Flow Loss Mechanism in Radial Variable Area Nozzles

Three dimensional flow fields of the variable area nozzle for radial turbines were calculated with CFD method.The static pressure contours and total pressure loss coefficients distribution were calculated with respect to different setting angles.Setting angle vary from 21° to 44° in the numerical model.Throat area changes from 50% to 116% of design one.The results show that with the guide vanes closing,blade loading and total pressure loss increase.Compared with the design conditions,total pressure loss increases by one time when the opening is-15°.Tip clearance increases flow loss of cascade.Tip clearance of 2 percent indicates approximate 1.5 percent total pressure loss while tip leakage mass flow rate is increased for near 1.3 percent range of endwall loss increases from 20% to 40% of span.When the opening decreases,endwall loss and profile loss have small increase.But clearance loss and proportion enhance significantly.Increase of clearance loss with the opening is main reason for total loss increase in off design condition.