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Subramani Sockalingam September 26, 2007 14:08

How to model hypersonic flow
 
Hi, I am trying to model hypersonic flow around a blunt body. I could go upto Mach number 3.5 after which the solution diverges. Any thoughts please? I am using the following Operating pressure 101325 Pa

If I make the operating pressure to 0 I get floating point error. I am relatively new to CFD and FLUENT.

Thanks, Subramani

Velan September 27, 2007 07:59

Re: How to model hypersonic flow
 
what is your boundary condition?. How much cfl you used?. try by reducing CFL. Are you running implicit or explicit ?. Is it viscous or inviscid?

Velan

Tristan SoubriƩ September 27, 2007 08:14

Re: How to model hypersonic flow
 
Some numerical schemes (e.g Roe) produce carbuncle = numerical instability. Playing with the mesh could solve the problem (align mesh with shock, increase ratio length over width where width is the size in direction of incoming flow)

Subramani Sockalingam September 27, 2007 12:32

Re: How to model hypersonic flow
 
Boundary conditions Pressure farfield Cfl 5 I have to try reducing it, yes. I am doing implicit and inviscid.

Have you guys done high Mach number flows? What about the operating pressure? Can I go ahead with 101325 Pa? Is there any tutorial available for high Mach number flows?

Thanks a lot for the response guys.

margarita September 28, 2007 05:32

Re: How to model hypersonic flow
 
Hi Subramani,

I know very well FLUENT. It's inable to simulate the flow with important Mach number. Use FASTRAN, or other CFD code which is specially developped for hypersoni (Mach>5).

Best,

MD.


Subramani Sockalingam September 28, 2007 07:39

Re: How to model hypersonic flow
 
Hi Margarita, Thanks for your response. When I increase the Mach number from lets say 0.55 to 2.5, I have to change the operating pressure and temperature right? Please let me know. I found a few papers where they have used FLUENT for hypersonic flow and that's why I started.

Thanks, Subramani

Praveen. C September 28, 2007 11:25

Re: How to model hypersonic flow
 
If you are simulating some experimental test case, you should get the conditions from the test. In hypersonic flows, temperature can be important, if you are considering reacting flows. If you are solving inviscid case, no viscosity, no reactions, then it does not matter. Just choose something realistic, say

density = 1 mach = given to you Temperature = 300 K sound speed = use formula and above data velocity = mach * sound_speed pressure = equation of state

Subramani Sockalingam September 28, 2007 16:30

Re: How to model hypersonic flow
 
Hi, I have a set of free stream conditions for hypersonic flow. My question is when I increase the Mach number from one value to another, do I need to change the operating pressure and temperature? What other things I have to do? I tried changing the operating pressure and temperature and I did not get the shock wave.

Deepak October 3, 2007 21:43

Re: How to model hypersonic flow
 
First of all, Mach number is a function of temperature (M=v/sqrt(gamma*R*T)), so when you change Mach number, temperature will change and temperature is a function of pressure (p=rho*R*T) as per the gas law, the pressure can be changed. If you have a set of free stream conditions, try running it first, if you want to change only the Mach number, keep the free Pressure and temperature constant and vary Mach number to see the change in flow field.


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