Development of a Preliminary Model-Scale Adaptive Jet Engine Chevron

Abstract

Reduction of jet noise continues to be an important research topic. Exhaust-nozzle chevrons have been shown to reduce jet noise, but parametric effects, including immersion amount and azimuthal distribution, are not well understood. Additionally, thrust loss due to static chevrons at cruise suggests a significant benefit from deployable chevrons. The focus of this study is the development of an adaptive-chevron concept for the primary purpose of parametric studies for jet noise reduction in the laboratory and secondarily for development of technology that can be leveraged for full-scale systems. The adaptive-chevron concept employed in this work consists of a laminated composite structure with embedded shape memory alloy actuators. The actuators are embedded on one side of the middle surface such that joule heating of the actuators causes them to attempt recovery of prestrain, thereby generating a moment and deflecting the structure. A brief description of the chevron design is given followed by details of the fabrication approach. Results from bench-top tests are presented and correlated with numerical predictions from a model for such structures that was previously implemented in MSC.Nastran and ABAQUS. Excellent performance and agreement with predictions is demonstrated. Results from tests in a representative flow environment are also presented. Excellent performance is again achieved for both open- and closed-loop tests, the latter demonstrating control of deflection to a specified immersion into the flow. The actuation authority and immersion performance is shown to be relatively insensitive to nozzle pressure ratio. Very repeatable immersion control with modest power requirements is demonstrated.