I have two problem,which are as follows:

1)I got some negative static pressures at suction side of the blade of a centrifugal pump,which are as low as -1.5 bar,is it reasonable?

2)I want to simulate a multistage centrifugal pump including rotor ,stator and deswirl blade. I use frozen rotor as the interface between rotor and stator,and stage between stator and deswirl blade(stator and deswirl are both stationary).but I got a error message: ******* ERROR #001100279 has occurred in subroutine ErrAction. Message: ****** FATAL ERROR ****** Rotation axis could not be found for GG-I interface.

who can help me?

thank you

Hi feng,

Some responses:

1) negative static pressures are relative to the reference pressure. Obviously the absolute pressure cannot go below zero, so if you have regions below absolute zero pressure you have some error in your simulation. It could be caused by numerical reasons such as poor convergence or insufficient mesh resolution. It could have a physical reason, such as in reality the fluid cavitates or has compressible properties in this region.

Whether this is a problem or not, and whether your simulation is good enough for what you want to do with is up to you.

2) I can only suggest you look into the error message. Have you defined the rotation axis for the rotating domain correctly?

Glenn

thank you very much.

1)for the first problem,my convergence is very good,my criterion is 1e-5.I asked someone else,who told me the reason maybe was the fluid cavication ate the suction side,nearly the same with what you said.

2)I have checked the the rotation axis for the rotating domain,there is no problem.I tried to delete return channel balde domain only to keep rotor and stator domain,it is ok.

Hi feng,

Be aware that the converge level required for an accurate simulation is problem dependant, but 1e-5 is usually a good level of convergence.

Assuming the simulation is good then I agree about the problem being cavitation. You have to decide whether it is significant in your simulation or not. If it is only a tiny little patch your results might be OK as they are. Otherwise you will probably need to change the physics to model cavitation.

Glenn

hi.. im looking for equation for calculation of water density with telorance in temprature and pressure. infact im looking for effect of T&P`s telorance in density. can u help me? thank u.