A Simulation On Internal Flow Field Of Variable Geometry Turbocharg Used In Diesel Engine

As an important part of diesel engines, the turbocharger affects on the tractive power,economical efficiency and the emission of a vehicle. With the increasingly attentions to theenergy saving and environmental protection, the variable geometry turbocharger (VGT)has been proposed and designed by some researchers based on the traditional ones. TheVGT, which can be used to adjust opening angle of the nozzle vane for satisfying differentworking conditions of a diesel, such as those of low-speed, high-speed and acceleration,has become one of the active topics in the area of diesel engineering.Focusing on a VGT used in a sample diesel, firstly, this thesis established a3-Dnumerical model of the VGT by using the CATIA software. According to the theory ofcomputational fluid dynamics (CFD), the CFX software is applied to simulate the innerflow fields of the volute under different parameters of the vane of nozzle ring. Thus, theflow movement characteristics inside the volute and the VGT matching problems arerevealed and discussed. Comparing the simulated and the tested results, an maximum errorless than ten percent suggests that the CFX simulation procesure is correct and feasible.The optimal height and length of the nozzle vane are determined by analyzing both theoutlet area variation of the nozzle ring and the distribution of inner flow field. Thesimulations under a fixed engine speed and different opening angle of the nozzle ring showthat, the outline of the scroll nozzle can be optimized by reducing the curvature variationsfrom the entrance to arc of the volute; an outlet optimization of the vane head may beconducted for cutting off its windward area; the vane with benting wings can be used torepress the gas stagnation occured in the volute, thereby, a lower loss of flow. Thesimulated results of six kinds of opening angle of the nozzle vane implies that, the openingangle of nozzle vane should be decreased and the turbine speed should be increased at lowspeed; the opening angle should be increased to prevent the over-speed phenomenon of theturbine occurred at high speed. Under the acceleration conditions, it is reasonable to adjust the opening angle to eliminate effects of the turbine delay.The approach adopted in this thesis can be extended to study any kind of turbocharger.And the above conclusions may be regarded as references for structure design and controlstrategy research of VGTs in the future.