Development of a SMA hybrid composite jet engine chevron concept

Abstract

Control of jet noise continues to be an important research topic. Exhaust-nozzle chevrons have been shown to reduce jet noise, but parametric effects are not well understood. Additionally, thrust loss due to chevrons at cruise suggests significant benefit from active chevrons. The focus of this study is development of an active chevron concept for the primary purpose of parametric studies for jet noise reduction in the laboratory and technology development to leverage for full scale systems. The active chevron concept employed in this work consists of a laminated composite structure with embedded shape memory alloy (SMA) actuators, termed a SMA hybrid composite (SMAHC). SMA actuators are embedded on one side of the bending axis of the structure such that thermal excitation generates a moment and deflects the structure. Two active chevron concepts are demonstrated; one that is powered to immerse and one that is powered to retract. A brief description of the chevron designs is followed by details of the fabrication approach. Results from bench-top tests are presented and correlated with predictions from a numerical model. Very repeatable performance is achieved with excellent agreement between predicted and measured results. Although the deflection requirement is not achieved in the presented results, the approach to meeting the performance requirement is evident.