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rhoCentralFoam velocity definition

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Old   May 2, 2016, 20:07
Default rhoCentralFoam velocity definition
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Grega Verdenik
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Hi guys,
I'm new to the forum and openFOAM. I've been following a youtube tutorial on the supersonic wedge case using rhoCentralFoam: https://www.youtube.com/watch?v=6jLn5cSCkd8

It seems they're specifying the airflow velocity in the boundary conditions at 5m/s. However, once the simulation has been executed the resulting Mach number is calculated to be about 5.
My question is, how does 5 m/s translate to Mach 5? Are they manipulating the Reynolds number?

Thanks!
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Old   May 3, 2016, 10:33
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Hello,

the local speed of sound depends on the specific gas constant, temperature and isentropic coefficient. As you change the fluid properties, you can achieve Ma = 1 at conditions like U = 1m/s and T = 1K.

Just have a look at the settings in the thermophysicalProperties file in the constant folder.

Kind regards,

Martin
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Old   May 3, 2016, 16:10
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Grega Verdenik
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Thank you Martin- that makes sense.
So, am I correct to assume the specific gas constant is calculated from the gas constant and molar mass; and the isentropic coefficient is 1.4 (for ideal gas)?
Also, does this case simulate an actual real-life gas (molar mass 11.6403 kg/mol; Cp =2.5) or are these numbers just randomly defined to simulate high Mach with low U conditions?
Thanks again!
Greg
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mach number, rhocentralfoam, supersonic flow

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