Research On The Characteristics Of The Rotating Flow Field And Performance Of The Rotary Jet Pump Based On The Rotating Shell Effect

The roto-jet pump is a low specific speed pump with a special structure,which has the characteristics of a flat flow-head curve and a high lift.After the liquid gains kinetic energy in the impeller,it flows into the rotating cavity,and obtains energy again under the action of the shearing force of the rotating cavity,and the secondary energy obtained by the liquid is determined by the rotating speed of the rotating shell.which is enough to see that the rotating shell rotation speed has a significant effect on the liquid flow characteristics.Aiming at this phenomenon,in order to study the effect of the rotating speed of the rotating shell on the rotating flow field and performance of the roto-jet pump,this paper adopts the research scheme that the impeller and the rotating shell rotate synchronously and the speed of the fixed impeller changes the rotating speed of the rotating shell.On the basis of highly verifying the accuracy of the test and simulation results of the synchronous rotation of the impeller and the rotary shell,numerical calculation is carried out on the roto-jet pump with variable rotary shell speed,and the changes of the liquid peripheral speed,pressure and other characteristics are analyzed.The theoretical knowledge is used to study the performance of the pump.The main research contents are as follows:(1)Taking the roto-jet pump test bench of Lanzhou University of Technology as the research object,the performance of roto-jet pumps with synchronous speed of1740r/min,2320 r/min and 2900 r/min was tested,and the pressure values at 72 mm,93mm,114 mm and 135 mm are measured.The pressure distribution formula in the cavity is given,and the liquid rotation coefficient at the piezometric tube is determined to be 0.5.Comparing the test and simulation results,it is found that the maximum error is within 7%,which provides experimental support for numerical calculation.(2)In order to facilitate the analysis of the problem,the speed ratio is defined as the ratio of the rotating shell speed to the impeller speed.Under the speed ratios of 0.5,0.8,1.0,1.2,and 1.5,numerical calculations were carried out for the roto-jet pumps with flow rates of 0.8Q,1.0Q,and 1.2Q.Explore the circumferential velocity at 0.70 R,0.81 R,0.86 R,0.95 R,the distribution law of the liquid rotation coefficient and pressure at the polar angles of 75°,120°,220°,320°,and the evolution law of the liquid vortex structure in the cavity.The results show that when the liquid in the cavity rotates non-rigidly,the peripheral speed and the rotation coefficient are positively correlated with the rotation speed ratio and the radius,and increase or decrease synchronously;the pressure in the cavity follows a parabolic law along the radial direction,and increases with the increase of the radius,the pressure gradient increases with the increase of the rotational speed ratio,and the pressure curves at each rotational speed ratio intersect at one point.The fluid vortices in the cavity are concentrated in the up-flow area and the wake area of the header.The velocity in the up-flow area is small and the pressure is high.The vortices are distributed near the inlet.In the wake area,the velocity is large and the pressure is low,and the vortices are distributed in the diffuser section of the header.(3)The research on the performance of the roto-jet pump at each speed ratio shows that with the increase of the speed ratio,the lift of the rotary jet pump increases and the efficiency decreases.A thorough analysis of the reasons for the reduction of the efficiency of the roto-jet pump was carried out,and the energy conversion loss in the header and the friction loss of the disc in the roto-jet pump were calculated using theoretical formulas.The principle of entropy generation was introduced to determine the main reasons for the energy dissipation of the roto-jet pump,as well as the position and size of the dissipation of the water passing parts.The results show that the loss in the header changes little with the increase of the rotational speed ratio,and the friction loss of the disc increases in the form of a power function.The energy dissipation in the pump is mainly caused by turbulent dissipation,and the entropy production in the rotating cavity accounts for 82.2% of the entropy production in the entire pump,which is the main energy loss.The energy loss in the wake area of the header,the inner wall of the swirl shell,and the inlet of the header is relatively large.(4)The structure is optimized for the position where the energy loss of the roto-jet pump is more obvious,and the orthogonal test method is used to optimize and improve the width-diameter ratio of the rotary shell.The results show that the pump head and efficiency are optimal when the inlet diameter of the header is 13 mm.After adding the airfoil,the efficiency of the pump is obviously improved,and the average efficiency of each speed ratio is increased by 3.76%.The radial radius of the rotary shell has the greatest impact on the efficiency of the pump.After optimization,the radial radius of the rotary shell is 141 mm,and the axial width is 75.4mm.Compared with the original model,the mean value of entropy production at each speed ratio is reduced by 5.29%,the mean value of lift is increased by 2.40%,and the mean value of efficiency is increased by 12.38%,and the optimization effect is more significant.