Surface pressure determination: a comparison between PIV-based methods and PSP measurements

The present work aims to investigate the challenges in determining the surface pressure distribution using particle image velocimetry (PIV) in comparison with pressure sensitive paint (PSP) measurements. The aim is to assess if PIV may be regarded as a complementary method to PSP, or even as a possible replacement. The investigation is based on two different test cases: 1. the attached flow around a NACA-0012 airfoil, 2. the separeted flow around a backward-facing step (BFS). Both cases are investigated at transonic flow conditions. For the airfoil both PIV and PSP measurements were conducted. The results of the PIV-based surface pressure reconstruction and the one of PSP are compared with the static pressure taps installed on the model surface. For the BFS test case synthetic PIV images are produced from a 2D LES simulation. In this case flow separation as well as strong viscous effects appear. Therefore, the Reynold averaged momentum equation is directly used and the pressure is determined solving the Poisson equation which is obtained applying the divergence operator to the momentum equation. The results are compared with the pressure distribution on the surface from the LES simulation. This case aims to analyze the accuracy of PIV-based surface pressure determination in case of massive flow separation. The deviations to the expected results are caused by the spatially discretization as well as by spatially averaging, which occurs in a standard PIV measurement. Additionally, the effect of the velocity uncertainty on the estimated surface pressure distribution biases the result significantly. Therefore, PSP will be hardly replaced by PIV for complex flows. Fig. 1 Mean-time velocity field from PIV and PSP pressure distribution on NACA 0012 airfoil .