Nonabsorptive Silencing System for Stationary Test Facilities and Portable Ground Mufflers

The development of this nonabsorptive silencing system is the result of the maintenance problem encountered by the Air Force and aviation industry through the use of absorptive silencing systems in connection with noise reduction installations for turbo-jet, ram-jet, and rocket engines. The problem of keeping absorptive blankets, copper-wool, or stainless steel wool intact while exposed to a high velocity and high temperature exhaust gas stream is well-known and has been responsible for the high replacement costs of exhaust silencing systems. Nearly one year of engineering development time was devoted to model studies before a working model of a silencing system was obtained which is entirely dependent on configuration. Using only acoustic filters and resonators this silencing method demonstrates that high acoustic attenuation can be obtained without the use of absorptive materials. Special consideration was given to maintaining a low pressure drop at high velocities. Full scale and model data will be presented giving acoustic performance and pressure drop characteristics as well as comparative cost charts. The name of the new silencing system is Dura-Stack.