Study on supersonic jet control with spoiler using Lagrangian coherent structures and dilatation gradient

Spoilers are widely used in rocket propulsion and turbine propulsion due to their maneuverability and ease of control. Since the traditional Euler frame can only describe the instantaneous state of flow fields, an improved method combined with Lagrangian coherent structures and dilatation gradient is introduced to analyze the change in flow field containing shock waves and the process of mass transport. First, the effects of spoiler inserted into the jet core of a thrust vector control system were studied. Subsequently, in order to reduce thrust loss and improve efficiency, the spoiler profile is optimized according to shock wave structures identified by finite-time Lyapunov exponent (FTLE) to dilatation fields. It is found that the vortex intensity near the nozzle wall gradually decreases with increase in the spoiler angle, and the intensity as well as the angle of oblique shock wave behind the spoiler gradually increases. Importantly, the thrust loss increases with the increment of angle, while the lateral force increases first but decreases subsequently. Moreover, according to the results using FTLE and dilatation gradient with different spoiler parameters, it is shown that the flow separation of the spoiler wall and the leakage flow of the spoiler gap are the key factors affecting spoiler performance. Consequently, the spoiler profile is optimized to reduce leakage flow and delay flow separation. Optimized spoilers can generate nearly the same lateral force, with only a maximum reduction of 5.89%, while reducing thrust loss up to 30%. In summary, the results obtained could be used to design one spoiler with higher aerodynamic performance.