The unsteady flow field during surge of the front rotor of an eight-stage axial aero engine compressor has been investigated experimentally and analytically. For that purpose, two newly designed multi-sensor probes are installed up- and downstream of the first rotor. Surge experiments are conducted at four different speed lines (75–93% speed) covering a wide range of the compressor map and measurements have been taken at two different channel heights (50% and 70% span). The results show that the flow field varies extremely during surge up- and downstream of the rotor. In contrast to the flow at the rotor leading edge, which is nearly independent of the rotor speed, the flow at the rotor trailing edge is highly dependent of the rotor speed. Therefore, the performance of the rotor during surge is dependent on the reverse through-flow of the stators. At low speeds the flow passes the stators without any changes in the flow direction. If speed is increased the reverse flow is guided more and more by the stators. These different flow conditions have a direct impact on the process of energy conversion of the rotor during the surge event. The incoming reverse flow at the rotor trailing edge impinges on the blade from the suction surface side at lower speeds and turns to the pressure surface side when speed is increased. Hence, the deviation and specific work grow.
In addition to the surge experiments simulations of the surge events are conducted with a 1D code called SYSQ3D. The simulations and experiments match well and underline the capability of the new multi-sensor probes to accurately measure the flow patterns during surge.