NUMERICAL SIMULATION OF ROTATING STALL IN A TWO-STAGE AXIAL FAN

Computational fluid dynamics calculations using high-performance parallel computing were conducted to simulate the prestall flow of a two-stage axial fan. The simulations were run with a full-annulus grid that models the 3-D, viscous, unsteady blade row interaction without the need for an artificial inlet distortion to induce stall. The simulation shows the initiation and development of the stall inception in two rotors of the axial fan. The results show that the stall inception first occurs in the second stage. The spike-type stall inception occurred in the second stage, which is different from the common views. The starting positions of stall inception in both rotors are in the same circumferential direction, and the stall inceptions in both rotors turn into mature stall cells at the same time. Also, the rotation speed of the stall inception and rotating stall in the two rotors are the same. The rotating stall in the first and second stage rotor impellers are both directly induced by the blade tip leakage flow. However, the blocked flow in the second stage rotor strengthens the leakage flow in the blade tip of the first stage rotor indirectly, resulting in the formation of stall inception.