Two-point correlations and POD analysis of the WALLTURB experiment using the hot-wire rake database

Abstract

We use the novel hot-wire rake of 143 single wire probes to measure 30 cm thick boundary layer of the large LML wind tunnel at Reynolds number based on momentum thickness of 9800 and 19 100. Multiple-point cross-correlation analysis using the data from the hot-wire rake show that the physical length of the correlation contour in the streamwise direction is about 7 boundary layer thickness. In addition, the shape of the correlations maps obtained from two-point correlations on the streamwise–wall-normal plane retains its shape approximately throughout the entire boundary layer. The data is also used for POD analysis of the boundary layer using only the streamwise turbulent fluctuations. The normalized eigenvalue distribution shows that the first POD mode has more than 40% of the turbulence kinetic energy, while the second one has about 20% of the total turbulence kinetic energy for both of the Reynolds number tested here. It is possible to recover about 90% of the kinetic energy only using the first four POD modes. The reconstructed velocity fluctuations on the spanwise–wall-normal plane show how organized motions of turbulence with significant amounts of energy interact with each other across the boundary layer. It is also possible to observe the strength of the interaction between the inner and outer layer using these reconstructed velocity fields.