Research On Gas-liquid Two-phase Flow Mechanism Of Centrifugal Pump Based On Roughness

During mechanical processing and use,due to the influence of industrial technology and operating conditions,the mechanical surface roughness will change,and the change in roughness will affect the hydraulic characteristics and operating stability of the centrifugal pump.When the centrifugal pump is operated under the gas-liquid two-phase condition,the roughness and bubble diameter,gas content and other factors jointly affect the flow characteristics of the centrifugal pump,which makes the internal flow of the centrifugal pump more complicated,and the result may cause system vibration.It will even seriously block the flow of the impeller flow channel,causing damage to its equipment.Therefore,based on the roughness,the study of the gas-liquid two-phase flow mechanism of the centrifugal pump is particularly important,and it also provides important reference value for practical engineering and design.Based on the existing theoretical,experimental research and numerical simulation research,this paper first analyzes the local roughness and roughness under the conditions of inflow velocity v of 10m/s,angle of attack?of 5°and cavitation number of 0.6.The influence of the degree on the cavitation characteristics of the hydrofoil;Secondly,based on the research of airfoil cavitation,this paper carried out a comprehensive three-dimensional steady and unsteady three-dimensional numerical simulation of the centrifugal pump gas-liquid two-phase flow mechanism based on roughness.The specific content is as follows:Fir st,the simulation calculation of different grid boundary layers and turbulence models was carried out,and the influence of the grid boundary layer and turbulence models on the calculation results and accuracy was analyzed;under different bubble diameters,the different levels of roughness of the blades affect the external characteristics of the centrifugal pump and the flow law of the internal gas-liquid two-phase flow.Multiple monitoring points are set at different parts to explore the unsteady characteristics of different levels of roughness on the gas-liquid two-phase flow of the centrifugal pump under different working conditions;finally,the different levels of roughness on the wall of the inlet pipe are analyzed The evolution of the special case of phase flow(cavitation caused by a drop in inlet pressure).The main research results are as follows:(1)The lift coefficient decreases with the increase of roughness,and the airfoil surface smoothness and surface roughness have a great influence on the lift coefficient;the airfoil surface roughness will cause the airfoil drag coefficient to increase;the angle of attack increases to a certain extent The effect of roughness on the airfoil is increased;the lift coefficient and drag coefficient of the airfoil are distributed as a periodic function with time.The effect of roughness on them is:the effect on their phase is basically the same,that is,When the roughness changes from 0?m to 16.44?m and 45.33?m,the phase shifts to the right by about 1.6s and 2.0s respectively;while the effect on their amplitudes is different,the effect on the amplitude of the lift coefficient is small,but the effect on the drag coefficient The amplitude has a greater influence.(2)Under the condition of v=10m/s,angle of attack of 5°and?=0.6,there is a sensitive roughness of 27.20?m.When the roughness is greater than 27.20?m,the distribution of the gas phase volume fraction of the airfoil,velocity vector distribution,velocity streamline The graph and pressure cloud diagram will change rapidly,and the most sensitive areas of the airfoil affected by roughness are the leading edge,upper wing surface and the area near the tail;secondly,increasing the roughness will lead to the occurrence of the resistance crisis phenomenon;at x=0.6m~1.0m.At the roughness of 0?m and 16.44?m,the distribution of the pressure coefficient of the lower wing surface of the airfoil is basically unchanged.When the roughness is 45.33?m,the pressure coefficient increases significantly.(3)Roughness will increase the maximum shear stress of the upper wing surface,so that its position moves to the front edge direction,and the roughness increases,the law of increase of the maximum shear stress of the upper wing surface is:first increase and then decrease;secondly,the airfoil For the trailing edge,the roughness tends to stabilize the flow state,break the vortex structure,and at the same time make the shear stress increase first and then decrease;for the leading edge,increase the roughness will gradually increase the shear stress to tend to stable.(4)The increase in roughness will reduce the head and efficiency of the centrifugal pump and increase the shaft power of the centrifugal pump,but the degree of influence is different under different flow conditions.There is also a roughness sensitivity value of 12.5?m.When the roughness is lower than this value,the roughness has a greater impact on the pump head,efficiency and shaft power.When the roughness is greater than this value,the roughness continues to increase.The head,efficiency and the degree of influence of shaft power becomes slower.(5)Increasing the roughness of the blade can reduce the pressure at the span.At different flow rates,the roughness has different degrees of impact,and the greatest impact on the flow condition is 1.0Q_d,followed by 1.2Q_d,and finally 0.4Q_d;second,the gas content And the increase of the gas phase particle size makes the centrifugal pump less sensitive to roughness.Increasing the bubble diameter will increase the pressure pulsation and increasing the roughness and inlet gas content will reduce the pressure pulsation at each monitoring point;increasing the roughness and bubble diameter will destroy the periodic pressure distribution at each monitoring point,but the roughness will affect the monitoring point.The periodic damage of pressure is greater.(6)Roughness can reduce the volume fraction of the gas phase,and the degree of influence on the volume fraction of the gas phase is the boundary point at the span position of a certain intermediate streamline,and as the flow rate increases,the location of the boundary point at the span will follow the blade Moving in the direction of the outlet;secondly,the gas content of the inlet basically does not change the trend of the effect of roughness on the gas volume fraction,and the cutoff point of the span does not change,but only moves the gas volume fraction distribution curve upward;increase The bubble diameter will make the degree of influence of the roughness on the volume fraction of the gas phase become larger.(7)The increase in roughness will cause the direction of the radial force on the blade under steady conditions to move clockwise,and the size will decrease first and then increase as the roughness increases.Increasing the inlet gas content can reduce the centrifugal pump's sensitivity to roughness,while increasing the bubble diameter can increase the centrifugal pump's sensitivity to roughness;the axial force increases as the roughness increases,changing the inlet gas content and bubbles The diameter will not change the distribution and change trend of the roughness-axial force relationship curve,but will only change the size of the axial force and increase the inlet air content,which will increase the axial force;roughness will make the blade suffer unsteady The eccentric movement of the lower radial force reduces the magnitude of the radial force;secondly,the roughness has a greater impact on the radial force of the centrifugal pump relative to the inlet gas content and bubble diameter.(8)The average turbulent kinetic energy of the monitoring point G1 is distributed as a cubic polynomial function with the roughness.Within these five roughness levels,maximum and minimum values appear.As the flow rate increases,the slope of roughness-average turbulent kinetic energy increases,which is consistent with the turbulent kinetic energy of G1.(9)Under cavitation conditions,the effect of roughness on the speed of the same monitoring point under different working conditions is consistent,but the degree of influence is different.It has the greatest impact on the inlet pressure of 25.019KPa and the working condition of 0.4Qd.When the roughness is Ra=0?m~12.5?m,it can reduce the strength of the backflow vortex,make the speed tend to be uniform,and at the same time improve the cavitation performance,especially when Ra=6.3?m,the improvement effect is obvious.Secondly,as the roughness increases,the radial force on the inlet pipe increases first and then slowly increases,and the center of the force is distributed eccentrically;the radial force received by the impeller is related to the inlet pipe wall roughness and has a complex distribution.When Ra=6.3?m,the radial force of the impeller tends to be evenly distributed;meanwhile,the distribution of cavitation in the impeller changes from uneven to uniform.