Using CFX-TASCflow version 2.12.1.beta and previous versions,
we performed computations of flat-plate compressible boundary
layers with the k-omega turbulence models.
There have been found problems when using the low-Re SST model.
The fluid used is a generic ideal gas (air at STP) with
molecular viscosity mu =1.88 x 10-5 kg m-1
Boundary conditions are defined in Table 1.
Fig.1. Grid sketch (L=3.048 m, h=0.0762 m)
|AD||Inflow||Velocity: U=132 m/s, V=W=0
Temperature: static 300 K
Turbulence: intensity (Tu) 0.25%, eddy length scale (L) 1.27x10-3 m
|CF||Outflow||Pressure: static 91715 Pa|
The following initial conditions were used for all runs:
(U, V, W) = (132, 0, 0) m s-1, Tu=2.5x10-3, L=1.27x10-3 m, P=91715 Pa, T = 300 K
|Case||Grid dimensions||Near-wall cell size||”Mean‘ y+ value||Maximum y+ value||Results (skin friction distributions for two turbulence models)|
|#1||121x43x3||1.62x10-6 m||0.4||0.87||See Figure 2 and 3|
|#2||121x43x3||2.94x10-6 m||0.8||1.7||No data for SST model (overflow)|
|#3||121x31x3||8.04x10-5 m||22||28||See Figure 4|
”Mean‘ y+ value was estimated at the plate“s midpoint (x=1.524 m).
Computations presented below were performed with CFX-TASCflow version 2.12.1beta (solver build 2.12.1-558 for WinXP). Similar results were obtained previously with versions 2.11, 2.12.0 and 2.12.1.alpha. Recommended values for computational parameters are: DTIME=5x10-4, KNTIME=100. All simulations were started from the same initial guess as specified in the solver parameter file. Computations with the Wilcox turbulence model were carried out with parameter TWO_EQUATION_MODEL = 2, and for the SST model special parameters were TWO_EQUATION_MODEL = 3, ZONAL_KW_MODEL = 2, SST_TRANSITION_MODEL=F.
Figures 2, 3 and 4 shows variations of computed skin friction coefficient, Cf, along the plate for the low-Re and high-Re computations respectively.
Fig.2. Skin friction distributions for case 1 (low-Re calculations with parameter FIXED_WALL_DISTANCE_MODEL=T as is by default)
Fig.3. Skin friction distributions for case 1 (low-Re calculations with parameter FIXED_WALL_DISTANCE_MODEL=F manually set in PRM file)
Fig.4. Skin friction distributions for case 3 (high-Re calculations)
Formulas used for postprocessing are standard combinations of these quantities:
Rex - current Reynolds number,
ro (x), U(x) - flow density and velocity along line EF,
tauwall(x) - wall shear stress.
Formula from CFX Theory documentation (Á4.4.4, formula 4.171) used for comparison is as follows:
Prof. Evgueni M.Smirnov, PhD Student A.M.Levchenya, March 10, 2003