SECONDARY FLOW CONTROL OF TURBOMACHINERY BLADES USING VORTEX GENERATORS

Secondary flow control is becoming increasingly important to improve the performance of highly-loaded axial fans and compressors, especially when considering multi-row interactions, where the main passage vortex can significantly reduce the life of downstream components. In this regard, vortex generators (VGs) are investigated to assess their potential to influence the secondary flow in an axial compressor, by increasing the mixing of the main flow with the low-momentum fluid of the boundary-layer. They can also be used to produce a strong vortex that is convected downstream in the desired direction to reduce the main passage vortex strength. They can be capable of reducing viscous effects at the hub and consequently contract the blade passage vortex, thereby mitigating the vorticity production and its effects on downstream components. Despite VGs having been studied extensively especially in external aerodynamics, there is still a lack of studies on their full potential to reduce secondary flows in axial fans and compressors. This work presents a novel way of using vortex generators to reduce secondary flows in the hub region of an axial compressor. The Rolls-Royce in-house CFD suite, with its overset (chimera) mesh capability, is used to generate high-quality multiblock structured meshes rapidly for complex configurations. A parametric analysis using several geometric factors is presented, together with a comparison of using different objective functions to select the optimal VG configuration from a DOE population. A detailed analysis of the effects on pressure loss and secondary flows is reported, paving the way for an automatic optimization of these devices.