Measurements of turbulent jet interacting with a cross flow over a flexible flat plate

This study characterizes the mean and fluctuating velocity fields, the resulting wall pressure fluctuations as well as structural vibrations caused by injection of a round, turbulent jet into a fully-developed, flat-plate, turbulent boundary layer. One of the channel walls is replaced by a vibration isolated, aluminum plate and the 1cm-diameter jet is injected from this wall. The cross flow is kept at 2 m/s and the velocity ratio, r (ratio of mean jet velocity to the cross flow), varies from 0 to 2.5. Flush-mounted, low-noise, pressure transducers located at 2-15 diameters behind the jet are used for the wall pressure measurements. Fourier auto-spectra of the pressure signals show the effect of the jet in the 10-100Hz range, such as an increase of 25dB for r=2.5 over r=0 in the 15-25Hz range. The fluctuations increase with r and decrease with distance from the jet. Mean Hilbert-Huang "pressure amplitude" spectra show an increase of an order of magnitude in the same range. The latter technique gives better insight on the related unsteady phenomena. High-resolution PIV measurements show the trajectory of the jet, the formation of wall-normal vortex structures and the interaction of the jet vorticity field with that of the boundary layer. Conditionally sampled PIV measurements based on the pressure signal relate between the flow and resulting wall pressure.