Studying On The Cavitation Characteristics Of The Upstream Geometric Boundary Of High-speed Inducer

Cavitation will cause unstable operation of fluid machinery,and then make the centrifugal pump unit operation failure.The study of cavitation phenomenon is significance to ensure the operation efficiently of the pump.Because the inducer itself has good anti-cavitation performance,the inducer is usually placed in front of the impeller to improve the cavitation performance of centrifugal pump.However,under the combined action of centrifugal force and inertial force,the t ip clearance of the inducer will produce leakage vortices.The leakage vortex will induce the cavitation phenomena such as rotating cavitation,asymmetric cavitation,shroud cavitation and hub cavitation.Moreover,since the leakage vortex mainly occurs at the inlet of the front inducer,if the leakage vortex can be suppressed,the cavitation phenomenon generated by it can also be suppressed or alleviated.This article takes a certain type of high-speed centrifugal pump as the research object.Based on the method of numerical calculation and experimental verification,the influence of the upstream width of the annular groove,the annular groove with different geometric parameters and different axial position on the cavitation performance of the high-speed inducer is studied.The specific research contents are as follows:1.The influence of annular groove with different cross-section area on the hydraulic performance and cavitation performance of high-speed inducer is studied.The optimal parameters of the annular groove are obtained.At the same time,the influence of the optimal parameters of the annular groove on the cavitation performance of the inducer under different working conditions is further studied.Under different conditions,with the increase of flow rate,the critical cavitation number of inducer increases.When annular is added,the critical cavitation number first decreases and then increases,which has a minimum value under rated working conditions.Both the original scheme and the annular gro ove scheme are prone to cavitation under high flow condition,and the annular groove scheme can significantly improve the cavitation performance of the inducer at 0.8Q_d and 1.0Q_d.Under the condition of 1.0Q_d,the annular groove can obviously reduce the ax ial vortex at the inlet of the inducer.The flow state of the inlet section and the turbulent kinetic energy distribution of the inducer blade suction surface are more stable.The results show that the annular groove reduces the non-uniform force of the inducer,the asymmetry of cavitation is obviously weakened,and the vortex band at the inducer inlet is broken.With the increase of flow rate,the pressure variation trend in the inducer is consistent with the cavitation distribution law.At 0.8Q_d and 1.0Q_d,the low pressure area in the inducer decreases significantly,and the anti-cavitation performance of the inducer improves significantly.2.To effectively improve the cavitation performance of high-speed centrifugal pump and avoid cavitation damage of inducer,the effect of annular groove with different upstream width on tip clearance leakage vortex cavitation is studied.The results show that the leakage vortex will induce cavitation in the shroud and hub of the inducer,rotating cavitation,and asymmetr ic cavitation under the combined action of centrifugal force and inertial force.The upstream width of the annular groove has a greater influence on the cavitation performance and hydraulic performance of the high-speed inducer.When the width of the annul ar groove is too small or too large,it can absorb part of the leakage vortex,which can improve the cavitation performance of the inducer to a certain extent.But it is a load relative to the inducer,which destroys the upstream flow state of the inducer and aggravates the downstream turbulent energy dissipation.It has a greater impact on pump head and efficiency.When the optimal width value b₃=10mm,the annular groove can eliminate the vortex in the circumferential and axial directions of the inducer up stream without affecting the external characteristics of the pump,pressurize the inducer and reduce the high turbulent kinetic energy zone in the flow channel.Therefore,the cavitation evolution induced by the leakage vortex is actively suppressed,and t he cavitation performance of the high-speed inducer is improved.At the same time,the required cavitation margin of the pump is reduced by 47.8%compared with the original scheme without an annular groove.3.To suppress the cavitation instability caused by the leakage vortex at the tip clearance of the high-speed inducer,this study establishes a structure（i.e.annular groove）at the upstream boundary of the high-speed inducer that can absorb the leakage vortex,and determined the original plan and diffe rent axial distances,a total of 6 groups of design plans.The effects of annular grooves on cavitation performance under different schemes are studied through a combination of experiment and numerical calculation.The cavitation appeared at the position w here the suction surface of the inducer intersected with the shroud.The volume of the bubble is gradiently distributed and a vortex band is formed at the inducer inlet,and then developed to the back of the centrifugal impeller blade.Vortex belt is formed at the inlet of the inducer.The axial position of the annular groove relative to the inducer is an important parameter suppressing the occurrence of clearance leakage vortex cavitation,asymmetric vortex cavitation and rotating vortex cavitation.In the proper position,annular groove can significantly suppress the bubbles incipient and improve the cavitation performance of the inducer.Thus,the anti-cavitation performance and head of centrifugal pump can be effectively improved under the condition of l ittle influence on the efficiency of centrifugal pump,indicating the annular groove has an axial optimal position in inhibiting cavitation and improving cavitation performance of the inducer,at this time L₁=0mm.