Investigation of trailing-edge noise sources by means of high-speed PIV

Kurzfassung

Turbulent boundary layers near the trailing-edge of a surface are known to generate intense, broadband scattering noise as well as surface pressure fluctuations. The noise generating mechanisms depend essentially on the radial components of the velocity fluctuations in respect to the trailing edge. Resulting forces may also cause model vibrations, which are additional low frequency noise sources. The high-speed PIV (HS-PIV) technique is applied to an investigation of the spatial and temporal development of coherent structures in a turbulent flat-plate boundary layer flow in the vicinity of the trailing-edge. With time resolved PIV data obtained in the region immediately up- and downstream of the trailing edge an identification of the flow structure movement, which cause the noise sources is possible. On the basis of a large number of time resolved instantaneous velocity vector fields the technique enables also the possibility of determining several statistical quantities of fluid mechanical significance: average velocity profiles, velocity fluctuations (u´, v´), rms-fields, probability density functions and space-time-correlations of the velocity fluctuations, the instantaneous Reynolds stresses (u´v´) of all four quadrants and the z-component of vorticity. A flat plate with an elliptic leading edge was mounted vertically in the AWB, the low noise wind tunnel of DLR, Braunschweig. At a free stream velocity of U = 40 and 50m/s and a stream-wise length of the flat plate of x = 2 m a turbulent boundary layer flow develops and the flow structures convect past the trailing edge.