momentum sink

Atit Koonsrisuk

I am trying to model the flow across a turbine in a horizontal circular tube by using momentum source. I create the thin fluid subdomain at the turbine position, then set it as the momentum source. I choose the 'general momentum source' option. I assume the power that the turbine can extract from the flow. I devide that power by (mdot)x(thickness of subdomain in the direction of source component)/(rho). I get this formula by checking the unit of the specifying value, kg.m^-2.s^-2. Then I use the minus of value obtained as the source value. However the different power before and after the subdomain is significantly less than the power value specified. In addition, I check the area averaged value of (rho x flow_area x velocity). The values are the same at the inlet and outlet of the tube, but the values in the subdomain and neiborhood planes are less than the value at the tube inlet noticeably.

Do anyone have a suggestion or example for this? Thank you very much for your kind consideration.

Atit