Experiments have been performed using the Air Force Research Laboratory (AFRL) Blade-Row Interaction (BRI) rig to investigate interactions between a loaded stator and transonic rotor. The BRI rig is a high-speed, highly loaded compressor consisting of a swirler/deswirler, a transonic rotor and a stator. The swirler/deswirler of the BRI rig is used to simulate an embedded transonic fan stage with realistic geometry which produces a wake through diffusion. Details of the unsteady flow field between the stator and rotor were obtained using Particle Image Velocimetry (PIV). Flow visualization images and PIV data that facilitate analysis of vortex shedding, wake motion, and wake-shock-interactions in the blade row are analyzed for three stator/rotor axial spacings and two stator loadings. The data analysis focuses on measuring and comparing, for the different spacings and loading, the vortex size, strength, and location as it forms on the stator trailing edge and propagates downstream into the rotor passage. It was observed that more than one vortex was shed with the passing of a rotor bow shock. These vortices were categorized as small and large vortices with a ~20% decrease in strength. The large vortices were compared at similar location and results show that vortex strength increased as spacing between stator and rotor decreased due to the increased strength of the rotor bow shock impacting the stator trailing edge. Changes in stator loading also affected shed vortex strength. A decrease in stator loading resulted in a decrease in the strength of the vortex shed. The smaller vortices were not affected by a change in spacing but strength was directly related to the loading.

Multiple high-fidelity, time-accurate computational fluid dynamics simulations were performed to investigate the effects of upstream stator loading and rotor shock strength on vortex shedding characteristics in a single stage transonic compressor. Various configurations of a transonic axial compressor stage, including three stator/rotor axial spacings of close, mid, and far in conjunction with three stator loadings of decreased, nominal, and increased were simulated in order to understand the flow physics of transonic blade-row interactions. Low-speed compressors typically have reduced stator/rotor axial spacing in order to decrease engine weight, and also because there is an increase in efficiency with reduced axial spacing. The presence of a rotor bow shock in high-speed compressors causes additional losses as the shock interacts with the upstream stator trailing edge. This research analyzes the strength of shock-induced vortices due to these unsteady blade-row interactions. The time-accurate URANS code, TURBO, was used to generate periodic, quarter annulus simulations of the Blade Row Interaction compressor rig. Both time-averaged and time-accurate results compare well with experimentally-observed trends. It was observed that vortex shedding was synchronized to the passing of a rotor bow shock. Normal and large shock-induced vortices formed on the stator trailing edge immediately after the shock passing, but the large vortices were strengthened at the trailing edge due to a low-velocity region on the suction surface. This low velocity region was generated upstream of mid-chord on the suction surface from a shock-induced thickening of the boundary layer or separation bubble, due to the rotor bow shock reflecting off the stator trailing edge and propagating upstream. The circulation of the shock-induced vortices increased with shock strength (decreased axial spacing) and stator loading. Most design tools do not directly account for unsteady effects such as blade-row interactions, so a model is developed to help designers account for shock-induced vortex strength with varying shock strength and stator loading. An understanding of the unsteady interactions associated with blade loading and rotor shock strength in transonic stages will help compressor designers account for unsteady flow physics early in the design process.