American Institute of Aeronautics and Astronautics 1 Jet Aircraft Propulsion Noise Reduction Research at University of Cincinnati Olaf Rask * , Seth Harrison † , David Munday ‡ , Chris Harris § , Dr. Mihai Mihaescu ** and Dr. Ephraim Gutmark †† University of Cincinnati, Cincinnati, Ohio, 45221 The University of Cincinnati has an active Aeroacoustics program studying the application of several flow control technologies to typical separate-flow exhaust systems like those found on modern jet engines. The University of Cincinnati Aeroacoustic Test Facility (UC-ATF) includes a high fidelity model of such an exhaust system with interchangeable hardware allowing the simulation of medium- and high-bypass geometries and the application of various nozzles with different technologies to reduce the generated noise. Various chevron geometries, steady and pulsed blowing, and other approaches are tested and evaluated. Those technologies which show merit are then selected for further test in collaboration with our industrial partners at GE Aviation and GE Global Research. Testing at GE allows larger scale and improved fidelity. This testing pipeline allows further down- selection path to full-scale engine tests for the best technologies. In this way UC contributes to the missions of our industrial partners while advancing the state of knowledge regarding jet noise reduction technologies. Nomenclature D eq = Equivalent diameter M = Mach number NPR = Nozzle pressure ratio OASPL = Overall sound pressure level SPL = Sound pressure level St = Strouhal number I. Introduction IRCRAFT noise is a significant concern to those who live near any large airport. As the volume of air traffic increases, so does the impact on those increasing numbers who live near our busy airports. The regulatory response to limiting aircraft noise is embodied in Federal Aviation Regulation (FAR) Chapter 36 in the Unites States and in International Civil Aeronautics Organization (ICAO) Annex 16 elsewhere which impose limits which become increasingly stringent with time. Manufacturers of aircraft and aircraft engines face the technical challenge of making aircraft simultaneously quieter, more powerful, and more efficient. The conflicting requirements of these goals motivate the present research, which seeks to apply flow control to one source of aircraft noise in a manner that will yield acoustic benefit while minimizing the impact on performance. 1 One of the more significant sources of aircraft noise in modern jet aircraft is the turbulence generated in the shear layers around the engine’s exhaust. For the separate flow exhaust designs common on large commercial aircraft there are two such shear layers generating noise, the inner and outer shear layers. The inner shear layer is the layer between the primary, or core flow, and the secondary, or fan flow. The outer shear layer lies between the secondary flow and the freestream. At any useful operating condition we will have a significant shear velocity across one or both of these shear layers. These shear layers are unstable and the instabilities lead to vortex rollup * Graduate Student, Aerospace Engineering, rasko@email.uc.edu, AIAA Student Member. † Graduate Student, Aerospace Engineering, Seth.Harrison@uc.edu, AIAA Student Member. ‡ Graduate Student, Aerospace Engineering, david.munday@uc.edu, AIAA Student Member. § Graduate Student, Aerospace Engineering, aeroharris@fastmail.fm, AIAA Student Member. ** Research Assistant Professor, Aerospace Engineering, mihai.mihaescu@uc.edu , AIAA Member. †† Professor, Ohio Eminent Scholar, Aerospace Engineering, ephraim.gutmark@uc.edu, AIAA Associate Fellow. A