Three-dimensional numerical analysis of internal flow phenomena in a diagonal rotor

A numerical analysis has been designed to study internal flow phenomena in a diagonal rotor. A calculated diagonal rotor was designed by a quasi-three-dimensional method. Its hub and casing walls were inclined 45o and 25o, respectively. The numerical simulation was based on the Navier-Stokes equations coupled with a k-ε turbulence model. We found that the rotor's wake was stronger near the hub and in the casing end wall region. The wake at a lower flow rate was stronger than that at a higher flow rate. Static pressure gradually increased from the hub to the casing along the height of a blade, on the rotor pressure surface and in the front 60% of the chord region of the suction surface. In the back 40% of the chord region of the suction surface, static pressure gradually decreased. A passage vortex formed in the stator flow passage and an 80% axial chord plane. It was located near the hub end-wall. The passage vortex developed into a large vortex centered near the midspan at a 99% axial chord plane of the stator. The casing wall boundary layer downstream of the rotor occupied approximately 10% of the flow passage. Along the height of a blade, the meridian velocity gradually increased upstream of rotor and decreased downstream. The calculated aerodynamic characteristic curve, the meridian velocity distribution upstream and downstream of the rotor, and the streamline distribution on the meridian surface were consistent with experimental results and design data. Our findings proved that the present numerical method is reliable and practicable. It can be used to design and analyze swept diagonal rotors in order to improve their surging and rotation stall state. The present results also provide comparative data for the design of highly-loaded swept diagonal rotors in future studies.