Design and Control of a Morphing Chevron for Takeoff and Cruise Noise Reduction

Abstract

‡Commercial high-bypass ratio turbofan engines generate high levels of noise as the jet exhaust mixes with the ambient air. Serrated aerodynamic devices, known as chevrons, positioned along the trailing edges of a jet engine’s primary and secondary exhaust nozzle have been shown to reduce jet noise at take off as well as shock-cell noise at cruise. Their optimum shape is a finely tuned compromise between noise-benefit and thrust-loss. We report here the development of a powered variable geometry chevron (PVGC) capable of transitioning between take off and cruise shapes. Actuators composed of thermally active nickel-titanium (NiTinol) shape memory alloy drive the shape change. A full scale PVGC was tested under representative flow conditions in Boeing’s Nozzle Test Facility (NTF). In this test a simple proportional-integral control system provided continuous control of the VGC tip immersion between take off and cruise conditions. The collected data supports the aerodynamic, thermal, and mechanical design of the PVGC as well as the control system approach.