Abstract: Abstract: Hydrodynamic coupling is used for power transmission in heavy duty drives, such as power stations, ship propulsion, band conveyers, mills, and larger transport vehicles. Their hydrodynamic principle enables a low-wear torque to convert from a drive to a load. The flow in a hydrodynamic coupling is one of the most complex problems encountered in engineering fluid mechanics. The external performance of hydrodynamic coupling is determined by its internal distribution of flow field. It is very important to make a deep research on the internal distribution of flow field for the performance improvement and structural optimization in the design of hydrodynamic coupling. Numerical simulation is a main way to study the internal flow field of hydrodynamic coupling. The results of numerical simulation that are calculated by different turbulence models are quite different. In order to obtain accurate and reliable results of numerical simulation, it is a key to choose a reasonable turbulence model. The integrated computer engineering and manufacturing (ICEM) software was used to mesh the whole flow channel model of hydrodynamic coupling by hexahedral grids, and the total mesh number was 470 944 and the number of nodes was 521 887. Numerical simulation of three-dimensional unsteady turbulent flows in hydrodynamic coupling was carried out by numerically solving the Navier-Stokes equations in a rotating coordinate system. In order to analyze the applicability of different turbulence models in the calculation of flow field in hydrodynamic coupling, 3 different turbulence models (standard k-ε model, detached eddy simulation model, large eddy simulation model) were chosen to simulate the internal flow field of square cavity hydrodynamic coupling under braking condition. The quantity and quality of mesh was consistent during the numerical simulation of different turbulence models. The velocity field and vorticity field of radial section in hydrodynamic coupling were simulated and extracted through ANSYS CFX software. In addition, the transparent prototype of hydrodynamic coupling was manufactured and used in the complex flow test experiment, the internal flow field of hydrodynamic coupling under braking condition was tested based on particle image velocimetry (PIV), the characteristics of flow images were extracted by image processing technique, and the velocity field and vorticity field of radial cross-section were calculated by image cross correlation algorithm. Then numerical simulation and PIV experimental results were compared. The PIV test results were used as the evaluation criteria, and the differences of numerical simulation results by 3 kinds of turbulence models were analyzed. Moreover, the applicability of 3 turbulence models was analyzed. The results showed that the simulation results by standard k-ε model were far different from PIV experimental results, the distribution of flow field in main flow region simulated by the large eddy simulation model was much more real than others, the simulation results could be used to explain the law of multi-scale vortex movement and the mechanism of energy dissipation in the main flow region, and the high-gradient flow field distribution of near-wall area and corner area could be captured more accurately by the detached eddy simulation model. The results of analysis will provide a basis for accurate calculation of flow field and performance prediction of hydrodynamic coupling.