| The development of impeller wake in centrifugal pump and the rotor-stator interaction between impeller and tongue make the pump present a complex unsteady flow structure and the generated fluid excitation force causes the vibration and noise of the pump.It is an important method to reduce the vibration and noise of centrifugal pump by optimizing the impeller structure and adding offset blades to improve the vortex shedding pattern in the impeller wake,and reduce the pressure pulsation caused by rotor and stator interference.Supported by the National Natural Science Foundation of China（the eddy dynamic characteristics of pump forced turbulence and its excitation mechanism NO:51576090）,Based on a low specific speed centrifugal pump as the research object,through the numerical computation and experiment methods,explore the airfoil blade,offset blade and offset winglet scheme of the internal flow and its incentive features.The influence of airfoil blade and offset blade on impeller wake and pressure pulsation characteristics is explored to provide a new idea for hydraulic design of low noise centrifugal pump.The main work and obtained results are as follows:（1）Based on a low specific speed centrifugal pump,three optimization schemes of airfoil blade impeller（AF）,offset blade impeller（SP）and offset winglet impeller（DAF）were designed.It was found that the efficiency of the three optimization schemes was significantly improved under the design condition compared with the ordinary impeller scheme（OR）.and high flow condition,and the efficient working area was widened.（2）The internal three-dimensional unsteady flow field of four kinds of impellers under typical working conditions is calculated by using the numerical calculation method of DDES（Delayed Detached Eddy Simulation）,and the focus is on the analysis of the flow structure distribution at the impeller outlet and the impeller wake shape in the diaphragm area.The development and evolution of the trailing edge shedding vortex of the blade in the volute channel is described in detail.The study found that airfoil blades and short blades can accelerate the energy dissipation of the impeller wake,accelerate the evolution of the wake,and inhibit the formation of complex flow structures in the tongue area.（3）By analyzing the pump pressure pulsation characteristics under four impeller schemes,it is found that the DAF scheme has the lowest pressure pulsation energy under the condition of small flow,while the SP scheme is more suitable for the operation under the condition of large flow,while the SP scheme is more suitable for the high flow rate.The correlation analysis between pressure pulsation and unsteady flow structure shows that the amplitude of pressure pulsation blade frequency is related to the large scale vortexes of banded blade trailing edge shedding,and the low frequency disorderly signal is related to the small scale vortexes of wake vortex evolution dissipation.（4）Laser Doppler Velocimetry（LDV）was used to carry out the internal flow field measurement of the pump for the AF,SP and DAF schemes.Point by point measurement of the volute diffuser,tongue area and interference area.Obtain the time-averaged velocity and velocity spectrum distribution law of the area.The addition of short blades can significantly suppress the low-frequency signal,f R,f BPFand high frequency of speed pulsation,and the SP scheme is better for large flow conditions.（5）The pressure pulsation of different impeller schemes in the pump was measured and analyzed by the micro high frequency pressure sensor.The results show that there is a big difference in the blade frequency amplitude in the tongue region under different optimization schemes.Compared with the other two schemes,the blade frequency amplitude of SP scheme is obviously decreased,and the high-order harmonic suppression effect of DAF scheme on the blade frequency is obvious.Under the condition of low flow rate,DAF scheme can obviously suppress low frequency chaotic signals,but its blade frequency amplitude is higher.With the increase of flow rate,the pulsation energy of SP scheme decreases gradually,while that of DAF scheme increases gradually.Therefore,SP scheme is suitable for large flow condition,and DAF scheme is suitable for small flow condition. |
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