Compressible transonic airfoil RAE2822 simulation

Stefano

Hello Everyone, I have a big problem with StarCD and I hope you can help me.

I'm using StarCD 3.22, and I have to simulate a transonic airfoil in a wind tunnel. The objective is to calculate lift and drag coefficients of the airfoil and compare them to wind tunnel experimental results (experimental results are: Cl=0.803; Cd=0.0168). My problem is that the mass doesn't converge, the mass residual stays high (about 3.e-1).

The airfoil is a RAE-2822, and the test conditions are:

Mach number at inlet: 0.73 Angle of Attack: 3.19 degrees Reynolds Number: 6.5e+6

From these data, and fixing a static temperature of 300K, I can obtain the following values (using the definition of Reynolds number, the equation of state for ideal gases and the isoentropic correlations between static values, stagnation values and Mach Number):

Stagnation Temperature: 331.974K Velocity Magnitude: 252.770738m/s Density: 0.469604kg/m^3 Static Pressure: 40449.81Pa Stagnation Pressure: 57657.57Pa K(inlet)=3/2*I^2*V^2=1.5*0.02^2*252.770738^2= 38.33583 Epsilon(inlet)=Cmu^(3/4)*K(inlet)^(3/2)/1= 39.0022

The walls of the wind tunnel are at a distance of +-20 chords in y direction, 10 chords in â€"x direction, 30 chords in +x direction.

I did the mesh with a macro written by me and the mesh around the airfoil is in this picture (click to enlarge):





There is about a total 100000 cells in the grid. As you noticed, I inclined the wind tunnel 3.19 degrees, so I calculated appropriate director cosines for boundaries definition. I applied Symmetry Boundaries (it's a 2d simulation), a Stagnation Boundaries (for the cells at the beginning of the wind tunnel, as an inlet boundary) and Pressure Boundary (for the cells at the end of the wind tunnel, as an outlet boundary), shown in this picture:



The settings of the boundaries are in these pictures:





I used manual initialization, initializing U=250; V=15; p=100000; T=300; K=K(inlet); Epsilon=Epsilon(inlet).

I use a pseudo-transient algorithm (SIMPISO) with 1.e-5 time step, and default relaxation factors. Differencing schemes are Upwind for all, but for density I use CD with 0.01 blending factor (that is, 1 percent of CD and the rest Upwind). Obviously I set density as Ideal-f(T,p). The residuals are shown in this figure, you can see that it simply doesn't converge!



Any suggestions? Is the grid ok or I have to redesign it? All suggestions are welcome, I tried almost everything but nothing worked for me.

Thanks