SBIR-STTR Award

With improvements in high performance military jet aircraft engines and the increase in complexity of the exhaust systems the noise produced has become problematic. Reducing these noise levels, while maintaining overall system performance, has become the driving issue in new nozzle designs. This proposal will focus on nozzle designs of practical application that can be implemented on current high NPR engine configurations, such as chevrons (or serrations) cut into the trailing edge of the nozzle. In Phase I we will address the practical aspects of making the noise/performance tradeoff for high pressure ratio nozzles. Data will be collected on models in a subscale test facility and evaluated using near field holography and shadowgraph imagery to identify the source characteristics. This will aid development of both CFD and noise prediction algorithms in Phase II.

Benefit:
This work will result in an efficient test service to asses the noise/performance tradeoff of hign NPR exhaust nozzle systems. We expect to identify the generic characteristics of exhaust nozzles that can reduce takeoff noise without a significant performance penalty. This will aid engine manufacturers in inplementing new quieter engines.

Keywords:
Performance Measurement, Performance Measurement, high NPR, acoustic holography, subscale testing, Jet noise

With improvements in high performance military jet aircraft engines and the increase in complexity of the exhaust systems the noise produced has become problematic. Reducing these noise levels, while maintaining overall system performance, has become the driving issue in new nozzle designs. This proposal will focus on nozzle designs of practical application that can be implemented on current high NPR engine configurations, such as chevrons (or serrations) cut into the trailing edge of the nozzle. Phase I demonstrated that noise measurement can be conducted simultaneously with performance measurement in a thrust stand using a near field microphone array. Phase will focus on demonstrating that the near field acoustic measurement can be extrapolated to the far field using acoustic holography in the forward flight environment. Near field and far field measurements will be conducted simultaneously in high quality jet noise facility to demonstrate that the extrapolation process can provide sufficient detail for design purposes. This will allow future programs to be conducted with confidence with just the near field array in the thrust stand.

Benefit:
This work will result in an efficient test service to asses the noise/performance tradeoff of high NPR exhaust nozzle systems. We expect to identify the generic characteristics of exhaust nozzles that can reduce takeoff noise without a significant performance penalty. This will aid engine manufacturers in implementing new quieter engines.

Keywords:
Jet noise, Performance Measurement, subscale testing, acoustic holography, high NPR