Research on the Vortex Structures of Flow around Surface-Mounted Obstcales

2013 ◽  
Vol 328 ◽  
pp. 623-628
Author(s):  
Shan Qun Chen ◽  
Bin Liao
Keyword(s):  
Large Eddy Simulation ◽  
Horseshoe Vortex ◽  
Wake Flow ◽  
Leeward Side ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Vortex Separation ◽  
Almost All ◽  
Good Agreement

The large eddy simulation (LES) method was employed to compute the flow past three types of obstacles on slope surface. The predictions give profile of mean velocity and flow reattachment length. The calculations in present paper are in good agreement with the experimental data. Wake characteristics are analyzed. The computational results show that the horseshoe vortex are formatted at upstream base of obstacles. The wake flow is controlled by the downwash flow on the free end, as well as, the upwash flow in the wake disappears completely. With the angle between the leeward side and the bottom becomes larger, the length of the vortex separation becomes larger, and the scope of vortices greater. The large eddy simulation can obtain almost all the flow pattern observed by the experiments.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Large Eddy Simulation of Turbulent Wake Behind a Square Cylinder With a Nearby Wall

2001 ◽  
Vol 124 (1) ◽  
pp. 81-90 ◽  
Author(s):  
Tong-Miin Liou ◽  
Shih-Hui Chen ◽  
Po-Wen Hwang
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Stokes Equations ◽  
Turbulent Wake ◽  
Wake Flow ◽  
Square Cylinder ◽  
Free Standing ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Computations of the time-averaged and phase-averaged fluid flow and heat transfer based on large eddy simulation (LES) are presented for turbulent flows past a square cylinder with and without a nearby wall at a fixed Reynolds number of 2.2×104. The finite-volume technique was used to solve the time-dependent filtered compressible Navier-Stokes equations with a dynamic subgrid-scale turbulence model, and the numerical fluxes were computed using alternating in time the second-order, explicit MacCormack’s and the modified Godunov’s scheme. Results show some improvements in predicting the streamwise evolutions of the long-time-averaged streamwise mean velocity and total fluctuation intensity along the centerline over those predicted by using Reynolds stress models. A better overall centerline streamwise mean velocity distribution is also predicted by the present LES than by other LES. The wall proximity effect is studied through the comparison of turbulent wake flow past one free standing cylinder and one with a nearby wall, and is illustrated by the phase-averaged spanwise vorticity components and the vortex celerity of spanwise vortices. Moreover, documentation is given on the mechanisms responsible for the augmentation of heat transfer through the spanwise and longitudinal vortices as well as periodic and random fluctuations.

Kinetic-energy-flux-constrained model using an artificial neural network for large-eddy simulation of compressible wall-bounded turbulence

2021 ◽  
Vol 932 ◽  
Author(s):  
Changping Yu ◽  
Zelong Yuan ◽  
Han Qi ◽  
Jianchun Wang ◽  
Xinliang Li ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Energy Flux ◽  
Mean Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Bounded Turbulence

Kinetic energy flux (KEF) is an important physical quantity that characterizes cascades of kinetic energy in turbulent flows. In large-eddy simulation (LES), it is crucial for the subgrid-scale (SGS) model to accurately predict the KEF in turbulence. In this paper, we propose a new eddy-viscosity SGS model constrained by the properly modelled KEF for LES of compressible wall-bounded turbulence. The new methodology has the advantages of both accurate prediction of the KEF and strong numerical stability in LES. We can obtain an approximate KEF by the tensor-diffusivity model, which has a high correlation with the real value. Then, using the artificial neural network method, the local ratios between the real KEF and the approximate KEF are accurately modelled. Consequently, the SGS model can be improved by the product of that ratio and the approximate KEF. In LES of compressible turbulent channel flow, the new model can accurately predict mean velocity profile, turbulence intensities, Reynolds stress, temperature–velocity correlation, etc. Additionally, for the case of a compressible flat-plate boundary layer, the new model can accurately predict some key quantities, including the onset of transitions and transition peaks, the skin-friction coefficient, the mean velocity in the turbulence region, etc., and it can also predict the energy backscatters in turbulence. Furthermore, the proposed model also shows more advantages for coarser grids.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
S. Sarkar ◽  
Harish Babu
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Downward Spiral

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using large eddy simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair (CRVP), and downward spiral separation node (DSSN) vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Large Eddy Simulation of Round Impinging Jets With Large Stand-Off Distance

2014 ◽  
Author(s):  
Mehrdad Shademan ◽  
Vesselina Roussinova ◽  
Ron Barron ◽  
Ram Balachandar
Keyword(s):  
Large Eddy Simulation ◽  
Flow Characteristics ◽  
Impinging Jet ◽  
Impinging Jets ◽  
Vortical Structures ◽  
Nozzle Height ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Mean ◽  
Good Agreement

Large Eddy Simulation (LES) has been carried out to study the flow of a turbulent impinging jet with large nozzle height-to-diameter ratio. The dynamic Smagorinsky model was used to simulate the subgrid-scale stresses. The jet exit Reynolds number is 28,000. The study presents a detailed evaluation of the flow characteristics of an impinging jet with nozzle height of 20 diameters above the plate. Results of the mean normalized centerline velocity and wall shear stress show good agreement with previous experiments. Analysis of the flow field shows that vortical structures generated due to the Kelvin-Helmholtz instabilities in the shear flow close to the nozzle undergo break down or merging when moving towards the plate. Unlike impinging jets with small stand-off distance where the ring-like vortices keep their interconnected shape upon reaching the plate, no sign of interconnection was observed on the plate for this large stand-off distance. A large deflection of the jet axis was observed for this type of impinging jet when compared to the cases with small nozzle height-to-diameter ratios.

Large-Eddy Simulation of a Swirl-Stabilized, Lean Direct Injection Spray Combustor

2006 ◽  
Author(s):  
Mehmet Kırtas¸ ◽  
Nayan Patel ◽  
Vaidyanathan Sankaran ◽  
Suresh Menon
Keyword(s):  
Large Eddy Simulation ◽  
Vortex Breakdown ◽  
Direct Injection ◽  
Reacting Flow ◽  
Mean Velocity ◽  
Recirculation Bubble ◽  
Lean Direct Injection ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Recirculation Zones

Large-eddy simulation (LES) of a lean-direct injection (LDI) combustor is reported in this paper. The full combustor and all the six swirl vanes are resolved and both cold and reacting flow simulations are performed. Cold flow predictions with LES indicate the presence of a broad central recirculation zone due to vortex breakdown phenomenon near the dump plane and two corner recirculation zones at the top and bottom corner of the combustor. These predicted features compare well with the experimental non-reacting data. Reacting case simulated a liquid Jet-A fuel spray using a Lagrangian approach. A three-step kinetics model that included CO and NO is used for the chemistry. Comparison of mean velocity field predicted in the reacting LES with experiments shows reasonable agreement. Comparison with the non-reacting case shows that the centerline recirculation bubble is shorter but more intense in the reacting case.

Large Eddy Simulation on the Interactions of Wake and Film-Cooling Near a Leading Edge

2014 ◽  
Author(s):  
Harish Babu ◽  
S. Sarkar
Keyword(s):  
Large Eddy Simulation ◽  
Film Cooling ◽  
Vortex Pair ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Constant Thickness ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Past A Cylinder ◽  
Rotor Stator Interaction

The unsteady flow physics due to interactions between a separated shear layer and film cooling jet apart from excitation of periodic passing wake are studied using Large Eddy Simulation (LES). An aerofoil of constant thickness with rounded leading edge induced flow separation, while film cooling jets were injected normal to the crossflow a short distance downstream of the blend point. Wake data extracted from precursor LES of flow past a cylinder are used to replicate a moving bar that generates wakes in front of a cascade (in this case, an infinite row of the model aerofoils). This setup is a simplified representation of rotor-stator interaction in a film cooled gas turbine. The results of numerical simulation are presented to elucidate the formation, convection and breakdown of flow structures associated with the highly anisotropic flow involved in film cooling perturbed by convective wakes. The various vortical structures namely, horseshoe vortex, roller vortex, upright wake vortex, counter rotating vortex pair and DSSN vortex associated with film cooling are resolved. The effects of wake on the evolution of these structures are then discussed.

Large-eddy simulation and parameterization of buoyant plume dynamics in stratified flow

2016 ◽  
Vol 794 ◽  
pp. 798-833 ◽  
Author(s):  
Di Yang ◽  
Bicheng Chen ◽  
Scott A. Socolofsky ◽  
Marcelo Chamecki ◽  
Charles Meneveau
Keyword(s):  
Large Eddy Simulation ◽  
Large Fraction ◽  
Bubble Plume ◽  
Mean Velocity ◽  
Neutral Buoyancy ◽  
Buoyant Plumes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Consistent Manner ◽  
Trap Height

Characteristics of laboratory-scale bubble-driven buoyant plumes in a stably stratified quiescent fluid are studied using large-eddy simulation (LES). As a bubble plume entrains stratified ambient water, its net buoyancy decreases due to the increasing density difference between the entrained and ambient fluids. A large fraction of the entrained fluid eventually detrains and falls along an annular outer plume from a height of maximum rise (peel height) to a neutral buoyancy level (trap height), during which less buoyant scalars (e.g. small droplets) are trapped and dispersed horizontally, forming quasi-horizontal intrusion layers. The inner/outer double-plume structure and the peel/intrusion process are found to be more distinct for cases with small bubble rise velocity, while weak and unstable when the slip velocity is large. LES results are averaged to generate distributions of mean velocity and turbulent fluxes. These distributions provide data for assessing the performance of previously developed closures used in one-dimensional integral plume models. In particular, the various LES cases considered in this study yield consistent behaviour for the entrainment coefficients for various plume cases. Furthermore, a new continuous peeling model is derived based on the insights obtained from LES results. Comparing to previous peeling models, the new model behaves in a more self-consistent manner, and it is expected to provide more reliable performance when applied in integral plume models.

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