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

2019 ◽  
Author(s):  
Anonymous
Keyword(s):  
Large Eddy Simulations ◽  
Atmospheric Conditions ◽  
Large Eddy ◽  
Inflow Turbulence ◽  
Turbulence Generator

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.

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.

Simulation study of wake encounters with straight and deformed vortices

2016 ◽  
Vol 120 (1226) ◽  
pp. 651-674 ◽  
Author(s):  
D. Vechtel
Keyword(s):  
Simulation Study ◽  
Thermal Stratification ◽  
Parameter Variation ◽  
Decay Process ◽  
Large Eddy Simulations ◽  
Vortex Rings ◽  
Atmospheric Conditions ◽  
Wide Range ◽  
Large Eddy ◽  
The Impact

ABSTRACTA simulation study was conducted in order to investigate the influence of vortex deformation on wake encounter characteristics. Wake vortices tend to be strongly deformed during the decay process, depending on the atmospheric conditions in terms of turbulence and thermal stratification. For quantification of the influence of vortex deformation, encounters of an aircraft of the ‘Medium’ category behind a generator aircraft of the ‘Heavy’ category were simulated with straight vortices and with realistically deformed vortices derived from large-eddy simulations. All relevant parameters that influence the encounter characteristics, such as encounter angles and positions, were varied within a wide range. In order to cover all kinds of vortex deformation, encounters with different vortex ages from 16-136 seconds were simulated. Hence, all relevant phases during the vortex decay from nearly straight and wavy vortices to vortex rings were considered.The parameter variation study revealed that on average the impact on the encountering aircraft is less with deformed vortices than with straight vortices of comparable strength. Especially with vortex rings, the encountering aircraft is exposed to a much smaller impact. However, the results also show a larger aircraft response during encounters with wavy vortices just prior to vortex linking. The maximum aircraft response with wavy vortices is stronger than with straight vortices of comparable strength. Also, the strongest encounters occur under greater encounter angles with deformed vortices than with straight ones.

A Total Turbulent Energy Closure Model for Neutrally and Stably Stratified Atmospheric Boundary Layers

2007 ◽  
Vol 64 (11) ◽  
pp. 4113-4126 ◽  
Author(s):  
Thorsten Mauritsen ◽  
Gunilla Svensson ◽  
Sergej S. Zilitinkevich ◽  
Igor Esau ◽  
Leif Enger ◽  
...  
Keyword(s):  
Potential Temperature ◽  
Stability Limit ◽  
Turbulent Energy ◽  
Large Eddy Simulations ◽  
Turbulence Closure ◽  
Turbulent Heat ◽  
Atmospheric Conditions ◽  
Mean Flow ◽  
Wide Range ◽  
Large Eddy

Abstract This paper presents a turbulence closure for neutral and stratified atmospheric conditions. The closure is based on the concept of the total turbulent energy. The total turbulent energy is the sum of the turbulent kinetic energy and turbulent potential energy, which is proportional to the potential temperature variance. The closure uses recent observational findings to take into account the mean flow stability. These observations indicate that turbulent transfer of heat and momentum behaves differently under very stable stratification. Whereas the turbulent heat flux tends toward zero beyond a certain stability limit, the turbulent stress stays finite. The suggested scheme avoids the problem of self-correlation. The latter is an improvement over the widely used Monin–Obukhov-based closures. Numerous large-eddy simulations, including a wide range of neutral and stably stratified cases, are used to estimate likely values of two free constants. In a benchmark case the new turbulence closure performs indistinguishably from independent large-eddy simulations.

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