Numerical Investigation of the Reynolds Number Effect on Five-Hole Probe Calibration

Five-hole probes are widely used in turbomachinery applications. However, the Reynolds number dependence of the probe calibration has not received enough attention. The experimental uncertainty remains unclear when a probe is applied to wind tunnel measurement with a Reynolds number range different from its calibration condition. This numerical study investigated the sensitivity of five-hole probe calibration for a range of Reynolds numbers (4500-138000). The detailed flow physics around five-hole probe tip at various flow regimes (incompressible flow and high subsonic flow) were analyzed. The deviation of surface pressure distribution and calibration coefficients at different Reynolds numbers were quantitatively evaluated. The results reveal that, two counter-rotating vortices are generated at probe tip at large flow angles, and regions affected by vortices vary much in pressure coefficient at different Reynolds numbers. A recommended region of hole positioning is found according to flow structure and calibration results. At lower Mach number, the calibration becomes more sensitive to Reynolds number, while at high Reynolds number range this sensitivity becomes lower. Also, a rounded front edge design of a five-hole probe is found to have higher Reynolds number sensitivity than a sharp front edge design. The present study provides a useful guidance to five-hole probe calibration strategy and probe geometry design, and also highlights the need for in-situ calibration rig development, particularly in turbomachinery experimental studies.