RIASSUNTO
ABSTRACT:
Large Eddy Simulation (LES) and infinite element method are carried out to simulate the non-cavitation noise of propeller behind the ship hull. The difference of total sound pressure level between experimental results and calculated results calculation results is 3.26dB, which shows that the numerical method is valid and credible. Under the condition of non-uniform flow field, the characteristics of the propeller non-cavitation noise are analyzed. It is shown that the propeller non-cavitation noise is mainly concentrated in the low frequency band, and the noise attenuation speed decreases with the increase of the frequency. It can be seen that the axial sound pressure level of the propeller is slightly higher than that of the radial direction, and acoustic directivity is similar to the characteristics of dipole noise.
INTRODUCTION
Both surface ships and underwater vehicles will produce severe noise during the voyage, the noise plays an important role in the concealment of the ship and the surrounding marine environment. Propeller noise as the major noise of ship, its importance is self-evident. The propeller noise can be divided into two categories, the cavitation noise and the non-cavitation noise. To eliminate the cavitation noise, many methods to delay or avoid the cavitation have been proposed. However, the noncavitation noise is still difficult to avoid, so it is very necessary to study the non-cavitation noise at present.
Seol H (2002) analyzed the non-cavitation and cavitation noise of DTRC4119 by the panel and FW-H coupled method. Xiong and Zhu (2009) studied the frequency spectrum noise and broadband noise combining the unsteady lifting surface theory and acoustic analogy method. Yang (2011) analyzed propeller noise using the LES coupled weak acoustic boundary element method. Leaper (2012) recommended that the frequency of propeller noise is mainly concentrated in low frequency, and summed up the methods to decrease noise. Ye (2013) calculated and analyzed the low frequency spectrum noise combined panel method and time domain prediction method. Wang (2015) carried out the acoustic performance of DTRC4119 in special flow field by LES and infinite element method.
In this research, a low noise propeller is selected as the computational object, which behind wake field simulated by dummy model is carried out in cavitation tunnel in Shanghai Ship and Shipping Research Institute(SSSRI). The hydrodynamic performance of propeller is calculated by CFD, and non-uniform wake is obtained by LES and sliding mesh. Finally, the acoustic properties are simulated by acoustic software based on infinite element method. The calculation results are discussed and the comparison between test data and simulation results validate the feasibility of this method.