Study On The Influence Of Centrifugal Impeller With Staggered Blade On The Rotor-stator Interacton Characteristics In Pump

Under the rotor-stator interaction of impeller and tongue,the centrifugal pump presents complex unsteady flow structure,and induces high amplitude pressure pulsation.The hydraulic excitation leads to vibration and noise of the pump,which is the main reason for the destruction of the stability of the system and equipment operation and the concealment of related underwater equipment.In this paper,a new staggered blade centrifugal impeller structure is proposed based on the control of the rotor-stator interaction phase difference between staggered blade and tongue,in order to reduce the pressure pulsation energy in pump.Taking a low specific speed centrifugal pump as the prototype pump,the unsteady flow and its excitation characteristics of the original impeller model pump and the impeller model pump with different staggered blades were studied by numerical calculation and experiment.The influence of staggered blade arrangement on the wake and pressure pulsation characteristics of the blade was analyzed.The research results can provide a new idea for the suppression of low frequency hydraulic excitation induced by rotor-stator interactionin the pump.The main work and achievements of this paper are as follows:（1）Model pumps with different staggered arrangement schemes of blades were designed.The two-layer blades were staggered by 10°,20°and 30°to form three impeller schemes of St10,St20and St30.By comparing the performance with the original model pump（Or scheme）,it was found that the uniform staggered arrangement of blades can improve the performance of the pump.（2）The large eddy simulation（LES）numerical calculation method is used to carry out unsteady numerical calculation for the internal flow of pump models with different impeller schemes,and the influence of blade stagger arrangement on the internal flow structure and wake evolution of impeller is emphatically analyzed.It is found that the staggered arrangement of blades will form a high vorticity area near the leading edge of the blade,where the high-energy vortex diverges in the flow channel along the blade wall and develops to the impeller outlet.With the increase of the stagger angle of the blade,the trailing edge vortex band is elongated and widened,and the trailing vortex falls off in advance and interferes with the downstream tongue.The trailing vortex of the front and rear blades interferes with the tongue successively,and there is a time difference.（3）Based on the numerical calculation,the pressure pulsation of model pumps with different impeller schemes is predicted.The fast Fourier transform（FFT）and short-time Fourier transform（STFT）are used to analyze the pressure pulsation signal.It is found that the staggered arrangement of blades can effectively suppress the pressure pulsation energy induced by rotor-stator interaction,and improve the pressure pulsation energy distribution in the pump.Through the time-frequency domain analysis of the pressure pulsation at the monitoring point of the impeller outlet,it is found that there is a phase difference in the pressure pulsation induced by the interference between the two layers of blades and the tongue.The peak value of the pressure pulsation signal in the low frequency section is staggered,which avoids the superposition of strength and effectively reduces the pressure pulsation energy in the low frequency section.（4）The LMS multi-channel vibration and noise test system was used to measure the pressure pulsation of Or scheme and St30 scheme under different working conditions,and the time-frequency domain distribution characteristics were compared and analyzed.It was found that the St30 scheme had a significant inhibitory effect on the 1-fold blade frequency(f_bpf),and the inhibition degree was higher than 80%in the Q/Q_d=0.8-1.2 working condition,but it had a certain increase in the 2-fold blade frequency(2 f_bpf),especially in the large flow condition,the maximum increase was 44.52%.Under each working condition,the distribution of pressure pulsation energy in different frequency bands is different,and the pressure pulsation energy near the tongue is prominent.In the blade frequency range,the pressure pulsation amplitude of St30scheme is larger;in the high-power blade frequency band,the pressure pulsation energy of St30scheme is smaller than that of Or scheme;the pressure pulsation energy drop is stable after 5 times blade frequency,and the minimum drop is 37.3%.（5）Based on the LES numerical method,the unsteady flow field in the pump with staggered blade impellers with different inner diameters of baffles was calculated to study the influence of inner diameter of baffles on the flow and pressure pulsation characteristics in the pump.When the inner diameter of the baffle is small,it is easy to cause inlet blockage and form a high vorticity area in the leading edge of the blade.With the increase of the inner diameter of the baffle,the impact of the fluid on the baffle and the front blade of the baffle makes the inlet and outlet channels of the impeller full of different scale vortex structures,which is easy to destroy the flow stability in the impeller channel.In contrast,when the inner diameter of the baffleΦ=0.34D₂,the flow in the pump is relatively stable.In addition,the amplitude of the characteristic frequency in the pump increases with the increase of the inner diameter of the baffle.When the inner diameter of the baffle is large,the pressure pulsation energy downstream of the tongue increases significantly.The comparison shows that in the frequency band of 10-1000 Hz,the pressure pulsation energy reaches a minimum when the inner diameter of the baffleΦ=0.34D₂.