79 research outputs found

    NAS Technical Summaries, March 1993 - February 1994

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    NASA created the Numerical Aerodynamic Simulation (NAS) Program in 1987 to focus resources on solving critical problems in aeroscience and related disciplines by utilizing the power of the most advanced supercomputers available. The NAS Program provides scientists with the necessary computing power to solve today's most demanding computational fluid dynamics problems and serves as a pathfinder in integrating leading-edge supercomputing technologies, thus benefitting other supercomputer centers in government and industry. The 1993-94 operational year concluded with 448 high-speed processor projects and 95 parallel projects representing NASA, the Department of Defense, other government agencies, private industry, and universities. This document provides a glimpse at some of the significant scientific results for the year

    The Numerical Simulation of Fluid Flow

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    This book collects the accepted contributions to the Special Issue "The Numerical Simulation of Fluid Flow" in the Energies journal of MDPI. It is focused more on practical applications of numerical codes than in its development. It covers a wide variety of topics, from aeroacoustics to aerodynamics and flow-particles interaction

    Aeronautical engineering: A continuing bibliography with indexes (supplement 262)

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    This bibliography lists 474 reports, articles, and other documents introduced into the NASA scientific and technical information system in Jan. 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

    ファンから生じる空力騒音の予測と低減に関する計算的研究

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    Turbomachinery is machinery device in which energy is delivered either to or from fluid that is continuously moving due to action of moving blades. Performance and flow noise are two major indices for evaluation of turbomachinery. In terms of energy transfer, researches on performance of turbomachinery have been conducted since long time ago; and these researches for performance improvement are still ongoing currently. In addition, flow noise produced by turbomachinery came to the fore as turbomachinery has been used in various fields and everyday life closely and frequently. Especially, consumers’ demand on improvement in affective quality has been increased and regulation on noise has been being reinforced due to damages and adverse effects caused by noise. Therefore, development of high performance and low noise turbomachinery is highly required. Meanwhile, experimental methods have been used to develop low noise turbomachinery; however, the experimental methods solely are not sufficient to achieve such aim since measuring in small turbomachinery is challenging. Hence, prediction technique, to which the numerical analysis method that yields complementary effects in combination with the experimental methods is applied, is required. This study was conducted with the aim of applying numerical analysis method for noise reduction in turbomachinery. Therefore, three-dimensional unsteady Navier-Stokes equations were solved to simulate the flow field. Turbulence models used to predict the flow field were SST k–ω model that provides outstanding simulation of separation and adverse pressure gradient in boundary layer and LES model that presents excellence in turbulence intensity modeling, respectively. Computational Aeroacoustics (CAA) used to predict the flow noise in this study was acoustic analogy that is one of the hybrid methods; and the acoustic analogy is the method analyzing unsteady flow field by using Computational Fluid Dynamics (CFD) and then predicting noise by using the information of unsteady flow field obtained from the results of CFD simulation. To conduct acoustic analogy, Lowson equation, which can be used to predict sound pressure for point force that is moving in a free field, was calculated. Despite of disadvantage that influence of an object including scattering, diffraction, and reflection within acoustic field is difficult to be considered, this method that directly reduces noise sources was able to be drawn since the locations of the noise source can be seen by numerical approach. Because predicting the location of the noise source is able to figure out the unsteady flow which causes the noise. As a result, the reduction method of flow-induced noise in this study is to find the way to reduce or remove the unsteady flow generating the noise, based on CAA and CFD. In order to indicate the location of the noise source, “Aeroacoustic source strength, Ast” was defined and compared with the location of the noise source measured by the acoustic camera to which beamforming technology is applied; and they were agreed qualitatively well each other. Due to miniaturization of electronics and maintenance of fan performance, whereas size of fan is getting smaller, the rotational speed of it getting higher. In this study following the current trend, three fans with each other different type were used for adopting numerical method to noise reduction; ⅰ) a small axial fan of rotor’s diameter D = 0.166 m and a rotation speed 2860 rpm with circular shroud, ⅱ) a small axial fan of rotor’s diameter D = 0.076 m and a rotation speed 7000 rpm with square-type shroud used in a rack mount server computer, ⅲ) a small centrifugal fan with rotor’s diameter D = 0.032 m and a rotation speed 10460 rpm used as a cooling fan in portable home electronics such as a small laptop computer. The noise of each type fan was predicted and compared with the measured noise. The predicted noise and measured noise presented agreement in tonal noise of the blade passing frequency (BPF) and its harmonic frequencies and in the broadband noise at low frequency. Although the broadband noise at high frequency was somewhat different due to random broadband noise, the shapes for noise reduction were able to be drawn effectively by predicting the location of the noise sources. Low noise models suggested for noise reduction provided the result of noise reduction from the prediction and specific noise level was used to evaluate the noise reduction considering the changes in fan performance. In case of the axial flow fan with circular shroud, the interaction between the rotating rotor blades and the flow separated from the inlet of the shroud was found to be the major cause of the noise through the analysis on the location of the noise sources and unsteady flow field. Consequently, reduction of the flow noise was predicted by correcting the shape of the shroud inlet. In the small axial flow fan installed in the rack mount server computer, the tonal noise occurring by irregular clearance between the blade tip and the shroud due to the square-shaped shroud was well predicted. In addition, coherence analysis was conducted to identify the relationship between the surface pressure fluctuation due to the flow and the sound pressure predicted from the microphone. As a result, the correlation for each frequency was well presented. For a centrifugal fan that is used as a cooling fan in home electronics such as a portable small laptop computer, the flow structure of the centrifugal fan was simulated by setting the condition to be analogous to the operating condition within the actual product. And then the reduction of the flow noise was predicted by correcting the tip of the impeller blades based on the location of the noise sources. This study aimed to apply the method of numerical analysis to the noise reduction in turbomachinery. For this, the unsteady flow field was analyzed, the result of noise prediction obtained from the flow filed information was compared and validated, and the location of the noise sources and the structure of the flow field causing the noise were understood; hence, the low noise design was able to be drawn effectively and properly. In this study, the reduction of the flow noise was successfully achieved by adopting the method of numerical analysis and the flow noise of the fan that were improved for noise reduction was predicted to be reduced by 0.8 and 3.7 dB, respectively.博士(工学)法政大学 (Hosei University

    Coupling road vehicle aerodynamics and dynamics in simulation

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    A fully coupled system in which a vehicle s aerodynamic and handling responses can be simulated has been designed and evaluated using a severe crosswind test. Simulations of this type provide vehicle manufacturers with a useful alternative to on road tests, which are usually performed at a late stage in the development process with a proto- type vehicle. The proposed simulations could be performed much earlier and help to identify and resolve any aerodynamic sensitivities and safety concerns before significant resources are place in the design. It was shown that for the simulation of an artificial, on-track crosswind event, the use of the fully coupled system was unnecessary. A simplified, one-way coupled system, in which there is no feedback from the vehicle s dynamics to the aerodynamic simulation was sufficient in order to capture the vehicle s path deviation. The realistic properties of the vehicle and accurately calibrated driver model prevented any large attitude changes whilst immersed in the gust, from which variations to the aerodynamics could arise. It was suggested that this system may be more suited to other vehicle geometries more sensitive to yaw motions or applications where a high positional accuracy of the vehicle is required

    Aeronautical Engineering: a Continuing Bibliography with Indexes (Supplement 243)

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    This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

    Aeronautical engineering: A continuing bibliography with indexes (supplement 258)

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    This bibliography lists 536 reports, articles, and other documents introduced into the NASA scientific and technical information system in October 1990. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

    Aeronautical engineering: A cumulative index to a continuing bibliography (supplement 274)

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    This publication is a cumulative index to the abstracts contained in supplements 262 through 273 of Aeronautical Engineering: A Continuing Bibliography. The bibliographic series is compiled through the cooperative efforts of the American Institute of Aeronautics and Astronautics (AIAA) and the National Aeronautics and Space Administration (NASA). Seven indexes are included: subject, personal author, corporate source, foreign technology, contract number, report number, and accession number

    Noise Generation by Airfoils and Rotors with Porous and Serrated Trailing Edges

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    Trailing-edge (TE) noise is an important noise source for airfoil applications that operate near populated areas. This thesis aims to develop novel (porous, serrated, and porous-serrated) geometries for the TE noise control of airfoils/rotors and investigate their noise generation mechanisms. First, the acoustic absorption of ten additively manufactured porous specimens is characterised to facilitate the design of porous TE geometries. The aeroacoustic performance and near-wake characteristics of eleven novel TE designs are then measured at various velocities in UNSW Anechoic Wind Tunnel. Their noise attenuation performance on laminar-transitional boundary layer TE (LBL-TE) and turbulent boundary layer TE (TBL-TE) noise are evaluated. Fluctuating velocity results indicate that the proposed designs influence LBL-TE noise generation by altering the flow characteristics around the TE. A TBL-TE noise intensity factor is proposed to relate near-wake flow statistics to TBL-TE noise generation, showing good consistency with the measured TBL-TE noise level. A high-frequency-broadband noise increase is observed for all porous TE designs. Moreover, the aeroacoustic performance of three sets of rotor blades with integrated novel TEs is evaluated at various pitch angles and RPMs on UNSW Rotor rig. Compared with serrated blades, porous blades show better low-frequency noise attenuation. At frequencies where the porous structures have good acoustic absorption, porous blades can effectively control TE noise at all operating conditions, indicating the acoustic absorption may contribute to TE noise attenuation by altering the acoustic scattering efficiency. In addition, Large-Eddy Simulations (LES) are performed on a porous and a reference airfoil. Ffowcs-Williams and Hawkings (FWH) acoustic analogy results of porous airfoil capture the high-frequency excessive noise and agree well with single microphone measurements. Flow simulation results reveal that the TBL-TE noise reduction for porous TE is mainly due to an attenuation of convection velocity and spanwise correlation, and the excessive noise is originated from the interaction of the permeated turbulent flow and pore geometries. Finally, a wind turbine noise prediction model based on a noise scaling function is proposed. It accurately predicts the noise spectra and overall noise levels of a full-scale wind turbine using the aerodynamic and acoustic data of lab-scale airfoil models

    Aeronautical engineering: A continuing bibliography with indexes, supplement 164, August 1983

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    This bibliography lists 296 reports, articles and other documents introduced into the NASA scientific and technical information system in July 1983
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