scholarly journals Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions

2019 ◽  
Author(s):  
Jian Zhong ◽  
Xiaoming Cai ◽  
Zheng-Tong Xie
Keyword(s):  
Three Dimensional ◽  
Inertial Subrange ◽  
Order Moment ◽  
Periodic Case ◽  
Atmospheric Conditions ◽  
Mean Velocity ◽  
Large Eddy ◽  
Inflow Turbulence ◽  
Turbulence Generation ◽  
Turbulence Generator

Abstract. A synthetic inflow turbulence generator was implemented in the idealised Weather Research and Forecasting large eddy simulation (WRF-LES v3.6.1) model under neutral atmospheric conditions. This method is based on an exponential correlation function, and generates a series of two-dimensional slices of data which are correlated both in space and in time. These data satisfy a spectrum with a near −5/3 inertial subrange, suggesting its excellent capability for high Reynolds number atmospheric flows. It is more computationally efficient than other synthetic turbulence generation approaches, such as three-dimensional digital filter methods. A WRF-LES model with periodic boundary conditions was configured to provide a priori turbulent information for the synthetic turbulence generation method and used as an evaluation for the inflow case. The comparison shows that the inflow case generated similar turbulence structures as these in the periodic case after a short adjustment distance. The inflow case yielded a mean velocity profile in a good agreement with the desired one, and 2nd order moment statistics profiles close to the desired ones after a short distance. For the range of the integral length scale which we tested, its influence on the profiles of the mean velocities is not significant, whereas its influence on the second moment statistics profiles is evident, in particular for very small integral length scales. This implementation can be extended to the WRF-LES simulation of a horizontally inhomogeneous case with non-repeated surface landuse pattern and a multi-scale seamless nesting case from a meso-scale domain with a km-resolution down to LES domains with metre resolutions.

scholarly journals Implementation of a synthetic inflow turbulence generator in idealised WRF v3.6.1 large eddy simulations under neutral atmospheric conditions

2021 ◽  
Vol 14 (1) ◽  
pp. 323-336
Author(s):  
Jian Zhong ◽  
Xiaoming Cai ◽  
Zheng-Tong Xie
Keyword(s):  
Boundary Conditions ◽  
Periodic Boundary ◽  
Periodic Boundary Conditions ◽  
Periodic Case ◽  
Atmospheric Conditions ◽  
Mean Velocity ◽  
Large Eddy ◽  
Inflow Turbulence ◽  
Turbulence Generation ◽  
Turbulence Generator

Abstract. A synthetic inflow turbulence generator was implemented in the idealised Weather Research and Forecasting large eddy simulation (WRF-LES v3.6.1) model under neutral atmospheric conditions. This method is based on an exponential correlation function and generates a series of two-dimensional slices of data which are correlated both in space and in time. These data satisfy a spectrum with a near “-5/3” inertial subrange, suggesting its excellent capability for high Reynolds number atmospheric flows. It is more computationally efficient than other synthetic turbulence generation approaches, such as three-dimensional digital filter methods. A WRF-LES simulation with periodic boundary conditions was conducted to provide prior mean profiles of first and second moments of turbulence for the synthetic turbulence generation method, and the results of the periodic case were also used to evaluate the inflow case. The inflow case generated similar turbulence structures to those of the periodic case after a short adjustment distance. The inflow case yielded a mean velocity profile and second-moment profiles that agreed well with those generated using periodic boundary conditions, after a short adjustment distance. For the range of the integral length scales of the inflow turbulence (±40 %), its effect on the mean velocity profiles is negligible, whereas its influence on the second-moment profiles is more visible, in particular for the smallest integral length scales, e.g. those with the friction velocity of less than 4 % error of the reference data at x/H=7. This implementation enables a WRF-LES simulation of a horizontally inhomogeneous case with non-repeated surface land-use patterns and can be extended so as to conduct a multi-scale seamless nesting simulation from a meso-scale domain with a kilometre-scale resolution down to LES domains with metre-scale resolutions.

A Large-Eddy Simulation of Bubble-Liquid Jets

2002 ◽  
Author(s):  
M. Yang ◽  
L. X. Zhou ◽  
L. S. Fan
Keyword(s):  
Large Eddy Simulation ◽  
Liquid Jets ◽  
Order Moment ◽  
Two Phase ◽  
Confined Jets ◽  
Bubble Liquid ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Turbulence Generation ◽  
Shear Production

A Large-Eddy Simulation (LES) with a two-way coupling is used to study bubble-liquid two-phase confined jets in a two-dimensional channel. The results show the large-eddy vortex structures of both liquid flow and bubble motion, the shear-generated and bubble-induced liquid turbulence. For comparison, the second-order moment (SOM) modeling was also carried out for the same case. Both LES and SOM results indicate much stronger bubble fluctuation than the liquid fluctuation, the enhancement of liquid turbulence by bubbles even for the higher velocity case. Both shear production and the production due to bubble-liquid interaction are important for the liquid turbulence generation in the case studied. The LES statistical results and the SOM simulation results are in qualitative agreement with each other.

Evaluation of a Statistically Targeted Forcing Method for Synthetic Turbulence Generation in Large-Eddy Simulations and Hybrid RANS-LES Simulations

2020 ◽  
Author(s):  
Olalekan O. Shobayo ◽  
D. Keith Walters
Keyword(s):  
Turbulent Flow ◽  
Momentum Equation ◽  
New Method ◽  
Navier Stokes ◽  
Model Parameters ◽  
Mean Velocity ◽  
Spectra Analysis ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Turbulence Generation

Abstract Computational fluid dynamics (CFD) results are presented for synthetic turbulence generation by a proposed statistically targeted forcing (STF) method. The new method seeks to introduce a fluctuating velocity field with a distribution of first and second moments that match a user-specified target mean velocity and Reynolds stress tensor, by incorporating deterministic time-dependent forcing terms into the momentum equation for the resolved flow. The STF method is formulated to extend the applicability of previously documented methods and provide flexibility in regions where synthetic turbulence needs to be generated or damped, for use in engineering level large-eddy and hybrid large-eddy/Reynolds-averaged Navier-Stokes CFD simulations. The objective of this study is to evaluate the performance of the proposed STF method in LES simulations of isotropic and anisotropic homogeneous turbulent flow test cases. Results are interrogated and compared to target statistical velocity and turbulent stress distributions and evaluated in terms of energy spectra. Analysis of the influence of STF model parameters, mesh resolution, and LES subgrid stress model on the results is investigated. Results show that the new method can successfully reproduce desired statistical distributions in a homogeneous turbulent flow.

Adaptive Detached-Eddy Simulation of Three-Dimensional Diffusers

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Paul Durbin ◽  
Zifei Yin ◽  
Elbert Jeyapaul
Keyword(s):  
Pressure Coefficient ◽  
Three Dimensional ◽  
Side Wall ◽  
Turbulence Models ◽  
Adaptive Method ◽  
Detached Eddy Simulation ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Default Data

An adaptive method for detached-eddy simulation (DES) is tested by simulations of flow in a family of three-dimensional (3D) diffusers. The adaptive method either adjusts the model constant or defaults to a bound if the grid is too coarse. On the present grids, the adaptive method adjusts the model constant over most of the flow, without resorting to the default. Data for the diffuser family were created by wall-resolved, large-eddy simulation (LES), using the dynamic Smagorinsky model, for the purpose of testing turbulence models. The family is a parameterized set of geometries that allows one to test whether the pattern of separation is moving correctly from the top to the side wall as the parameter increases. The adaptive DES model is quite accurate in this regard. It is found to predict the mean velocity accurately, but the pressure coefficient is underpredicted. The latter is due to the onset of separation being slightly earlier in the DES than in the LES.

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