Model of pump nonoptimal regimes get bad results

Georg

Hi all! I try to model a stage of a water pump. I use 'stage' and 'frozen rotor' interface. Results for optimal regime are quite good (well coincidence with experiment). But when I solve the problem for small (non optima)l flow rates (left part of head vs. flow rate curve) results can very differ from experiment (100% or more). What is the reason? What can you recommend to improve the results? Thank you for your responses!