Technologies for Suppression of Screech

A passive screech suppressing augmentor liner concept is proposed to absorb acoustic energy at frequencies below 1 kHz. Acoustic, or screech, liners have historically been designed to affect modes whose frequencies are greater than 1 kHz. Liners have proven to be a cost effective and lightweight way to control screech modes above 1 kHz, but they are impractical for lower frequencies. The proposed screech suppressing liner concept absorbs screech modes below 1 kHz using a mechanical spring-mass-damper system integrated within the liner design. This is provided through use of floating liner panels installed in the augmentor using spring retainers in a manner that allows them to resonate at the desired frequency. Damping, provided through use of metal foam in a constrained layer viscoelastic damper, absorbs the acoustic energy, thereby attenuating the pressure oscillations that lead to screech. This Phase I program will evaluate the proposed concept, develop a conceptual configuration, compare it to several other potential integration approaches, and verify feasibility of the concept through cold flow tests that utilize existing SPIRITECH hardware to save costs. The Phase II program will further develop the concept through a detail design and hot flow testing. BENEFIT: This SBIR effort (Phases I and II) will result in the development and demonstration of a new acoustic damping approach that will work in concert with current acoustic liners to address lower frequency screech phenomena. This is needed due to the potential for significant structural damage and/or performance degradation in future advanced afterburner designs, where non-axisymmetric exhaust ducts may be required. Specifically, the earliest immediate application is for the 6th generation fighter engine, where a radical redesign of historical afterburner architectures may be required to address low observables challenges. Several additional government programs could benefit from this technology, including RATTLRS, Supersonic Cruise Missiles, UAV/UCAV Aircraft, and Hypersonic Aircraft with TBCC propulsion. These near-term applications suggest the need for immediate government funding to transition results of Phase II to a product with specific application to the 6th generation engine for use in a future multi-role fighter. Beyond these needs, there is also potential for application to future commercial space transportation vehicles.