S) Equations. This method is proved to be efficient and stable by the experiment and corresponding numerical simulation. After obtaining the stable shape of the canopy, the parachute in different angles and velocities are considered.
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Genç, Mustafa Serdar, Hacımurat Demir, Mustafa Özden, and Tuna Murat Bodur. "Experimental analysis of fluid-structure interaction in flexible wings at low Reynolds number flows." Aircraft Engineering and Aerospace Technology 93, no. 6 (July 13, 2021): 1060–75. http://dx.doi.org/10.1108/aeat-04-2021-0120.
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Purpose The purpose of this exhaustive experimental study is to investigate the fluid-structure interaction in the flexible membrane wings over a range of angles of attack for various Reynolds numbers. Design/methodology/approach In this paper, an experimental study on fluid-structure interaction of flexible membrane wings was presented at Reynolds numbers of 2.5 × 104, 5 × 104 and 7.5 × 104. In the experimental studies, flow visualization, velocity and deformation measurements for flexible membrane wings were performed by the smoke-wire technique, multichannel constant temperature anemometer and digital image correlation system, respectively. All experimental results were combined and fluid-structure interaction was discussed. Findings In the flexible wings with the higher aspect ratio, higher vibration modes were noticed because the leading-edge separation was dominant at lower angles of attack. As both Reynolds number and the aspect ratio increased, the maximum membrane deformations increased and the vibrations became visible, secondary vibration modes were observed with growing the leading-edge vortices at moderate angles of attack. Moreover, in the graphs of the spectral analysis of the membrane displacement and the velocity; the dominant frequencies coincided because of the interaction of the flow over the wings and the membrane deformations. Originality/value Unlike available literature, obtained results were presented comparatively using the sketches of the smoke-wire photographs with deformation measurement or turbulence statistics from the velocity measurements. In this study, fluid-structure interaction and leading-edge vortices of membrane wings were investigated in detail with increasing both Reynolds number and the aspect ratio.
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Gomang, Greg G., and Ann Lee. "An Assessment of Turbulence Models in Simulating a Synthetic Jet." Applied Mechanics and Materials 465-466 (December 2013): 603–7. http://dx.doi.org/10.4028/www.scientific.net/amm.465-466.603.
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This paper presents a two-dimensional numerical study on the interaction of synthetic jet and the cross flow inside a microchannel. Three different turbulence models namely the standard k-, Shear Stress Transport (SST) and Scale Adaptive Simulation Shear Stress Transport (SAS SST) were tested for their ability to predict the flow structure generated by a synthetic jet. The results are validated against existing experimental data. The SAS SST model was found to give the most realistic prediction of the fluid flow based on the good agreement with experimental data.
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Andreopoulos, J. "Wind Tunnel Experiments on Cooling Tower Plumes: Part 2—In a Nonuniform Crossflow of Boundary Layer Type." Journal of Heat Transfer 111, no. 4 (November 1, 1989): 949–55. http://dx.doi.org/10.1115/1.3250810.
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The basic characteristics of plumes issuing into a boundary layer-type crossflow are reported. The flow can be considered as an interaction between two vorticity fields with different length scales and turbulence intensities. The large eddies of the oncoming boundary layer are responsible for the observed sudden changes in the plume direction. The type of structure emanating from the tower depends on the instantaneous velocity ratio. Mean velocities and normal velocity gradients are smaller than those in the case of uniform crossflow and therefore, the measured turbulence intensities are lower too. The cross-stream turbulence brings high-momentum fluid into the wake region and the velocity defect decays very rapidly. Dilution of the plumes takes place faster in the presence of external turbulence than in the case with uniform crossflow. The spreading rate is increased dramatically by the external turbulence, which causes different effects on the hydrodynamic and thermal fields.
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Tian, Yu Feng, and Yan Huang. "Numerical Simulation of Interactions between Waves and Pendulum Wave Power Converter." Applied Mechanics and Materials 291-294 (February 2013): 1949–53. http://dx.doi.org/10.4028/www.scientific.net/amm.291-294.1949.
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The interactions between waves and the pendulum wave power converter were simulated, considering Navier-Stokes (N-S) equations as governing equations of the fluid, using the k-ε turbulence model and finite element software ADINA. The setting wave-generating boundary method and viscosity damping region method were developed in the numerical wave tank. Nodal velocities were applied on each layer of the inflow boundary in the setting wave-generating boundary method. The viscosity of the fluid in the damping region was obtained artificially in the viscosity damping region method, and the energy in the fluid was decreased by the viscosity in governing equations. The physical model tests were simulated with the fluid-structure interaction (FSI) numerical model. The numerical results were compared with the experimental data, and then the results were discussed. A reference method is advanced to design the pendulum wave power converter. The method to solve the complex FSI problems is explored.
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Lara, Javier, Inigo Javier Losada, Manuel Del Jesus, Gabriel Barajas, and Raul Guanche. "IH-3VOF: A THREE-DIMENSIONAL NAVIER-STOKES MODEL FOR WAVE AND STRUCTURE INTERACTION." Coastal Engineering Proceedings 1, no. 32 (January 27, 2011): 55. http://dx.doi.org/10.9753/icce.v32.waves.55.
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This paper describes the capability of a new model, called IH-3VOF to simulate wave-structure interaction problems using a three-dimensional approach. The model is able to deal with physical processes associated with wave interaction with porous structures. The model considers the VARANS equations, a volume-averaged version of the traditional RANS (Reynolds Averaged Navier-Stokes) equations. Turbulence is modeled using a k- approach, not only at the clear fluid region (outside the porous media) but also inside the porous media. The model has been validated using laboratory data of free surface time evolution in a fish tank containing a porous dam. Numerical simulations were calibrated by adjusting the porous flow empirical coefficients for two granular material characteristics. Sensitivity analysis of porous parameters has also been performed. The model is proven to reproduce with a high degree of agreement the free surface evolution during the seeping process. Simulations of a three- dimensional porous dam breaking problem has been studied, showing the excellent performance of the model in reproducing fluid patterns around a porous structure. The model is powerful tool to examine the near-field flow characteristics around porous structures in three dimensional flow conditions.
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Xia, H., N. Francois, H. Punzmann, and M. Shats. "Tunable diffusion in wave-driven two-dimensional turbulence." Journal of Fluid Mechanics 865 (February 27, 2019): 811–30. http://dx.doi.org/10.1017/jfm.2019.82.
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We report an abrupt change in the diffusive transport of inertial objects in wave-driven turbulence as a function of the object size. In these non-equilibrium two-dimensional flows, the turbulent diffusion coefficient $D$ of finite-size objects undergoes a sharp change for values of the object size $r_{p}$ close to the flow forcing scale $L_{f}$. For objects larger than the forcing scale ($r_{p}>L_{f}$), the diffusion coefficient is proportional to the flow energy $U^{2}$ and inversely proportional to the size $r_{p}$. This behaviour, $D\sim U^{2}/r_{p}$ , observed in a chaotic macroscopic system is reminiscent of a fluctuation–dissipation relation. In contrast, the diffusion coefficient of smaller objects ($r_{p}<L_{f}$) follows $D\sim U/r_{p}^{0.35}$. This result does not allow simple analogies to be drawn but instead it reflects strong coupling of the small objects with the fabric and memory of the out-of-equilibrium flow. In these turbulent flows, the flow structure is dominated by transient but long-living bundles of fluid particle trajectories executing random walk. The characteristic widths of the bundles are close to $L_{f}$. We propose a simple phenomenology in which large objects interact with many bundles. This interaction with many degrees of freedom is the source of the fluctuation–dissipation-like relation. In contrast, smaller objects are advected within coherent bundles, resulting in diffusion properties closely related to those of fluid tracers.
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Lotfi, Babak, Bengt Sunden, and Qiu-Wang Wang. "3D fluid-structure interaction (FSI) simulation of new type vortex generators in smooth wavy fin-and-elliptical tube heat exchanger." Engineering Computations 33, no. 8 (November 7, 2016): 2504–29. http://dx.doi.org/10.1108/ec-04-2015-0091.
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Purpose The purpose of this paper is to investigate the numerical fluid-structure interaction (FSI) framework for the simulations of mechanical behavior of new vortex generators (VGs) in smooth wavy fin-and-elliptical tube (SWFET) heat exchanger using the ANSYS MFX Multi-field® solver. Design/methodology/approach A three-dimensional FSI approach is proposed in this paper to provide better understanding of the performance of the VG structures in SWFET heat exchangers associated with the alloy material properties and geometric factors. The Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model are applied for modeling of the turbulent flow in SWFET heat exchanger and the linear elastic Cauchy-Navier model is solved for the structural von Mises stress and elastic strain analysis in the VGs region. Findings Parametric studies conducted in the course of this research successfully identified illustrate that the maximum magnitude of von Mises stress and elastic strain occurs at the root of the VGs and depends on geometrical parameters and material types. These results reveal that the titanium alloy VGs shows a slightly higher strength and lower elastic strain compared to the aluminum alloy VGs. Originality/value This paper is one of the first in the literature that provides original information mechanical behavior of a SWFET heat exchanger model with new VGs in the field of FSI coupling technique.
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Duan, Lunliang, Meiling Fan, Duoyin Wang, Caixia Meng, and Lei Xing. "Numerical Study of Wave- and Current-Induced Oscillatory Seabed Response near a Fully Buried Subsea Pipeline." Advances in Civil Engineering 2021 (August 4, 2021): 1–15. http://dx.doi.org/10.1155/2021/9976278.
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To investigate the wave- and current-induced seabed response near a fully buried subsea pipeline, a two-dimensional coupled model for fluid-seabed-pipeline interaction (FSPI-2D) is developed within the framework of COMSOL multiphysics. Different from previous studies, both the wave-current interaction and the nonlinear pipeline-soil contacts are considered in the present model. In this paper, Biot’s consolidation mode is used to govern the fluid-induced seabed response, and combined Reynolds averaged Navier–Stokes (RANS) equation with the k-ε turbulence model is employed to simulate the fluid propagation. Meanwhile, the pipeline is treated as a linear elasticity. Firstly, the effectiveness of the new model is verified by laboratory experiments from previous reports. Then, the numerical model is employed to examine the effects of nonlinear pipeline-seabed contacts and fluid characteristics on the seabed response around the structure. Finally, the momentary liquefaction near the fully buried pipeline is studied based on the 2D coupled model.
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Ghazanfarian, Jafar, Roozbeh Saghatchi, and Mofid Gorji-Bandpy. "Turbulent fluid-structure interaction of water-entry/exit of a rotating circular cylinder using SPH method." International Journal of Modern Physics C 26, no. 08 (May 3, 2015): 1550088. http://dx.doi.org/10.1142/s0129183115500886.
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This paper studies the two-dimensional (2D) water-entry and exit of a rotating circular cylinder using the Sub-Particle Scale (SPS) turbulence model of a Lagrangian particle-based Smoothed-Particle Hydrodynamics (SPH) method. The full Navier–Stokes (NS) equations along with the continuity have been solved as the governing equations of the problem. The accuracy of the numerical code is verified using the case of water-entry and exit of a nonrotating circular cylinder. The numerical simulations of water-entry and exit of the rotating circular cylinder are performed at Froude numbers of 2, 5, 8, and specific gravities of 0.25, 0.5, 0.75, 1, 1.75, rotating at the dimensionless rates of 0, 0.25, 0.5, 0.75. The effect of governing parameters and vortex shedding behind the cylinder on the trajectory curves, velocity components in the flow field, and the deformation of free surface for both cases have been investigated in detail. It is seen that the rotation has a great effect on the curvature of the trajectory path and velocity components in water-entry and exit cases due to the interaction of imposed lift and drag forces with the inertia force.
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Ran, Zilin, Wenxing Ma, and Chunbao Liu. "3D Cavitation Shedding Dynamics: Cavitation Flow-Fluid Vortex Formation Interaction in a Hydrodynamic Torque Converter." Applied Sciences 11, no. 6 (March 21, 2021): 2798. http://dx.doi.org/10.3390/app11062798.
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Recent experiments have shown interactions between the cavitation and fluid vortex formation in a hydrodynamic torque converter. This study aimed to clarify the unsteady cavitation trigger mechanism and flow-induced vibration caused by turbulence–cavitation interactions. The mass transfer cavitation model and modified Reynolds-averaged Navier–Stokes k–ω model were used with a local density correction for turbulent eddy viscosity to investigate the cavitation structure in a hydrodynamic torque converter under various operating conditions. The model results were then validated against test data. The multi-block structured gridding technique was used to develop an orthogonally structured grid of a three-dimensional full-flow passage as an alternative analysis method for the cavitation flow. The results indicated that the re-entrant jet is the main cause of the shedding cavitation and breaking O-type cavitation. The re-entrant jet is driven by the reverse pressure gradient to move upstream towards the stator nose, and it lifts and splits the attached cavitation, which periodically induces shedding cavitation. When the cavitation was considered, the prediction error of the capacity constant was reduced from 13.23% to <5%. This work provides an insight into the cavitation–vortex interactions in a hydrodynamic torque converter, which can be used to improve the prediction accuracy of the hydrodynamic performance.
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Šekutkovski, Bojan, Ivan Kostić, Aleksandar Simonović, Philip Cardiff, and Vladimir Jazarević. "Three-dimensional fluid–structure interaction simulation with a hybrid RANS–LES turbulence model for applications in transonic flow domain." Aerospace Science and Technology 49 (February 2016): 1–16. http://dx.doi.org/10.1016/j.ast.2015.11.028.
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Hall, Philip. "Vortex–wave interaction arrays: a sustaining mechanism for the log layer?" Journal of Fluid Mechanics 850 (July 2, 2018): 46–82. http://dx.doi.org/10.1017/jfm.2018.425.
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Vortex–wave interaction theory is used to describe new kinds of localised and distributed exact coherent structures. Starting with a localised vortex–wave interaction state driven by a single inviscid wave, regular arrays of interacting vortex–wave states are investigated. In the first instance the arrays described are operational in an infinite uniform shear flow; we refer to them as ‘uniform shear vortex–wave arrays’. The basic form of the interaction remains identical to the canonical one found by Hall & Smith (J. Fluid Mech., vol. 227, 1991, pp. 641–666) and subsequently used to describe exact coherent structures by Hall & Sherwin (J. Fluid Mech., vol. 661, 2010, pp. 178–205). Thus in each cell of a vortex–wave array a roll stress jump is induced across the critical layer of an inviscid wave riding on the streak part of the flow. The theory is extended to arbitrary shear flows using a nonlinear Wentzel–Kramers–Brillouin–Jeffreys or ray theory approach with the wave–roll–streak field operating on a shorter length scale than the mean flow. The evolution equation governing the slow dynamics of the interaction turns out to be a modified form of the well-known mean equation for a turbulent flow, and its particular form can be interpreted as a ‘closure’ between the small and large scales of the flow. If the array structure is taken to be universal, in the sense that it applies to arbitrary shear flows, then the array takes on a form which supports a logarithmic mean velocity profile trapped between what can be identified with the ‘wake region’ and a ‘buffer layer’ well known in the context of wall-bounded turbulent flows. The many similarities between the distributed structures described and wall-bounded turbulence suggest that vortex–wave arrays might be involved in the self-sustaining process supporting the log layer. The modification of the mean profile within each cell of the array leads to ‘staircase’-like streamwise velocity profiles similar to those observed experimentally in turbulent flows. The wave field supporting the ‘staircase’ is concentrated in critical layers which can be associated with the shear layer structures that have been attributed by experimentalists to be the mechanism supporting the uniform-momentum zones of the staircase.
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Jensen, Bjarne, Erik Damgaard Christensen, and B. Mutlu Sumer. "WAVE INTERACTION WITH LARGE ROUGHNESS ELEMENTS ON AN IMPERMEABLE SLOPING BED." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 23. http://dx.doi.org/10.9753/icce.v33.waves.23.
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The present paper presents the results of an experimental and numerical investigation of the flow between large roughness elements on a steep sloping impermeable bed during wave action. The setup is designed to resemble a breakwater structure. The work is part of a study where the focus is on the details in the porous core flow and the armour layer flow i.e. the interaction between the two flow domains and the effect on the armour layer stability. In order to isolate the processes involved with the flow in the porous core the investigations are first carried out with a completely impermeable bed and successively repeated with a porous bed. In this paper the focus is on the impermeable bed. Results are obtained experimentally for flow and turbulence between the roughness elements on the sloping bed. Numerical simulations have reproduced the experimental results with good agreements and can hereby add more details to the understanding of the fluid-structure interaction.
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Laouedj, Samir, Juan P. Solano, and Abdelylah Benazza. "Synthetic jet cross-flow interaction with orifice obstruction." International Journal of Numerical Methods for Heat & Fluid Flow 25, no. 4 (May 5, 2015): 749–61. http://dx.doi.org/10.1108/hff-01-2014-0013.
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Purpose – The purpose of this paper is to describe the flow structure and the time-resolved and time-mean heat transfer characteristics in the interaction between a synthetic jet and a cross flow, when an obstruction reduces the cross-section of the orifice where the jet is formed. Design/methodology/approach – The microchannel flow interacted by the pulsed jet is modeled using a two-dimensional finite volume simulation with unsteady Reynolds-averaged Navier-Stokes equations while using the Shear-Stress-Transport (SST) k-ω turbulence model to account for fluid turbulence. Findings – The computational results show a good and rapid increase of the synthetic jet influence on heat transfer enhancement when the obstruction of the orifice is superior to 30 per cent and the synthetic jet oscillating amplitudes are below 50 µm. It is found that when the obstruction is close to the exit orifice, the heat transfer enhancement is significant. The obstruction has proved to accelerate the jet and change the formation of large vortical structures. Additional windward vortices appear, which influence the flow field and enhance the heat transfer. Research limitations/implications – The work proposes the use of a compound enhancement technique for electronics cooling. A limited range of operating conditions and geometrical configurations is presented. A further analysis of the performance evaluation, based on the increased energy consumption of the device, would complement the study. Originality/value – The authors provide a compound technique to enhance heat transfer in synthetic-jet electronic cooling devices.
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Boychev, K., G. N. Barakos, R. Steijl, and S. Shaw. "Parametric study of multiple shock-wave/turbulent-boundary-layer interactions with a Reynolds stress model." Shock Waves 31, no. 3 (April 2021): 255–70. http://dx.doi.org/10.1007/s00193-021-01011-z.
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AbstractThe flow of high-speed air in ducts may result in the occurrence of multiple shock-wave/boundary-layer interactions. Understanding the consequences of such interactions, which may include distortion of the velocity field, enhanced turbulence production, and flow separation, is of great importance in understanding the operating limits and performance of a number of systems, for example, the high-speed intake of an air-breathing missile. In this paper, the results of a computational study of multiple shock-wave/boundary-layer interactions occurring within a high-speed intake are presented. All of the results were obtained using the in-house computational fluid dynamics solver of Glasgow University, HMB3. First simulations of a Mach $$M=1.61$$ M = 1.61 multiple shock-wave/boundary-layer interaction in a rectangular duct were performed. The $$M=1.61$$ M = 1.61 case, for which experimental data is available, was used to establish a robust numerical approach, particularly with respect to initial and boundary conditions. A number of turbulence modelling strategies were also investigated. The results suggest that Reynolds-stress-based turbulence models are better suited than linear eddy-viscosity models. This is attributed to better handling of complex strain, in particular modelling of the corner separation. The corner separations affect the separation at the centre of the domain which in turn alters the structure of the initial shock and the subsequent interaction. Having established a robust numerical approach, the results of a parametric study investigating the effect of Mach number, Reynolds number, and confinement on the baseline solution are then presented. Performance metrics are defined to help characterize the effect of the interactions. The results suggest that reduced flow confinement is beneficial for higher-pressure recovery.
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Albatati, F. A., A. M. Hegab, M. A. Rady, A. A. Abuhabaya, and S. M. El-Behery. "Turbulent Flow Characteristics in a Model of a Solid Rocket Motor Chamber with Sidewall Mass Injection and End-Wall Disturbance." Mathematical Problems in Engineering 2021 (June 15, 2021): 1–17. http://dx.doi.org/10.1155/2021/9978102.
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The present analytical, numerical, and experimental investigations are performed to study the flow field in acoustically simulated solid rocket motor (SRM) chamber geometry. The computational solution is carried out for a high Reynolds number and low Mach number internal flows driven by sidewall mass addition in a long chamber with end-wall disturbances. This kind of flow (transient, weakly viscous, and contains vorticity) have several features in common with a turbulent flow field. The numerical study is performed by solving the unsteady Reynolds-averaged Navier–Stokes equations along with the energy equation using the control volume approach based on a staggered grid system. The v2-f turbulence model has been implemented in the current study. A comparison of the SIMPLE and PISO algorithms showed that both algorithms provide identical results, and the computational time using the PISO algorithm is higher by about 6% than the corresponding value of the SIMPLE algorithm. A fair agreement has been obtained between the numerical, analytical, and experimental results. Moreover, the results showed that the complex turbulent internal flow patterns are induced inside the chamber due to the strong interaction of the sidewall injection with the traveling acoustic waves. Such a complex internal structure is shown to be dependent on the piston frequency and sidewall mass flux. The current study, for the first time, emphasizes the acoustic-fluid dynamics interaction mechanism and the accompanying unsteady rotational fields along with the effect of the generated turbulence on the unsteady vorticity and its impact on the real burning rate.
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Chow, Yi-Chih, Oguz Uzol, and Joseph Katz. "Flow Nonuniformities and Turbulent “Hot Spots” Due to Wake-Blade and Wake-Wake Interactions in a Multi-Stage Turbomachine." Journal of Turbomachinery 124, no. 4 (October 1, 2002): 553–63. http://dx.doi.org/10.1115/1.1509078.
Full textAbstract:
This experimental study provides striking examples of the complex flow and turbulence structure resulting from blade-wake and wake-wake interactions in a multi-stage turbomachine. Particle image velocimetry (PIV) measurements are performed within the entire 2nd stage of a two-stage turbomachine. The experiments are performed in a facility that allows unobstructed view of the entire flow field, facilitated using transparent rotor and stator and a fluid that has the same optical index of refraction as the blades. This paper contains data on the phase-averaged flow structure including velocity, vorticity and strain-rate, as well as the turbulent kinetic energy and shear stress, at mid span, for several orientation of the rotor relative to the stator. Two different test setups with different blade geometries are used in order to highlight and elucidate complex phenomena involved, as well as to demonstrate that some of the interactions are characteristic to turbomachines and can be found in a variety of geometries. The first part of the paper deals with the interaction of a 2nd-stage rotor with the wakes of both the rotor and the stator of the 1st stage. Even before interacting with the blade, localized regions with concentrated mean vorticity and elevated turbulence levels form at the intersection of the rotor and stator wakes of the 1st stage. These phenomena persist even after being ingested by the rotor blade of the 2nd stage. As the wake segment of the 1st-stage rotor blade arrives to the 2nd stage, the rotor blades become submerged in its elevated turbulence levels, and separate the region with negative vorticity that travels along the pressure side of the blade, from the region with positive vorticity that remains on the suction side. The 1st-stage stator wake is chopped-off by the blades. Due to difference in mean lateral velocity, the stator wake segment on the pressure side is advected faster than the segment on the suction side (in the absolute frame of reference), creating discontinuities in the stator wake trajectory. The nonuniformities in phase-averaged velocity distributions generated by the wakes of the 1st stage persist while passing through the 2nd-stage rotor. The combined effects of the 1st-stage blade rows cause 10–12 deg variations of flow angle along the pressure side of the blade. Thus, in spite of the large gap between the 1st and 2nd rotors (compared to typical rotor-stator spacings in axial compressors), 6.5 rotor axial chords, the wake-blade interactions are substantial. The second part focuses on the flow structure at the intersection of the wakes generated by a rotor and a stator located upstream of it. In both test setups the rotor wake is sheared by the nonuniformities in the axial velocity distributions, which are a direct result of the “discontinuities” in the trajectories of the stator wake. This shearing creates a kink in the trajectory of the rotor wake, a quadruple structure in the distribution of strain, regions with concentrated vorticity, high turbulence levels and high shear stresses, the latter with a complex structure that resembles the mean strain. Although the “hot spots” diffuse as they are advected downstream, they still have elevated turbulence levels compared to the local levels around them. In fact, every region of wake intersection has an elevated turbulence level.
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Duffy, Peter. "Bohm Diffusion and Cosmic-Ray-Modified Shocks." International Astronomical Union Colloquium 142 (1994): 981–83. http://dx.doi.org/10.1017/s0252921100078428.
Full textAbstract:
AbstractA numerical solution to the problem of self-consistent diffusive shock acceleration is presented. The cosmic rays are scattered, accelerated and exert a back-reaction on the gas through their interaction with turbulence frozen into the local fluid frame. Using a grid with a hierarchical spacetime structure the physically interesting limit of Bohm diffusion (к ∝ pv), which introduces a wide range of diffusion lengthscales and acceleration timescales, can be studied. Some implications for modified shocks and particle acceleration are presented.Subject headings: acceleration of particles — cosmic rays — diffusion — shock waves