Technical notes: Ramp shock regulation of supersonic inlet with shape memory alloy plate

Abstract

THE aeroengine inlet, or the air intake system, shows a considerable influence on a vehicle, especially in the flight performance aspect. When considering the efficiency of the longrange supersonic cruise vehicles, such as supersonic transports, the performance of the inlet system can account for 10-20% loss in range [1]. Thus, a well-designed inlet is quite necessary. The main concerns with the inlet design are total pressure recovery, mass flow ratio, and starting characteristics. The former two are directly related to the engine thrust and efficiency, whereas the last one determines the operating capability of the engine. To achieve a better total pressure recovery, the shock-on-lip (SOL) condition is often adopted at the cruise stage for a conventional supersonic inlet with fixed geometry. However, it suffers undesirable performance penalties at offdesign conditions because the shock angle varies with the upstream Mach number. In some occasions, a severe case named inlet unstart may occur. Thus, to obtain good performance over awide operating Mach number range, the control of the ramp shock system is needed. Multiple variable-geometry approaches have been widely studied and practiced in supersonic inlets, such as translating spike [2], rotating ramp and cowl lip, varying diffuser [3, 4], etc. Unfortunately, one major drawback of these methods is the heavy and complex structure, owing to the existence of indispensable regulating systems. By contrast, a driving concept for variable inlets, which is based on shape memory alloy (SMA), offers a clear advantage because it integrates the role of the sensors, actuators, and structures [5-10]. SMA had already been used for inlet regulation in the Smart Aircraft and Marine Propulsion System Demonstration (SAMPSON) program, which was funded by the Defense Advanced Research Projects Agency. Inthe SAMPSON program, the SMAwire bundles were used to rotate the compression surface of the full-scale F-15 fighter engine inlet instead of the traditional hydraulics control system [11, 12]. However, in the SAMPSON plan, the SMA bundles acted only as the actuator and the complex mechanical control system was still retained. More recently, The Boeing Company developed an active serrated aerodynamic device with SMA actuators, which is also known as a variable-geometry chevron. This device has been installed on a GE90-115B jet engine and proven to be effective in reducing noise during takeoff by maximizing the chevron deflection, as well as increasing the cruise efficiency by minimizing the chevron deflection during the remainder of the flight [13-15]. Inspired by Boeing's variable-geometry chevron, a new method based on a SMA plate to regulate the external ramp shock of a supersonic inlet is brought forward in this Note. The design method of the ramp profile and the implementation of the SMA plate are discussed. Also, the morphing behavior and the external ramp shock control effect of the SMA plate in a supersonic wind tunnel are demonstrated.