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 Valery Ponyavin March 25, 2004 14:37

Supersonic flow calculation

I use FLUENT for simulation supersonic flow around bodies of different forms. I need to simulate flow during the moving the body (bodies) into container and observe shock waves around. When I use motionless body and change surrounding velocity (using UDF for changing total pressure on boundaries) everything is OK and behavior of shock is quite reasonable. But when I trying to move the body with big velocity (1000-8000 m/s) within container with motionless air (using remeshing procedures) the results look not reasonable and no clear shocks in front of the body. For example when body moving within air with v=1000 m/sec FLUENT shows Mach number less then 1 in front of the body.

Could anyone help me with the problem? Does FLUENT capable to solve such kind of problem correctly?

Thank you,

Valery

 FJ March 26, 2004 06:15

Re: Supersonic flow calculation

Hi,

In your case, velocity boundary condition is not suitable.

When thinking mass flux at your inlet, mass flux doesn't change because gas is compressed. (In other words, gas density goes high but velocity goes down. Therefore mass flux is constant.) But, under the specified velocity condition, density goes high, but velocity is constant. Therefore mass flux is not constant. This behavior doesn't occur in gas flow.

So specifed mass flow rate or mass flux at your inlet is suitable and gas density should be compressible ideal gas law, Fluent's solver is "Coupled" much better. (If mach number is less than two or three,it is O.K ,even the "Segregated solver" in my experiences)

Thank you.

FJ

 Valery Ponyavin March 26, 2004 13:00

Re: Supersonic flow calculation

Hi,

If I calculate supersonic flow within some chamber, the mass flow rate for inlet conditions works well. But if I calculate flow around the body which is moving with supersonic velocity within chamber with motionless air, what condition except for velocity of the body can I put? When body is moving I need just to remesh domain automatically, bacause coordinates of the body are changing all of time.

Thank you.

Valery

 FJ March 28, 2004 22:28

Re: Supersonic flow calculation

Hi,

How about "Pressure Far Field" boundary condition. Specified Mach number can be allowed. I think this BC will be suitable for your issue.

See Fluent tutorial 3 "Modeling External Compresible Flow".

Thank you.

FJ

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