| Under the condition of small flow,the internal flow field structure of centrifugal pump is extremely unstable.At this time,the head curve of some pumps will produce hump phenomenon.When there is a hump in the head curve,the stability of the pump in the system becomes worse,which will lead to a series of problems such as vibration and noise in the pump and pipeline system.Therefore,in the hydraulic design of centrifugal pump,the combination optimization measures of various geometric parameters should be considered as much as possible,so as to avoid hump in its head curve.The change characteristics of the pump performance curve with the increase of flow is the external embodiment of the change of the internal flow field structure of the pump,and the change of the flow field structure is closely related to the hydraulic structure of each flow passage component.In order to make the change characteristics of the pump performance curve meet the design requirements,it is necessary to make the hydraulic design of each flow passage component meet the specific geometric structure characteristics.As the main work component in centrifugal pump,the hydraulic structure of impeller has a vital impact on the variation characteristics of pump performance curve.This paper takes the throat area of the impeller channel inlet as the focus,starts with the hydraulic design of the impeller,explores the influence mechanism of the change of the throat area of the impeller channel inlet on the hump phenomenon,and further discusses the optimization direction and measures to eliminate the hump phenomenon of the head curve,in order to provide valuable theoretical reference and direction guidance for the hydraulic optimization of the centrifugal pump impeller.In order to clarify the mechanism of the hump phenomenon of the head curve,firstly,the flow field structure in front of and inside the impeller of the original model under the full flow condition is analyzed by using the numerical simulation method,and the difference of the flow field structure in front of and inside the impeller under the conditions near the hump point and other conditions is explored.The results show that under low flow conditions,especially near the hump point,there is an obvious reflux area at the inlet of the impeller,and at this time,the circumferential velocity at the inlet becomes larger,there is a strong pre-swirl effect at the inlet,and the stability of the flow field structure in front of and inside the impeller is very poor;Under the condition far from the hump point,the flow field structure in front of and inside the impeller is improved,and the stability of fluid flow is improved;At the design operating point,the flow field structure at the inlet of the impeller and inside the impeller is the most stable.Through the analysis of the internal flow field structure,it is found that the pre-swirl and reflux at the inlet of the impeller are one of the important reasons for the hump phenomenon,which provides a certain direction for the follow-up study of the impact of the change of impeller hydraulic design on the hump phenomenon.In order to explore the influence mechanism of the change of the inlet throat area of the impeller channel on the hump phenomenon,starting from the blade grid streamline,on the premise of keeping the geometric parameters such as the inlet edge position,inlet angle,outlet angle and wrap angle of the blade unchanged,the hydraulic structure of the impeller is changed by changing the change trend of the grid streamline along the flow direction,so as to achieve the purpose of changing the inlet throat area of the impeller channel,The variation of pump hydraulic performance curve under different throat area is analyzed and studied.When the area of the inlet throat of the impeller channel changes,the shape of the head curve changes obviously;The area of the inlet throat of the impeller channel decreases,the overflow capacity at the inlet of the channel decreases,the stability of the flow field in front of and inside the impeller becomes worse,and the hydraulic loss in the channel increases,which promotes the hump phenomenon;The area of the inlet throat of the impeller channel increases,the overflow capacity at the inlet of the impeller channel increases,the backflow phenomenon and pre-swirl effect at the impeller inlet weaken,and the stability of the flow field structure in front of and inside the impeller inlet improves,which is conducive to the elimination of humps.Changing the blade inlet angle,inlet edge position and blade wrap angle will have a corresponding impact on the throat area of the impeller channel inlet.This paper starts with changing the two single geometric parameters of blade inlet angle and inlet edge position to change the area of channel inlet throat,and then further modify the wrap angle of blade to enhance the change degree of channel throat area based on the adjustment of inlet edge position.Through this mixed optimization measure,the influence mechanism of channel throat area change caused by non single factors on hump phenomenon is comprehensively studied and analyzed.When the blade inlet angle decreases,the position of the blade inlet edge moves backward or the blade wrap angle increases,the area of the inlet throat of the impeller channel will decrease accordingly,the backflow phenomenon and pre-swirl effect at the impeller inlet will increase,the impeller inlet and internal flow field will be affected,the degree of disorder will increase,and the hump phenomenon of the head curve will be promoted;When the blade inlet angle increases,the position of the blade inlet edge moves forward or the blade wrap angle decreases,the throat area of the impeller channel inlet will increase accordingly,the overflow capacity at the channel inlet will be enhanced,the reflux phenomenon and pre-swirl effect at the impeller inlet will be weakened,the stability of the internal flow field structure of the impeller will be improved,and it is conducive to eliminating the hump of the head curve;By taking the comprehensive optimization measures of moving the blade inlet edge forward,increasing the blade inlet angle and reducing the blade wrap angle at the same time,the hump phenomenon of the pump head curve is obviously eliminated,and the efficiency of the high flow operating point is improved.Among them,the hydraulic efficiency of the design operating point is 0.86 percentage points higher than that of the original model.The above comprehensive results show that the throat area at the impeller inlet is an important factor affecting the hump phenomenon of the lift curve of centrifugal pump.No matter how the geometric parameters of the impeller change,as long as the throat area at the impeller inlet can be increased and the flow capacity at the impeller inlet can be enhanced,the backflow phenomenon and pre-swirl effect at the impeller inlet can be reduced,so that the hump phenomenon of the lift curve can be weakened or even eliminated.Therefore,in the hydraulic design of impeller,it is the key to improve and eliminate hump phenomenon to reasonably control the throat area at the inlet of impeller runner. |
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