Sub-boundary-layer disturbance effects on supersonic base-pressure fluctuations

Fluctuating base pressures were measured for an axisymmetric blunt afterbody modified with two different sub-boundary-layer disturbance tabs, a triangle-tab configuration, and a strip-tab configuration, in a Mach 2.46 flowfield. Normalized rms levels indicate that base-pressure fluctuations increase with addition of the triangle tabs and decrease with the addition of the strip tab. Power-spectral-density (PSD) estimates recorded at the two outermost radial locations for the triangle-tab configuration demonstrated that the fluctuation energy increased when compared to the no-tab case at nearly all frequencies, particularly at frequencies above 1 kHz. This suggests that the triangular tabs energize turbulent structures in the free shear layer because of the introduction of stream-wise vorticity. It was also found that a prominent peak in the PSD estimate at the outer two radial locations, found in the no-tab case, is absent for the triangle-tab configuration. Dual-transducer measurements for both tab configurations suggest that correlated pressure fluctuations are realized at most locations across the base simultaneously, lending credence to the idea that a global mechanism acts as a source of the base-pressure fluctuations.