Investigate On The Mechanism Of Roughness Influence On The Flow Characteristics Of Centripetal Flow Rotor-Stator Cavity

In centrifugal pumps and turbines,centripetal through-flow from the outer diameter of the impeller to the rotating shaft is common.The chamber formed between the rotating impeller and the stationary chamber is a typical rotor-stator cavity.In the presence of centripetal through-flow,the radial pressure on the turntable face changes,which may cause excessive axial forces.In production,the walls of the rotating and stationary parts are not smooth.When the roughness of the rotor and stator exceeds a certain value,the flow characteristics in the rotor-stator cavity change and losses increase.However,the available studies in the literature for this type of disc cavity with rough rotor and stator surfaces are still very inadequate.In order to fill the gap,this paper investigates the mechanisms influencing the flow characteristics of a typical centripetal through-flow rotor-stator cavity based on fluid simulation software for low speed centripetal through-flow rotor-stator cavity.The accuracy of the numerical calculation results is verified through experiments to ensure the reliability of the calculation.This paper considers two different media,water(incompressible fluid)and air(compressible fluid),and investigates the effects of different rotor and stator surface roughness on the flow characteristics and macroscopic characteristics of a centripetal throughflow rotorstator cavity under various operating conditions with six rotational speeds(n=1000～4000 rpm)and roughness of the rotor,stator,and two disk surfaces(ks=0～76.81 μm),the specific conclusions are as follows:(1)In the flow characteristics,for the velocity field,the roughness of the rotor has a more significant effect on the velocity of the fluid in the disk cavity.Whereas when the stator is rough,the resistance to flow due to stator roughness in the core area is less and the flow in the disk cavity is insensitive to stator roughness.For core swirl ratio,both media increase with increasing rotor roughness at different Reynolds numbers,the difference being that for incompressible fluids the core swirl ratio is negative.For the roughness of the rotor surface,the core swirl ratio is positively correlated with the roughness and varies significantly;For the roughness of the stator surface,the compressible fluid core swirl ratio is negatively correlated with the roughness and varies less,with the overall effect of the roughness of the rotor surface on the core swirl ratio being greater than that of the stator surface.For the pressure field,there is a large difference in pressure orders of magnitude between the two fluids due to their physical properties,but the overall decrease with decreasing radius,especially at low radii where there is a large gradient of pressure variation.As the Reynolds number increases,the compressible fluid pressure coefficient increases and the incompressible fluid pressure coefficient first decreases and then increases.The overall pressure in the disk cavity is increasing by increasing the roughness of the rotor,but the increase is smaller at low Reynolds numbers.The increase in pressure coefficient with Reynolds number and the decrease with equivalent roughness when the stator is rough are extremely small.When both disk surfaces are rough,the flow field changes in line with the rough disk,indicating that under the influence of the coupling of the two disk surfaces,the disk roughness plays a dominant role in the flow characteristics in the disk cavity.(2)In the macroscopic characteristics,for the rotor moment coefficient,both media show an overall decrease with increasing Re.As the rotor ks increases,so does the rotor moment coefficient,especially at large roughness(i.e.ks=3 8.41 and 76.81 μm)where the compressible fluid increases by around 35%.However,water is less sensitive to roughness than air.For the stator moment coefficient,which increases overall with Re,the CM of the stator is overall smaller than that of the rotor.Compared to the moment coefficient when only one of the rotor and stator has a rough surface,the moment coefficient with a compressible fluid is greater when both the rotor and stator have a rough surface.For the rotor axial thrust coefficient,the compressible fluid as an increase as Re increases and the incompressible fluid as a decrease as Re increases.As the surface ks of the rotor increases,the axial thrust increases continuously,especially at large roughness(i.e.ks=38.41 and 76.81 μm),and the increase in the axial thrust coefficient of the rotor reaches about 18%in both media.For the stator axial thrust coefficient,both fluids maintain the same trend as their rotor axial thrust coefficients,and whole the stator axial thrust coefficient is less than the rotor.The increase in roughness of the rotor will increase the axial thrust coefficient of the rotor and stator,and the increase in roughness of the stator surface will decrease the axial thrust coefficient of the rotor and stator.At the same time increasing the roughness of the rotor and stator will increase the axial thrust coefficients of the rotor and stator,indicating that in the case of centripetal flow,rotor roughness plays a dominant role in the effect of disk roughness on axial thrust.