Baseline Noise Measurements from the Engine Validation of Noise and Emissions Reduction Technology Program

Abstract

The Engine Validation of Noise and Emissions Reduction Technologies is a test program in which NASA funded engine validations of integrated technologies that reduce aircraft engine noise. These technologies address the reduction of engine fan and jet noise, and noise associated with propulsion/airframe integration. As part of this program, an extensive set of far field noise data was taken to characterize the noise sources of Honeywell’s TECH977 engine. Baseline characterization of this engine included the use of inlet and exhaust barriers for noise shielding. These results showed that the transition from inlet-radiated to aft-radiated noise occurs at a polar directivity angle of 70° to 80° from the inlet and provide a peak noise attenuation approaching 10 dB for the inlet and 20 dB for the exhaust. Treatment sensitivity testing showed that the incremental benefit of additional treatment reduces as the liner length increases. The axial extent of acoustic treatment is a key design parameter for the acoustic attenuation. Comparisons were made between separate flow and mixed flow nozzle exhaust configurations. At the sideline condition, the separate flow nozzle has higher noise levels than the mixed flow nozzle for directivity angles greater than 120 degrees. In addition, the separate flow nozzle has higher noise levels for directivity angles from 60 to 90 degrees at the sideline condition due to an increase in the inlet radiation of the blade passage tone. Turbine noise is better attenuated with mixed flow nozzle exhaust. Smaller reductions in jet noise with the mixed flow nozzle were seen at the cutback and approach operating conditions. Comparison of the pretest predictions with the measured far field data from the baseline testing identified the need for improvements in all source prediction models; however, the prediction methods were a useful tool in performing noise source separations.