Wall-pressure fluctuations of laminar separation bubble based on direct numerical simulation and experiments over a hydrofoil at Re = 450,000

Abstract

Abstract The objective of this paper is to investigate wall-pressure fluctuations downstream of a Laminar Separation Bubble (LSB) on a laminar NACA66 hydrofoil section, based on Direct Numerical Simulation (DNS) and experimental analysis. DNS is performed using the massively parallelized open source code Nek5000 , which uses the high order spectral element method to solve the incompressible Navier–Stokes equations. It is compared to measurements performed in a hydrodynamic tunnel at the French Naval Academy Research Institute (IRENav). A Reynolds numbers of R e = 450 , 000 with an angle of attack of α = 4 ∘ is considered, which induces an LSB to the rear of the maximum thickness of the boundary layer. The local wall pressures at three different locations are compared: just downstream of the LSB at x/c=0.7, in the breakdown region of the LSB at x/c=0.8 and in the fully turbulent region at x/c=0.9. The DNS results compare very well with the measured wall pressures. The DNS captures efficiently the periodic fluctuations downstream of the LSB, up to the random behavior induced by the transition to turbulence. Analysis of the boundary layer flow obtained by DNS suggests that an H-type or K-type transition occurs, characterized by 2D TS waves and typical Λ structures, that break down and generate turbulence. Moreover, it shows that intense and localized pressure fluctuations occur in the breakdown region.