| The variable speed hydrodynamic coupling with its light load start,overload protection,coordination of multi-power machine operation and other advantages,has become an important speed regulating device for miners,electric power,ships and other industries.During the speed regulation operation,the gas-liquid two-phase circulation movement in the working chamber of the coupling is very complicated,especially when the rotation speed is high or the slip difference between the two wheels is large,there will be violent irregular flow inside.It has a great impact on the speed regulation stability and energy conversion rate of the hydrodynamic coupling.At present,most of the designs of hydrodynamic couplings in my country are based on products imported from abroad.It is precisely because of the lack of long-term accumulation of flow theory and in-depth research on key technologies that it is difficult to break through the bottleneck of more energy-saving and high-efficiency.In this thesis based on CFD simulation technology,the internal flow conversion mechanism and the influence of blade structure on the internal and external characteristics of the variable speed hydrodynamic coupling are studied.Taking the YOTcx560 hydrodynamic coupling as the research object,the VOF model and the Mixture model are used to numerically simulate the two-phase transient flow field under three liquid filling rates and different working conditions.The gas-liquid two-phase distribution,pressure distribution and velocity distribution of the axial section of the working chamber under three typical working conditions(i=0、i=0.6、i=0.96)are analyzed.The internal circulation conversion mechanism of the speed-regulating hydrodynamic coupling is revealed,and the change law of its external characteristics is explored in combination with the output torque characteristic curve of the pump impeller.Comparing the torque curves monitored by the two models,it is found that the VOF model can better simulate the torque drop caused by the fluid state transition of the coupling,but the Mixture model cannot simulate this effect.However,the simulated torque value still has certain reference significance under the conditions of high and low speed ratios.In order to further understand the influence of the hydrodynamic coupling blade structure on its internal and external characteristics,the shape of the turbine blade is changed under the condition that other parameters remained unchanged,and it is adjusted so that the long and short blades are evenly spaced.Three groups of short blade pitches of 10°,15°,and 20° are designed for simulation.Combined with the output torque characteristic curve,and selecting the gas-liquid two-phase distribution,streamline and vorticity as the judgment basis,the influence of the blade structure change on the coupling is analyzed through the axial section,radial section and chord plane of the working cavity.The results show that the design of modifying part of the long blades into short blades can effectively reduce the generation of secondary flow,reduce the hydraulic loss,and improve the torque transmission capacity of the pump impeller.However,if the inclination of the short blade is too large,the torque value will decrease in the starting state.The simulation results show that the slanted 10° short blade scheme has the best effect on improving the torque transmission capacity.This thesis reveals the internal circulation conversion law of the variable speed hydrodynamic coupling,compares the simulation methods,and explores the influence of the blade structure on the internal and external characteristics of the coupling,which provides a reference for the internal flow field research and structural design of the variable speed hydrodynamic coupling. |
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