slove the problem?decreaing pressure force in 2phase model
 

Dear all ,
I am handling with a 2phase model.it's a ship moving in the water with air injecting from its bottom ,I wanna get the drag coefficient of the hull.the model as fllows
my model is a 1/4 clinder field with a hull in it .the boundary is :
hull:wall.;
hole under the hull bottom:velocity inlet(air) ;i can set it as wall when without injecting air ;
end face of the cylinder:velocity inlet ,outflow ;
two rectangle face of the cylinder: symmetry ,
the arc face of the cylinder : velocity inlet whose velocity is equal to the velocity inlet.


http://www.pikipimp.com/pp/pimped_ph...-compiled.JPG?

http://www.pikipimp.com/pp/pimped_ph...-compiled.JPG?




first I compute hull resistance without injecting air.the hole is set as wall.1 phase ,only water without air ,I can get good result ,the pressure force is stable ,so my model is correct.
then I compute hull force with air injecting. I use a mixture model ,rng k-e ,2nd order ,with gravity,to get the result of the drag of the hull ,but i only get a stable vicous friction ,the pressure force is keeping falling down ,which is not correct with the real condition, for example ,the right coefficient of pressure force is -0.24*10-3,the result of pressure force coefficient will go to -1.9*10-3 and keepingdown more and more close to 0,I dont konw why this happen.
if you have some good advice ,please give me some tips!
Thanks for your help !
regards
Michael