Pressure coefficient calculation in LES
 

I have problem with my LES output. I used PALM code to calculate my pressure coefficient. When I calculate the Cp the value that I got from LES 10 times lower than experiment value. In this PALM code they uses the Navier-Stokes equations in a Boussinesq approximated form and this is done using the so called fractional step method.
any one can help me or may be have some experience in this problem.