| The hydrodynamic retarder derived from fluid coupling is an important kind ofelement for hydrodynamic transmission , which has been widely used in the fieldsof braking and deceleration for vehicles and some facilities. In abroad, with thedevelopment and application of the automatic transmission, some in-depth researchand application of the hydrodynamic retarder has been developed. Equipped withthe hydrodynamic retarder, the performance of the running and manipulation of bus,tour coach, heavy carrying truck, tank and camion can be greatly improved. Theearlest devices of hydrodynamic transmission in our country appeared in 1950's.Now the hydrodynamic transmission has been paid more attention than before inour country.Some research on hydrodynamic retarder has been developed, whilethe technique is not perfect, and it is just beginning in China.There are two ways for the study of the internal flow field of hydrodynamicretarder , the test methods and the calculational methods. The purpose of this paperis simulating the internal three-dimension flow field of hydrodynamic retarder byusing the CFD software FLUENT, then the internal flow field can be achieved bysolving N-S equation directly. The braking torque is predicted on the base of theresult. The calculated results agree well with the test results. Because there aresome incomplete supposals for the software and fluid mechanics, many problemsstill need solving during calculating.The flow of fluid in the hydrodynamic retarder is three dimensional,incompressible and viscous. For the incompressible viscous flow, the continuityequation and momentum equation are called as Navier-Stokes equations, short forN-S equations. Reynolds averaging are the most basal method for simulating theturbulence. But in the Reynolds averaging equations, Reynolds stress made theequations unclosed, so the turbulent viscosity method is introduced, and then manyturbulence models are established to make the equations closed. Among them thek ?ε two-equation model is used widely, and then the control equations includetime averaging N-S equations and k ?ε turbulent equations. After comparison todifferent methods, Finite Volume Method is chosen to solve the equation, andUpwind method is the way to accomplish the space discretion. SIMPLE ,SIMPLEC and PISO are three strategies in the Press-Velocity Coupling Method.For this paper, the SIMPLE method is more favorable.The internal flow of the hydrodynamic retarder is very complex, so somesimplification and supposal are made before numerical simulation. First, thethree-dimension geometric model is finished by the UG soft, then the model isimported into GAMBIT to mesh and define the boundary conditions. The flow fieldis calculated by CFD software FLUENT. The sliding mesh theory is used duringthe simulation of unsteady flow, and the divided face of flow way is defined asperiodic boundary conditions.At last the distributing characteristic of the flow field in different rotate speedsis obtained. The results of simulation in different speeds are compared andanalyzed, and the braking torque of hydrodynamic retarder is also calculated, thenthe characteristic of braking torque is predicted. The results show that thecalculation of the braking torque which is about of 3D flow field is high precision.The calculated results agree well with the test results, and the most tolerance isonly 5%. The coherence of comparison show the calculated results is believable.The results of this paper is very valuable for the analysis of three-dimension flowfield in hydrodynamic retarder. On the base of that, some further research on thesimulation of hydrodynamic retarder can be well continued.
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