Sound signature of propeller tip vortex cavitation

Pepijn Pennings,Tom Van Terwisga,Jerry Westerweel

doi:10.1088/1742-6596/656/1/012186

Pepijn Pennings, Tom Van Terwisga + Show 1 more

Open Access

https://doi.org/10.1088/1742-6596/656/1/012186

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Abstract

The design of an efficient propeller is limited by the harmful effects of cavitation. The insufficient understanding of the role of vortex cavitation in noise and vibration reduces the maximum efficiency by a necessary safety margin. The aim in the present study is to directly relate propeller cavitation sound to tip vortex cavity dynamics. This is achieved by a dedicated experiment in a cavitation tunnel on a specially designed two-bladed propeller using a high-speed video camera and a hydrophone. The sound signature of a tip vortex cavity is not evidently present in the sound spectrum above the tunnel background. The addition of a simulated wake inflow results in a high amplitude broadband sound. With a decrease in the free-stream pressure the centre frequency of this sound decreases as a result of a larger vortex cavity diameter. In the near future each blade passage in the high-speed video will be analyzed in detail. The frequency content of the cavity dynamics can then be directly related to the measured sound. An analytic model for vortex cavity dynamics resulting in a cavity eigenfrequency using a vortex velocity model can finally be evaluated as a design instrument for estimation of broadband sound from propeller cavitation.

Highlights

Introduction and experimental setupThe design of an efficient propeller is often limited by various forms of cavitation
The experimental results in this study show the effect of a varying cavity size on the resulting sound by looking at the difference in sound power density spectrum between a uniform inflow and simulated wake field
From the sound spectrum it is clear that a steady tip vortex cavity in uniform inflow does not contribute significantly to the sound above the level of the background noise of the cavitation tunnel

Summary

Introduction

Introduction and experimental setupThe design of an efficient propeller is often limited by various forms of cavitation. Vortex cavitation is expected to be responsible for a broadband contribution to the pressure fluctuation spectrum, typically between 40 to 70 Hz for a full-scale propeller [1]. A simultaneous registration of high speed video and hydrophone measurements is used to obtain the properties of the dynamics of the tip vortex cavity and the resulting sound.

Results

Conclusion