EFFECTS OF A LARGE-EDDY BREAKUP DEVICE ON THE FLUCTUATING WALL-PRESSURE FIELD

Wall pressure spectra and mean velocity profiles were measured with an d without a large eddy breakup device (LEBU) located upstream in high R(theta) turbulent boundary layers. Changes of the order of 5 percent occurred in the mean wall shear stress. The wall pressure spectra of t he manipulated flow did not show the existence of any highly energized coherent structures, but rather moderate changes occurring over broad frequency ranges. Reductions in the wall pressure autospectra occurre d at lower frequencies associated with turbulence activity in the oute r layer and the outer portion of the log law layer. Increases occurred at higher frequencies associated with the inner portion of the log la w layer. The changes in the wall pressure coherence levels were simila r, but generally more complex with greater spatial persistence. The ch anges in both the autospectra and coherence indicate a conversion of e nergy from lower to higher convective wavenumbers.