Research On The Influence Of Wall Roughness On The Hydraulic Performance And Energy Loss Characteristics Of Centrifugal Pumps

The existence of roughness of the centrifugal pump not only aggravates the turbulent phenomena near the wall but also destroys the viscous structure of the boundary layer,which makes the flow characteristics near the wall change.As far as possible to reduce the surface roughness of flow passage parts in manufacturing,operation and maintenance,it can improve the head and efficiency of pumps and reduce the shaft power to achieve the goal of Energy Conservation&Emission Reduction.Therefore,it is of great research value and engineering application value to study the influence of the wall roughness of centrifugal pump on the flow characteristics of turbulent boundary layer.Under 7 diferent wall roughness are researched by numerical simulation to the flow characteristics and energy loss of medium specific speed centrifugal pump in this study.The main research contents are as follows:1.Performance curves at seven different wall roughnesses indicate that under the same operating condition,the head decreases with the increase of wall roughness and wall roughness has little influence on head under the condition of small flow rate and wall roughness has great influence on head under large flow condition.At 0.4Q-1.2Q,the efficiency decreases with the increase of wall roughness under the same working condition.The static pressure of each monitoring point on the pressure surface of the blade indicate that it decreases with the increase of wall roughness.2.With the increase of wall roughness the turbulent kinetic energy on the wall boundary layer increases,that is,the energy dissipated by turbulent flow on the boundary layer is increased which is also one of the important reasons for the reduction of efficiency.The flow characteristics of small flow 0.6Q,designed flow 1.0Q and large flow 1.2Q indicated that the turbulent kinetic energy is the largest on the blade pressure surface under the condition of 0.6Q.On the suction surface,when the wall roughness Ra?50?m that the turbulent kinetic energy of 0.6Q is the largest and the wall roughness 100?m?Ra?750 ?m turbulent kinetic energy of 0.6Q is the smallest.The turbulent kinetic energy at the wall surface of the volute are increases with the increase of flow under the same wall roughness.3.Under 0.6Q condition,the turbulent dissipation rate is pressure surface greater than volute than suction surface and than radial center section of impeller.The turbulent dissipation rate of the same wall roughness under the condition of 1.0Q and 1.2Q is volute greater than suction surface than pressure surface and than radial center section of impeller.4.With the increase of wall roughness that the shear stress of the flow passage parts is increasing.The maximum wall shear stress corresponding to the 7 different wall roughness takes place along the section 0 to the section ? of the volute and followed by the impeller outlet.5.Along the blade pressure plane radial direction,the relative velocity decreases first and then increases.At the blade head,the relative velocity is decreasing with the increase of wall roughness and at the middle and posterior is increasing with the increase of wall roughness.6.Under the same roughness,the energy loss caused by the friction between impeller flow channel and fluid is the largest and followed by impeller diffusion and last caused by the outlet of impeller.The energy loss by friction,diffusion and impeller outlet is increasing with the increase of wall roughness.Compared with the energy loss in the volute is small that in the impeller.With the increase of wall roughness,the friction loss in volute channel and diffusion loss is increasing gradually.