Experimental Study Of Flow Characteristics At Groove Walls And Resistance Reduction In Rotating Discs

In engineering,centrifugal pumps as a common rotating machinery,its working process of centrifugal impeller cover plate will produce friction with the flow of media,resulting in energy loss,the energy loss generated to a large extent from the resistance generated when the fluid flow.Therefore,reducing the frictional resistance on the surface of the centrifugal pump flow channel is an effective way to improve pump efficiency.This paper is based on the application of groove wall turbulence reduction technology to centrifugal pump resistance reduction.Using a rotating machine such as a centrifugal pump as a reference,the resistance reduction characteristics of the groove under rotating conditions are investigated.A combination of numerical simulations and experiments is used to investigate the drag reduction characteristics of the grooves.The smooth wall friction coefficient C_f obtained from numerical simulations of three turbulence models is compared with the smooth wall friction coefficient C_f calculated by Plante’s empirical formula,and the SST k-ω model is found to be the most suitable for numerical simulations of grooves.The effect of different groove angles and Reynolds numbers on the drag reduction effect of the groove is investigated by numerical simulation.The results show that an increase in groove angle leads to an increase and then a decrease in drag reduction,and an increase in Reynolds number leads to an increase and then a decrease in drag reduction.The shear stress is lower at the bottom of the groove and higher at the top,but the average shear stress at the wall of the groove is lower than that of the smooth wall,resulting in a lower friction coefficient at the wall of the groove than that of the smooth wall,resulting in reduced resistance.At the same time,the bottom of the groove is able to store more low velocity fluid and avoid the intrusion of high velocity fluid.Observation of the groove wall spreading velocity flow diagram reveals that the presence of secondary vortex pairs in opposite directions at the top of the groove inhibits the spreading motion of the flow vortex,converting fluid-wall friction into fluid-fluid friction,thereby reducing wall friction resistance.Furthermore,the maximum values of turbulence statistics(turbulent kinetic energy,turbulent intensity and turbulent dissipation rate)at the wall of the groove are all smaller than those at the smooth wall,indicating that the groove can inhibit turbulence development,weaken energy transfer near the wall,reduce fluid momentum loss and weaken the transport of momentum pulsations at the wall area,which together make the groove have a drag reduction effect.The grooves with the best drag reduction effect were etched onto the disc and the effect of four submergence depths(35mm,45mm,55mm,65mm,)on the torque and six Reynolds numbers(2.8 × 10~4,1.1 × 10~5,1.9×10~5,2.9×10~5,3.6×10~5,4.5×10~5)on the drag reduction effect of the grooves were investigated by means of a rotating test bench.At 60 mm,the torque of the groove discs and smooth discs remains constant,and under this condition,the resistance reduction of the groove increases and then decreases as the Reynolds number increases.At a Reynolds number of 1.1 × 10~5,the resistance reduction of the groove was the highest,17.14%,and at a Reynolds number of 4.5 × 10~5,the resistance reduction of the groove was the lowest,9.09%.