Two sets of experiments were performed to investigate the coupling between the flowfield and wall pressure in a turbulent boundary layer. In the first, a stochastic estimation technique on the streamwise velocity field was implemented for the cases of high-amplitude wall pressure conditions. The comparisons of both the linear and quadratic estimate to the conditional average provides insight into the dependence of the wall pressure on the linear and non-linear source terms in Poisson's equation. It is shown that the quadratic stochastic estimation technique approximates the trend and the magnitude of the conditionally-averaged velocity fluctuations very well; whereas, the linear stochastic estimation underestimates the magnitude of the velocity, for both positive and negative wall-pressure detections. This suggests that the non-linear source terms are important in the generation of the wall pressure. The second investigation concerns the correspondence between the conditionally averaged and instantaneous flow. High-resolution PIV, simultaneously acquired with an array of wall-pressure sensors, provided several independent realizations of the instantaneous flowfield and associated wall pressure. A large-scale shear layer is evident for both positive as well as negative wall-pressure events where fluid with positive momentum is upstream of fluid with momentum deficit. For the case of a positive wall pressure detection, p¢w/p¢wrms ³ +2.5, the streamwise location of the shear layer in the region close to the wall coincides with the detection point of the maximum wall pressure signal; whereas, the shear layer is displaced in the streamwise direction by » 400 wall units for p¢w/p¢wrms£ -2.5.
* This work was supported under grants from the Office of Naval Research, NASA Space Grant and National Science Foundation.