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Different Boundary Conditions For LES Solver PALM 6.0 Used for ABL in Tunnel Experiment
Řezníček, Hynek ; Geletič, Jan ; Bureš, Martin ; Krč, Pavel ; Resler, Jaroslav ; Vrbová, Kateřina ; Trush, Arsenii ; Michálek, Petr ; Beneš, L. ; Sühring, M.
We tried to reproduce results measured in the wind tunnel experiment with a CFD simulation provided by numerical model PALM. A realistic buildings layout from the Prague-Dejvice quarter has been chosen as a testing domain because solid validation campaign for PALM simulation of Atmospheric Boundary Layer (ABL) over this quarter was documented in the past. The question of input data needed for such simulation and capability of the model to capture correctly the inlet profile and its turbulence structure provided by the wind-tunnel is discussed in the study The PALM dynamical core contains a solver for the Navier-Stokes equations. By default, the model uses the Large Eddy Simulation (LES) approach in which the bulk of the turbulent motions is explicitly resolved. It is well validated tool for simulations of the complex air-flow within the real urban canopy and also within its reduced scale provided by wind tunnel experiments. However the computed flow field between the testing buildings did not correspond well to the measured wind velocity in some points. Different setting of the inlet boundary condition was tested but none of them gave completely developed turbulent flow generated by vortex generators and castellated barrier wall place at the entrance of the aerodynamic section of the wind tunnel.
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Numerical tests of far-field boundary conditions for stably stratified flows
Bodnár, Tomáš ; Fraunié, P. ; Řezníček, Hynek
This numerical study presents the results of simulations of stably stratified wall-bounded flows. The effect of artificial far-field boundary conditions is studied in detail. The standard homogeneous Neumann condition for pressure is replaced by a non-homogeneous condition depending on local velocity and its gradient. The two-dimensional tests are performed for the case of flow over a low isolated hill. The simulations on computational domains with three different heights are discussed to evaluate the performance of the new far-field artifcial boundary condition. The model is based on Boussinesq approximation of non-homogeneous Navier-Stokes equations, solved using artificial compressibility method, looking for a steady solution.
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Okrajové podmínky pro stratifikované proudění
Řezníček, Hynek ; Beneš, Luděk (vedoucí práce) ; Brechler, Josef (oponent)
V předložené práci je popsán matematický model stratifikovaného 2D proudění vazké ne- stlačitelné tekutiny a jeho programová realizace. Základní rovnice pro proudění tekutiny v Boussinesqově aproximaci byly řešeny metodou konečných objemů na strukturované neor- togonální síti. Pro diskretizaci byla použita metoda přímek. Diskretizace v prostoru byla řešena metodou AUSM s MUSCL rekonstrukcí rychlostí. Vazké členy byly řešeny diskre- tizací na pomocné síti. Při časové diskretizaci byla použita metoda umělé stlačitelnosti v duálním čase. Kroky duálního času byly řešeny metodou Runge-Kutta 3.stupně. Nume- rické experimenty byly počítány pro proudění s Reynoldsovým číslem rovným 1000. Dále jsou popsány 3 numerické experimenty pro různé okrajové podmínky. 1
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