The Influence Of The Uneven Spaced Stator Cascade On The Flowinduced Noise Characteristics In A Vaned Centrifugal Pump

The six stator cascade schemes with different modulation angles were designed according to the sine uneven space distribution,referring to the uneven space cascade noise reduction method in the fan field.Based on the RNG k-?turbulence model,the unsteady flow in the vaned centrifugal pump was simulated.The sound boundary-element and finite element method were employed to solve the internal and external sound fields respectively.The influence of the uneven space stator cascade on the hydraulic characteristics and acoustic field characteristics of the guide vane centrifugal pump was emphatically analyzed,and the inflow mechanism of the uneven space stator cascade to reduce flow induced noise was explored.The stator cascade non-uniform coefficient C_S was introduced,and the head changing coefficient C_H,the efficiency changing coefficient C_?and the power changing coefficient C_P were defined to describe the sensitivity of the external characteristic parameters.The diffuser component static pressure recovery coefficient C_HR and energy loss coefficient C_HL were selected to measure their energy index.And then the effect on the impeller radial and axial forces of the uneven space stator cascades was analyzed.The natural frequencies and noise danger frequency bands were obtained with the modal analysis of the impeller and the pump body.The direct boundary element method is applied to calculate the characteristics of the internal sound field caused by the blade rotation dipole source and the flow channel wall dipole source.The method united with the acoustic finite element and the automatic matched layer technology is adopted to analyze the sound pressure level and its directivity distribution at different frequencies,and the flow-induced noise performance is comprehensively characterized by the RMS value of the sound pressure level.The intrinsic relationship between the uneven space stator cascade and the reduction of the flow-induced noise is analyzed from the three aspects,i.e.the relation between sound pressure and pressure distribution on the blade surface,the jet wake structure and the vortex distribution in the impeller and vane channel.The results show that the appropriate distribution of the uneven space stator cascades can improve the hydraulic and cavitation performance of the vaned centrifugal pump,optimize the distribution of the impeller radial force,while the expense of the hydraulic performance improvement is based on the increasing the input of external energy.The mechanical vibration noise and the flow-induced noise of the pump body are less likely to resonate,and the second-order harmonic frequency of the shaft frequency is close to the resonance dangerous frequency.The uneven space stator cascade has a limited effect on the internal sound field sound pressure level response curve at the shaft frequency.The external sound field decreases first and then increase with the non-uniform coefficient increasing,and a suitable uneven space stator cascade distribution can reduce the flow-induced noise.There is a positive correlation between the dipole source sound pressure and pressure distribution on the pressure surface,while their correlation on the suction surface is relatively poor.The separation flow near the impeller outlet causes the thickness changing of the channel boundary layer,which intensifies the turbulence of the velocity distribution in the circumferential direction,motivates the maximum velocity of the region near the vane and impeller outlet increasing and rotates along the direction the volute wrap angle decreasing.Those regulations are the main reason why the external sound field directional curve,the internal sound field sound pressure level increases at the shaft frequency and the local peak deviated from the shaft harmonic frequency.The vorticity norm as the criterion of vortex can accurately reflect the distribution of vortex in the vaned centrifugal pump flow channel.The regions with large value of vorticity norm are concentrated at the inlet of the vanes and guide,and the district near the exit of the impeller where the vortex shedding occurs due to the jet wake effect.The main cause of the fluid radiating dipole sound waves is that both shear and tension terms have a bidirectional effect on the rate of vorticity changing.