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This paper investigates the dominant noise components of a full-scale high performance tactical aircraft. The present study uses acoustic measurements of the exhaust jet from a single General Electric F414-400 turbofan engine installed in a Boeing F/A-18E Super Hornet aircraft operating from flight idle to maximum afterburner. The full-scale measurements are to the ANSI S12.75–2012 standard employing about 200 microphones. By comparing measured noise spectra with those from hot supersonic jets observed in the laboratory, the dominant noise components specific to the F/A-18E aircraft at different operating power levels are identified. At intermediate power, it is found that the dominant noise components of an F/A-18E aircraft are essentially the same as those of high temperature supersonic laboratory jets. However, at military and afterburner powers, there are new dominant noise components. Their characteristics are then documented and analyzed. This is followed by an investigation of their origin and noise generation mechanisms.

Recent improvements in the algorithms and associated processes have resulted in significant improvements in the users’ ability to obtain aeroacoustics analysis of hot supersonic jets in a timely manner using only moderate computational resources. This paper discusses these approaches using the example of the Compressible High Order Parallel Acoustics (CHOPA) solver. The fundamental strategy looks to balance computational expense with the accuracy required to predict the most important effects. The objective is to resolve the larger eddies accurately, but exchanges the resolution of fine turbulent structures in return for decreased computational resource requirements. These strategies continue to be developed, along with the corresponding software. As the work progresses, the team expects additional improvements in the near future.Copyright © 2013 by ASME

High-fidelity large eddy simulation (LES) is used to investigate the source of crackle noise generated heated supersonic jets. Crackle is associated with intermittent N-shaped acoustics waves consisting of a sudden compression followed by a more gradual expansion, and is extremely irritating to human auditory perception. Results from four different simulations of jets produced by an experimental military-style nozzle reveal that N-shaped waves are generated directly by the jet turbulence, and thus nonlinear propagation effects are not a necessary component of their formation. Different operating points for the simulations were chosen such that jet velocity and jet temperature were varied independently. While crackle levels are sensitive to jet velocity, full field pressure skewness results suggest that increasing temperature may also play an independent role in enhancing crackle. The structure of the crackle source in the most strongly crackling jet is investigated by a backtracking algorithm applied to the simulation resulting in conditional averages.

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, “The Effect of Chevrons on Crackle—Engine and Scale Model Results,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.

GE and the USN continue to work together to find and develop practical techniques to reduce jet noise on tactical aircraft such as the F/A-18 E/F/G. Noise is an important issue for the Navy because of the harsh acoustic environment induced during operations of these aircraft on aircraft carriers and the impact to communities around Naval Air Bases and training sites. The noise generated by these systems is predominantly the noise generated by the exhaust plume due to the low bypass ratio of the engine and very high exhaust jet velocities. The main components of this jet noise are the jet mixing, shock and crackle noise. The present paper reports on progress, following Reference [1] with the F/A-18 E/F/G jet noise reduction program, which is currently focused on the USN near term goal of up to 3 dB reduction in the peak directivity direction. This goal also includes the reduction of the shock and crackle noise components. These goals are currently being pursued with nozzle plume mixing enhancement employing mechanical chevrons. These chevrons can be incorporated in the production version as a redesign of the F414 nozzle seals and do not involve the introduction of additional parts to the nozzle. This paper focuses on the effect of chevrons on the crackle noise component both in full scale on the F404 engine, and in small scale on the F414 engine nozzle in the twin configuration. The paper aims to make the case that this effect, which was first observed during ground engine testing of prototype chevrons, is a beneficial one in reducing/eliminating crackle which continues to be prevalent in high performance tactical aircraft engines today.Copyright © 2011 by ASME

Noise from high performance military fighter aircraft impacts the hearing and performance of personnel working near these aircraft and can be a source of annoyance to people living near airbases, airports 1 , and ranges where these aircraft are operated. Developers and operators of these aircraft must report the noise produced in communities as part of the NEPA (National Environmental Policy Act of 1974) process. Additionally, overexposure of personnel to high levels/durations of noise can result in permanent hearing loss, the number one veteran disability in the United States, and negatively impact voice communication capability. Additionally, the widely varying techniques used to acquire aircraft noise data make comparisons of aircraft noise and noise reduction technology performance more difficult.

This paper extends earlier research in numerical analysis and computational fluid dynamics (CFD) to obtain a novel finite element method for transient 3-D incompressible Navier-Stokes equations, along with efficient, parallelizable algorithms to cary out an implementation of the method in such a fashion as to be useful in mainstream industrial settings. The approach is based on a flexible operator-splitting technique due to one of the authors that allows the introduction of increasingly complex physics one step at a time. The approach should also allow treating potential flow, Euler flow, and Navier-Stokes flow simultaneously in different parts of the flow region. Parallelization is achieved through domain decomposition techniques. A new type of Eulerian time discretization is employed to increase accuracy and maintain computational efficiency. This new finite element procedure employs alternating-direction operator splittings in conjuction with Strang-type splittings to model problems of increasing complexity in a step-by-step and natural manner. Later, it can be extended to include additional operators e.g. for turbulence modeling, chemical reactions, etc. In addition to being practical from the standpoint of software design and of engineering analysis, its development and implementation allows the use of specialized numerical methods for the solution of each phys

Le schema est base sur la resolution des equations d'ecoulement potentiel pour des blocs individuels representant des sous-volumes du champ d'ecoulement

A block-structured solution scheme is developed for the solution of Euler equations for steady three-dimensional transonic flows*. The Euler equations are expressed in terms of Clebsch variables w = v + Svn. The resulting set of equations for conservation of mass, entropy (5) and the Clebsch variable j\ are solved using a block-based relaxation scheme. The flowfield is divided into a series of individual blocks representing local regions of the flowfield. The employed grid generation scheme provides local refinement of each block yet ensures one-to-one matching of grid points on the surfaces of adjoining blocks. For each of the blocks, either potential or Euler equations can be solved. For every block, the conservation of mass equation is solved to determine . For blocks with rotationality, two additional equations for determining S and T\ are solved. In this paper, the basic steps of the developed solution scheme are presented. The computational considerations involved in utilizing the present scheme are demonstrated for several two-dimensional sample problems.

A finite element grid generation scheme is presented. This scheme was developed particularly for generating computational grids for complex three-dimensional configurations . It provides simple numerical tools for automatically generating grids for a three-dimensional geometry. It also allows the user to control the description of appropriate grids for particular flow regions. It is based on a block structure for both the definition of the geometry and the generation of the grid. The user constructs the grid gradually with increasing details and can interactively make modifications on an existing grid with minimum restrictions. In this paper, the applications of the developed grid generation scheme are provided for a wing-body combination and for a more complex aircraft configuration.