Internal Flow And Induced Vibration And Noise Characteristics Of Cooling Pump In Internal Combustion Engine

This study is supported by National Natural Science Foundation of China“Study on the Mechanism of Distortion Flow Induced Noise in Centrifugal Pump”(51509108),“Research on Flow Field Distortion and Induced Noise Mechanism of Automotive Engine Cooling Pump”(2016T90422),“Multi-objective Hydraulic Design Method of Vane Pump and Key Technologies of Gas-liquid Two-phase Supercharging Transportation”(2018YFB06103).This paper is also funded by the national key research and development project"Key Technologies Research and Application DemonstrationofComplexEnvironmentalEngineeringRescue"(No.2018YFC0810505).The cooling pump of internal combustion engine has the characteristics of limited structure size,excessive temperature of coolant and wide variation of speed range.The unsteady inlet flow leads to extremely complex internal flow field,and the excitation force causes serious vibration and noise problems of cooling pumps.How to improve cooling efficiency,operation stability and stability has become a technical problem restricting the development of products in the market.Therefore,it is of great engineering value and theoretical significance to study the internal flow and induced vibration and noise of cooling pumps in internal combustion engines.In this paper,the internal flow and induced vibration and noise characteristics of cooling pump of internal combustion engine are studied by means of mechanism analysis,experimental study and numerical calculation.The main research contents and innovations of this paper are as follows:1.The source of vibration and noise of cooling pump is analyzed,and the induction mechanism is classified.The research status at home and abroad is summarized.Based on the real machine,the model is built.A performance test system for cooling pump is built and its performance under different rotating speed is tested.The test results show that the dimensionless head curve of rotating speed has a high similarity,and the applicability of the similarity law is good.With the increase of rotational speed,the dimensionless head curve decreases faster,which indicates that the internal flow stability decreases.In addition,the flow loss increases at higher rotational speed.While with the decrease of rotational speed,the high efficiency region of the efficiency curve reduces and moves towards the direction of small flow rate,and the maximum efficiency decreases continuously.2.the vibration and noise characteristics of the cooling pump under different working conditions are obtained through the vibration and noise test under5000r/min~6750r/min conditions in the semi-anechoic chamber.The results show that the main frequency of the radial vibration acceleration is about 2 times of the axial frequency under the designed flow rate.The whole amplitude of axial vibration acceleration is lower than that of radial vibration.By analyzing the relationship between radiated noise intensity and flow rate at different rotational speeds,we can see that the sound pressure level decreases first and then increases with the increase of flow rate,and the high efficiency zone covers the flow point corresponding to the minimum sound pressure level.When the cooling pump exceeds the optimal operating condition,the sound pressure level increases greatly.From the test results,improving the efficiency has a certain effect on reducing noise.When the valve is fully open,the noise spectrum components corresponding to the three rotational speeds are discrete noise in low frequency band and wide frequency noise in high frequency band.With the increase of rotational speed,the corresponding amplitude of characteristic frequency of radiated noise increases correspondingly.At low flow rate,the noise directivity in the direction of vertical inlet tube shows quadrupole characteristics,and with the increase of flow rate,dipole sound source gradually becomes the main noise source.The directivity characteristic of oblique 45 degree measurement point is not obvious,which indicates that the directivity characteristic of radiated noise is closely related to the spatial distribution.3.On the basis of vibration and noise test,the internal flow field of cooling pump under design condition was numerically simulated.The simulation results show that the hydraulic performance of the pump is severely weakened due to the increase of pressure gradient in the whole flow passage and the spread of flow separation area appears from the tongue to the outlet.At the same time,a large number of strong vorticity clusters are concentrated in the tongue-separated area,which is a strong source of sound.Return vortices and rotating stalls occur in the impeller passage,and the outlet vortices dominate the vibration characteristics of the cooling pump under the condition of small flow rate.The frequency domain analysis of pressure fluctuation at two flow points shows that the intensity of pressure fluctuation at the monitoring point near the tongue is significantly higher than that at other monitoring points,and the flow deterioration is more serious.The results of impeller inlet quality analysis show that the lowest non-uniformity coefficient corresponds to the 0.7Q_d operating point in the high efficiency area,while the vertical degree of the outflow has little difference,which is close to the ideal flow direction,indicating that the inlet flow direction of cooling pump impeller has good stability.From the axial velocity distribution,the velocity distribution of the channel section becomes more uniform with the increase of flow rate.The change of flow rate will affect the unstable degree of the inlet flow,thus affecting the flow rate of the working fluid flowing into the impeller.The unstable degree of the inlet is more serious when the cooling pump runs under the condition of small flow rate.4.Based on Lighthill’s acoustic analogy theory,CFD/CA method is used to calculate flow-induced noise of cooling pump.The flow-induced noise characteristics of the cooling pump under different working conditions are studied.The results show that the frequency spectrum of the noise under the two working conditions is mainly discrete frequency,and the discrete peak value in the intermediate frequency band is slightly higher than that in the low frequency band.From the inlet to the outlet of the volute,the intensity of the sound pressure level decreases continuously.In the area where the impeller and volute are connected,the noise intensity changes alternately.In the area where impeller and volute are connected,there is alternating variation of noise intensity,especially in the case of 0.5 times design flow rate.Compared with the design condition,the intensity of sound pressure level is greater and the gradient is more obvious under the condition of small flow rate.Directivity curves show dipole characteristics,indicating that dipole source is the main source of flow-induced noise in cooling water pumps.