UNSTEADY FLOW DEVELOPMENT AND REYNOLDS STRESS MEASUREMENTS IN A CENTRIFUGAL COMPRESSOR VANED DIFFUSER

Modern aeroengine designers face the challenge of reducing fuel consumption, which is pushing compressor technology into new design spaces. To optimize these design spaces, high-fidelity computational models are crucial to the compressor design process. It is important to validate these models with experimental data. Non-intrusive measurement techniques allow for acquisition of data well suited for this comparison, as they do not lead to local disruptions of the flow field. This investigation utilized three-component laser Doppler velocimetry to acquire a unique dataset of detailed unsteady velocity measurements in the vaned diffuser of an aeroengine centrifugal compressor. These measurements allowed for a thorough study of the flow development in the vaneless & semi-vaneless space of the diffuser as well as through the diffuser passage. The components of the Reynolds stress tensor were also determined at multiple locations in the diffuser flow field. These data are used to study the jet and wake propagation from the impeller exit flow field into the diffuser passage and the resulting secondary flow structures. Predictions from unsteady CFD simulations using the SST and BSL-EARSM turbulence models are also compared with these experimental data. Both turbulence models yielded results that qualitatively agreed with the experimental radial velocity profile through the vaneless and semi-vaneless space. With the experimentally determined Reynolds stress tensor, the turbulent kinetic energy (TKE) is calculated at multiple points through the flow field and is compared to the TKE at the same geometric locations in the computational flow field. This comparison highlights the difference in dissipation and production of turbulence between the experimental data and the computational predictions. Investigating the differences in TKE throughout the diffuser helps elucidate the differences in predicted flow structures in the diffuser passage.