JT8D Engine Internal Exhaust Mixer Technology Program.

This technology program was directed towards demonstrating the reduction in jet noise achieved by the use of an internal exhaust mixer. The effort focused on static engine acoustic testing of different mixer configurations suitable for JT8D-powered commercial aircraft. A series of 12 lobe mixers with different lobe geometries was evaluated for performance and acoustic characteristics. On the basis of test results, the final mixer configuration selected for JT8D-17-powered DC-9 aircraft showed a reduction in jet noise of 2.0 PNdB at static takeoff power with an attendant 0.3 percent improvement in fuel consumption. A second mixer configuration, define on a preliminary basis for JT8D-powered 727 aircraft, demonstrated a 4.7 PNdB reduction in jet noise at takeoff power. However, a penalty of 1.3 percent in fuel consumption was incurred, and this, combined with an incompatibility in the reverse thrust mode, indicated that significant additional development work is required to demonstrate a viable configuration for 727 aircraft. Testing was also successful in demonstrating the structural integrity of the mixer. In addition, the presence of the mixer did not impart any adverse interactive effects on the stress levels of other engine components. Author