The Numerical Simulation Of Turbine Non-steady Characteristics Under Pulse Flow Conditions

As the increasingly stringent emission regulations and the growing energy crisis, turbocharger has become the key technology to save energy and reduce emission for the vehicle engine. Recently, pulse turbocharging system is widely used. The design, calculation and experiment of turbine are carried out under steady flow condition. In fact, the flow of the gas in the turbine under pulse flow condition is highly unstable. The performance of the turbine under pulse flow condition deviates greatly from that of steady condition. In order to realize the better design of the turbine and the accurate matching with ICE, it is necessary to study the unsteady characteristics of turbine under pulse flow conditions.The unsteady characteristics of turbine under pulse flow conditions is studied by the numerical simulation software named Numeca in this paper. The working process of the studied engine is calculated using the numerical simulation software named AVL Boost. Turbine inlet parameters are gotten as boundary condition of the numerical simulation of non-steady-state characteristics for turbine. The calculation results and the experimental results are compared to prove the feasibility of this method.Steady-state calculation is investigated firstly in order to understand the steady performance of turbine and which results are used as the initial solution of the numerical simulation of non-steady characteristics of turbine. And the turbulence model is determined then the non-steady characteristics of turbine are calculated. The results show that in a pulsed cycle turbine flow mass and isentropic efficiency relative to the expansion ratio change into "ring-like" which is typical. This paper proposes a new calculation method to calculate the transient efficiency of turbine which uses the unit quality fluid micelle as the studied object. In order to ensure the import and export parameters of turbine is belonging to the same fluid particles, the export parameters calculated are corrected by phase shift, then the turbine transient efficiency are calculated renewedly. Turbine’s flow and work capacity are analyzed from the circle average view. This paper proposes a new calculation method of flow mass weighted average to calculate the turbine circle average efficiency. Compared with the steady calculation, the turbine transient cycle average flow mass and efficiency is lower, but the transient cycle average unit quality work is higher. This paper selects six characteristic time of a pulsed cycle and the turbine flow fields are analyzed to find the reasons.