Unsteady flow and shock motion in a transonic compressor rotor

The results of an experimental and numerical comparison of the unsteadiness 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 phenomena within the blade passage and not related to blade row interaction, Unsteady static pressures were measured at the casing over the rotor that operates at a tip relative Mach number of 1.6. An unsteady three-dimensional Navier-Stokes computational study was performed with tip 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 approximately live times blade pass frequency. The results in the clearance gap were retained from the computational solution and compared with the experimental measurements. Both indicated deterministic unsteadiness near the location of the shock, nigh levels of unsteadiness were also measured downstream of the shock in the path of the clearance vortex, but this phenomenon was not predicted by the computation, The unsteadiness near the shock was shown to be a result of movement of the shock. The amplitude and frequency of shock position oscillation was estimated from the results to be about 2% chord and 2 kHz, respectively, Analysis of loss caused by the shock unsteadiness suggested that losses because of shock motion were insignificant relative to the steady shock loss at the relative Mach number studied.