| With the rapid development of pump station engineering,bulb tubular pump,as a pump with large flow,high efficiency and excellent hydraulic performance,is widely used in the optimal operation of water resources.During the operation of the pump station,in case of eccentric operation,blade angle deviation or excessive blade top clearance,it may lead to abnormal water pressure fluctuation in the unit,aggravate the vibration of the unit,cause hydraulic excitation,affect the normal operation of the pump station and even cause unit failure.Therefore,the research on water pressure fluctuation of pump station is of great significance.At present,the analysis of pressure fluctuation is mainly time-dependent transient analysis.This method has some limitations in analyzing pulsation signals with no obvious law in time-frequency domain.Based on computational fluid dynamics and chaotic fractal theory,the pressure fluctuation characteristics and chaotic characteristics under different design conditions,blade installation angle deviation and different blade tip clearance are analyzed and studied in this paper.The main research contents of this paper include:（1）Pressure fluctuation characteristics of unit under deviation from design conditions.The hydraulic characteristics,pressure fluctuation characteristics and chaotic characteristics of pressure fluctuation when the unit deviates from the design condition are studied and analyzed.The results show that the overall flow pattern of the unit under low lift condition and design condition is better than that under high lift condition,and the flow velocity uniformity of the characteristic section under high lift condition is lower than that under low lift condition and design condition.The main frequency of pressure fluctuation in the guide vane area of the impeller under three working conditions is the whole blade frequency,and the main frequency of pressure fluctuation in the bulb body area and the flow channel is chaotic.The main frequency amplitude of the pressure in the guide vane area of the impeller decreases gradually from the rim to the hub.The main frequency amplitude of pressure fluctuation under high lift condition of each section is greater than that under design condition,which can reach 2.5 times of the main frequency amplitude under design condition,and the low lift condition is close to the design condition.Under the design condition,the maximum Lyapunov exponent and fractal scale of the pressure fluctuation signal at the internal monitoring point of the unit are greater than 0.The time series of pressure fluctuation of the unit has chaotic characteristics.The phase trajectory diagram of the monitoring point under different operating conditions contains the spatial domain information of the pressure fluctuation signal.The correlation dimension of the monitoring point changes with the change of the operating conditions such as the unit head condition and the location of the monitoring point.The maximum difference between the low head condition and the design condition is 20%,The maximum difference between high lift condition and design condition is 37.5%.（2）Pressure fluctuation characteristics of the unit under the condition of blade installation angle deviation.The hydraulic characteristics,pressure fluctuation characteristics and chaotic characteristics of pressure fluctuation signal of the unit under the condition of blade installation angle deviation are studied and analyzed.The results show that the scheme of angle deviation of two blades offsets the streamline at the back of the bulb body,and the more the number of blade deflectors at the outlet section of the impeller,the larger the area of the high-speed area.The blade angle of the inlet and outlet section of the impeller increases,and the area of the low-pressure area increases.The overall velocity uniformity of each scheme section is less than that of the design working condition,and the scheme section with increased angle of two blades has the lowest overall velocity uniformity.The increase of blade angle will increase the unit head and reduce the efficiency.The overall optimal working condition point will move to the right.The more blades with increased angle,the lower the overall efficiency.The increase or decrease of blade installation angle will increase the main frequency amplitude of pressure fluctuation.The more the number of blades with increased angle,the greater the pulsation amplitude,the more the number of offset blades,and the greater the pulsation amplitude generally.The chaotic fractal characteristics of pressure fluctuation signal are also sensitive to blade angle.The correlation dimension difference between the scheme of increasing the angle of double blades at the guide vane outlet and the design condition is 80%.The angle of single blade at the inlet and outlet section of impeller increases,the correlation dimension decreases,and the opposite is true at the outlet of guide vane.（3）pressure fluctuation characteristics of unit under different blade tip clearance.The hydraulic characteristics and chaotic characteristics of pressure fluctuation of the unit under different blade top clearance are studied and analyzed.The results show that with the increase of blade top clearance,the distribution of velocity cloud and pressure cloud at section I is uneven and the boundary is fuzzy,and the head efficiency of the unit also shows a downward trend.The phase trajectories of monitoring points under different tip clearances contain the spatial domain information of pressure fluctuation signal.Similar to the blade installation angle,the chaotic fractal characteristics of the signal also have a certain sensitivity to the change of blade tip clearance,but the change of correlation dimension of some monitoring points is small,so other characteristic quantities need to be introduced to further improve the research.（4）Developed a program for calculating the maximum Lyapunov exponent of time-domain signals which is based on MATLAB platform.The interface and function of the program are introduced,and the time-domain signal of pressure fluctuation under the design working condition is demonstrated as an example.The results show that the maximum Lyapunov exponent of the pressure fluctuation signal is greater than 0,and the signal has chaotic characteristics,which shows that the program can calculate the maximum Lyapunov exponent simply and quickly. |
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