Visualization of multiple stall cells propagating in an axial compressor rotor

This paper describes visualization of multiple stall cells propagating in an axial compressor rotor. The multiple stall cells have appeared at equal intervals under a mild stall condition of the compressor test rig in Kyushu University. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor, and the pressure distributions on the casing wall have been obtained by a so-called 'double phase-locked averaging technique' in which the outputs of a hot-wire and high response pressure transducers are averaged phase-locked to both of the rotor and the cell rotation. On the basis of the 25 time dependent averaged flow fields, the animations have been made to visualize the flow behavior of the stall cell propagation. The structure of the stall cell is characterized by the length-scale of a few blade spacing and a part-span type. It consists of the separation vortex bubble with a leg travelling ahead of the rotor, changing the blade in turn on which the vortex leg stands. The reverse flows appeared upstream and downstream of the rotor are resulted from this vortical flow.