Research On Vibration Characteristics Of Jiuqu River Pump House Under Water Pressure Pulsation And Ultra-low Head Condition

The Jiuqu River pumping station has a two-way pumping capacity and is a two-way flow axial flow pumping station.In a two-way flow pumping station,factors such as self-vibration and hydraulic vibration in the pump house can affect the operational efficiency and structural stability of the pumping station,and in serious cases even threaten the operational safety of the pumping station.The Jiuqu River pumping station along the river is a large two-way flow channel pumping station,with occasional hydraulic failures such as undesirable pressure pulsations,cavitation and mechanical failures caused by unit vibrations during operation.This paper takes the Jiuqu River pumping station as the research object,study the dynamic response of the pumping station under ultra-low head operating conditions,using harmonic response analysis method to analyze the effect of different vane placement angles corresponding to the water pressure pulsation on the dynamic response of the pump house when the Jiuqu River pumping station is in forward diversion and reverse drainage ultra-low head operating conditions,the main contents of the paper are as follows:(1)To investigate the influence of the difference in boundary conditions on the self-vibration of the pump house,the self-vibration frequency of the submerged part of the pump house should be calculated by considering the participation of the fill in the vibration,and the full boundary conditions should be set with the scheme of solid end restraint at the bottom of the fill,normal restraint all around,normal contact between the boundary nodes of the pump house side wall and the fill,common deformation in the normal direction,and no restraint in the tangential direction.Through the resonance calibration calculation,it can be seen that the separation between the self-oscillation frequency of the first 50 orders of the Jiuqu River pump house structure and the rotational frequency of the pump station unit under rated and flyaway conditions meets the requirements,and the middle and low frequencies between the 9th and 23rd orders are closer to the passing frequency of the rotor blades,and the separation is less than 20%.(2)To study the dynamic response characteristics of the Jiuqu River pumping station structure under the action of water pressure pulsation load at ultra-low head operating conditions during forward flooding operation.By numerically simulating the water pressure pulsation signals under different vane installation angle conditions,it is found that the corresponding principal frequency values in the same area are approximately the same under different vane angles,and the principal frequency at the impeller inlet(7.45Hz)is very close to the passing frequency of the runner blade(7.5Hz),which is a resonance-prone area.In the harmonic response analysis,the maximum dynamic displacement and dynamic stress are used as the vibration characteristics indicators,and the characteristic parts are numbered and analysed,and it is found that as the blade angle changes from negative to positive,the maximum dynamic displacement gradually increases,and the change in the vertical direction is more obvious than that in the horizontal axis.The overall maximum dynamic displacement of the pump room is symmetrically distributed along the longitudinal axis,and the pump room basically shows that the longitudinal amplitude is larger than the transverse and vertical amplitudes.The maximum dynamic stress in the transverse axis,longitudinal axis and vertical direction of each characteristic part is larger with the angle of the blade,which is consistent with the distribution law of the maximum dynamic displacement.The maximum dynamic stress in the longitudinal direction of each characteristic part is the largest,followed by the transverse direction and the smallest in the vertical direction.The dynamic stresses in the vertical and longitudinal directions in the inlet channel of the pump house are greater than those in the outlet channel.(3)The dynamic response of the pumping station in reverse diversion operation under ultra-low head conditions is investigated by comparing the water pressure pulsation signals of different vane installation angles.The pumping station is operated in the reverse direction from the outer river to the inner river,with a vane angle of-2 degrees and an operating flow rate of 32 m3/s.The water pressure pulsation in the reverse direction is similar to that in the forward drainage condition.Harmonic response analysis was used to investigate the response of the pump house under different blade placement angle conditions,and the maximum dynamic displacement and maximum dynamic stress of the characteristic parts were used as indicators.It was found that the maximum dynamic displacement and dynamic stress basically increased with the increase of the blade angle,and the amplitude of the 0°blade angle condition was greater than that of the-2° and 2° conditions,and the structural amplitude met the vibration control standard.