[759599290]

Hi everyone,
Recently i am conducting a simulation of water flow in porous media using FLUENT. It is known that the density of water changes with temperature and pressure, so I programmed a udf to adjust the properties of water according to IAPWS-IF97. here I am puzzled by a problem and hope for your help:
when I defined the speed of sound of the materials, i.e. water, the simulation can run well, while if I set it to none, then back flow occurs and the calculation break down only after three steps. And if I don't invoke pressure, that is to say neglect the influnce of pressure, then no matter what value the speed of sound is, the calculation can run well. I use pressure-based solver.
I searched a lot data and could not found how the speed of sound can lead to such a huge difference in this simulation. Hope for your help.