Performance and Exit Flow Characteristics ofMixed-Flow Turbines

[摘要] The performance and exit flow characteristics of two mixed-flow turbines have beeninvestigated under steady-state conditions. The two rotors differ mainly in their inlet anglegeometry, one has a nominal constant incidence (rotor B) and the other has a constant bladeangle (rotor C), but also in the number of blades. The results showed that the overall peakefficiency of rotor C is higher than that of rotor B. Two different volutes were also used forthe tests, differing in their cross-sectional area, which confirm that the new larger areavolute turbine has a higher efficiency than the old one, particularly at lower speeds, and afairly uniform variation with velocity ratio.The flow exiting the blades has been quantified by laser Doppler velocimetry. A differencein the exit flow velocity for rotors B and C with the new volute was observed which isexpected given their variation in geometry and performance. The tangential velocities nearthe shroud resemble a forced vortex flow structure, while a uniform tangential velocitycomponent was measured near the hub. The exit flow angles for both rotor cases decreasedrapidly from the shroud to a minimum value in the annular core region before increasinggradually towards the hub. In addition, the exit flow angles with both rotors were reducedwith increasing rotational speeds. The magnitude of the absolute flow angle was reduced inthe case of rotor C, which may explain the improved steady state performance with thisrotor. The results also revealed a correlation between the exit flow angle and theperformance of the turbines; a reduction in flow angle resulted in an increase in the overallturbine efficiency.

[学科分类] 力学，机械学