UNSTEADY-FLOW AND SHOCK MOTION IN A TRANSONIC COMPRESSOR ROTOR

The results of an experimental and numerical comparison of the unstead iness and shock motion that occurs in the tip region within a modern, low-aspect-ratio, high-through-flow, axial-how transonic fan rotor are presented, The unsteadiness studied here is associated with local phe nomena within the blade passage and not related to blade row interacti on, Unsteady static pressures were measured at the casing over the rot or that operates at a tip relative Mach number of 1.6. An unsteady thr ee-dimensional Navier-Stokes computational study was performed with ti p clearance comparable to the test rotor. The fully three-dimensional, unsteady, Reynolds-averaged Navier-Stokes equations were solved with time steps, each nominally of 2.8 x 10(-5) s in duration or approximat ely live times blade pass frequency. The results in the clearance gap were retained from the computational solution and compared with the ex perimental measurements. Both indicated deterministic unsteadiness nea r the location of the shock, nigh levels of unsteadiness were also mea sured downstream of the shock in the path of the clearance vortex, but this phenomenon was not predicted by the computation, The unsteadines s near the shock was shown to be a result of movement of the shock. Th e amplitude and frequency of shock position oscillation was estimated from the results to be about 2% chord and 2 kHz, respectively, Analysi s of loss caused by the shock unsteadiness suggested that losses becau se of shock motion were insignificant relative to the steady shock los s at the relative Mach number studied.