| A jet pump transfers mass and energy through the entrainment and collision between fluids.The structure of the non-adjustable jet pump is fixed,and the adjustable jet pump can adjust the cross-section of the nozzle outlet through the auxiliary needle structure,giving itself a wider range of applications.In this paper,numerical simulations of the adjustable jet pump are carried out.The fundamental performance and cavitation performance of the adjustable jet pump are analyzed respectively.The main research contents and results of this paper are as follows:(1)The simulation scheme was verified by comparison with the experimental results,and the performance and flow fields characteristics of the adjustable jet pump with different needle positions at difference pressure ratios were followed.The comparison shows that: with the same pressure ratio,as the needle moves forward,the pressure value in the throat increases,and the upward trend of the axial speed in the throat gradually becomes steeper.Due to the presence of the needle,there is a lowspeed zone in the core of the jet.The normal velocity distribution of the wall of the needle presents a concentrated concentration of the jet.(2)Through the numerical simulation method to calculate the performance curves of the normal working conditions of the jet pump under different inlet pressures and different needle positions,it is found that the performance curves of the normal working conditions of different inlet pressures are on the same straight line.Besides the performance curve family with the needle at different positions has an envelope.(3)According to the trend of the adjustable jet pump performance curve,the operating conditions can be divided into four areas,and the area where intense cavitation happens should be avoided while optimizing the structure of adjustable jet pump.(4)Through the steady solution to simulate the cavitation state at different needle positions and different pressure ratios,the distribution of cavitation in the adjustable jet pump was analyzed,and a number of important cavitation parameters are calculated.It can be seen from the results: as the needle moves forward,the length of cavitation in the throat gradually increases,and correspondingly flow ratio also increases,and the pressure ratio gradually decreases;the length of the attached cavitation in the throat increases as the pressure ratio decreases.On the other hand,the growth of cavity length is rather slow before the limited working conditions,and rapid after reaching the limited working condition,and the thickness of the sheet cavitation increases linearly with the decrease of the pressure ratio.Under the same pressure ratio,cavitation flow ratio increases and cavitation pressure ratio stays the same if needle move forward.With the needle at the same position,both cavitation flow ratio and cavitation pressure ratio decrease if the working pressure increases.(5)Through the transient solution to simulate the cavitation process under the limited conditions at the needle position of 44.7mm,the cavitation initiation,development and collapse process was presented. |
