Design and control of a proof-of-concept variable area exhaust nozzle using shape-memory alloy actuators

Abstract

There is no reported research in the literature of using shape-memory alloy (SMA) actuators for variable area exhaust nozzles for a jet engine, to the authors' best knowledge. SMA actuators have the advantage of a high power-to-weight ratio and can result in dramatic weight reduction as compared to hydraulic systems. However, the difficulty of using SMA actuators for controlling variable area exhaust nozzles lies in the fact that the temperature near the exhaust nozzle is far higher than the transformation temperature of an SMA actuator. Due to the flexibility and small volume of SMA wire actuators, they can be remotely replaced in a region where the temperature is lower than that of its transformation temperature. By exploiting this fact, this paper presents a novel design of a proof-of-concept variable area exhaust nozzle using shape-memory alloy wire actuators. The SMA actuators are remotely placed away from the exhaust nozzle area so that the environmental temperature is below their transformation temperature. By electrically heating the SMA actuators, the exhaust nozzle will experience an area reduction of up to 40%. Bias springs will apply forces to return the exhaust nozzle to the open-up configuration. A feedback controller based sliding-mode method is used to regulate the SMA actuator position. Experimental results demonstrate that the proposed design meets the desired area variation specifications and shows the promise of a lightweight and simple exhaust nozzle design by using shape-memory alloy actuators.