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  • 1
    Publication Date: 2004-12-03
    Description: The simulation of sound generation and propagation in three space dimensions with realistic aircraft components is a very large time dependent computation with fine details. Simulations in open domains with embedded objects require accurate and robust algorithms for propagation, for artificial inflow and outflow boundaries, and for the definition of geometrically complex objects. The development, implementation, and validation of methods for solving these demanding problems is being done to support the NASA pillar goals for reducing aircraft noise levels. Our goal is to provide algorithms which are sufficiently accurate and efficient to produce usable results rapidly enough to allow design engineers to study the effects on sound levels of design changes in propulsion systems, and in the integration of propulsion systems with airframes. There is a lack of design tools for these purposes at this time. Our technical approach to this problem combines the development of new, algorithms with the use of Mathematica and Unix utilities to automate the algorithm development, code implementation, and validation. We use explicit methods to ensure effective implementation by domain decomposition for SPMD parallel computing. There are several orders of magnitude difference in the computational efficiencies of the algorithms which we have considered. We currently have new artificial inflow and outflow boundary conditions that are stable, accurate, and unobtrusive, with implementations that match the accuracy and efficiency of the propagation methods. The artificial numerical boundary treatments have been proven to have solutions which converge to the full open domain problems, so that the error from the boundary treatments can be driven as low as is required. The purpose of this paper is to briefly present a method for developing highly accurate algorithms for computational aeroacoustics, the use of computer automation in this process, and a brief survey of the algorithms that have resulted from this work. A review of computational aeroacoustics has recently been given by Lele.
    Keywords: Acoustics
    Type: HPCCP/CAS Workshop Proceedings 1998; 9-14; NASA/CP-1999-208757
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  • 2
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    In:  CASI
    Publication Date: 2018-06-06
    Description: Computational aero-acoustics (CAA) requires efficient, high-resolution simulation tools. Most current techniques utilize finite-difference approaches because high order accuracy is considered too difficult or expensive to achieve with finite volume or finite element methods. However, a novel finite volume approach (Ultra HI-FI or UHF) which utilizes Hermite fluxes is presented which can achieve both arbitrary accuracy and fidelity in space and time. The technique can be applied to unstructured grids with some loss of fidelity or with multi-block structured grids for maximum efficiency and resolution. In either paradigm, it is possible to resolve ultra-short waves (less than 2 PPW). This is demonstrated here by solving the 4th CAA workshop Category 1 Problem 1.
    Keywords: Numerical Analysis
    Type: Fourth Computational Aeroacoustics (CAA) Workshop on Benchmark Problems; 423-430; NASA/CP-2004-212954
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  • 3
    Publication Date: 2019-07-13
    Description: This talk will provide an overview of the field of computational aero-acoustics and its use in fan noise prediction. After a brief history of computational fluid dynamics, some of the recent developments in computational aero-acoustics will be explored. Computational issues concerning sound wave production, propagation, and reflection in practical turbo-machinery applications will be discussed including: (a) High order/High Resolution Numerical Techniques. (b) High Resolution Boundary Conditions. [c] MIMD Parallel Computing. [d] Form of Governing Equations Useful for Simulations. In addition, the basic design of our Broadband Analysis Stator Simulator (BASS) code and its application to a 2 D rotor wake-stator interaction will be shown. An example of the noise produced by the wakes from a rotor impinging upon a stator cascade will be shown.
    Keywords: Acoustics
    Type: Computational Aero-acoustics As a Tool For Turbo-machinery Noise Reduction; Apr 18, 2003; Akron, OH; United States
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  • 4
    Publication Date: 2019-07-13
    Description: Computational aeroacoustics requires efficient, high-resolution simulation tools. And for smooth problems, this is best accomplished with very high order in space and time methods on small stencils. But the complexity of highly accurate numerical methods can inhibit their practical application, especially in irregular geometries. This complexity is reduced by using a special form of Hermite divided-difference spatial interpolation on Cartesian grids, and a Cauchy-Kowalewslci recursion procedure for time advancement. In addition, a stencil constraint tree reduces the complexity of interpolating grid points that are located near wall boundaries. These procedures are used to automatically develop and implement very high order methods (〉15) for solving the linearized Euler equations that can achieve less than one grid point per wavelength resolution away from boundaries by including spatial derivatives of the primitive variables at each grid point. The accuracy of stable surface treatments is currently limited to 11th order for grid aligned boundaries and to 2nd order for irregular boundaries.
    Keywords: Acoustics
    Type: NASA/TM-2000-210378 , E-12433 , AIAA Paper 2000-2006 , NAS 1.15:210378 , Aeroacoustics; Jun 12, 2000 - Jun 14, 2000; Lahaina, HI; United States
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  • 5
    Publication Date: 2019-07-13
    Description: The GMRES method is parallelized, and combined with local preconditioning to construct an implicit parallel solver to obtain steady-state solutions for the Navier-Stokes equations of fluid flow on distributed-memory machines. The new implicit parallel solver is designed to preserve the convergence rate of the equivalent 'serial' solver. A static domain-decomposition is used to partition the computational domain amongst the available processing nodes of the parallel machine. The SPMD (Single-Program Multiple-Data) programming model is combined with message-passing tools to develop the parallel code on a 32-node Intel Hypercube and a 512-node Intel Delta machine. The implicit parallel solver is validated for internal and external flow problems, and is found to compare identically with flow solutions obtained on a Cray Y-MP/8. A peak computational speed of 2300 MFlops/sec has been achieved on 512 nodes of the Intel Delta machine,k for a problem size of 1024 K equations (256 K grid points).
    Keywords: NUMERICAL ANALYSIS
    Type: NASA-TM-106449 , E-8302 , ICOMP-93-49 , NAS 1.15:106449 , AIAA PAPER 94-0408 , Aerospace Sciences Meeting and Exhibit; Jan 10, 1994 - Jan 13, 1994; Reno, NV; United States
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  • 6
    Publication Date: 2019-07-13
    Description: Objectives of this work are: (1) Assist the Science Mission Directorate in developing technologies for space missions. (2) Explore the capability of computational modeling to assist in the development of the Advanced Stirling Convertor. (3) Baseline computational simulation with available experimental data of the ASC. (4) Calculate peak external pressure vessel wall temperatures and compare them with anticipated values. (5) Calculated peak magnet temperature inside the ASC over a range of operational scenarios.
    Keywords: Spacecraft Propulsion and Power
    Type: E-17396-1 , IECEC-2010-17396 , 8th International Energy Conversion Engineering Conference; Jul 25, 2010 - Jul 28, 2010; Nashville, TN; United States
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  • 7
    Publication Date: 2019-07-13
    Description: NASA has been developing power systems capable of long-term operation in extreme environments such as the surface of Venus. This technology can use any external heat source to efficiently provide electrical power and cooling; and it is designed to be extremely efficient and reliable for extended space missions. Terrestrial applications include: use in electric hybrid vehicles; distributed home co-generation/cooling; and quiet recreational vehicle power generation. This technology can reduce environmental emissions, petroleum consumption, and noise while eliminating maintenance and environmental damage from automotive fluids such as oil lubricants and air conditioning coolant. This report will provide an overview of this new technology and its applications.
    Keywords: Electronics and Electrical Engineering
    Type: E-18245 , Institute of Electrical and Electronics Engineers Energy Tech 2012; May 29, 2012 - May 31, 2012; Cleveland, OH; United States
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  • 8
    Publication Date: 2019-07-13
    Description: NASA has begun the development of a combined Stirling cycle power and cooling system (duplex) to enable the long-lived surface exploration of Venus and other harsh environments in the solar system. The duplex system will operate from the heat provided by decaying radioisotope plutonium-238 or its substitute. Since the surface of Venus has a thick, hot, and corrosive atmosphere, it is a challenging proposition to maintain sensitive lander electronics under survivable conditions. This development effort requires the integration of: a radioisotope or fission heat source; heat pipes; high-temperature, corrosion-resistant material; multistage cooling; a novel free-displacer Stirling convertor for the lander; and a minimal vibration thermoacoustic Stirling convertor for the seismometer. The first year effort includes conceptual system design and control studies, materials development, and prototype hardware testing. A summary of these findings and test results is presented in this report.
    Keywords: Spacecraft Propulsion and Power
    Type: NASA/TM-2011-217018 , AIAA Paper 2010-6917 , E-17389-1 , 8th International Energy Conversion Engineering Conference (IECEC); Jul 25, 2010 - Jul 28, 2010; Nashville, Tn; United States
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  • 9
    Publication Date: 2019-07-12
    Description: As large airline companies compete to reduce emissions, fuel, noise, and maintenance costs, it is expected that more of their aircraft systems will shift from using turbofan propulsion, pneumatic bleed power, and hydraulic actuation, to instead using electrical motor propulsion, generator power, and electrical actuation. This requires new flight-weight and flight-efficient powertrain components, fault tolerant power management, and electromagnetic interference mitigation technologies. Moreover, initial studies indicate some combination of ambient and cryogenic thermal management and relatively high bus voltages when compared to state of practice will be required to achieve a net system benefit. Developing all these powertrain technologies within a realistic aircraft architectural geometry and under realistic operational conditions requires a unique electric aircraft testbed. This report will summarize existing testbed capabilities located in the U.S. and details the development of a unique complementary testbed that industry and government can utilize to further mature electric aircraft technologies.
    Keywords: Aircraft Propulsion and Power; Aircraft Design, Testing and Performance
    Type: NASA/TM-2016-219085 , E-19212 , GRC-E-DAA-TN30267
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  • 10
    Publication Date: 2019-07-13
    Description: Future air vehicles will increasingly incorporate electrical powertrains that require very tight integration of power, propulsion, thermal, and airframe technologies. This paper provides an overview of a new category of thermal energy conversion technologies that can be used to provide highly efficient turbo-generation and electric propulsion, while synergistically managing and recycling both the low grade waste heat from electrical components and the high grade waste heat from engine components.
    Keywords: Engineering (General)
    Type: GRC-E-DAA-TN57694 , AIAA/IEEE Electric Aircraft Technologies Symposium (EATS); Jul 12, 2018 - Jul 13, 2018; Cincinnati, OH; United States
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