Experimental Investigation of the Unsteady Pressure Field in Decelerated Swirling Flow with 74° Sharp Heel Elbow

The unsteady pressure at the wall of the conical diffuser without and with a 74° heel elbow is examined. The self-induced instability is experimentally investigated on the swirl generator test rig. As a result, the asynchronous (rotating) pressure pulsation associated with the vortex rope and it second harmonic are discriminated. The discriminated Fourier spectra with plunging and rotating components of the unsteady pressure signals are analyzed for several geometrical configurations in order to identify the frequency associated to the heel elbow. It is shown that a plunging component of 8 Hz corresponds to a 74° heel elbow in the Fourier spectra.