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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
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NASA NTRS2011

Research Of Airborne Precision Spacing to Improve Airport Arrival Operations

In September 2004, the European Organization for the Safety of Air Navigation (EUROCONTROL) and the United States Federal Aviation Administration (FAA) signed a Memorandum of Cooperation to mutually develop, modify, test, and evaluate systems, procedures, facilities, and devices to meet the need for safe and efficient air navigation and air traffic control in the future. In the United States and Europe, these efforts are defined within the architectures of the Next Generation Air Transportation System (NextGen) Program and Single European Sky Air Traffic Management Research (SESAR) Program respectively. Both programs have identified Airborne Spacing as a critical component, with Automatic Dependent Surveillance Broadcast (ADS-B) as a key enabler. Increased interest in reducing airport community noise and the escalating cost of aviation fuel has led to the use of Continuous Descent Arrival (CDA) procedures to reduce noise, emissions, and fuel usage compared to current procedures. To provide these operational enhancements, arrival flight paths into terminal areas are planned around continuous vertical descents that are closer to an optimum trajectory than those in use today. The profiles are designed to be near-idle descents from cruise altitude to the Final Approach Fix (FAF) and are typically without any level segments. By staying higher and faster than conventional arrivals, CDAs also save flight time for the aircraft operator. The drawback is that the variation of optimized trajectories for different types and weights of aircraft requires the Air Traffic Controller to provide more airspace around an aircraft on a CDA than on a conventional arrival procedure. This additional space decreases the throughput rate of the destination airport. Airborne self-spacing concepts have been developed to increase the throughput at high-demand airports by managing the inter-arrival spacing to be more precise and consistent using on-board guidance. It has been proposed that the additional space needed around an aircraft performing a CDA could be reduced or eliminated when using airborne spacing techniques.

Barmore, Bryan E.↗
NASA NTRS2018

Aircraft System Noise Prediction Uncertainty Quantification for a Hybrid Wing Body Subsonic Transport Concept

Aircraft system level noise prediction for advanced, unconventional concepts has undergone significant improvement over the past two decades. The prediction modeling uncertainty must be quantified so that potential benefits of unconventional configurations, which are outside of the range of empirical models, can be reliably assessed. This paper builds on previous work in an effort to improve estimates of element prediction uncertainties where the prediction methodology has been improved, or new experimental validation data are available, to provide an estimate of the system level uncertainty in the prediction process. In general, the uncertainty of the prediction will be strongly dependent on the aircraft configuration as well as which technologies are integrated. While the quantitative uncertainty values contained here are specific to the hybrid wing body design presented, the underlying process is the same regardless of configuration. A refined process for determining the uncertainty for each element of the noise prediction is detailed in this paper. The system level uncertainty in the prediction of the aircraft noise is determined at the three certification points, using a Monte Carlo method. Comparisons with previous work show a reduction of 1 EPNdB in the 95%coverage interval of the cumulative noise level. The largest impediment for continued reduction in uncertainty for the hybrid wing body concept is the need for improved modeling and validation experiments for fan noise, propulsion airframe aeroacoustic effects, and the Krueger flap, which comprise the bulk of the uncertainty in the cumulative certification noise level.

June, Jason C.↗
NASA NTRS2004

Design and Testing of a Low Noise Flight Guidance Concept

A flight guidance concept was developed to assist in flying continuous descent approach (CDA) procedures designed to lower the noise under the flight path of jet transport aircraft during arrival operations at an airport. The guidance consists of a trajectory prediction algorithm that was tuned to produce a high-efficiency, low noise flight profile with accompanying autopilot and flight display elements needed by the flight control system and pilot to fly the approach. A key component of the flight guidance was a real-time display of energy error relative to the predicted flight path. The guidance was integrated with the conventional Flight Management System (FMS) guidance of a modern jet transport airplane and tested in a high fidelity flight simulation. A charted arrival procedure, which allowed flying conventional arrivals, CDA arrivals with standard guidance, and CDA arrivals with the new low noise guidance, was developed to assist in the testing and evaluation of the low noise guidance concept. Results of the simulation testing showed the low noise guidance was easy to use by airline pilot test subjects and effective in achieving the desired noise reduction. Noise under the flight path was reduced by at least 2 decibels in Sound Exposure Level (SEL) at distances from about 3 nautical miles out to about 17.5 nautical miles from the runway, with a peak reduction of 8.5 decibels at about 10.5 nautical miles. Fuel consumption was also reduced by about 17% for the LNG conditions compared to baseline runs for the same flight distance. Pilot acceptance and understanding of the guidance was quite high with favorable comments and ratings received from all test subjects.

Williams, David H.↗
NASA NTRS1973

Simulation results for an innovative anti-multipath digital receiver

Simulation results are presented for the error rate performance of the recursive digital MAP detector for known M-ary signals in multiplicative and additive Gaussian noise. Plots of detection error rate versus additive signal to noise ratio are given, with multipath interference strength as a parameter. For comparison, the error rates of conventional coherent and noncoherent digital MAP detectors are simultaneously simulated and graphed. It is shown that with nonzero multiplicative noise, the error rates of the conventional detectors saturate at an irreducible level as additive signal to noise ratio increases. The error rate for the innovative detector continues to decrease rapidly with increasing additive signal to noise ratio. In the absence of multiplicative interference, the conventional coherent detector and the innovative detector are shown to exhibit identical performance.-

Painter, J. H.↗
NASA NTRSDate not supplied

NASA’s Efficient Quiet Integrated Propulsors (Equip) Technical Challenge

Advances in aircraft propulsor technology - ducted and unducted - are key elements to developing a sustainable aviation future. Increasing propulsive efficiency comes with significant challenges. The long-term trend in aircraft engine design has been towards higher bypass ratios to increase efficiency and decrease noise. Current designs are pushing against limits on engine size; the engine must fit under the wing and overcome the nacelle weight, aerodynamic drag, and airframe integration penalties associated with an ultra-high bypass ratio. The next-generation ducted engines will have shorter inlets and smaller rotor-stator spacing to minimize nacelle area. This increases the potential for non-uniform flow at the fan face and less area for acoustic liners. Unducted engines eliminate the nacelle penalty while presenting challenges to noise and operability in distorted flow environments. The overall diameter in both cases raises questions about engine-airframe integration to maximize efficiency gains and minimize installation penalties. The National Aeronautics and Space Administration (NASA) Advanced Air Vehicles Program (AAVP) approved the Efficient Quiet Integrated Propulsor (EQuIP) Technical Challenge (TC) under the Advanced Air Transport Technology (AATT) Project to work on next-generation propulsor technologies in collaboration with NASA’s government and industry partners in the Sustainable Flight National Partnership. The EQuIP TC leverages NASA resources with Federal Aviation Administration (FAA) and industry investments under the FAA’s Continuous Lower Energy Emissions and Noise (CLEEN) program to address technical challenges on the propulsor subject to the flow field imposed by the engine-airframe-flight environment. The EQuIP TC complements NASA Aeronautics Research Mission Directorate’s (ARMD) existing investments in sustainable aviation for the next-generation of commercial aircraft and contributes to meeting the noise and efficiency goals set by the Sustainable Flight National Partnership and U.S. Aviation Climate Action Plan. This paper introduces the EQuIP TC, describes key parts of its development, and presents the background research used to scope its impact.

Propulsion↗
NASA NTRS2010

Simulation of Turbine Tone Noise Generation Using a Turbomachinery Aerodynamics Solver

As turbofan engine bypass ratios continue to increase, the contribution of the turbine to the engine noise signature is receiving more attention. Understanding the relative importance of the various turbine noise generation mechanisms and the characteristics of the turbine acoustic transmission loss are essential ingredients in developing robust reduced-order models for predicting the turbine noise signature. A computationally based investigation has been undertaken to help guide the development of a turbine noise prediction capability that does not rely on empiricism. As proof-of-concept for this approach, two highly detailed numerical simulations of the unsteady flow field inside the first stage of a modern high-pressure turbine were carried out. The simulations were computed using TURBO, which is an unsteady Reynolds-Averaged Navier-Stokes code capable of multi-stage simulations. Spectral and modal analysis of the unsteady pressure data from the numerical simulation of the turbine stage show a circumferential modal distribution that is consistent with the Tyler-Sofrin rule. Within the high-pressure turbine, the interaction of velocity, pressure and temperature fluctuations with the downstream blade rows are all possible tone noise source mechanisms. We have taken the initial step in determining the source strength hierarchy by artificially reducing the level of temperature fluctuations in the turbine flowfield. This was accomplished by changing the vane cooling flow temperature in order to mitigate the vane thermal wake in the second of the two simulations. The results indicated that, despite a dramatic change in the vane cooling flow, the computed modal levels changed very little indicating that the contribution of temperature fluctuations to the overall pressure field is rather small compared with the viscous and potential field interaction mechanisms.

VanZante, Dale↗
NASA NTRS1997

MEASUREMENT OF THE NOISE IMPROVEMENT OF A 34-METER CASSEGRAIN ANTENNA RETROFITTED WITH A LOW-BACKSCATTERING STRUT

Large axially-symmetric ground-based dual-reflector antennas are used in a variety of applications simultaneously requiring very high gain and very low noise (e.g., satellite communications, radio astronomy, deep-space communications, and radar). In these systems, reducing the noise by 10 % is equivalent to increasing the antenna gain by roughly 0.5 dB. Since the early days of radio-astronomy this fact has continuously driven efforts to reduce the noise of front-end low-noise amplifiers--a major noise contributor. As the performance of the front-end amplifiers improved, the relative importance of the noise generated by the surrounding warm ground increased, causing the antenna noise to become a major factor in the overall system sensitivity. Since large ground-based reflectors have been around for several decades, the various electrical and mechanical parameters affecting their performance have received considerable attention and are generally well understood. However, the impact of the subreflector supporting struts on the antenna noise performance remains a source of uncertainty. The reason for this stems from the usually large electrical dimensions involved, which precludes the accurate modeling of the various strut-scattering mechanisms. For the particular antennas used on NASA's Deep Space Network, which have been designed to minimize all noise sources, several studies have typically reported measured noise temperatures between 2 and 3 K (at approx. 8.45 GHz, antenna pointing at zenith), attributed to the struts and other unknown effects (see for example [1] and [2]). With this in mind, an effort has recently been conducted to determine optimal strut shapes to reduce the associated noise contribution [3].

Prata, A., Jr.↗
NASA NTRS2007

Optimization of Acoustic Pressure Measurements for Impedance Eduction

As noise constraints become increasingly stringent, there is continued emphasis on the development of improved acoustic liner concepts to reduce the amount of fan noise radiated to communities surrounding airports. As a result, multiple analytical prediction tools and experimental rigs have been developed by industry and academia to support liner evaluation. NASA Langley has also placed considerable effort in this area over the last three decades. More recently, a finite element code (Q3D) based on a quasi-3D implementation of the convected Helmholtz equation has been combined with measured data acquired in the Langley Grazing Incidence Tube (GIT) to reduce liner impedance in the presence of grazing flow. A new Curved Duct Test Rig (CDTR) has also been developed to allow evaluation of liners in the presence of grazing flow and controlled, higher-order modes, with straight and curved waveguides. Upgraded versions of each of these two test rigs are expected to begin operation by early 2008. The Grazing Flow Impedance Tube (GFIT) will replace the GIT, and additional capabilities will be incorporated into the CDTR. The current investigation uses the Q3D finite element code to evaluate some of the key capabilities of these two test rigs. First, the Q3D code is used to evaluate the microphone distribution designed for the GFIT. Liners ranging in length from 51 to 610 mm are investigated to determine whether acceptable impedance eduction can be achieved with microphones placed on the wall opposite the liner. This analysis indicates the best results are achieved for liner lengths of at least 203 mm. Next, the effects of moving this GFIT microphone array to the wall adjacent to the liner are evaluated, and acceptable results are achieved if the microphones are placed off the centerline. Finally, the code is used to investigate potential microphone placements in the CDTR rigid wall adjacent to the wall containing an acoustic liner, to determine if sufficient fidelity can be achieved with 32 microphones available for this purpose. Initial results indicate 32 microphones can provide acceptable measurements to support impedance eduction with this test rig.

Jones, M. G.↗
NASA NTRS1973

Inexpensive high vacuum feedthroughs.

Description of the use of rigid coaxial cable in the construction of high vacuum coaxial and coaxial push-pull rotary motion feedthroughs. This type of feedthroughs is shown to be extremely cheap and simple to make and modify. It can be used for moderately high voltages and provides a continuous, well shielded, low-noise feedthrough cable in any desired configuration.

Gerber, S.↗
NASA NTRS1978

Improved "spectrophone"

Spectral lines of gas sample are modulated by electric field in optoacoustic gas analyzer. Pressure fluctuations caused by local heating of absorbing gas are picked up by microphone. Since laser is operated in continuous-wave (CW) mode, background noise due to heating of windows is eliminated.

Margolis, J. S.↗
NASA NTRS1978

The impact of urban operations on helicopter noise requirements

The interrelationship of urban helicopter operations, helicopter noise, and the establishment of urban public-use heliports is discussed. Public resistance to urban helicopter operations due to concern for safety and noise is shown to negatively impact the establishment of public-use heliports in urban centers. It is indicated that increased government and industry effort to reduce helicopter noise is needed to ensure continued growth in the helicopter industry.

Spector, S. R.↗
NASA NTRS1982

Error probabilities in optical PPM receivers with Gaussian mixture densities

A Gaussian mixture density arises when a discrete variable (e.g., a photodetector count variable) is added to a continuous Gaussian variable (e.g., thermal noise). Making use of some properties of photomultiplier Gaussian mixture distributions, some approximate error probability formulas can be derived. These appear as averages of M-ary orthogonal Gaussian error probabilities. The use of a pure Gaussian assumption is considered, and when properly defined, appears as an accurate upper bound to performance.

Gagliardi, R. M.↗
NASA NTRS1987

Identification and proposed control of helicopter transmission noise at the source

Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed.

Coy, John J.↗
NASA NTRS1988

Identification and proposed control of helicopter transmission noise at the source

Helicopter cabin interiors require noise treatment which is expensive and adds weight. The gears inside the main power transmission are major sources of cabin noise. Work conducted by the NASA Lewis Research Center in measuring cabin interior noise and in relating the noise spectrum to the gear vibration of the Army OH-58 helicopter is described. Flight test data indicate that the planetary gear train is a major source of cabin noise and that other low frequency sources are present that could dominate the cabin noise. Companion vibration measurements were made in a transmission test stand, revealing that the single largest contributor to the transmission vibration was the spiral bevel gear mesh. The current understanding of the nature and causes of gear and transmission noise is discussed. It is believed that the kinematical errors of the gear mesh have a strong influence on that noise. The completed NASA/Army sponsored research that applies to transmission noise reduction is summarized. The continuing research program is also reviewed.

Coy, John J.↗
NASA NTRS1990

CMOS output buffer wave shaper

As the switching speeds and densities of Digital CMOS integrated circuits continue to increase, output switching noise becomes more of a problem. A design technique which aids in the reduction of switching noise is reported. The output driver stage is analyzed through the use of an equivalent RLC circuit. The results of the analysis are used in the design of an output driver stage. A test circuit based on these techniques is being submitted to MOSIS for fabrication.

Albertson, L.↗
NASA NTRS1995

Reconstruction of an infrared band of meteorological satellite imagery with abductive networks

As the current fleet of meteorological satellites age, the accuracy of the imagery sensed on a spectral channel of the image scanning system is continually and progressively degraded by noise. In time, that data may even become unusable. We describe a novel approach to the reconstruction of the noisy satellite imagery according to empirical functional relationships that tie the spectral channels together. Abductive networks are applied to automatically learn the empirical functional relationships between the data sensed on the other spectral channels to calculate the data that should have been sensed on the corrupted channel. Using imagery unaffected by noise, it is demonstrated that abductive networks correctly predict the noise-free observed data.

Singer, Harvey A.↗