Launch phase simulator.
Launch phase simulation facility incorporates vibration and acoustic testing techniques
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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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Damping of thermal acoustic oscillations in hydrogen systems
Acoustic waves initiated by a large temperature gradient along a tube are defined as thermal acoustic oscillations (TAOs). These oscillations have been damped by introducing such sound absorbing techniques as acoustic filters, resonators, etc.. These devices serve as an acoustic sink that is used to absorb or dissipate the acoustic energy thereby eliminating or damping such oscillations. Several empirical damping techniques, such as attaching a resonator as a side branch or inserting a wire in the tube, have been developed in the past and have provided reasonable success. However, the effect of connecting tube radius, length, and resonator volume on the damping of thermal acoustic oscillations has not been evaluated quantitatively. Further, these methods have not been effective when the oscillating tube radius was relatively large. Detailed theoretical analyses of these techniques including a newly developed method for damping oscillations in a tube of relatively large radius are provided in this presentation.
Gu, Youfan↗
Tensile strain measurements of ceramic fibers using scanning laser acoustic microscopy
A noncontacting technique using scanning laser acoustic microscopy for making in situ tensile strain measurements of small diameter fibers was implemented for the tensile strain analysis of individual Nicalon SiC fibers (nominal diameter 15 microns). Stress versus strain curves for the fibers were plotted from the experimental data. The mean elastic modulus of the fibers was determined to be 185.3 GPa. Similar measurements were made for Carborundum SiC fibers (nominal diameter 28 microns) and Saphikon sapphire fibers (nominal diameter 140 microns), yielding and elastic modulus of 401 and 466.8 GPa, respectively.
Kent, Renee M.↗
Tensile strain measurements of ceramic fibers using scanning laser acoustic microscopy
A noncontacting technique using scanning laser acoustic microscopy for making in situ tensile strain measurements of small diameter fibers was implemented for the tensile strain analysis of individual Nicalon SiC fibers (nominal diameter 15 microns). Stress vs strain curves for the fibers were plotted from the experimental data. The mean elastic modulus of the fibers was determined to be 185.3 GPa. Similar measurements were made for Carborundum SiC fibers (nominal diameter 28 microns) and Saphikon sapphire fibers (nominal diameter 140 microns).
Kent, Renee M.↗
Doppler techniques for measuring fluid velocities
Report gives detailed overview of current laser- and acoustic-Doppler techniques and is used as reference for application of technology to measurement of fluid velocities. Report provides background information, gives detailed summary of specific techniques with emphasis on advantages and disadvantages of each, error sources, and appropriateness of each method for particular applications.
Cliff, W. C.↗
Mechanical systems readiness assessment and performance monitoring study
The problem of mechanical devices which lack the real-time readiness assessment and performance monitoring capability required for future space missions is studied. The results of a test program to establish the feasibility of implementing structure borne acoustics, a nondestructive test technique, are described. The program included the monitoring of operational acoustic signatures of five separate mechanical components, each possessing distinct sound characteristics. Acoustic signatures were established for normal operation of each component. Critical failure modes were then inserted into the test components, and faulted acoustic signatures obtained. Predominant features of the sound signature were related back to operational events occurring within the components both for normal and failure mode operations. All of these steps can be automated. The structure borne acoustics technique lends itself to reducing checkout time, simplifying maintenance procedures, and reducing manual involvement in the checkout, operation, maintenance, and fault diagnosis of mechanical systems.
Source record↗
The role of unsteady aerodynamics in aeroacoustics
The role of acoustics and unsteady aerodynamics research in understanding the fundamental physics of time-dependent fluid phenomena is reviewed. The key issues are illustrated by considering the sound radiation of turbulent jets and the aeroacoustics of rotating bodies such as helicopter rotors. The importance of computational methods as a link between aerodynamics and acoustics is also discussed. It is noted that where acoustic analogy techniques are sufficiently accurate, unsteady aerodynamics can be used for acoustic prediction. In supersonic problems where acoustics and aerodynamics are coupled, an integrated nonlinear analysis can provide an accurate problem solution.
Pao, S. Paul↗
Electrochemical Processes Enhanced by Acoustic Liquid Manipulation
Acoustic liquid manipulation is a family of techniques that employ the nonlinear acoustic effects of acoustic radiation pressure and acoustic streaming to manipulate the behavior of liquids. Researchers at the NASA Glenn Research Center are exploring new methods of manipulating liquids for a variety of space applications, and we have found that acoustic techniques may also be used in the normal Earth gravity environment to enhance the performance of existing fluid processes. Working in concert with the NASA Commercial Technology Office, the Great Lakes Industrial Technology Center, and Alchemitron Corporation (Elgin, IL), researchers at Glenn have applied nonlinear acoustic principles to industrial applications. Collaborating with Alchemitron Corporation, we have adapted the devices to create acoustic streaming in a conventional electroplating process.
Oeftering, Richard C.↗
Application of scanning acoustic microscopy to advanced structural ceramics
A review is presentod of research investigations of several acoustic microscopy techniques for application to structural ceramics for advanced heat engines. Results obtained with scanning acoustic microscopy (SAM), scanning laser acoustic microscopy (SLAM), scanning electron acoustic microscopy (SEAM), and photoacoustic microscopy (PAM) are compared. The techniques were evaluated on research samples of green and sintered monolithic silicon nitrides and silicon carbides in the form of modulus-of-rupture bars containing deliberately introduced flaws. Strengths and limitations of the techniques are described with emphasis on statistics of detectability of flaws that constitute potential fracture origins.
Vary, Alex↗
Acoustic analysis of aft noise reduction techniques measured on a subsonic tip speed 50.8 cm (twenty inch) diameter fan
Sound data which were obtained during tests of a 50.8 cm diameter, subsonic tip speed, low pressure ratio fan were analyzed. The test matrix was divided into two major investigations: (1) source noise reduction techniques; and (2) aft duct noise reduction with acoustic treatment. Source noise reduction techniques were investigated which include minimizing second harmonic noise by varying vane/blade ratio, variation in spacing, and lowering the Mach number through the vane row to lower fan broadband noise. Treatment in the aft duct which includes flow noise effects, faceplate porosity, rotor OGV treatment, slant cell treatment, and splitter simulation with variable depth on the outer wall and constant thickness treatment on the inner wall was investigated. Variable boundary conditions such as variation in treatment panel thickness and orientation, and mixed porosity combined with variable thickness were examined. Significant results are reported.
Stimpert, D. L.↗
Flight Acoustic Testing and For the Rotorcraft Noise Data Acquisition Model (RNM)
Two acoustic flight tests have been conducted on a remote test range at Eglin Air Force Base in the panhandle of Florida. The first was the "Acoustics Week" flight test conducted in September 2003. The second was the NASA Heavy Lift Rotorcraft Acoustics Flight Test conducted in October-November 2005. Benchmark acoustic databases were obtained for a number of rotorcraft and limited fixed wing vehicles for a variety of flight conditions. The databases are important for validation of acoustic prediction programs such as the Rotorcraft Noise Model (RNM), as well as for the development of low noise flight procedures and for environmental impact assessments. An overview of RNM capabilities and a detailed description of the RNM/ART (Acoustic Repropagation Technique) process are presented. The RNM/ART process is demonstrated using measured acoustic data for the MD600N. The RNM predictions for a level flyover speed sweep show the highest SEL noise levels on the flight track centerline occurred at the slowest vehicle speeds. At these slower speeds, broadband noise content is elevated compared to noise levels obtained at the higher speeds. A descent angle sweep shows that, in general, ground noise levels increased with increasing descent rates. Vehicle orientation in addition to vehicle position was found to significantly affect the RNM/ART creation of source noise semi-spheres for vehicles with highly directional noise characteristics and only mildly affect those with weak acoustic directionality. Based on these findings, modifications are proposed for RNM/ART to more accurately define vehicle and rotor orientation.
Burley, Casey L.↗
Flight Acoustic Testing and Data Acquisition For the Rotor Noise Model (RNM)
Two acoustic flight tests have been conducted on a remote test range at Eglin Air Force Base in the panhandle of Florida. The first was the Acoustics Week flight test conducted in September 2003. The second was the NASA Heavy Lift Rotorcraft Acoustics Flight Test conducted in October-November 2005. Benchmark acoustic databases were obtained for a number of rotorcraft and limited fixed wing vehicles for a variety of flight conditions. The databases are important for validation of acoustic prediction programs such as the Rotorcraft Noise Model (RNM), as well as for the development of low noise flight procedures and for environmental impact assessments. An overview of RNM capabilities and a detailed description of the RNM/ART (Acoustic Repropagation Technique) process are presented. The RNM/ART process is demonstrated using measured acoustic data for the MD600N. The RNM predictions for a level flyover speed sweep show the highest SEL noise levels on the flight track centerline occurred at the slowest vehicle speeds. At these slower speeds, broadband noise content is elevated compared to noise levels obtained at the higher speeds. A descent angle sweep shows that, in general, ground noise levels increased with increasing descent rates. Vehicle orientation in addition to vehicle position was found to significantly affect the RNM/ART creation of source noise semi-spheres for vehicles with highly directional noise characteristics and only mildly affect those with weak acoustic directionality. Based on these findings, modifications are proposed for RNM/ART to more accurately define vehicle and rotor orientation.
Conner, David A.↗
Acoustic Source Bearing Estimation (ASBE) computer program development
A new bearing estimation algorithm (Acoustic Source Analysis Technique - ASAT) and an acoustic analysis computer program (Acoustic Source Bearing Estimation - ASBE) are described, which were developed by Computer Sciences Corporation for NASA Langley Research Center. The ASBE program is used by the Acoustics Division/Applied Acoustics Branch and the Instrument Research Division/Electro-Mechanical Instrumentation Branch to analyze acoustic data and estimate the azimuths from which the source signals radiated. Included are the input and output from a benchmark test case.
Wiese, Michael R.↗
The Effects of Linear Microphone Array Changes on Computed Sound Exposure Level Footprints
Airport land planning commissions often are faced with determining how much area around an airport is affected by the sound exposure levels (SELS) associated with helicopter operations. This paper presents a study of the effects changing the size and composition of a microphone array has on the computed SEL contour (ground footprint) areas used by such commissions. Descent flight acoustic data measured by a fifteen microphone array were reprocessed for five different combinations of microphones within this array. This resulted in data for six different arrays for which SEL contours were computed. The fifteen microphone array was defined as the 'baseline' array since it contained the greatest amount of data. The computations used a newly developed technique, the Acoustic Re-propagation Technique (ART), which uses parts of the NASA noise prediction program ROTONET. After the areas of the SEL contours were calculated the differences between the areas were determined. The area differences for the six arrays are presented that show a five and a three microphone array (with spacing typical of that required by the FAA FAR Part 36 noise certification procedure) compare well with the fifteen microphone array. All data were obtained from a database resulting from a joint project conducted by NASA and U.S. Army researchers at Langley and Ames Research Centers. A brief description of the joint project test design, microphone array set-up, and data reduction methodology associated with the database are discussed.
Mueller, Arnold W.↗
Ducted fan acoustic radiation including the effects of nonuniform mean flow and acoustic treatment
Forward and aft acoustic propagation and radiation from a ducted fan is modeled using a finite element discretization of the acoustic field equations. The fan noise source is introduced as equivalent body forces representing distributed blade loading. The flow in and around the nacelle is assumed to be nonuniform, reflecting the effects of forward flight and flow into the inlet. Refraction due to the fan exit jet shear layer is not represented. Acoustic treatment on the inlet and exhaust duct surfaces provides a mechanism for attenuation. In a region enclosing the fan a pressure formulation is used with the assumption of locally uniform flow. Away from the fan a velocity potential formulation is used and the flow is assumed nonuniform but irrotational. A procedure is developed for matching the two regions by making use of local duct modal amplitudes as transition state variables and determining the amplitudes by enforcing natural boundary conditions at the interface between adjacent regions in which pressure and velocity potential are used. Simple models of rotor alone and rotor/exit guide vane generated noise are used to demonstrate the calculation of the radiated acoustic field and to show the effect of acoustic treatment. The model has been used to assess the success of four techniques for acoustic lining optimization in reducing far field noise.
Eversman, Walter↗
Acoustic spectral analysis and testing techniques
Subjects covered in four reports are described including: (1) mathematical techniques for combining decibel levels of octaves or constant bandwidth: (2) techniques for determining equation for power spectral density function; (3) computer program to analyze acoustical test data; and (4) computer simulation of horn responses utilizing hyperbolic horn theory.
Hayes, C. D.↗
Sound radiation from annular ducts/nozzles using modal decomposition of in-duct acoustic power
Using a refined acoustic impulse technique, an experimental program was carried out to determine the proper procedure for measuring the acoustic power for both incident and reflected sound fields for annular ducts with and without nozzles at various flow conditions. Several radial and azimuthal pressure measurements were made, and using these complex pressure data, the modal content of the pressure field was determined. A mathematical approach for the modal decomposition of annular duct acoustic power was developed. The acoustic power due to each individual mode and also their total sum were derived. The acoustic characteristics of annular duct-nozzle systems were studied at various flow conditions. The results derived from the experiments include the termination reflection coefficient, the normalized transmission coefficients, the power transfer functions and the power imbalance.
Salikuddin, M.↗
Application of Air Coupled Acoustic Thermography (ACAT) for Inspection of Honeycomb Sandwich Structures
The application of a noncontact air coupled acoustic heating technique is investigated for the inspection of advanced honeycomb composite structures. A weakness in the out of plane stiffness of the structure, caused by a delamination or core damage, allows for the coupling of acoustic energy and thus this area will have a higher temperature than the surrounding area. Air coupled acoustic thermography (ACAT) measurements were made on composite sandwich structures with damage and were compared to conventional flash thermography. A vibrating plate model is presented to predict the optimal acoustic source frequency. Improvements to the measurement technique are also discussed.
Winfree, William P.↗