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Boeing is applying cutting edge smart material actuators to the next generation morphing technologies for aircraft. This effort has led to the Variable Geometry Chevrons (VGC), which utilize compact, light weight, and robust shape memory alloy (SMA) actuators. These actuators morph the shape of chevrons on a jet engine fan nozzle trailing edge in order to optimize acoustic and performance objectives at multiple flight conditions. We have completed a flight test of the VGC system on a Boeing 777-300ER with GE-115B engines. In this paper we describe the VGC design, development and performance during flight test. We demonstrated autonomous operation of the VGCs, which did not require a control system or aircraft power. The VGC concept demonstrated an exciting capability to optimize jet nozzle performance at multiple flight conditions. The VGC system provided a robust test vehicle to explore chevron configurations for community and shock-cell noise reduction. This capability was demonstrated with two examples of a parametric study which showed the influence of VGC configurations on community noise reduction and shock-cell generated cabin noise reduction during cruise.

Many investigators have successfully used acoustic or mechanical actuators to promote increased mixing in the initial shear layers of jets. Actuator designs for active noise control must be further refined to control the production of large scale turbulence and its contribution to the low frequency jet noise spectrum. Although many concepts reduce energy associated with large turbulence scales, a commensurate energy increase at smaller scales is often observed. Actuators better tuned to the flow and acoustic environment are needed if active flow control is to successfully negotiate this difficulty. This work focuses on the development of a numerical performance model to better understand the coupling between the actuators and the turbulent flow field. Los Alamos National Laboratory’s CFDLib provides the framework for our modeling effort. We have incorporated a “realizable” turbulence model, spatial filtering to better resolve the turbulent structures, and numerical sampling to generate time-averaged turbulence parameters. Performance predictions are presented for a cold, M=0.9 jet issuing from a nozzle fitted with 13 piezoelectric tab-type actuators. Comparisons of predictions with and without actuators demonstrate the potential benefit of this approach.

Boeing is applying cutting edge smart material actuators to the next generation morphing technologies for aircraft. This effort has led to the Variable Geometry Chevrons (VGC), which utilize compact, light weight, and robust shape memory alloy (SMA) actuators. These actuators morph the shape of chevrons on the trailing edge of a jet engine in order to optimize acoustic and performance objectives at multiple flight conditions. We have demonstrated a technical readiness level of 7 by successfully flight testing the VGCs on a Boeing 777-300ER with GE-115B engines. In this paper we describe the VGC design, development and performance during flight test. Autonomous operation of the VGCs, which did not require a control system or aircraft power, was demonstrated. A parametric study was conducted showing the influence of VGC configurations on shockcell generated cabin noise reduction during cruise. The VGC system provided a robust test vehicle to explore chevron configurations for community and shockcell noise reduction. Most importantly, the VGC concept demonstrated an exciting capability to optimize jet nozzle performance at multiple flight conditions.

Boeing has recently flight tested a Variable Geometry Chevron (VGC) system which used shape memory alloy (NiTinol) actuators to drive changes in shape. At take off, the VGCs immersed into the fan stream to reduce jet noise; at cruise they were actively morphed to investigate shock cell noise and performance losses. A set of three strain gages mounted on each chevron provided estimates of its tip position (shape) and feedback to the on-board control system. During the development of the VGC flight system, Luna Innovations instrumented two VGC test articles with shape probes, a new technology in which multi-core fiber provides distributed and axially co-located differential strain measurements to generate complex shape data. This technology shows promise of providing a more direct correlation of NiTinol actuation to chevron shape and tip immersion. Additionally, Luna Innovations instrumented each VGC with high density distributed strain fiber to provide hundreds of discrete strain measurements over the surface of the chevron.

Turbulent mixing of jet engine exhaust streams contributes significantly to airport community noise. Serrated aerodynamic devices along the trailing edge of exhaust nozzles, known as chevrons, have been shown to greatly reduce jet noise by promoting advantageous mixing of the streams. The design of these devices represents a delicate compromise between noise reduction at take off conditions, engine operability, and thrust loss at cruise. We report here the successful design and test of a full-scale variable geometry chevron for the fan-nozzle exhaust whose shape change is driven by a shape memory alloy actuator. The collected data supports the aerodynamic, thermal, and mechanical modeling of the chevron. The test results demonstrate that the device can operate autonomously and can reproducibly transition between take-off and cruise shapes. Having validated the concept, this data will facilitate the development of the next generation, variable geometry chevron.

A noise reduction system for use with an exhaust nozzle associated with a jet engine of an aircraft. The noise reduction system employs a plurality of flow-altering components disposed circumferentially about a lip portion of an exhaust nozzle. In one preferred form the flow-altering components each comprise piezoelectric transduction layers. The flow-altering components are caused to move in an oscillating manner by an AC signal applied thereto such that they move into and out of the exhaust gas emitted from the exhaust nozzle to achieve a desired degree of intermixing of the exhaust flow with the flow adjacent the exhaust nozzle. This produces a reduction in the noise generated by the jet engine. The noise reduction can be utilized during takeoff conditions of an aircraft. The flow-altering components are maintained out of the exhaust gas flowpath during cruise conditions of the aircraft so as not to cause a reduction of thrust, that would in turn result in an increase in the fuel burn during cruise conditions.

The results of a direct simulation of high-intensit y methane/air combustion are compared to previously reported measurements of OH and O atom concentrations in a jet-stirred reactor. The simulation uses a zerodimensional coalescence/dispersion model that requires only the initial reactor feed conditions, an appropriate chemical rate mechanism, and estimates of the fluid mixing time scales. Empirical time scales, determined by forcing agreement between simulation and experiment, are of the same order of magnitude as those estimated from either global fluid dissipation length and velocity scales or inviscid arguments based on reactor length and velocity scales. Simulations using these estimates satisfactorily represent the measured temperature and species profiles over a wide range of fuel-air equivalence ratios and, in direct contrast to perfectly stirred reactor predictions, show close agreement with the measured values near stoichiometric conditions. Nomenclature c = concentration C/D = coalescence dispersion L = reactor length scale M = total mass flow rate N = number of Monte Carlo particles TV = time rate of change of TV TV5 = number of time series samples P(c) = concentration probability density function P0(c) = reactor inlet stream concentration probability density function pdf = probability density function PSR = perfectly stirred reactor