Effects of the airfoil probes on the aerodynamic performance of a transonic compressor cascade

Abstract

The airfoil probe is typical instrumentation for measuring total pressure/temperature in the research fields of turbomachinery. Besides causing measurement error itself, it also generates extra flow loss inevitably and further affects the measuring accuracy. This paper utilizes the Reynolds-averaged Navier Stokes (RANS) and high-fidelity methods to understand the effects of airfoil probes on the aerodynamic performance of a compressor cascade. With the inclusion of airfoil probes, the load capacity and the shock waves decline, to some extent, mainly because of the streamwise vortex. The shedding vortex induced by the probes triggers an earlier and non-separated flow transition, which contributes to a suppression of the separation bubble on the suction surface and a reduction of the profile loss. However, through the quantitative traceability analysis of the flow loss, the extra loss is generated and redistributed to the overall flow field. The separated flow forms at the junction of the end wall, blade, and probe's pipes, due to the high adverse pressure gradient aggravated by shock waves. It is one of the reasons why the measuring accuracy of airfoil probes is quite sensitive to the Mach numbers. The Delayed-Detached Eddy Simulation (DDES) shows superiority in capturing small-scale coherent vortex structures. The shedding streamwise vortex generated by the probe's pipe is distinguished for the first time. Its transport progression to the wake region is revealed basically, which has been masked previously by the conventional RANS method. In addition, due to the supplement of the streamwise vortex generated by probes, the wake vortices maintain a higher shedding frequency. This work offers a glimpse of the complex fluid mechanisms in a transonic regime, which suggests carefully considering the size of instruments in the design and measurement process.