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NASA NTRS1980

Two-photon excitation of nitric oxide fluorescence as a temperature indicator in unsteady gas-dynamic processes

A laser induced fluorescence technique, suitable for measuring fluctuating temperatures in cold turbulent flows containing very low concentrations of nitric oxide is described. Temperatures below 300 K may be resolved with signal to noise ratios greater than 50 to 1 using high peak power, tunable dye lasers. The method relies on the two photon excitation of selected ro-vibronic transitions. The analysis includes the effects of fluorescence quenching and shows the technique to be effective at all densities below ambient. Signal to noise ratio estimates are based on a preliminary measurement of the two photon absorptivity for a selected rotational transition in the NO gamma (0,0) band.

Mckenzie, R. L.↗

NASA NTRS2021

Adaptive Aerostructures for Revolutionary Civil Supersonic Transportation

To enable commercially viable civil supersonic transport (SST) aircraft, innovative solutions must be developed to meet noise and efficiency requirements for overland flight. This research effort consists of a multidisciplinary team of academic and industrial experts exploring for the first time the potential of small real-time geometric outer mold line (OML) reconfigurations to minimize sonic boom signatures and aircraft drag in response to changing ambient conditions, thereby enabling noise-compliant overland supersonic flight. The team utilizes recent advances in supersonic computational fluid dynamic (CFD) methods, new noise prediction tools, and new design approaches to consider embedded highly energy-dense shape memory alloy (SMA) actuators for local shape modifications to an SST aircraft leading to optimal low boom signature and low drag in different environments. This university-led program will provide strategic leadership toward technology convergence that advances NASA's Aerospace Research Mission Directorate's (ARMD) research objectives with regard to Thrust 2: “Innovation in Commercial Supersonic Aircraft” by exploring for the first time enabling low-boom operation across a range of flight conditions via structural adaptivity, and will promote education of the next generation of engineers. The overall research strategy is to pursue three critical areas: the design of configurations for reducing boom, SMA material development and modeling, and technology feasibility demonstration in a relevant environment. Initially, the team will identify potential applications where structure or geometry adaptivity provides a benefit in noise or drag across the entire flight envelope. For selected applications/structural locations, required OML geometry changes will be determined based on analysis of sonic boom ground signature and drag reduction using new design tools, trade studies, and atmospheric sensing techniques. Designs will be developed and evaluated against requirements on loading, stroke length, and operational temperature. New alloy formulations will be developed tailored for both autonomous and controlled actuation modes. As the SMA material development matures, integrated system-level factors will be investigated. Optimized designs for small-scale distributed adaptivity applications of maximum benefit will then be matured and tested, moving toward demonstration of the innovative technology approaches at a TRL 4-5 and showing that sonic booms can be reduced by reconfiguration on demand.

Koushik Datta↗

NASA NTRS1996

Measurement of Noise Produced by a Plasma Contactor Operating in Ground Based Facilities

Methods to measure electric field fluctuations accurately in a plasma with an active monopole antenna are described. It is shown that the conductive surfaces of the antenna must be adequately isolated from the ambient plasma and that the monopole must be sufficiently short to avoid antenna amplifier saturation. Experimental results illustrate that the noise produced by plasma contactor operation and sensed by the antenna is due to plasma phenomena and is not induced by laboratory power supplies. A good correlation is shown between the current fluctuations in the contactor electrical circuit and the noise detected by the antenna. A large body of experimental data support the conclusion that the majority of noise sensed by the antenna at frequencies less than 1 MHz is due to current fluctuations (electrostatic waves) in the plasma adjacent to the antenna and not to electromagnetic wave radiation. Caution is suggested when comparing antenna noise measurements to conventional specifications for radiated emissions.

Snyder, Steve↗

NASA NTRS2014

Direct Signal-to-Noise Quality Comparison between an Electronic and Conventional Stethoscope aboard the International Space Station

Introduction: Evaluation of heart, lung, and bowel sounds is routinely performed with the use of a stethoscope to help detect a broad range of medical conditions. Stethoscope acquired information is even more valuable in a resource limited environments such as the International Space Station (ISS) where additional testing is not available. The high ambient noise level aboard the ISS poses a specific challenge to auscultation by stethoscope. An electronic stethoscope's ambient noise‐reduction, greater sound amplification, recording capabilities, and sound visualization software may be an advantage to a conventional stethoscope in this environment. Methods: A single operator rated signal‐to‐noise quality from a conventional stethoscope (Littman 2218BE) and an electronic stethoscope (Litmann 3200). Borborygmi, pulmonic, and cardiac sound quality was ranked with both stethoscopes. Signal‐to‐noise rankings were preformed on a 1 to 10 subjective scale with 1 being inaudible, 6 the expected quality in an emergency department, 8 the expected quality in a clinic, and 10 the clearest possible quality. Testing took place in the Japanese Pressurized Module (JPM), Unity (Node 2), Destiny (US Lab), Tranquility (Node 3), and the Cupola of the International Space Station. All examinations were conducted at a single point in time. Results: The electronic stethoscope's performance ranked higher than the conventional stethoscope for each body sound in all modules tested. The electronic stethoscope's sound quality was rated between 7 and 10 in all modules tested. In comparison, the traditional stethoscope's sound quality was rated between 4 and 7. The signal to noise ratio of borborygmi showed the biggest difference between stethoscopes. In the modules tested, the auscultation of borborygmi was rated between 5 and 7 by the conventional stethoscope and consistently 10 by the electronic stethoscope. Discussion: This stethoscope comparison was limited to a single operator. However, we believe the results are noteworthy. The electronic stethoscope out preformed the traditional stethoscope in each direct comparison. Consideration should be made to incorporate an electronic stethoscope into current and future space vehicle medical kits.

Marshburn, Thomas↗

NASA NTRS1983

Apparatus and method for jet noise suppression

A method and apparatus for jet noise suppression through control of the static pressure of the jet and control of the rate of entrainment of ambient fluid into the jet downstream of the exhaust nozzle is disclosed. The momentum flux over an extended region of the jet is regulated, affecting Reynolds stresses in the jet and the spreading angle of the jet. Static pressure is controlled through a long hollow, porous nozzle plug centerbody which may be selectively vented to ambient conditions, connected to a vacuum source, or supplied with fluids of various densities for injection into the stream. Sound in the jet may be channeled along the nozzle plug centerbody by injecting coolant such as a cryogenic fluid throughout the center-body into the jet.

Maestrello, L.↗

NASA NTRS1975

Density fluctuations and radiated noise for a high-temperature supersonic jet

Experimental data on density fluctuations were obtained by the laser Schlieren method in a supersonic jet which at the nozzle exit had a Mach number of 1.43 and a stagnation temperature of about 1090 K. The jet emerged into the ambient atmosphere in an anechoic chamber, correctly expanded from a nozzle which had an exit diameter of 10.8 cm. Using the information on the density fluctuations and the mean shear obtained by probes, the autocorrelation of the radiated noise was calculated by a theory that is suitable for Mach wave emission. This theory is a modification of that developed by Ffowcs Williams and Maidanik (1965). The calculated noise field agrees well with that obtained by using microphones outside the jet.

Parthasarathy, S. P.↗

NASA NTRS2021

Methods for Recording and Documenting Ambient Environmental Sound for use in Listening Devices

The potential for implementing Advanced Air Mobility (AAM) vehicles as a viable new transportation system into communities will likely be significantly affected by the psychoacoustic impact of these new noise sources into the existing ambient soundscape. This document addresses a need within the research community for a consistent means of documenting recordings of the ambient soundscape via a metadata framework (Rizzi, et al. 2020). Such recordings can provide a cognitive context for AAM vehicle sounds, as well as a fixed condition or independent variable against which experimental manipulations of vehicle sounds can be evaluated in listening tests. This document also provides recommendations for recording and reproduction techniques of ambient sound. A brief review is made of the use of ambient recordings in prior aircraft noise studies, and of psychoacoustic motivations for its implementation is reviewed from the fields of soundscape, auditory scene analysis, and time-varying partial specific loudness research.

urban air mobility↗

NASA NTRS2017

Reduced Noise Gas Turbine Engine System and Supersonic Exhaust Nozzle System Using Elector to Entrain Ambient Air

One embodiment of the present invention is a unique gas turbine engine system. Another embodiment is a unique exhaust nozzle system for a gas turbine engine. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engine systems and exhaust nozzle systems for gas turbine engines. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Sokhey, Jagdish S.↗

NASA NTRS1981

Effects of noise frequency on performance and annoyance for women and men

Effects of noise frequencies on both performance on a complex psychomotor task and annoyance were investigated for men (n = 30) and women (n = 30). Each subject performed a complex psychomotor task for 50 min in the presence of low-frequency noise, high-frequency noise, or ambient noise. Women and men learned the task at different rates. Little effect of noise was shown. Annoyance ratings were subsequently obtained from each subject for noises of various frequencies by the method of magnitude estimation. High-frequency noises were more annoying than low-frequency noises regardless of sex and immediate prior exposure to noise. Sex differences in annoyance did not occur. No direct relationship between learning to perform a complex task while exposed to noise and annoyance by that noise was demonstrated.

Key, K. F.↗

NASA NTRSDate not supplied

PVT+AUDIO. Online Psychoacoustic Testing iOS App for Evaluating AAM/UAM Noise Resonse

PVT+AUDIO is an extension of the existing Psychomoter Vigilance Task application that NASA released over 2 years ago for evaluating pilot fatigue. PVT+AUDIO is designed to present audio stimuli using a method of limits to determine the relationship between objective acoustic parameters and psychacoustic response, for application to Urban Air Mobility (UAM) and Advanced Air Mobility (AAM). Responses include annoyance, acceptance, blend with ambient sound, and detection. The app runs within Apple's iOS ecosystem and utilizes binaural audio simulations of vehicles and ambient sound, and is designed to compensate for headphone response. A prototype experiment is described, along with issues related to calibration and subject engagement.

aircraft noise disturbance↗

NASA NTRS2001

Acoustical and Flowfield Characterization of a Scaled Tabletop Rocket

An analysis of the acoustical and flowfield environment for the scaled 1-pound-force (lbf) thrust tabletop motor was performed. This tabletop motor from NASA Stennis Space Center Is composed of Plexiglas burning In gaseous oxygen with a graphite insert for the nozzle portion. The nozzle has a throat diameter of 0.2 inch and an exit diameter of 0.38 Inch. With a chamber pressure at 55 pounds per square Inch absolute (psia), a normal shock is formed immediately downstream of the nozzle exit plane as the combustion products exhaust into the ambient at atmospheric pressure. The jet characterization Is based on computational fluid dynamics (CFD) in conjunction with Kirchhoff surface integral formulation and compared with correlations developed for measured rocket noise and a pressure fluctuation scaling (PFS) method. Predictions and comparisons are made for the overall sound pressure levels (OASPL's) and spectral dependence of sound pressure level (SPL). The overall objective of this effort is to develop methods for scaling the acoustic and flowfield environment of rockets with a wide range of thrust (1 lbf to 1 million lbf).

Kandula, Max↗

NASA NTRS2001

Comparison of Modal Analysis Methods Applied to a Vibro-Acoustic Test Article

Modal testing of a vibro-acoustic test article referred to as the Aluminum Testbed Cylinder (ATC) has provided frequency response data for the development of validated numerical models of complex structures for interior noise prediction and control. The ATC is an all aluminum, ring and stringer stiffened cylinder, 12 feet in length and 4 feet in diameter. The cylinder was designed to represent typical aircraft construction. Modal tests were conducted for several different configurations of the cylinder assembly under ambient and pressurized conditions. The purpose of this paper is to present results from dynamic testing of different ATC configurations using two modal analysis software methods: Eigensystem Realization Algorithm (ERA) and MTS IDEAS Polyreference method. The paper compares results from the two analysis methods as well as the results from various test configurations. The effects of pressurization on the modal characteristics are discussed.

Pritchard, Jocelyn↗

NASA NTRS2000

Thermographic Nondestructive Evaluation of the Space Shuttle Main Engine Nozzle

The methods and results presented in this summary address the thermographic identification of interstitial leaks in the Space Shuttle Main Engine nozzles. A highly sensitive digital infrared camera is used to record the minute cooling effects associated with a leak source, such as a crack or pinhole, hidden within the nozzle wall by observing the inner "hot wall" surface as the nozzle is pressurized. These images are enhanced by digitally subtracting a thermal reference image taken before pressurization, greatly diminishing background noise. The method provides a nonintrusive way of localizing the tube that is leaking and the exact leak source position to within a very small axial distance. Many of the factors that influence the inspectability of the nozzle are addressed; including pressure rate, peak pressure, gas type, ambient temperature and surface preparation.

Walker, James L.↗

NASA NTRS2001

Thermographic/Nondestructive Evaluation of the Space Shuttle Main Engine Nozzle

The methods and results presented in this summary address the thermographic identification of interstitial leaks in the Space Shuttle Main Engine nozzles. A highly sensitive digital infrared camera is used to record the minute cooling effects associated with a leak source, such as a crack or pinhole, hidden within the nozzle wall by observing the inner 'hot wall' surface as the nozzle is pressurized. These images are enhanced by digitally subtracting a thermal reference image taken before pressurization, greatly diminishing background noise. The method provides a nonintrusive way of localizing the tube that is leaking and the exact leak source position to within a very small axial distance. Many of the factors that influence the inspectability of the nozzle are addressed; including pressure rate, peak pressure, gas type, ambient temperature and surface preparation.

Walker, J. L.↗

NASA NTRS2003

Leak Location and Classification in the Space Shuttle Main Engine Nozzle by Infrared Testing

The Space Shuttle Main Engine (SSME) is composed of cooling tubes brazed to the inside of a conical structural jacket. Because of the geometry there are regions that can't be inspected for leaks using the bubble solution and low-pressure method. The temperature change due escaping gas is detectable on the surface of the nozzle under the correct conditions. The methods and results presented in this summary address the thermographic identification of leaks in the Space Shuttle Main Engine nozzles. A highly sensitive digital infrared camera is used to record the minute temperature change associated with a leak source, such as a crack or pinhole, hidden within the nozzle wall by observing the inner "hot wall" surface as the nozzle is pressurized. These images are enhanced by digitally subtracting a thermal reference image taken before pressurization, greatly diminishing background noise. The method provides a nonintrusive way of localizing the tube that is leaking and the exact leak source position to within a very small axial distance. Many of the factors that influence the inspectability of the nozzle are addressed; including pressure rate, peak pressure, gas type, ambient temperature and surface preparation.

Russell, Samuel S.↗

NASA NTRS1992

Human factors with nonhumans - Factors that affect computer-task performance

There are two general strategies that may be employed for 'doing human factors research with nonhuman animals'. First, one may use the methods of traditional human factors investigations to examine the nonhuman animal-to-machine interface. Alternatively, one might use performance by nonhuman animals as a surrogate for or model of performance by a human operator. Each of these approaches is illustrated with data in the present review. Chronic ambient noise was found to have a significant but inconsequential effect on computer-task performance by rhesus monkeys (Macaca mulatta). Additional data supported the generality of findings such as these to humans, showing that rhesus monkeys are appropriate models of human psychomotor performance. It is argued that ultimately the interface between comparative psychology and technology will depend on the coordinated use of both strategies of investigation.

Washburn, David A.↗

NASA NTRSDate not supplied

A Procedure for Obtaining Forecast Turbulence Parameters in the Atmospheric Boundary Layer for Acoustic Propagation

Propagation through turbulence causes a mean reduction in loudness of sonic booms and in some cases can cause significant fluctuations in loudness about that mean. Understanding these effects is important for accurately planning loudness levels during upcoming community noise tests with the X-59 aircraft as well as mitigating the risk for excessive loudness due to turbulence. Current methods for modeling acoustic propagation through turbulence require several atmospheric parameters including the atmospheric boundary layer (ABL) height, friction velocity, mixed-layer velocity scale, surface-layer temperature scale, as well as ambient pressure, temperature, and humidity within the ABL. Accurate forecasts of these parameters are needed for X-59 flight planning and may also be useful for planning future supersonic aircraft certification flight tests. This presentation showcases one method for obtaining the forecast turbulence and ambient atmospheric parameters from freely available Climate Forecast System Version 2 data. Forecast parameters are compared to measurements to assess accuracy and utility.

sonic boom↗

NASA NTRS1985

Microwave Surface Resistivity of Several Materials at Ambient Temperature

Microwave surface resistivity of a number of metal and other sample materials was measured at X-band, approximately 8400 MHz. The method of measurement uses a TE sub 011 mode circular waveguide cavity resonator wherein the sample is used as one end of the cavity. This method has been used previously in JPL work with good results. Microwave reflection loss and noise arising from the dissipative loss are given, for materials having negligible transmission leakage.

H. F. Reilly↗