Numerical study on the endwall flow of variable geometry turbine with adjustable flap and rotating envelope endwall

As an essential component of variable cycle engine, the variable geometry turbine plays an important role in regulating the flow rate, controlling the thrust and adjusting the thermodynamic cycle of the engine, which makes it one of the key technologies. However, the rotation of conventional adjustable guide vine leads to a substantial increase in endwall losses. Balancing flow rate regulation with loss suppression in variable geometry turbine presents a critical challenge demanding urgent resolution. This study employs three-dimensional flow field numerical simulation to focus on the endwall leakage flow in a variable geometry turbine with adjustable flap and rotating envelope endwall. The effects of adjustable flap and conventional adjustable guide vane on the flow field and aerodynamic performance of variable-geometry turbines are compared. Additionally, the effects of different adjustable flap angles on the performance and flow field of variablegeometry turbines are further analyzed. The conclusions are as follows: Compared to conventional adjustable guide vane, adjustable flap more effectively suppresses endwall leakage losses. However, within a specified angle range, adjustable guide vanes provide a broader flow regulation range. As the adjustable flap angle decreases, the turbine throat area reduces, leading to a corresponding decrease in the flow rate of the variable-geometry turbine. While the mass flow rate of the endwall increases with the decrease of flap angle, resulting in a gradual reduction in turbine efficiency. At the same time, changes in the flap angle have a large effect on the secondary flow structure of the turbine guide vane. With the decrease of the angle of the adjustable flap, the intensity of the original leakage vortex decreases, while the newly generated leakage vortex intensifies and gradually moves away from the original leakage vortex.