Numerical Simulation And Improvement Of The Structure And Performance For Turbine Of A Ship Turbocharger

Turbocharger is a combined component used to increase pressure in diesel, a kind of turbo-machine, which consists of a turbine and a compressor and is installed at the flange of exhaust pipe.Nowadays, the requirement for exhaust-gas turbochargers is getting higher and higher. Security, reliability and high efficiency are the developing trends of modern turbocharger, through which the performance and quality of the diesel can be improved, whether for automotive diesel engines or marine diesel engines. And the total performance of a turbocharger lies on that of each component.In this thesis, based on the design requirements put forward by a company, an axial turbine used in ship turbocharger was designed by using pulse turbine method, and the calculated results are in close accord with experimental data, which indicates that the designed axial flow turbine can meet the company's requirements. Moreover, the numerical calculation and analysis platform was established for the axial turbine on the basis of actual geometrical model by using commercial CFD software-NUMECA, specially developed for turbo-machinery, and three- dimensional numerical study for the inner flow field of the axial turbine under designed condition was particularly investigated. In addition, the three-dimensional numerical study and analysis were also done respectively under the other two conditions with different rotational speeds and mass flow for examining the turbocharger performance under off-design conditions. The numerical simulation results are approximated to the experimental results under the three different working conditions, which indicates that the selection of the turbulent model and the related parameters are adapt to the numerical simulation of the turbocharger and can also express the flow condition of the turbocharger under both the design and off-design conditions. However, compared with the results under the design condition, the velocity distribution on the moving blade back deteriorates which causes the increase of the profile loss under off-design conditions.On the basis of the analysis and calculation above, flow passage structure of the axial turbine was partly improved and redesigned. By reforming the throughflow of the turbocharger, the isentropic efficiency has been increased by 2.36%...