# Freestream initialization in compressible flow

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October 7, 2021, 05:00
Freestream initialization in compressible flow
#1
Senior Member

Arijit Saha
Join Date: Feb 2019
Location: Singapore
Posts: 132
Rep Power: 7
Hi SU2 user,
This might be a lame doubt to ask for but somehow if I could get some understanding it will be of great help.
I am simulating an airfoil with M=0.8 and below are my freestream parameters
Quote:
 M=0.8, Stagnation or total pressure (P0)= 101325 Pa, Static pressure= 66486.2 Stagnation Temperature(T0)= 297 K, Static temperature= 263.3 K Now applying the ideal gas law Stagnation density= P0/(R*T0)= 1.188 Similarly static density = 0.875 Dynamic viscosity (Sutherland on)= 1.81 E-5 Now as per my knowledge the Reynolds number should be based on the static values which gives = 1.335 E7
Now my doubt is the Freestream Pressure or Temperature in the cfg file should be the stagnation or static one?

If I put Stagnation
Pressure, Temp and density all will be stagnation one and den how will the Reynolds no. of the freestream be calculated?

Quote:
 MACH_NUMBER= 0.8 % % Angle of attack (degrees, only for compressible flows) AOA= 0.0 % % Init option to choose between Reynolds (default) or thermodynamics quantities % for initializing the solution (REYNOLDS, TD_CONDITIONS) INIT_OPTION= REYNOLDS % % De-Dimensionalization REF_DIMENSIONALIZATION = DIMENSIONAL % FREESTREAM_OPTION= TEMPERATURE_FS % % Free-stream temperature (288.15 K by default) FREESTREAM_TEMPERATURE= 297 % % Reynolds number (non-dimensional, based on the free-stream values) REYNOLDS_NUMBER= 1.335e+7 % % Reynolds length (1 m by default) REYNOLDS_LENGTH= 1.0 % --------------------------- VISCOSITY MODEL ---------------------------------% % % Viscosity model (SUTHERLAND, CONSTANT_VISCOSITY). VISCOSITY_MODEL= SUTHERLAND % % Molecular Viscosity that would be constant (1.716E-5 by default) MU_CONSTANT= 1.716e-05
This is the cfg file I was using but the physics of the freestream case will be wrong if I proceed with this. Because the density is calculated from Reynolds which gives the static density. Now the pressure is calculated from the ideal gas law employing the Temp(stagnation) specified and the density (static) obtained which simply cant be made to done.
So, what will be the right way to define my freestream condition?
Thanks .

 October 7, 2021, 13:32 #2 Senior Member   Pay D. Join Date: Aug 2011 Posts: 166 Blog Entries: 1 Rep Power: 14 This might help: https://arc.aiaa.org/doi/10.2514/6.2013-287 ari003 likes this. __________________ since every contribution counts, always good ones are appreciated!

October 7, 2021, 15:40
#3
Senior Member

Arijit Saha
Join Date: Feb 2019
Location: Singapore
Posts: 132
Rep Power: 7
Quote:
 Originally Posted by pdp.aero This might help: https://arc.aiaa.org/doi/10.2514/6.2013-287
Thanks for your generous response. Somehow I figured out that the freestream values should be static one and not the stagnation values.

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