Internal Mixer Investigation for JT8D Engine Jet Noise Reduction. Volume 1 Results.

A scale model experimental program was conducted to determine the noise reduction and the impact on propulsive performance that would result from installing a multi-lobed internal mixer on the JT8D engine. Long and short mixer designs were investigated. One-seventh scale mixer models, designed to permit lobe geometry variations, were fabricated and tested along with a model of the JT8D reference exhaust system. The test results indicated that, in general, the long and short mixers produced 3-4 PNdB reduction in Peak Perceived Noise Level relative to the reference exhaust system. Exhaust system performance, in terms of improvement in cruise thrust specific fuel consumption TSFC, and impact on takeoff thrust, was somewhat better for the long mixer than for the short mixer configurations. However, the short mixers offer significant advantages in terms of weight savings and minimized the hardware changes required for installation in the current JT8D engines. Based on the noise and performance test results in conjunction with the installation considerations, a short mixer design was recommended for evaluation in a full scale engine test.