Confined flow cavitation in hydraulic oil: Test rig design, pressure measurement, and PIV

Jeffrey K Dougan, Purdue University

Abstract

Numerical advances in cavitation modeling require experimental measurements to validate them. For this purpose an oil cavitation test rig was designed to generate experimental data of a submerged cavitating orifice in oil. An important feature of the test section was the ability to have optical access while preserving structural integrity. Experiments showed that visible inception occurred coincidently with both noise detection and the point where flow starts to undershoot predicted values. With cavitation at constant flow it was observed that upstream pressure was strongly independent of downstream pressure compared to single-phase flow where the two are linked. A serendipitous aside of related measurements was the notion that the traditional definition of cavitation number may not be valid for confined flows because of its tie to flow rate. Using experimental data and two different approaches, a new definition was proven to be unaffected by the existence of cavitation and shown to closely match theoretical values. Dynamic pressure data showed that higher back pressures led to higher frequency noise and the suppression of lower frequency noise; data was collected that shows the spectral shift at 1 bar decrements. Particle Image Velocimetry was used to capture instantaneous and average velocity fields. Entrainment and recirculation were evident in all the flow fields. Under certain flow conditions, the entire cavitating jet velocity could be resolved using bubbles as tracer particles. With high speed imagery, the jet length was observed to shorten with increased pressures while the averaged flow fields remained broadly uninfluenced by the pressure.

Degree

M.S.M.E.

Advisors

Wereley, Purdue University.

Subject Area

Mechanical engineering

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