FLOW-FIELD UNSTEADINESS IN THE TIP REGION OF A TRANSONIC COMPRESSOR ROTOR

An experimental investigation concerning tip flow field unsteadiness w as performed for a high-performance, state-of-the-art transonic compre ssor rotor. Casing-mounted high frequency response pressure transducer s were used to indicate both the ensemble averaged and time varying fl ow structure present in the tip region of the rotor at four different operating points at design speed. The ensemble averaged information re vealed the shock structure as it evolved from a dual shock system at o pen throttle to an attached shock at peak efficiency to a detached ori entation at near stall. Steady three-dimensional Navier Stokes analysi s reveals the dominant flow structures in the tip region in support of the ensemble averaged measurements. A tip leakage vortex is evident a t all operating points as regions of low static pressure and appears i n the same location as the vortex found in the numerical solution. An unsteadiness parameter was calculated to quantify the unsteadiness in the tip cascade plane. In general, regions of peak unsteadiness appear near shocks and in the area interpreted as the shock-tip leakage vort ex interaction. Local peaks of unsteadiness appear in mid-passage down stream of the shock-vortex interaction. Flow field features not eviden t in the ensemble averaged delta are examined via a Navier-Stokes solu tion obtained at the near stall operating point.