VELOCITY-MEASUREMENTS IN A PRECESSING JET FLOW USING A 3-DIMENSIONAL LDA SYSTEM

The turbulent, three dimensional and time dependent flow field of a pr ecessing jet is investigated. In the present case the jet precession i s generated by mechanically rotating a round jet inclined relative to the axis of rotation. A conditional flow visualisation technique is us ed to complement three dimensional laser Doppler velocity data, time-a veraged and phase-averaged at the frequency of precession. The conditi onal phase-averaging technique enables phase-averaged velocity contour s and vectors to be obtained which reveal flow patterns and structures within the flow field. Time-averaging of the velocity data shows that these structures are significant in that they generate a reverse flow (recirculation) region between the jet and its spinning axis. They ar e found also to cause a rapid decay of the mean velocity. The characte ristics of the precessing jet found here are compared with previous in vestigations of the same flow and with investigations of other turbule nt jets.