Acoustic Performance Of An Advanced Model Turbofan In Three Aeroacoustic Test Facilities

Author : Adrian Sescu
Publisher :
ISBN 13 :
Total Pages : 271 pages
Book Rating : 4.:/5 (779 download)

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Download or read book Towards Computational Aeroacoustics Prediction of Realistic Turbofan Broadband Noise Using Synthetic Turbulence Modeling written by Adrian Sescu and published by . This book was released on 2011 with total page 271 pages. Available in PDF, EPUB and Kindle. Book excerpt: The prediction of broadband noise radiating from realistic turbulent flows interacting with complex geometries, using nonlinear time-domain algorithms, is still in infancy. The main obstacle is related to the computational efficiency--both in terms of processing time and storage capacity--but equally important is the accuracy of imposing realistic turbulence superposed on deterministic vortical gusts at the inflow boundary, or the initiation of the solution with a realistic turbulent flow. The main objective of this thesis is to derive a divergence-free synthetic turbulence model, and to impose turbulent wakes at the inflow boundary, for the prediction of broadband noise radiating from the interaction between rotor wakes and stator vanes in a realistic bypass turbofan engine. The tool is an advanced Computational Aeroacoustics code, NASA Broadband Aeroacoustic Stator Simulation (BASS) code, which employs state-of-the-art spatial and temporal schemes, and accurate boundary conditions. A number of synthetic turbulence models have been implemented in BASS code, including a new divergence free model based on the assumption that turbulence can be considered as a superposition of random eddies satisfying certain conditions. The divergence free condition is satisfied by using a streamfunction which is a scalar in two dimensions and a vector in three dimensions, and the momentum equations linearized about the mean flow. The synthetic turbulence model uses the statistics from the experimental turbulent data taken from NASA Source Diagnostic Test rig. The thesis also includes the derivation and analysis of the multidimensional finite difference schemes designed to improve the isotropy of waves propagating in multidimensions. The dispersion properties of the schemes in multidimensions are analyzed using Fourier analysis, and the isotropy error is found to be very low. The stability of the multidimensional schemes in combination with either linear multistep time marching methods and Runge-Kutta schemes are extensively analyzed. Various test cases in two or three dimensions show that the multidimensional schemes have low isotropy error, and perform more efficiently when compared to corresponding conventional schemes. The thesis begins with a thorough introduction on turbofan broadband noise prediction techniques, including a comprehensive literature review on turbofan noise and synthetic turbulence modeling. In chapter 2, an overview of Computational Aeroacoustics is included, with a description of actual fields of research, and available tools and techniques. Here, the derivation and analysis of multidimensional finite difference schemes in terms of isotropy error and stability are also included. In chapter 3, the nonlinear time-domain analysis tool, BASS code, is described, and the description and derivation of the new synthetic turbulence model are included. Chapter 4 is reserved to various results from different tests cases, and chapter 5 to comments, conclusions and remarks on future directions related to the research in this thesis.