| Hydrodynamic coupling has the advantages of load starting,overload protection,vibration buffer,etc.,showing excellent transmission performance in the field of speed control drive,energy saving and emission reduction,commonly used in mining machinery,petrochemical,natural gas,power generation,ships and other industries.Under the new pattern of low carbon development led by technological innovation,the popularization and application of hydrodynamic coupling acts a vital role in promoting the progress of our energy conservation and emission reduction.The flow characteristics within the hydrodynamic coupling directly affect its output characteristics.The inner flow field is non-constant vortex flow,accompanied by complex nonlinear multi-scale flow characteristics.How to accurately reconstruct the structure of its internal vortex flow field and extract the structural characteristics of three-dimensional space vortex system has important scientific research value for deeply understanding the complex flow phenomenon and accurately revealing the space-time evolution law and dynamic characteristics of multi-scale flow field.It also has important engineering application value for promoting the structural optimization and performance improvement of hydrodynamic coupling cascade from the flow essence.Relying on the "Research on Multi-scale Evolution Characteristics and Energy Loss Mechanism of Unsteady Vortex Flow Field of Hydrodynamic Coupling(51405184)" of the National Natural Science Foundation of China(Youth Science Foundation),the flow field of ordinary hydrodynamic coupling under braking and rated conditions was reconstructed based on interactive technical means of numerical simulation and experimental measurement.The structure characteristics of multi-scale vortex system inside the flow field were extracted and the spatio-temporal evolution and dynamic characteristics of the flow field were analyzed to reveal the energy transformation mechanism.The main research contents are as follows:(1)Analysis of applicability of three-dimensional vortex system reconstruction method and dynamic evolution characteristics of full-filled liquid flow fieldA simplified channel model of hydrodynamic couplings was established,hexahedral grids were divided and grid-independent analysis was carried out.The Stress-Blended Eddy Simulation model was used to numerically simulate the flow field under full liquid-filled braking conditions and rated conditions.Based on the research of three-dimensional vortex identification theory and method,the Q criterion,Omega(Ω)method and Omega-Liutex(ΩL)method were used to reconstruct the threedimensional multi-scale vortex system in the pump wheel and turbine channel under braking conditions.The applicability of different vortex recognition methods was compared comprehensively from the aspects of reconstruction effect,threshold sensitivity and optional threshold range.The optimal vortex recognition method was selected to reconstruct the three-dimensional multi-scale vortex system in the pump wheel and turbine runner at rated conditions,extracted the structural characteristics of the vortex system,radial section flow field information and circumferential section flow field information,and analyzed the evolution law and dynamic characteristics of the multi-scale flow field of the fully filled hydrodynamic coupling from the perspective of time and space,so as to revealed the energy conversion mechanism.(2)Multi-scale vortex reconstruction and flow characteristics analysis of gasliquid two phase flow fieldThe Stress-Blended Eddy Simulation method was studied.The Mixture model was used to simulate the multiphase flow field under braking condition and rated condition with liquid filling rate of 80% and 40% respectively.Based on the theory and method of three-dimensional vortex identification,the three-dimensional vortex system reconstruction in the flow passage of pump wheel and turbine under two working conditions was studied.The structure characteristics of the vortex system,the evolution pattern of the vortex system and the influence of the liquid filling rate on the vortex system were analyzed.Through the analysis of the overall flow field,the circumferential section flow field and the interface flow field,the flow characteristics and energy transduction mechanism of the gas-liquid two phase flow field under the braking and rated conditions were revealed.(3)Construction of flow field visualization test system and identification method of flow field characteristic parametersThe visualization test system of flow field was constructed based on particle image velocity technology,and the calibration algorithm and graphic preprocessing method were researched to improve the calculation precision.The velocity and vorticity information of the flow field in full-charged braking conditions and rated conditions were extracted by the image cross-correlation algorithm.The precision of the numerical simulation was validated by the information,and the spatio-temporal evolution law of the multi-scale flow field and the energy loss mechanism were revealed through the multi-dimensional comparison analysis of the test and simulation. |
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