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Roozbeh July 13, 2003 06:26

Negative Absolut Pressure In Cavitating Flow
Hi all; I want to work with cavitation option of Fluent. In help of fluent6.0 there is an example: velosity inlet=10m/s , Pv=101175pa For this case I have no problem and my results is the same as fluent help results. But for the same cavitation number and inlet velosity=40m/s , Pv=2400pa(at ambient temprature) ,I have a negative absolute pressure i.e. a very low gage pressure. I am now trying to get a better resuls by low underrelaxation factors at O(.001). Note that both liquid and vapor assumed incompressible. What's your opinion?

mateus July 13, 2003 09:33

Re: Negative Absolut Pressure In Cavitating Flow

I allready answered this question by email and sent you some papers on barotropic model. Maybe it's ok to say the same once more here for othetr people to see.... To get a converged solution I have to do the foolowing things: - increase velocity from 0 to 16 m/s (thats my operating condition) in about 0.001 s (50time steps)(thats about 3 preiods of cavitation cloud shadding in my case) - the other option is to decrease pressure (I tried that and got the same solution - I had to start with very very very high pressure cca 50bar and the decreased it to 3.5 bar) - it good to set operating pressure to cca 100000pa and pressure outlet to desired pressure - operating pressure (operating pressure should be somwhere in the middle) - time step should be very small - 100 time steps per period... - don't play to much with underrelaxation (0.001 is too too small - you shouldn't set them to less than 0.2 - i don't know what they were thinking in tutorial).

Regards Mateus

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