Control characteristics of a two-dimensional jet based on movable Coanda wall deflection

Conventional mechanical thrust vectoring nozzles feature complex structures despite providing large jet deflection angles, whereas fluidic thrust vectoring offers a simpler structure but suffers from small deflection angles, control hysteresis, and sudden vector angle jumps. To address these limitations, a two-dimensional (2D) jet control device based on movable Coanda wall deflection is proposed, utilizing walls of different lengths to induce large-angle jet deflection. Experimental investigations are conducted to analyze the variation laws of the thrust vector angle and the underlying flow structures, providing the jet deflection control characteristics at various ratios (K) of the wall length to the jet exit height. Furthermore, the jet deflection characteristics under high-speed conditions and various Nozzle Pressure Ratios (NPRs) are captured using schlieren flow visualization. The experimental results demonstrate that during the forward and return deflection processes of the movable Coanda wall, the jet undergoes three distinct states: attachment, unstable fluctuation, and detachment. The wall length inherently affects the maximum deflection angles during jet detachment and reattachment. Specifically, at K=20°, a 3° hysteresis is observed, with the jet reaching a maximum deflection angle of 56°. As K decreases, the hysteresis gradually diminishes; at K=5, the hysteresis disappears completely, and a deflection angle of 42° is achieved. Under high-speed conditions at NPR=4.5, a wall-induced deflection angle of 31° can still be successfully realized.