Noise Characteristics of a Four-Jet Impingement Device Inside a Broadband Engine Noise Simulator
Speaker: Christoph Brehm, Science & Technology Corporation / Applied Modeling and Simulation Branch, NASA Ames Research Center
Presentation
Abstract
The noise generation mechanisms for four directly impinging supersonic jets are investigated employing implicit large eddy simulations with a higher-order accurate weighted essentially non-oscillatory shock-capturing scheme. Impinging jet devices are often used as an experimental apparatus to emulate a broadband noise source. Although such devices have been used in many experiments, a detailed investigation of the noise generation mechanisms has not been conducted before. Thus, the underlying physical mechanisms that are responsible for the generation of sound waves are not well understood. The flow field is highly complex and contains a wide range of temporal and spatial scales relevant for noise generation. Proper orthogonal decomposition of the flow field is utilized to characterize the unsteady nature of the flow field involving unsteady shock oscillations, large coherent turbulent flow structures, and the sporadic appearance of vortices in the center of the impingement region. The causality method based on Lighthill’s acoustic analogy is applied to link fluctuations of flow quantities inside the source region to the acoustic pressure in the far field. It will be demonstrated that the entropy fluctuation term in the Lighthill’s stress tensor plays a vital role in the noise generation process. Consequently, the understanding of the noise generation mechanisms is employed to develop a reduced-order linear acoustic model of the four-jet impingement device. Finally, three linear acoustic four-jet impingement device models are used as broadband noise sources inside an engine nacelle and the acoustic scattering results are validated against far-field acoustic experimental data.
Biography
Christoph Brehm joined the Science & Technology Corporation (STC) / Applied Modeling and Simulation branch at NASA Ames in 2012. He has been working in the LAVA group with special emphasis on higher-order shock-capturing schemes, immersed boundary methods, fluid-structure interaction and acoustics. He received a B.S./M.S. equivalent degree at the University of Stuttgart (Germany) and a Ph.D. at the University of Arizona under the supervision of Professor H.F. Fasel working on active flow control, immersed boundary methods and transition research.