LES Simulation in a Thin Liquid Film Subjected to High Thermal Stresses

2003 ◽  
Author(s):  
M. V. Pham ◽  
F. Plourde ◽  
S. K. Doan
Keyword(s):  
Thermal Stress ◽  
Flow Field ◽  
Liquid Film ◽  
Power Law ◽  
Thermal Stresses ◽  
Thin Liquid Film ◽  
Strong Mixing ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Air Liquid Interface

Thermal transfers occurring in the vicinity of an air-liquid interface have been studied numerically through a Large Eddy Simulation technique. Results obtained clearly show the unsteady response of the liquid film submitted to such thermal stress. Structures are created at the interface in a very small layer and it has been found that turbulence acts strongly in that layer. Moreover, even if the configuration studied tends to weaken buoyancy, the dissipation was found to obey a −3 power law. This clearly indicates that the buoyancy pilots the way turbulence behaves on the flow field; the latter is mainly characterized by a strong mixing phenomenon taking place in the already identified layer at the interface.

Large Eddy Simulation of Flow and Heat Transfer Mechanism in Matrix Cooling Channel

2017 ◽  
Author(s):  
Yigang Luan ◽  
Lianfeng Yang ◽  
Bo Wan ◽  
Tao Sun
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Gas Turbine ◽  
Transfer Mechanism ◽  
Heat Transfer Mechanism ◽  
Longitudinal Vortices ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy

Gas turbine engines have been widely used in modern industry especially in the aviation, marine and energy fields. The efficiency of gas turbines directly affects the economy and emissions. It’s acknowledged that the higher turbine inlet temperatures contribute to the overall gas turbine engine efficiency. Since the components are subject to the heat load, the internal cooling technology of turbine blades is of vital importance to ensure the safe and normal operation. This paper is focused on exploring the flow and heat transfer mechanism in matrix cooling channels. In order to analyze the internal flow field characteristics of this cooling configuration at a Reynolds number of 30000 accurately, large eddy simulation method is carried out. Methods of vortex identification and field synergy are employed to study its flow field. Cross-sectional views of velocity in three subchannels at different positions have been presented. The results show that the airflow is strongly disturbed by the bending part. It’s concluded that due to the bending structure, the airflow becomes complex and disordered. When the airflow goes from the inlet to the turning, some small-sized and discontinuous vortices are formed. Behind the bending structure, the size of the vortices becomes big and the vortices fill the subchannels. Because of the structure of latticework, the airflow is affected by each other. Airflow in one subchannel can exert a shear force on another airflow in the opposite subchannel. It’s the force whose direction is the same as the vortex that enhances the longitudinal vortices. And the longitudinal vortices contribute to the energy exchange of the internal airflow and the heat transfer between airflow and walls. Besides, a comparison of the CFD results and the experimental data is made to prove that the numerical simulation methods are reasonable and acceptable.

scholarly journals Investigation of the velocity field downstream of a benchmark vent using numerical simulation and hot-wire anemometry

2019 ◽  
Vol 213 ◽  
pp. 02076
Author(s):  
Jan Sip ◽  
Frantisek Lizal ◽  
Jakub Elcner ◽  
Jan Pokorny ◽  
Miroslav Jicha
Keyword(s):  
Fluid Dynamics ◽  
Numerical Simulation ◽  
Velocity Field ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Turbulence Models ◽  
Hot Wire ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Precise Prediction

The velocity field in the area behind the automotive vent was measured by hot-wire anenemometry in detail and intensity of turbulence was calculated. Numerical simulation of the same flow field was performed using Computational fluid dynamics in commecial software STAR-CCM+. Several turbulence models were tested and compared with Large Eddy Simulation. The influence of turbulence model on the results of air flow from the vent was investigated. The comparison of simulations and experimental results showed that most precise prediction of flow field was provided by Spalart-Allmaras model. Large eddy simulation did not provide results in quality that would compensate for the increased computing cost.

scholarly journals Large eddy simulation of turbulent channel flow using differential equation wall model

2018 ◽  
Vol 15 (2) ◽  
pp. 75-89
Author(s):  
Muhammad Saiful Islam Mallik ◽  
Md. Ashraf Uddin
Keyword(s):  
Differential Equation ◽  
Flow Field ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Wall Region ◽  
Computational Domain ◽  
Wall Model ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

A large eddy simulation (LES) of a plane turbulent channel flow is performed at a Reynolds number Re? = 590 based on the channel half width, ? and wall shear velocity, u? by approximating the near wall region using differential equation wall model (DEWM). The simulation is performed in a computational domain of 2?? x 2? x ??. The computational domain is discretized by staggered grid system with 32 x 30 x 32 grid points. In this domain the governing equations of LES are discretized spatially by second order finite difference formulation, and for temporal discretization the third order low-storage Runge-Kutta method is used. Essential turbulence statistics of the computed flow field based on this LES approach are calculated and compared with the available Direct Numerical Simulation (DNS) and LES data where no wall model was used. Comparing the results throughout the calculation domain we have found that the LES results based on DEWM show closer agreement with the DNS data, especially at the near wall region. That is, the LES approach based on DEWM can capture the effects of near wall structures more accurately. Flow structures in the computed flow field in the 3D turbulent channel have also been discussed and compared with LES data using no wall model.

scholarly journals Optimization of the Turbulence Model on Numerical Simulations of Flow Field within a Hydrocyclone

2015 ◽  
Vol 2015 ◽  
pp. 1-7
Author(s):  
Yan Xu ◽  
Zunce Wang ◽  
Lin Ke ◽  
Sen Li ◽  
Jinglong Zhang
Keyword(s):  
Flow Field ◽  
Large Eddy Simulation ◽  
Cross Sections ◽  
Three Dimensional ◽  
Reynolds Stress Model ◽  
Computational Grids ◽  
Test Results ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Simulation Results

Reynolds Stress Model and Large Eddy Simulation are used to respectively perform numerical simulation for the flow field of a hydrocyclone. The three-dimensional hexahedral computational grids were generated. Turbulence intensity, vorticity, and the velocity distribution of different cross sections were gained. The velocity simulation results were compared with the LDV test results, and the results indicated that Large Eddy Simulation was more close to LDV experimental data. Large Eddy Simulation was a relatively appropriate method for simulation of flow field within a hydrocyclone.

Dynamic roughness model for large-eddy simulation of turbulent flow over multiscale, fractal-like rough surfaces

2011 ◽  
Vol 679 ◽  
pp. 288-314 ◽  
Author(s):  
W. ANDERSON ◽  
C. MENEVEAU
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Power Law ◽  
Rough Surfaces ◽  
Scale Height ◽  
Small Scale ◽  
Height Distribution ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Large Eddy

Many flows especially in geophysics involve turbulent boundary layers forming over rough surfaces with multiscale height distribution. Such surfaces pose special challenges for large-eddy simulation (LES) when the filter scale is such that only part of the roughness elements of the surface can be resolved. Here we consider LES of flows over rough surfaces with power-law height spectra Eh(k) ~ kβs (−3 ≤ βs < −1), as often encountered in natural terrains. The surface is decomposed into resolved and subgrid-scale height contributions. The effects of the unresolved small-scale height fluctuations are modelled using a local equilibrium wall model (log-law or Monin–Obukhov similarity), but the required hydrodynamic roughness length must be specified. It is expressed as the product of the subgrid-scale root-mean-square of the height distribution and an unknown dimensionless quantity, α, the roughness parameter. Instead of specifying this parameter in an ad hoc empirical fashion, a dynamic methodology is proposed based on test-filtering the surface forces and requiring that the total drag force be independent of filter scale or resolution. This dynamic surface roughness (DSR) model is inspired by the Germano identity traditionally used to determine model parameters for closing subgrid-scale stresses in the bulk of a turbulent flow. A series of LES of fully developed flow over rough surfaces are performed, with surfaces built using random-phase Fourier modes with prescribed power-law spectra. Results show that the DSR model yields well-defined, rapidly converging, values of α. Effects of spatial resolution and spectral slopes are investigated. The accuracy of the DSR model is tested by showing that predicted mean velocity profiles are approximately independent of resolution for the dynamically computed values of α, whereas resolution-dependent results are obtained when using other, incorrect, α values. Also, strong dependence of α on βs is found, where α ranges from α ~ 0.1 for βs = −1.2 to α ~ 10−5 for βs = −3.

Large-eddy simulation of the Richtmyer–Meshkov instability

2015 ◽  
Vol 93 (10) ◽  
pp. 1124-1130 ◽  
Author(s):  
T. Wang ◽  
P. Li ◽  
J.S. Bai ◽  
G. Tao ◽  
B. Wang ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Flow Field ◽  
Large Eddy Simulation ◽  
Turbulent Kinetic Energy ◽  
Interface Instability ◽  
Simulation Code ◽  
Interface Evolution ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulence Mixing

The subgrid-scale (SGS) terms of turbulence transport are modelled by the stretched-vortex SGS stress model, and a large-eddy simulation code multi-viscous fluid and turbulence (MVFT) is developed to investigate the MVFT problems. Then one AWE shock tube experiment of interface instability is simulated numerically by MVFT code, which reproduces the development process of the interface. The obtained numerical images of interface evolution and wave structures in flow field are consistent with the experimental results. The evolution of perturbed interface and propagation of shock waves in flow field and their interactions are analyzed in detail. The statistics features of turbulence mixing in the form of finer quantities, such as the turbulent kinetic energy, enstrophy, density variance, and turbulent mass flux are investigated, which also proves that the SGS model has a key role in large-eddy simulation. The turbulent kinetic energy and enstrophy decay with time as a power law.

Numerical Simulation of Three Dimensional Unsteady Flow of the Ruston Turbine in Stirred Tank

2014 ◽  
Vol 1008-1009 ◽  
pp. 906-909
Author(s):  
Xiao Bing Wang
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Three Dimensional ◽  
Stirred Tank ◽  
Eddy Simulation ◽  
Cavitation Phenomenon ◽  
Large Size ◽  
Velocity Flow ◽  
Large Eddy ◽  
Turbine Installation

Unsteady flow of a single six-blade ruston turbine in stirred tank is numerically simulated by using the large eddy simulation. Then the effect of the turbine installation position on mixing flow field is studied. The result shows that with a relatively low paddle installation position, mixing effect at the bottom of tank is obvious, while which go against the materials at the top layer mixing. When the paddle is installed at the top of the stirred tank, liquid splash and a concave downward liquid surface are easily caused. Finally the cavitation phenomenon is generated. When the paddle is installed from 1/3H to 2/3H, there are a uniform flow field distribution and higher average velocity flow. Large size vortex structures at the top and the bottom of the paddle are obvious which is beneficial to mix the materials.

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