Investigation On A Improved Laminar Kinetic Energy Transition Model

Laminar-turbulence transition and separation transition of boundary layer are the main flow state of blade surface in a turbine engine, and crucial factors for the performance of a gas turbine. Simulation and prediction transition accurately are the main content of modern flow field analysis and evaluation of a gas turbine, which have great guiding significance to the design of modern high-load (ultra-high-load) turbine. However, the process of disturbance development, as well as the interaction process of disturbance and boundary layer, are highly non-linear and complexity, and the physical mechanism has not been fully understood. At present, there is no mature turbulence model can simulate transitional flows accurately. But the laminar kinetic energy transition model is totally based on transitional phenomenon and local information, which satisfies modern complex three-dimensional flow and parallel computing, so it has great application prospects. In this paper, a laminar kinetic energy transition model is studied, and improved methods are proposed. The transition model is based on the concept of laminar kinetic energy and the k-ω turbulence model. In the model, the turbulent kinetic energy is divided into small-scale and large-scale by an effective length scale. The small-scale turbulent kinetic energy promotes the production of turbulent kinetic energy, and the large-scale turbulent kinetic energy promotes the production and development of laminar kinetic energy. Natural and bypass transition are modeled respectively by two productive terms, which have the opposition signs in the laminar and turbulent kinetic energy transportation equations. Because the transportation equations of the model has the same structure as the common one-and two-equation eddy viscosity model, the same numerical methods can be applied to solve the model. Moreover, the model can accurately calculate turbulent flows as same as the original two-equation turbulent model.The model is modified by adding the curvature factor and intermittency factor into the small-scale turbulent viscosity coefficient and turbulent viscosity coefficient. The ERCOFTAC T3series experiments, the double circular arc compressor cascade, the S809wind blade and the RAE2822transonic airfoil are used to test the new model. The numerical results indicate that the introduction of the intermittency factor in the turbulent viscosity coefficient can weaken the role of large-scale turbulent viscosity in the laminar region, and accelerate the transition process from laminar kinetic energy to turbulent kinetic energy. So the model’s ability of predicting bypass transition is improved. The new small-scale turbulent viscosity coefficient expression can increase the turbulence generation in separation zone, and improve the capability of simulating separation transition by means of the streamline curvature factor. But the simulation results of the S809blade and the RAE2822airfoil show that the model’s ability of simulation separation transition needs further research and improvement.