eulerian multiphase pressure drop
 

hello.
I am trying to calculate the pressure drop in a horizontal pipe.
What i'm trying to find is the pressure drop of slurry according to volume fraction.
I'm using eulerian multiphase model, turbulence model as k-omega and per phases model.
i tried drag models such as syamlal, wen yu, gidaspow, and the default one.
i tried default granular viscosity models too.
in my assuming, as volume fraction goes up, the pressure drop has to go up too.
however, in my simulation, it doesn't show that kind of trend.
theoretically, from 21% volume fraction to 42% volume fraction, the pressure drop has to be about 3times, but the difference is slight.
please help me...