Aerodynamic-Aeroacoustic Investigation of Rotating Stall in Conventional and Skewed Rotors

An experimental investigation and a numerical simulation of aerodynamic-aeroacoustic performance of an axial-flow fan at the rotating stall condition are reported in this paper. The wake profiles of rotors were measured using two-channel, hot wire probes. The Reynolds-averaged Navier-Stokes equations of the flow field were numerically solved. The two rotors studied included a conventional and a skewed-swept rotor with the objective being to determine the influence of skew and sweep on the sound levels and rotating stall characteristic. In both cases, a single stall cell was observed in fully developed stall conditions. The experimental results showed a significant difference in stall cell hysteresis, size, circumference and spanwise position, and cell propagation velocity between the two rotors. The stall cell in the skewed rotor propagated faster than the one in the conventional rotor. A fully developed stall cell was observed near the mid-span in the skewed rotor whereas it was situated near the hub in the conventional rotor. The noise level in the skewed rotor at the stall condition was more than 2 dBA lower than in the conventional rotor. Sound frequency spectra were obtained and analyzed in the near and far fields between the skewed and conventional radial rotors at rotating stall point and at design point. Significant differences in the sound directivity between the two types of rotors at steady and unsteady operating conditions were observed throughout the measured sound region. Results showed that the numerical models predicted at the rotating stall condition with good accuracy.Copyright © 2004 by ASME