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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Thermal structure of Jupiter's atmosphere obtained by inversion of Voyager 1 infrared measurements

Data from the Voyager 1 infrared spectroscopy investigation have been used to retrieve temperature profiles in the atmosphere of Jupiter. An analysis of information content indicates good vertical resolution with low measurement noise propagation in the Jovian troposphere and reduced resolution in the stratosphere. Among the problems found in common with the sounding of the terrestrial atmosphere are limited tropopause definition and dependence on upper boundary constraints. Preliminary results obtained by using a constrained linear algorithm and a filtered Chahine approach are presented.

Conrath, B. J.↗
NASA NTRS1982

Analysis of combustion spectra containing organ pipe tone by cepstral techniques

Signal reinforcements and cancellations due to standing waves may distort constant bandwidth combustion spectra. Cepstral techniques previously applied to the ground reflection echo problem are used to obtain smooth broadband data and information on combustion noise propagation. Internal fluctuating pressure measurements made using a J47 combustor attached to a 6.44 m long duct are analyzed. Measurements made with Jet A and hydrogen fuels are compared. The acoustic power levels inferred from the measurements are presented for a range of low heat release rate operating conditions near atmospheric pressure. For these cases, the variation with operating condition of the overall acoustic broadband power level for both hydrogen and Jet A fuels is consistent with previous results showing it was proportional to the square of the heat release rate. However, the overall acoustic broadband power level generally is greater for hydrogen than for Jet A.

Miles, J. H.↗
NASA NTRS1981

Spectral line inversion for sounding of stratospheric minor constituents by infrared heterodyne technique from balloon altitudes

A combination of two different techniques for the inversion of infrared laser heterodyne measurements of tenuous gases in the stratosphere by solar occulation is presented which incorporates the advantages of each technique. An experimental approach and inversion technique are developed which optimize the retrieval of concentration profiles by incorporating the onion peel collection scheme into the spectral inversion technique. A description of an infrared heterodyne spectrometer and the mode of observations for solar occulation measurement is presented, and the results of inversions of some synthetic ClO spectral lines corresponding to solar occulation limb-scans of the stratosphere are examined. A comparison between the new techniques and one of the current techniques indicates that considerable improvement in the accuracy of the retrieved profiles can be achieved. It is found that noise affects the accuracy of both techniques but not in a straightforward manner since there is interaction between the noise level, noise propagation through inversion, and the number of scans leading to an optimum retrieval.

Abbas, M. M.↗
NASA NTRS1982

Generation of desired signals from acoustic drivers

A procedure to control transient signal generation is developed for the study of internal noise propagation from aircraft engines. A simple algorithm incorporating transform techniques is used to produce signals of any desired waveform from acoustic drivers. The accurate driver response is then calculated, and from this the limiting frequency characteristics are determined and the undesirable frequencies where the driver response is poor are eliminated from the analysis. A synthesized signal is then produced by convolving the inverse of the response function with the desired signal. Although the shape of the synthesized signal is in general quite awkward, the driver generates the desired signal when the distorted signal is fed into the driver. The results of operating the driver in two environments, in a free field and in a duct, are presented in order to show the impedance matching effect of the driver. In addition, results using a high frequency cut-off value as a parameter is presented in order to demonstrate the extent of the applicability of the synthesis procedure. It is concluded that the desired signals can be generated through the signal synthesis procedure.

Ramakrishnan, R.↗
NASA NTRS1983

Measurements and predictions of turboprop noise at high cruise speed

Acoustic tests of advanced turboprop (Prop-Fan) models have taken place in or on three facilities: an acoustic wind tunnel, an aerodynamic wind tunnel, and a flight vehicle. Comparisons of data from the three facilities are made for two model designs, the unswept SR-2 and the swept SR-3. The importance of noise propagation through the boundary layer to microphones mounted on the surface of a flight vehicle is discussed and limited comparisons between predictions and measurements are shown. It is concluded that existing methodology is adequate for predictions at high cruise Mach number and that further development is required to improve the methodology for predicting fuselage and wind tunnel boundary layer propagation effects.

Metzger, F. B.↗
NASA NTRS1983

Cross spectra between pressure and temperature in a constant-area duct downstream of a hydrogen-fueled combustor

Pressure temperature cross spectra are necessary in predicting noise propagation in regions of velocity gradients downstream of combustors if the effect of convective entropy disturbances is included. Pressure temperature cross spectra and coherences were measured at spatially separated points in a combustion rig fueled with hydrogen. Temperature-temperature and pressure-pressure cross spectra and coherences between the spatially separated points as well as temperature and pressure autospectra were measured. These test results were compared with previous results obtained in the same combustion rig using Jet A fuel in order to investigate their dependence on the type of combustion process. The phase relationships are not consistent with a simple source model that assumes that pressure and temperature are in phase at a point in the combustor and at all other points downstream are related to one another by only a time delay due to convection of temperature disturbances. Thus these test results indicate that a more complex model of the source is required.

Miles, J. H.↗
NASA NTRS1985

An evaluation of proposed acoustic treatments for the NASA LaRC 4 x 7 meter wind tunnel

The NASA LaRC 4 x 7 Meter Wind Tunnel is an existing facility specially designed for powered low speed (V/STOL) testing of large scale fixed wing and rotorcraft models. The enhancement of the facility for scale model acoustic testing is examined. The results are critically reviewed and comparisons are drawn with a similar wind tunnel (the DNW Facility in the Netherlands). Discrepancies observed in the comparison stimulated a theoretical investigation using the acoustic finite element ADAM System, of the ways in which noise propagating around the tunnel circuit radiates into the open test section. The reasons for the discrepancies noted above are clarified and assists in the selection of acoustic treatment options for the facility.

Abrahamson, A. L.↗
NASA NTRS1988

Asteroid shapes from radar echo spectra - A new theoretical approach

Asteroid shape determinations are presently made by means of a novel technique based on the geometric relation between spectral edge frequencies and the shape of a rotating, rigid radar target. By employing the echo spectra obtained at many rotational phases, the asteroid's convex polar silhouette hull is obtained; noise content is treated as a problem in weighted-least-squares optimization, subject to inequality constraints. The performance of this estimation method is assessed in a series of simulated data giving attention to spectral noise propagation into hull error; sensitivity to echo strength and spectral resolution are also evaluated.

Ostro, Steven J.↗
NASA NTRS1990

En route noise: NASA propfan test aircraft (corrected data - simplified procedure)

Surface noise measurements were made during a joint National Aeronautics and Space Administration (NASA) and Federal Aviation Administration (FAA) program to study the high-altitude, low-frequency acoustic noise propagation characteristics of the Advanced Turboprop (propfan) Aircraft. The measurements were made on October 26-31, 1987 in Huntsville, Alabama and on April 3-13, 1989 at the White Sands Missile Range (WSMR), New Mexico. To effectively compare flight-to-flight data as received on the ground, the procedures and practices of Federal Air Regulation (FAR) Part 36 were used as a guide in adjusting the measured ground data at the time of LA(sub MAX) to a set of reference conditions. After the data for each event were processed using slow detector characteristics, the data record at LA(sub MAX) was then identified and the coordinates of the aircraft at the time of emission were calculated, taking into account atmospheric refraction effects. The effects of atmospheric absorption through the test day and reference day atmosphere were also taken into account and the 1/3-octave data were adjusted accordingly.

Rickley, E. J.↗
NASA NTRS1990

COBE attitude as seen from the FDF

The goal of the Flight Dynamics Facility (FDF) attitude support is twofold: to determine spacecraft attitude and to explain deviations from nominal attitude behavior. Attitude determination often requires resolving contradictions in the sensor observations. This may be accomplished by applying calibration corrections or by revising the observation models. After accounting for all known sources of error, solution accuracy should be limited only by observation and propagation noise. The second half of the goal is to explain why the attitude may not be as originally intended. Reasons for such deviations include sensor or actuator misalignments and control system performance. In these cases, the ability to explain the behavior should, in principle, be limited only by knowledge of the sensor and actuator data and external torques. Documented here are some results obtained to date in support of the Cosmic Background Explorer (COBE). Advantages and shortcomings of the integrated attitude determination/sensor calibration software are discussed. Some preliminary attitude solutions using data from the Diffuse Infrared Background Experiment (DIRBE) instrument are presented and compared to solutions using Sun and Earth sensors. A dynamical model is constructed to illustrate the relative importance of the various sensor imprefections. This model also shows the connection between the high- and low-frequency attitude oscillations.

Sedlak, J.↗
NASA NTRS1992

ANOPP/VMS HSCT ground contour system

This viewgraph shows the integration of the Visual Motion Simulator with ANOPP. ANOPP is an acronym for the Aircraft NOise Prediction Program. It is a computer code consisting of dedicated noise prediction modules for jet, propeller, and rotor powered aircraft along with flight support and noise propagation modules, all executed under the control of an executive system. The Visual Motion Simulator (VMS) is a ground based motion simulator with six degrees of freedom. The transport-type cockpit is equipped with conventional flight and engine-thrust controls and with flight instrument displays. Control forces on the wheel, column, and rudder pedals are provided by a hydraulic system coupled with an analog computer. The simulator provides variable-feel characteristics of stiffness, damping, coulomb friction, breakout forces, and inertia. The VMS provides a wide range of realistic flight trajectories necessary for computing accurate ground contours. The NASA VMS will be discussed in detail later in this presentation. An equally important part of the system for both ANOPP and VMS is the engine performance. This will also be discussed in the presentation.

Rawls, John, Jr.↗
NASA NTRS1999

A Simple Derivation of the Acoustic Boundary Condition in the Presence of Flow

In modelling the noise propagation in a duct of a ducted fan engine, the authors needed the boundary condition satisfied by the acoustic pressure on a lined duct wall in the presence of flow. The result in the form used by the authors was derived by M. K. Myers who presented a formal derivation of a related result by K. Taylor. A good review of the subject can be found in reference. Here, a brief and simple derivation of the acoustic boundary condition of Myers is given. The main difference in the derivation from that in reference is that the Gaussian co-ordinate system (q(sup 1), q(sup 2), q(sup 3)(q(sup 1), q(sup 2), t)) is used to specify the instantaneous position, i.e., Lagrangian variable, of the point on the mean position of the wall with curvilinear (Gaussian) co-ordinates (q(sup 1), q(sup 2)). Myers uses a locally orthogonal coordinate system which is somewhat less specific than what is used here.

Farassat, F.↗
NASA NTRS1999

A Simple Derivation of the Acoustic Boundary Condition in the Presence of Flow

In modeling the noise propagation in a duct of a ducted fan engine, the authors needed the boundary condition satisfied by the acoustic pressure on a lined duct wall in the presence of flow. The results, in the form used by the authors, was derived by M.K. Myers, who presented a formal derivation of a related results by K. Taylor. Here, a brief and simple derivation of the acoustic boundary condition of Myers is given. The main difference in the derivation from that by Myers is that the Gaussian coordinate system (q(exp 1, q(exp 2), q(exp 3)(q(exp 1, q(exp 2), t)) is used to specify the instantaneous position, i.e. Lagrangian variable, of the point on the mean position of the wall with curvilinear (Gaussian) coordinates (q(exp 1), q(exp 2)). Myers uses a locally orthogonal coordinate system which is somewhat less specific than what is used here.

Farassat, F.↗
NASA NTRS2006

Procedure for Separating Noise Sources in Measurements of Turbofan Engine Core Noise

The study of core noise from turbofan engines has become more important as noise from other sources like the fan and jet have been reduced. A multiple microphone and acoustic source modeling method to separate correlated and uncorrelated sources has been developed. The auto and cross spectrum in the frequency range below 1000 Hz is fitted with a noise propagation model based on a source couplet consisting of a single incoherent source with a single coherent source or a source triplet consisting of a single incoherent source with two coherent point sources. Examples are presented using data from a Pratt & Whitney PW4098 turbofan engine. The method works well.

Miles, Jeffrey Hilton↗
NASA NTRS2011

Development and Validation of a Multidisciplinary Tool for Accurate and Efficient Rotorcraft Noise Prediction (MUTE)

A physics-based, systematically coupled, multidisciplinary prediction tool (MUTE) for rotorcraft noise was developed and validated with a wide range of flight configurations and conditions. MUTE is an aggregation of multidisciplinary computational tools that accurately and efficiently model the physics of the source of rotorcraft noise, and predict the noise at far-field observer locations. It uses systematic coupling approaches among multiple disciplines including Computational Fluid Dynamics (CFD), Computational Structural Dynamics (CSD), and high fidelity acoustics. Within MUTE, advanced high-order CFD tools are used around the rotor blade to predict the transonic flow (shock wave) effects, which generate the high-speed impulsive noise. Predictions of the blade-vortex interaction noise in low speed flight are also improved by using the Particle Vortex Transport Method (PVTM), which preserves the wake flow details required for blade/wake and fuselage/wake interactions. The accuracy of the source noise prediction is further improved by utilizing a coupling approach between CFD and CSD, so that the effects of key structural dynamics, elastic blade deformations, and trim solutions are correctly represented in the analysis. The blade loading information and/or the flow field parameters around the rotor blade predicted by the CFD/CSD coupling approach are used to predict the acoustic signatures at far-field observer locations with a high-fidelity noise propagation code (WOPWOP3). The predicted results from the MUTE tool for rotor blade aerodynamic loading and far-field acoustic signatures are compared and validated with a variation of experimental data sets, such as UH60-A data, DNW test data and HART II test data.

Liu, Yi↗
NASA NTRS2004

Phase Contrast Wavefront Sensing for Adaptive Optics

Most ground-based adaptive optics systems use one of a small number of wavefront sensor technologies, notably (for relatively high-order systems) the Shack-Hartmann sensor, which provides local measurements of the phase slope (first-derivative) at a number of regularly-spaced points across the telescope pupil. The curvature sensor, with response proportional to the second derivative of the phase, is also sometimes used, but has undesirable noise propagation properties during wavefront reconstruction as the number of actuators becomes large. It is interesting to consider the use for astronomical adaptive optics of the "phase contrast" technique, originally developed for microscopy by Zemike to allow convenient viewing of phase objects. In this technique, the wavefront sensor provides a direct measurement of the local value of phase in each sub-aperture of the pupil. This approach has some obvious disadvantages compared to Shack-Hartmann wavefront sensing, but has some less obvious but substantial advantages as well. Here we evaluate the relative merits in a practical ground-based adaptive optics system.

adaptive optics↗
NASA NTRSDate not supplied

Phased Microphone Array on Aircraft Fuselage

This paper studies some challenging features for phased microphone arrays on aircraft fuselage, including the effects of sound scattering such as refraction by nonuniform boundary layer flows, reflection by curved surfaces, and diffraction by sharp edges and smooth geometry. The objective is to show if and how source locations and source amplitudes can be accurately captured by the array data analysis, in the presence of these features. The study starts with canonical problems to separately examine the individual features, making use of their respective analytical solutions, which provide exact results for all quantities needed for the array data processing. To simulate realistic flight environments, a generic aircraft geometry is then utilized, involving multiple scattering mechanisms and multiple noise sources to model aircraft engine noise. For this application, numerical solutions are computed to provide noise propagation and scattering from the sources to the microphones, as well as the quantities needed for array data analysis. The study reveals the effects of various features on fuselage-mounted arrays and provides guidelines to account for these effects in array data analysis.

Yueping Guo↗
NASA NTRS2004

Development in Source Modeling and Sound Propagation for Jet Noise Predictions

The purpose of the research carried out under this cooperative agreement was to develop tools that could be used to improve upon the current state of the art in the prediction of noise emitted by turbulent exhaust jets. Both the source modeling and sound propagation aspects of the prediction of jet noise by acoustic analogy were examined with a view toward the development of methods which yield improved predictions over a wider range of operating conditions.

Leib, Steward↗