The Prediction of Vibratory Stresses in Wall-Bounded Jets due to Unsteady Aeroacoustic Loading
Open Access
- Graduate Program:
- Acoustics
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- September 18, 2017
- Committee Members:
- Philip John Morris, Thesis Advisor
- Victor Ward Sparrow, Committee Member
- Kenneth Steven Brentner, Committee Member
- Keywords:
- acoustics
- turbulence
- jet
- noise
- deck
- vibratory
- stresses
- aeroacosutic
- claudio
- notarangelo
- acoustic
- Abstract:
- Aircraft noise emissions reduction has become a driving factor for competitive stealth aircraft design. One of the features of many stealth aircraft is a high aspect ratio rectangular nozzle that is mounted above the aircraft fuselage. This nozzle configuration allows the aircraft fuselage to shield the noise and other detectible properties generated by the jet engine. While this type of wall bounded jet produces a lower acoustic signature, it also introduces additional issues. The jet stream exiting the nozzle can travel at supersonic speeds and potentially generate shocks and expansion waves that impinge on the aircraft fuselage. Additionally, the turbulent eddies from the jet shear layer can impinge on the flight deck and produce additional unsteady forces on the aircraft. All of these forces can cause the deck to vibrate with a resulting decrease in the fatigue life of the structure. A coordinated project has been underway at the Pennsylvania State University in an effort to improve CFD predictions of unsteady aerodynamic loading generated by the exhaust of a rectangular jet on a deck downstream of the nozzle exit. Numerical simulations are conducted using Wind-US, a computational platform developed by the NASA Glenn Research Center and the Arnold Engineering Development Center. Parametric studies are carried out to investigate the effects of several numerical parameters, including time discretization, grid density, upstream forcing, turbulence dissipation and numerical schemes on the computed turbulent flow. The impact of a boundary layer shield on the Large-Eddy Simulation (LES) solution is also investigated. The numerical models included a boundary layer stability preservation technique which combined a time accurate solution with a constant CFL solution in the boundary layer to maintain numerical stability, independent of the boundary layer spacing. Results from the LES running with the boundary layer preservation scheme showed a 20-fold decrease in wall-clock time compared to the fully time-accurate simulations. Numerical predictions characterizing the structural loading on the deck surface are compared to experimental values measured at the United Technology Research Center (UTRC). A proper orthogonal decomposition (POD) method is applied to several of the CFD solutions to provide further insight into some of the non-physical behaviors found in the LES simulations running with the boundary layer stability preservation algorithm. Sub-scale experiments of wall bounded jets are designed and run in the Penn State high speed noise facility with the purpose of furthering the understanding of the unsteady pressures on a plate over which a turbulent jet is exhausting. A patch-and-scan nearfield acoustic holography technique (NAH) is attempted to reconstruct the cross-spectra and cross-correlations of the wall-pressure fluctuations on the flight deck.