Study On Near Field Radiation Noise Performance Of Large-scale Circulating Water Tank Propulsion Impeller

Circulating water tank is a kind of hydrodynamic test equipment that can make water flow.It has been widely used in hydrodynamic tests in the fields of ships,marine engineering,sports science and other fields.The impeller is the core component of the circulating water tank,which can realize the circulating flow of water and start the test.However,the process of advancing the impeller and the fluid will generate strong radiant noise.Moreover,the circulating water tank belongs to the inflow movement,and the noise attenuation rate is low,which seriously affects the quietness of the circulating water tank.It can be seen that it is of great significance to study the near-field radiation noise problem of the impeller of the circulating water tank.In this paper,a model of impeller in a long straight pipe is first established and numerical simulation is performed.The CFD method is adopted to realize the rotation of the impeller using the sliding grid method.The hydrodynamic and acoustic radiation of the impeller in steady flow field is studied.A ring-shaped measuring point and a series of axial measuring points are arranged around the impeller and the rear of the propeller shaft.The pressure pulsations at the radial and axial measuring points of the impeller are monitored,and the noise spectrum of each measuring point is obtained by Fourier transform.By analyzing the noise spectrum,the near-field radiation noise distribution characteristics of the impeller are obtained.The results show that the noise at the impeller wheel flange is approximately the same,the sound pressure level changes periodically at low frequencies,and the sound pressure value continuously decreases at high frequencies.The sound pressure at the axial measurement point behind the propeller shaft of the impeller becomes smaller as the distance increases.Next,a model of the impeller in a curved pipe is established and numerically simulated.Using the same calculation method as the impeller in the steady flow field,the hydrodynamic and acoustic radiation of the impeller in the unsteady flow field is studied.The results show that the sound pressure values of the measuring points at the symmetrical position of the impeller flange are roughly the same.The eight measuring points around the flange are divided into two groups according to the sound pressure value.The sound pressure curves of measuring points at low frequency change periodically,and the sound pressure value decreases continuously at high frequency.The sound pressure at the axial measuring points after the propeller shaft of the impeller decreases with distance.Geometric parameters such as the speed of the impeller and the change of the position of the impeller in the circulating water tank will affect the hydrodynamic and noise performance of the impeller.When designing the propulsion impeller in the circulating water tank,it is necessary to understand the specific impact of these parameter changes on the hydrodynamic and noise performance of the impeller,so as to improve the efficiency of the impeller and improve the hydrodynamic performance of the impeller,and reduce the radiated noise generated by the impeller when working in the circulating water tank.Using the models of the impeller and curved pipe in Chapter 4,change the impeller speed,the number of blades,the disk surface ratio,and the position of the impeller in the curved pipe respectively,to study the effect of changing parameters on the hydrodynamic performance of the impeller in the unsteady flow field and the distribution characteristics of near field radiation noise.