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-   -   why the static pressure in inlet of fans was high (http://www.cfd-online.com/Forums/numeca/50911-why-static-pressure-inlet-fans-high.html)

 jimmy October 9, 2003 22:15

why the static pressure in inlet of fans was high

I'm computing a flow field of a fans working in a low mass flow. Because the velocity inside the fans is small, I used the precondition. The convergence history is good ,but the inlet static pressure in the inlet is higher than the pressure of atmosphere, this is not right. The bondary condition which i used is that the inlet is mass flow and the outlet is static pressure. All the value of bondary condition is meassured by experiment, so they are exact. The Re=10000(estimated by characteristic scale and velocity in the tip of centifugal impeller),and the beita* is equal to 300. Now i can not find the reason ,who can help me.

 Remi lestriez October 10, 2003 06:40

Re: why the static pressure in inlet of fans was h

Hello Jimmy,

I recently computed a couple of fans and get very good results (convergence and accuracy). However, the methodology used was different: - I did not used preconditionning; a way to avoid that and keeping a low number of iterations to get a stable solution is to increase the number of sweeps on coarsers grids in the multigrid strategy. As you know, the preconditionning introduce extra dissipation and for example a value of 300 is high. If you still want to use preconditionning you should use lower value for beta (for example restarting your computation witt beta = 30 then 3). Note as well that the impact of preconditionning is function of your grid size: if you have a very fine mesh, the impact of beta is less important. - For boundary conditions, the mass flow was imposed but at the outlet through pressure adaptation. For inlet, total conditions were imposed: atmospheric conditions. Hope this help. Remi

 jimmy October 10, 2003 07:25

Re: why the static pressure in inlet of fans was h

hello, Remi lestriez Thank you for your help.I will try it again as your advice. If I still have any question ,i will ask you and hope you to help me continuously.

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