Effect of speed of sound (Mach number) on pressure results

salehmeiabadi · March 2022

Hello to all

I did a simulation test and an experimental test of the injection process to validate simulation results.

One of the interesting points of the simulation test was that speed of sound has a remarkable effect on pressure results not on velocity results.

The second point is the difference between experimental pressure and SPH pressure.

SOS eg. speed of sound.

I would be appreciated if anyone can give an explanation on this.

Asalih3d · March 2022

In weakly compressible SPH which DualSPHysics uses for now, the speed of sound is used to estimate the pressure, through the barotropic pressure equation seen in DualSPHysics wiki. Here in the constant b, the speed of sound is present, with a controllable factor, gamma, often taken as 7 to ensure a very incompressible fluid.

https://github.com/DualSPHysics/DualSPHysics/wiki/3.-SPH-formulation Equation of State

You should ensure that the speed of sound at minimum is 10 times higher than the expected speed you have in your simulation, to ensure 99% percent incompressibility.

Kind regards

salehmeiabadi · March 2022

Thank you for your comments.

It was interesting to see despite the contribution of pressure in momentum equation the effect of speed of sound and consequently pressure in velocity results is negligible.

Asalih3d · March 2022

https://forums.dual.sphysics.org/discussion/comment/5019#Comment_5019

I suspect this is due to the gradient of pressure being used in the momentum equation, and not pressure it self directly.

Kind regards

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Effect of speed of sound (Mach number) on pressure results

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