Ideal vs constant gas model

chris12345 · January 2, 2013, 05:38

Ive been doing unsteady simulations on rotating helicopter blades using overset meshing. There has been problems with convergence of the residuals and the results deviate from experimental values.

I've been trying to isolate the problem and i'm trying to simplify my model. In my past model i've been using a ideal gas model but im thinking of switching to a constant gas model. I checked how the denisty changes close to the rotor blades and it doesnt seem to change alot (initial density 1.225kg/m^3, close to the blades is around 1.1-1.3 kg/m^3).

So my question is, when is it appropriate to go from ideal to a constant gas model? Will this affect my model alot?

//Chris

Sixkillers · January 2, 2013, 07:49

Density difference is negligible when Mach number in whole domain is less than 0.3. Of course there are some cases where density difference are important even if Ma < 0.3 (e.g. free convection simulation).

January 2, 2013, 05:38	Ideal vs constant gas model	#1
chris12345 New Member Christian Rodriguez Join Date: Jan 2012 Posts: 9 Rep Power: 14	Ive been doing unsteady simulations on rotating helicopter blades using overset meshing. There has been problems with convergence of the residuals and the results deviate from experimental values. I've been trying to isolate the problem and i'm trying to simplify my model. In my past model i've been using a ideal gas model but im thinking of switching to a constant gas model. I checked how the denisty changes close to the rotor blades and it doesnt seem to change alot (initial density 1.225kg/m^3, close to the blades is around 1.1-1.3 kg/m^3). So my question is, when is it appropriate to go from ideal to a constant gas model? Will this affect my model alot? //Chris

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Calculation of the Governing Equations	Mihail	CFX	7	September 7, 2014 07:27
How to install CGNS under windows xp?	lzgwhy	Main CFD Forum	1	January 11, 2011 19:44
CGNS lib and Fortran compiler	manaliac	Main CFD Forum	2	November 29, 2010 07:25
Shall I use ideal gas model or other?	summer	FLUENT	6	January 24, 2006 11:43
compressible only for ideal gas	yann	FLUENT	1	February 19, 2004 07:58

January 2, 2013, 07:49		#2
Sixkillers Member Join Date: Nov 2011 Location: Czech Republic Posts: 97 Rep Power: 14	Density difference is negligible when Mach number in whole domain is less than 0.3. Of course there are some cases where density difference are important even if Ma < 0.3 (e.g. free convection simulation).