The Analysis Of Flow Field In A Scroll For The Turbocharger Of Truck Engine

Nowadays the request of the energy and environmental protection makes the adoption of turbo in diesel engine become a big trend. The air flow in turbine scroll has great influence to the function of turbine. A scroll reasonably designed has low loss and uniform airflow in nozzle outlet and has no phenomenon of reflux, eddy, abrupt inflation etc, and airflow from which has small impact. These advantages not only increase the efficiency of the supercharger but also help to extend the life of the impeller. Therefore, the overall and meticulous research in the flow field of volute is very necessary. But, presently, the design of turbine scroll still based on one-dimensional flow assumption that the flow field of nozzle is evenly distributed along the circle. Fluid loss is estimated using empirical formulas. As the complex shape and viscous flow, the flow in turbine scroll is three-dimensional and the non-stationary. Since gas viscosity, the boundary layer flow will be created in the wall surface ,which develop along the air flow in the turbine scroll as a blocking role. As a result, there are different mass-flow and different angle.In this paper, a new method has been used to study Turbocharger volute based on the analysis of the volute in the domestic and abroad. In this research we take not only the engine condition but also the flow field of turbine wheel into consideration that effect on volute. Fluent software is used to simulate and calculate the 3D constant flow field of the turbine scroll. In order to study the flowing circumstance which entrance conditions such as mass-flow, temperature and pressure were changed with the engine mode. At first, Pro/e software is used to create the 3D model of turbine scroll. And then, the model input Gambit software to mesh meshes and to create boundary. Then the software Fluent is used to simulate steady flow in different engine operating conditions. The results from the analysis are as follows: the value of boundary coming from the simulation coincides with the value from test, so it is feasible to simulate turbine scroll with Fluent; in different conditions of engine there are different distribution of pressure and velocity, but there is not obvious difference distribution of temperature; there also are different distribution of nozzle velocity in different engine mode. Due to bypass valve opened in the high speed the regional jet speed and pressure significantly less than the medial region.An improvement on the original turbine scroll is to change tongue from one by one inlet into simultaneous inlet. Compared the results of the new turbine scroll and the old one, we found that the entropy efficiency of the new turbine scroll is higher than it of the old one. At the same time, distribution of pressure and velocity became more evenly, which reduces the flow resistance and improves the efficiency of the turbine scroll.Research the mutual influence between the flow field of turbine wheel and the flow field of turbine scroll. Through studying the reaction of turbine in different engine operating conditions, we found that the reaction of turbine reduce with the increasing of engine speed. Studying the flow field of turbine housing with and without impeller under the 1600r/min engine speed condition, we found that impeller has a little influence on the flow field of turbine scroll. So we can simulate the flow field of turbine scroll without considering the influence of impeller under moderate accuracy requirement.Studying how the nozzle width influences on the flow field of turbine scroll. Under 1600r/min engine speed conditions, respectively study the original width nozzle, the width 10% reduced nozzle and 20% reduced nozzle without the impeller, by analyzing the results we found the air angle becomes evenly with nozzle width decreases, but it began to deteriorate when the value decreases sequentially.Studying how bypass valve influences on the flow field of turbine scroll when it is on and off. By comparing the simulation results, we can draw follow conclusion: to dual-channel turbine scroll, bypass valve influences on the lateral flow field significantly, which can reduce the inlet pressure and help the exhaust flow out from cylinder to a large extent; the opening of bypass valve can reduce the average velocity, but make the velocity distribution very uneven, which may be caused the injury of impeller.Primarily research the 3-D inconstant flow field of turbine scroll. Through thermodynamic process simulation of a diesel engine using AVL BOOST software, we can get mass-flow, temperature and pressure in entrance of volute, which changes with the crank-angle, set these parameters as the boundary conditions of 3-D inconstant flow field calculation inside the scroll we take the simulation computing. Then could get the distribution trend like the trend in constant flow field, thus validate the feasibility that research the instant state of volute flow field by using fluent software.Through the work of this paper we can conclude: it is feasible to use fluent software to carry on the simulation of volute flow field; the results indicate that distribution trend of temperature, pressure and velocity matches air dynamics; streamlines of the gas in scroll approximate log spiral; abnormal flows founded in flow field and curves of the scroll need to be optimized.