Investigation into the Hydrodynamic Noise Characteristics of Electric Ducted Propeller

Mengfei Chen,Qiaorui Si,Jinfeng Liu,Yun Liang,Zhongkun Jin,Jianping Yuan

doi:10.3390/jmse10030378

Abstract

Ducted propeller is a kind of special propeller widely used in unmanned underwater vehicles, its flow characteristics and hydrodynamic noise are very important for marine environmental protection and equipment concealment. The hybrid techniques based on the acoustic analogy theory are adopted in the present study to calculate the unsteady flow field and sound field characteristics of a ducted propeller. The full scale flow filed and hydro-acoustic sources of the propulsion system are simulated by Detached-Eddy computational fluid dynamics (CFD) method. Hydrodynamic noise are calculated by FWH equation based on the CFD results. The frequency domain and directivity of sound pressure level at different sound field monitoring points are analyzed at four navigational speeds. The results show that the navigational speed that is in the inflow condition of the ducted propeller play important roles in the flow structure and underwater radiated noise. Under the fixed impeller rotational speed, the propulsion efficiency of ducted propeller increases first and then decreases with the raise of navigational speed. The maximum errors of thrust and power between simulation and experiment values are 0.5% and 0.1% respectively, which means that the adopted DES numerical simulation method has high credibility in calculating the acoustic source. At impeller rotational speed of 2000 r/min, the best state of flow field distribution is at the navigational speed of 1.54 m/s, which is corresponding to the highest propulsion efficiency condition. The propeller noise presents dipole characteristic in all working conditions, and at the obvious blade passing frequency, multiple characteristics are presented; most of the noise contribution is also concentrated below four times of the blade passing frequency. The total sound pressure level of the hydrodynamic noise is the smallest at the optimal efficiency condition (the navigational speed is 1.54 m/s). At high navigational speed, the low frequency characteristics below blade passing frequency increase and the amplitude becomes larger. This indicates that the component of turbulent noise becomes more important with the increase of navigational speed. The research focuses on analyzing the relationship between the energy loss of the ducted propeller wake field and the noise level, and it is found that the vortex at the tail makes a certain contribution to the noise. The research conclusions could provide some reference for the acoustic performance evaluation and noise reduction optimization of ducted propeller design as well as the improvement of UUV stealth performance.

Highlights

For years research has been performed to improve the performance of the existing propellers and to design new propellers according to the market needs [5]
This might be because the ducted propeller has a smaller flowrate under the mooring state, and the rotating impeller brings about a bigger lift to the flow
The thrust is at its maximum at the mooring state with the biggest impeller rotational speed

Summary

Introduction

With the attention paid to marine development, the interest in the underwater field development of specific tools for the sub-sea inspection is increasing. Because it is suitable for long-period and large-scale investigation tasks, unmanned underwater vehicles (UUV). Due to the simple structure and convenient operation characteristics, the electric ducted propeller is widely used as the propulsion device of UUV. It is an important energy consumption equipment and a noise source for UUV in reconnaissance, intelligence collection and ocean exploration [3]

Methods

Results

Conclusion