Effects of the Inlet Boundary Layer Thickness on the Rotating Stall in an Axial Compressor

Abstract

A three-dimensional numerical simulation is conducted to study an effect of the inlet boundary layer thickness on the rotating stall in an axial compressor. The inlet boundary layer thickness has significant effects on the hub-corner-separation in the junction of the hub and suction surface. As the load is increased, the size of the hub-corner-separation is increased dramatically for the thick inlet boundary layer but it is diminished to be indistinguishable from the wake of the blade for the thin inlet boundary layer. The difference induced by different inlet conditions at high load should have affected characteristics of the rotating stall such as the inception process and propagation speed of the stall cells. For two cases of different inlet boundary layers, the numerical simulation is progressed as the flow coefficient is decreased until the rotating stall begins and then effects of the inlet boundary layer thickness on the rotating stall are analyzed by using the axial velocity history and the rotary total pressure distribution. For the thick inlet boundary layer, a pre-stall disturbance arises firstly in the hub-corner-separation and then in the tip leakage flow as the load is increased. For the thin inlet boundary layer, however, an asymmetric disturbance is initially generated in the tip region because of the corner-separation in the junction of the casing and suction surface. The disturbance of the tip leakage flow grows to be a stationary stall cell which is adhered to the blade passage by throttling process in case of the thick inlet boundary layer. When the stationary stall cell reach a critical size, this cell moves along the blade row and becomes a short-length-scale rotating stall. However, the rotating stall is not found at a smaller flow rate for the thin inlet boundary layer because the flow in the tip region is more energetic than that of its counterpart. In addition, it is found that the inlet boundary layer thickness has an effect on the cause of the initial disturbance which collapses the axi-symmetric flow under high load and the internal flow with a thick boundary layer on the casing is susceptible to the rotating stall.

Numerical analysis of non-equilibrium steam condensing flows in various Laval nozzles and cascades

“…A local time-stepping method based on the Courant-Friedrichs-Lewy number and a message-passing interface (MPI) are used for rapid calculation. The governing equations and descritization methods used in T-Flow are described in detail in Choi (2008).…”

Controlling Secondary Flows in Highly-Loaded Compressor Cascades

“…The shape factor in the current study is similar to the values obtained by Knezevici et al (2008) and MacIsaac et al (2010) in their turbine cascade studies performed in the same wind tunnel. Choi et al (2008) conducted numerical investigations of the effect of inlet boundary layer thickness on the rotating stall using a low-speed axial compressor rotor blade (NACA 65 profile) at a constant Reynolds number of 244,000 (based on axial chord and inlet velocity at design condition). The investigations showed that, at design condition, the inlet boundary layer thickness had minimal effect on the size of the hub-corner separation.…”