density standard air

Marco_Vanderbijl · June 14, 2019, 05:11

in the default Su2.cfg file there are several air density default settings
like
% Initial density for incompressible flows
% (1.2886 kg/m^3 by default (air), 998.2 Kg/m^3 (water))
INC_DENSITY_INIT= 1.2886
and
% Free-stream density (1.2886 Kg/m^3, 0.0025 slug/ft^3 by default)
FREESTREAM_DENSITY= 1.2886

however I thought the standard air density was
1.2250 [kg/m3]

It seems that all the other default settings are following the regular standard atmosphere model.
What standard is SU2 using and why is the air density default value different?

Marco_Vanderbijl · June 15, 2019, 14:52

I am asking because my external flow over an airplane wing is converging to CL=0.64
I know this is too much as I designed it with no sweep lifting line theory to be CL=0.6 and then I added 24 degrees of sweep (leading edge). So if anything, then SU2 should come back with something less then 0.6CL
I am trying to figure out what settings I should use to get an accurate result.

Using a smaller density seemed like the obvious first candidate.

What techniques are you using to come to accurate results and how do you know the result is (reasonably)correct?

aero_amit · June 18, 2019, 12:04

To clarify few things -
1- Two options...
% Regime type (COMPRESSIBLE, INCOMPRESSIBLE)
So INC_DENSITY_INIT is used with INCOMPRESSIBLE option.

2- For COMPRESSIBLE options, you can use solution initialization option -
INIT_OPTIONS=REYNOLDS or TD_CONDITIONS (Thermodynamic conditions).

3- With REYNOLDS Option you need to specify Mach number, Reynolds number and Temperature or Density (FREESTREAM _OPTION = TEMPERATURE_FS or DENSITY _FS).

You can set the combination as you want (like in your case, use the value of density (FREESTREAM_DENSITY) you have along with corresponding other inputs)

Just follow any similar test case for you problem (check TestCases folder) for figuring out suitable options.

Best
Amit

June 14, 2019, 05:11	mach 0.047 swept wing overestimated CL? and density standard air	#1
Marco_Vanderbijl New Member marco Join Date: May 2019 Posts: 12 Rep Power: 7	in the default Su2.cfg file there are several air density default settings like % Initial density for incompressible flows % (1.2886 kg/m^3 by default (air), 998.2 Kg/m^3 (water)) INC_DENSITY_INIT= 1.2886 and % Free-stream density (1.2886 Kg/m^3, 0.0025 slug/ft^3 by default) FREESTREAM_DENSITY= 1.2886 however I thought the standard air density was 1.2250 [kg/m3] It seems that all the other default settings are following the regular standard atmosphere model. What standard is SU2 using and why is the air density default value different? Last edited by Marco_Vanderbijl; June 16, 2019 at 14:12.

June 15, 2019, 14:52		#2
Marco_Vanderbijl New Member marco Join Date: May 2019 Posts: 12 Rep Power: 7	I am asking because my external flow over an airplane wing is converging to CL=0.64 I know this is too much as I designed it with no sweep lifting line theory to be CL=0.6 and then I added 24 degrees of sweep (leading edge). So if anything, then SU2 should come back with something less then 0.6CL I am trying to figure out what settings I should use to get an accurate result. Using a smaller density seemed like the obvious first candidate. What techniques are you using to come to accurate results and how do you know the result is (reasonably)correct? Last edited by Marco_Vanderbijl; June 16, 2019 at 14:13.

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June 18, 2019, 12:04		#3
aero_amit Member Amit Join Date: May 2013 Posts: 85 Rep Power: 13	To clarify few things - 1- Two options... % Regime type (COMPRESSIBLE, INCOMPRESSIBLE) So INC_DENSITY_INIT is used with INCOMPRESSIBLE option. 2- For COMPRESSIBLE options, you can use solution initialization option - INIT_OPTIONS=REYNOLDS or TD_CONDITIONS (Thermodynamic conditions). 3- With REYNOLDS Option you need to specify Mach number, Reynolds number and Temperature or Density (FREESTREAM _OPTION = TEMPERATURE_FS or DENSITY _FS). You can set the combination as you want (like in your case, use the value of density (FREESTREAM_DENSITY) you have along with corresponding other inputs) Just follow any similar test case for you problem (check TestCases folder) for figuring out suitable options. Best Amit