Wall-pressure fluctuations of separated and reattaching flow over blunt plate with chord-to-thickness ratio c/d = 9.0

Abstract

The separated and reattaching turbulent flow over a finite blunt plate with the chord-to-thickness ratio c/d=9.0 was experimentally studied; the Reynolds number based on the plate’s thickness (d) was Red=1.58×104. Wall-pressure fluctuations on the plate surface were taken into extensive consideration, which are closely related to unsteady flow behaviors buried in the separated and reattaching flow and the unsteady wake. Toward this end, synchronized measurements of wall-pressure fluctuations and velocity fluctuations were performed by using a microphone array and a split-fiber film probe, respectively. Characteristics of the separated and reattaching flow were discussed in terms of time-averaged streamwise velocity and its fluctuation intensity, reverse-flow intermittency, wall-pressure fluctuation coefficient, cross-correlation and coherence of wall pressure and velocity. The results showed that the peaked wall-pressure fluctuation coefficient (x/d=4.25) appears 1d behind the time-mean reattachment point (x/d=3.25), which is due to the intensified impingement fluid induced by the growing large-scale vortical structures in the reattachment zone. Two characteristic frequencies fd/U0=0.118 and 0.162 were determined, which correspond to the shedding large-scale vortical structures and the unsteady wake, respectively. Cross-correlation of the wall-pressure field demonstrated rapid decay of the large-scale vortical structures beyond the reattachment zone (x/d>4.75), which might be due to strong interference with the unsteady wake at higher frequency fd/U0=0.162. The wall-pressure auto-spectra showed that wall-pressure fluctuations near the trailing edge are overwhelmingly dominated by the unsteady wake at fd/U0=0.162. Coherence of the wall-pressure field and the streamwise velocity at x/d⩾7.75 elucidated that unsteady behaviors of the redeveloping boundary layer at both frequencies fd/U0=0.118 and 0.162 play important role in wall-pressure fluctuations in large upstream area of the surface.