| In the context of domestic industrial upgrading,centrifugal pump is widely used in shipbuilding,marine,aerospace,chemical,nuclear power and other important fields.In the process of practical application,a practical problem is gradually emerging in front of designers: centrifugal pumps are often equipped with inlet elbows which are limited by the harsh installation environment,and the distorted flow excited by the elbows interferes with the operation of centrifugal pumps,resulting in the decline or even instability of the efficiency of centrifugal pumps.At the same time,the rotor-stator interference between volute tongue and blade is recognized as the main hydraulic excitation source of centrifugal pump.However,the coupling mechanism of the two excitation sources in centrifugal pump is still unclear.Therefore,it is urgent to study the influence of the circumferential position of the inlet elbow and volute on the flow mechanism and hydraulic excitation.In this paper,funded by the Jiangsu Natural Science Foundation(BK20190847)and the General Program of the China Postdoctoral Science Foundation(2019M661744),a centrifugal pipeline pump with an inflow elbow is selected as the research object.The adjustment of the circumferential installation angle φ of the inlet elbow resulted in several sets of new pipeline pump models with different φ values,and numerical simulation were carried out in sequence.Through the comparative analysis of the internal flow field and pressure pulsation of the new pump and the prototype pump,it is found that the inflow distortion and the rotor-stator interference have a joint suppression of the hydraulic excitation effect,which we call " peak clipping and valley filling ",and further explore the mechanism of this effect.The corresponding main research work and content are as follows:(1)Based on previous studies on the influence of the outflow distortion of the elbow suction chamber of the prototype pump,it is known that the pressure fluctuation curve near the blade inlet has three periodic peaks in the time domain.The second peak is caused by the rotor-stator interference.The first and third peaks are mainly caused by the inflow distortion.Therefore,this paper also monitors the pressure near the blade and volute of the studied pump models during the numerical simulation process,striving to explore the influence of the inlet elbow with different φvalues on the pump from the perspective of pressure pulsation.(2)After the steady numerical simulation of the prototype pump and the derivative model,the steady distribution of the flow field in each model pump under different φ values is obtained.Focus on the analysis of the difference between the static pressure,velocity and turbulent kinetic energy in the pump from the impeller inlet area to the volute area due to the distortion of the inflow and the rotor-stator interference.The main findings after comparison are: First of all,in terms of external characteristics,the circumferential installation angle φ of the inlet elbow mainly interferes with the head value of the pump : when φ is a positive angle,the head gradually increases with the increase of the angle,while when φ is a negative angle,the head gradually decreases with the increase of the negative angle.Secondly,in terms of internal flow characteristics,there is a main distortion zone that follows the rotation of the elbow in the circumferential direction near the impeller inlet area,and there are always two low-pressure vortex cores in the main distortion zone,which are the main sources of disturbance that affect the impeller’s work.Each pump model has a more obvious "jet-wake" structure near the trailing edge of the blade.And affected by the distortion of the inflow,there is a low-speed separation flow zone in the blade channel of the main distortion zone.When φ is a positive angle,the flow separation zone is smaller,and when φ is a negative angle,the flow separation zone is larger.(3)After the unsteady numerical simulation of the prototype pump and the derivative model,the pressure pulsation at the representative monitoring point from the blade inlet to the outlet and the volute tongue in each model pump is extracted,and the decoupling in the time domain and frequency domain finds that: when φ=45°,due to the phase difference adjustment,the inflow distortion and the rotor-stator interference form the "peak clipping and valley filling " of the pressure pulsation,which jointly suppresses the hydraulic excitation in the pump,and makes the second peak of the pressure pulsation at the monitoring point Pb1 on the back of the blade inlet,and the largest drop.reached 40.55%.The formation mechanism of " peak clipping and valley filling " is further studied: the inlet elbow causes the main distortion zone composed of low static vortex cores LP1 and LP3 that always exist at the impeller inlet.They not only rotate with the rotation of the elbow,but also propagate back to neighboring blades with the rotation of the impeller.Therefore,when the pump is fixed under the influence of dynamic and static interference(high static pressure zone),changing the installation angle of the inlet elbow to adjust the phase difference between the high/low static pressure zone will promote the low static pressure zone generated by the distortion inflow gradually approach the high static pressure zone created by rotor-stator interference.The two offset each other,and then achieve the effect of " peak clipping and valley filling " of the pressure pulsation.(4)On the basis of the above analysis of " peak clipping and valley filling ",it is speculated that when the installation angle of the elbow is greater than 45°,the hydraulic excitation may be better suppressed.However,due to the solid interference between the elbow of the prototype pump and the volute,the original elbow suction chamber needs to be stretched appropriately,and a new 0° model pump and 3 sets of elbow installation angles greater than 45° are constructed.Numerical simulation are carried out to further compare and analyze the pressure pulsation differences at the same monitoring point.The results show that: in the model of φ = 60°,the pressure pulsation at Pb2 in the middle section of the impeller also has a similar " peak clipping and valley filling " effect.As a result,the second peak value of the pressure pulsation curve is greatly reduced,with a maximum decrease of 64.75%. |
PDF Full Text Request