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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

The influence of inlet design on the aeroacoustic performance of a JT15D turbofan engine as measured in the NASA-Ames 40 x 80 foot wind tunnel

The influence of inlet design on the aeroacoustic performance of a JT15D turbofan engine was investigated in the NASA-Ames 40 x 80 ft wind tunnel. Four inlet designs representative of those found in commercial service were evaluated at a forward velocity of 80 kn. The inlet designs considered were selected to evaluate the importance of circumferential static pressure distortion (SPD) for a diffusing sound suppressing inlet and throat Mach number (Mth) for a hardwall inlet on the acoustic characteristics of the JT15D engine. Several speed points were studied simulating the operating conditions spanning approach to take-off. Results demonstrated that the dependency of the forward radiated noise on inlet aerodynamic design parameters was significant (about 5 dB) for the range of SPD (0.1-3.0%) and Mth (0.3-0.6) tested. The performance of the bulk absorber acoustic treatment used in the diffusing sound suppressing inlet is also discussed.

Holm, R. G.↗
NASA NTRSDate not supplied

Trajectory Generation for Distributed Electric Propulsion Vehicles with Propeller Synchronization

In this paper, we propose a method for generating dynamically feasible trajectories for an acoustically aware vehicle with propeller phase control. The trajectory generation procedure allows both propeller phase control and navigation objectives to be considered simultaneously. The presented method is demonstrated where the mission objectives are given as a desired position and phase trajectory. From these trajectories, the full desired state of the vehicle is calculated. Furthermore, the control inputs that realize the desired mission objectives are computed. The acoustic performance for the given trajectory is estimated in terms of sound pressure level as a function of tracking performance. The method is demonstrated in simulation, where the vehicle must navigate through an urban environment with both spatial and acoustic constraints. In the presented scenario, the vehicle must follow a given flight path, and can only reduce sound pressure level by changing the propeller phase targets.

acoustically-aware vehicle↗
NASA NTRSDate not supplied

Trajectory Generation for Distributed Electric Propulsion Vehicles with Propeller Synchronization

In this paper, we propose a method for generating dynamically feasible trajectories for an acoustically aware vehicle with propeller phase control. The trajectory generation procedure allows both propeller phase control and navigation objectives to be considered simultaneously. The presented method is demonstrated where the mission objectives are given as a desired position and phase trajectory. From these trajectories, the full desired state of the vehicle is calculated. Furthermore, the control inputs that realize the desired mission objectives are computed. The acoustic performance for the given trajectory is estimated in terms of sound pressure level as a function of tracking performance. The method is demonstrated in simulation, where the vehicle must navigate through an urban environment with both spatial and acoustic constraints. In the presented scenario, the vehicle must follow a given flight path, and can only reduce sound pressure level by changing the propeller phase targets.

Acoustically-aware vehicle↗
NASA NTRS1972

Design of a TF34 turbofan mixer for reduction of flap impingement noise

This portion of the TF-34 turbofan quiet engine studies has been devoted to the selection and design of a special mixer exhaust nozzle system to reduce the maximum 150 m (500 foot) sideline noise generated by the impingement of four engine exhausts on a STOL wing flap system to less than 92 PNdB. The design concept selected consists of a 12-lobe internal mixer and a 12-lobe external mixer mounted in series. The internal mixer reduces maximum exhaust velocities by mixing the fan and turbine streams. The external mixer is designed to reduce the velocity of the exhaust stream striking the wing flap surfaces. A ground test version of this concept has been designed to be installed and tested on an acoustically treated TF-34 engine nacelle, with flexibility to simulate a flight version of this concept which has also been defined. Estimated noise levels are 2 PNdB below the objective at approach and 2 PNdB above the objective at takeoff, with an uncertainty band of +3, -2 PNdB.

Chamay, A.↗
NASA NTRS1975

Simulation by vortex rings of the unsteady pressure field near a jet

A coordinated theoretical and experimental program has been undertaken to construct a model for the shedding of vortex rings in order to simulate the real-time pressure variation in the acoustic region near the jet. The basic parameters in the analytic solutions are the eddy viscosity coefficient and the time intervals between successive shedding of vortex rings from the nozzle lip. The experimental and theoretical results show good qualitative agreement.

Liu, C. H.↗
NASA NTRS1977

Aircraft-noise synthesizer

Digital synthesis system has been designed and is being used for aircraft noise simulation. Device is extremely desirable for research into effects of aircraft noise on people. Unit could be modified for use in road or rail vehicle noise simulation, and most other applications that involve time varying acoustical parameters.

Brown, T. J.↗
NASA NTRS1977

Non-linear duct acoustics and its application to fan noise

Quite often the scalar Helmholtz equation is assumed to be the fundamental equation of duct acoustics and various relations are derived from it. An investigation is, therefore, conducted regarding the underlying assumptions leading to the Helmholtz equation. It is found that serious errors, even well below 186 dB, are possible if the assumption of linearity were to be made. In duct acoustics these errors are highest near the cutoff points and in the case of ducts with transonic flow. It is pointed out that serious errors could arise if a nonlinear problem is analyzed by linear methods. At times, an entire phenomenon remains unpredictable by linear methods. Attention is given to the characteristics of nonlinear systems, the phenomenon of multiple pure tones in the case of noise from the aircraft engine fans, the limitations of the conventional acoustics equation, duct shape and nonlinearity, and the numerical simulation of a fan with 8 blades.

Vaidya, P. G.↗
NASA NTRS1981

Simulation of the current-driven electrostatic ion cyclotron instability

Results are presented of a self-consistent particle simulation of the growth and saturation of electrostatic ion cyclotron (EIC) waves along auroral field lines. The driving mechanism for the waves is an initial drifting Maxwellian distribution for the electrons. The magnetic field is taken to lie in the simulation plane, so that modes such as the ion acoustic instability and the EIC instability can be excited, thus making it possible to study the behavior of EIC waves in the presence of ion acoustic turbulence. A dc electric field, which tends to keep the current constant along the field lines, is included. It is shown that the EIC instability grows to a moderate level before saturating due to plateau formation. The perpendicular ion temperature increases by typically 40%, with an increase arising from bulk heating only. The anomalous resistivity, associated with the EIC instability is determined and compared with previous calculations and with that due to the ion acoustic instability. Implications of the results for observation of ion cyclotron waves on auroral field lines are discussed.

Pritchett, P. L.↗
NASA NTRS1982

Interior noise considerations for advanced high-speed turboprop aircraft

This paper describes recent research on noise generated by high-speed propellers, on noise transmission through acoustically treated aircraft sidewalls and on subjective response to simulated turboprop noise. Propeller noise discussion focuses on theoretical prediction methods for complex blade shapes designed for low noise at Mach = 0.8 flight and on comparisons with experimental test results. Noise transmission experiments using a 168 cm. diameter aircraft fuselage model and scaled heavy-double-wall treatments indicate that the treatments perform well and that the predictions are usually conservative. Studies of subjective comfort response in an anechoic environment are described for noise signatures having combinations of broadband and propeller-type tone components.

Mixson, J. S.↗
NASA NTRS1980

Results of tests on a specimen of the SRB aft skirt heat shield curtain in the MSFC LRLF

A full scale segment of the actual Solid Rocket Booster aft skirt heat shield curtain was tested in the Large Radiant Lamp Facility (LRLF) at Marshall Space Flight Center. The curtain was mounted in the horizontal position in the same manner as it is to be mounted on the SRB. A shaker rig was designed and used to provide a motion of the curtain, simulating that to be caused in flight by vehicle acoustics. Thermocouples were used to monitor curtain materials temperatures. Both ascent and reentry heat loads were applied to the test specimen. All aspects of the test setup performed as expected, and the test was declared successful.

Dean, W. G.↗
NASA NTRS1993

Driving a car with custom-designed fuzzy inferencing VLSI chips and boards

Vehicle control in a-priori unknown, unpredictable, and dynamic environments requires many calculational and reasoning schemes to operate on the basis of very imprecise, incomplete, or unreliable data. For such systems, in which all the uncertainties can not be engineered away, approximate reasoning may provide an alternative to the complexity and computational requirements of conventional uncertainty analysis and propagation techniques. Two types of computer boards including custom-designed VLSI chips were developed to add a fuzzy inferencing capability to real-time control systems. All inferencing rules on a chip are processed in parallel, allowing execution of the entire rule base in about 30 microseconds, and therefore, making control of 'reflex-type' of motions envisionable. The use of these boards and the approach using superposition of elemental sensor-based behaviors for the development of qualitative reasoning schemes emulating human-like navigation in a-priori unknown environments are first discussed. Then how the human-like navigation scheme implemented on one of the qualitative inferencing boards was installed on a test-bed platform to investigate two control modes for driving a car in a-priori unknown environments on the basis of sparse and imprecise sensor data is described. In the first mode, the car navigates fully autonomously, while in the second mode, the system acts as a driver's aid providing the driver with linguistic (fuzzy) commands to turn left or right and speed up or slow down depending on the obstacles perceived by the sensors. Experiments with both modes of control are described in which the system uses only three acoustic range (sonar) sensor channels to perceive the environment. Simulation results as well as indoors and outdoors experiments are presented and discussed to illustrate the feasibility and robustness of autonomous navigation and/or safety enhancing driver's aid using the new fuzzy inferencing hardware system and some human-like reasoning schemes which may include as little as six elemental behaviors embodied in fourteen qualitative rules.

Pin, Francois G.↗
NASA NTRS1993

Accuracy considerations in the computational analysis of jet noise

The application of computational fluid dynamics methods to the analysis of problems in aerodynamic noise has resulted in the extension and adaptation of conventional CFD to the discipline now referred to as computational aeroacoustics (CAA). In the analysis of jet noise accurate resolution of a wide range of spatial and temporal scales in the flow field is essential if the acoustic far field is to be predicted. The numerical simulation of unsteady jet flow has been successfully demonstrated and many flow features have been computed with reasonable accuracy. Grid refinement and increased solution time are discussed as means of improving accuracy of Navier-Stokes solutions of unsteady jet flow. In addition various properties of different numerical procedures which influence accuracy are examined with particular emphasis on dispersion and dissipation characteristics. These properties are investigated by using selected schemes to solve model problems for the propagation of a shock wave and a sinusoidal disturbance. The results are compared for the different schemes.

Scott, James N.↗
NASA NTRS1994

Development of a nondestructive vibration technique for bond assessment of Space Shuttle tiles

This final report describes the achievements of the above titled project. The project is funded by NASA-KSC (Grant No. NAG 10-0117) for the period of 1 Jan. to 31 Dec. 1993. The purpose of this project was to develop a nondestructive, noncontact technique based on 'vibration signature' of tile systems to quantify the bond conditions of the thermal protection system) tiles of Space Shuttle orbiters. The technique uses a laser rapid scan system, modal measurements, and finite element modeling. Finite element models were developed for tiles bonded to both clamped and deformable integrated skin-stringer orbiter mid-fuselage. Results showed that the size and location of a disbonded tile can be determined from frequency and mode shape information. Moreover, a frequency response survey was used to quickly identify the disbonded tiles. The finite element results were compared with experimentally determined frequency responses of a 17-tile test panel, where a rapidscan laser system was employed. An excellent degree of correlation between the mathematical simulation and experimental results was realized. An inverse solution for single-tile assemblies was also derived and is being implemented into a computer program that can interact with the modal testing software. The output of the program displays the size and location of disbond. This program has been tested with simulated input (i.e., finite element data), and excellent agreement between predicted and simulated disbonds was shown. Finally, laser vibration imaging and acoustic emission techniques were shown to be well suited for detecting and monitoring the progressive damage in Graphite/Epoxy composite materials.

Moslehy, Faissal A.↗
NASA NTRS2001

Determination of the Accommodation Coefficient Using Vapor/gas Bubble Dynamics in an Acoustic Field

Nonequilibrium liquid/vapor phase transformations can occur in superheated or subcooled liquids in fast processes such as in evaporation in a vacuum. The rate at which such a phase transformation occurs depends on the "condensation" or "accommodation" coefficient, Beta, which is a property of the interface. Existing measurement techniques for Beta are complex and expensive. The development of a relatively inexpensive and reliable technique for measurement of Beta for a wide range of substances and temperatures is of great practical importance. The dynamics of a bubble in an acoustic field strongly depends on the value of Beta. It is known that near the saturation temperature, small vapor bubbles grow under the action of an acoustic field due to "rectified heat transfer." This finding can be used as the basis for an effective measurement technique of Beta. We developed a theory of vapor bubble behavior in an isotropic acoustic wave and in a plane standing acoustic wave. A numerical code was developed which enables simulation of a variety of experimental situations and accurately takes into account slowly evolving temperature. A parametric study showed that the measurement of Beta can be made over a broad range of frequencies and bubble sizes. We found several interesting regimes and conditions which can be efficiently used for measurements of Beta. Measurements of Beta can be performed in both reduced and normal gravity environments.

Gumerov, Nail A.↗
NASA NTRS1995

Evaluation of Aircraft Platforms for SOFIA by Computational Fluid Dynamics

The selection of an airborne platform for the Stratospheric Observatory for Infrared Astronomy (SOFIA) is based not only on economic cost, but technical criteria, as well. Technical issues include aircraft fatigue, resonant characteristics of the cavity-port shear layer, aircraft stability, the drag penalty of the open telescope bay, and telescope performance. Recently, two versions of the Boeing 747 aircraft, viz., the -SP and -200 configurations, were evaluated by computational fluid dynamics (CFD) for their suitability as SOFIA platforms. In each configuration the telescope was mounted behind the wings in an open bay with nearly circular aperture. The geometry of the cavity, cavity aperture, and telescope was identical in both platforms. The aperture was located on the port side of the aircraft and the elevation angle of the telescope, measured with respect to the vertical axis, was 500. The unsteady, viscous, three-dimensional, aerodynamic and acoustic flow fields in the vicinity of SOFIA were simulated by an implicit, finite-difference Navier-Stokes flow solver (OVERFLOW) on a Chimera, overset grid system. The computational domain was discretized by structured grids. Computations were performed at wind-tunnel and flight Reynolds numbers corresponding to one free-stream flow condition (M = 0.85, angle of attack alpha = 2.50, and sideslip angle beta = 0 degrees). The computational domains consisted of twenty-nine(29) overset grids in the wind-tunnel simulations and forty-five(45) grids in the simulations run at cruise flight conditions. The maximum number of grid points in the simulations was approximately 4 x 10(exp 6). Issues considered in the evaluation study included analysis of the unsteady flow field in the cavity, the influence of the cavity on the flow across empennage surfaces, the drag penalty caused by the open telescope bay, and the noise radiating from cavity surfaces and the cavity-port shear layer. Wind-tunnel data were also available to compare to the CFD results; the data permitted an assessment of CFD as a design tool for the SOFIA program.

Klotz, S. P.↗
NASA NTRS2008

Effects of Wall Cooling on Hypersonic Boundary Layer Receptivity Over a Cone

Effects of wall cooling on the receptivity process induced by the interaction of slow acoustic disturbances in the free-stream are numerically investigated for a boundary layer flow over a 5-degrees straight cone. The free-stream Mach number is 6.0 and the Reynolds number is 7.8x10(exp 6)/ft. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using 3rd-order total variation diminishing (T VD) Runge-K utta scheme for time integration. Computations are performed for a cone with nose radius of 0.001 inch for adiabatic wall temperature (T(sub aw)), 0.75*T(sub aw), 0.5*T(sub aw), 0.40*T(sub aw), 0.30*T(sub aw), and 0.20*T(sub aw). Once the mean flow field is computed, disturbances are introduced at the upstream end of the computational domain. Generation of instability waves from leading edge region and receptivity of boundary layer to slow acoustic waves are investigated. Computations showed that wall cooling has strong stabilization effect on the first mode disturbances as was observed in the experiments. T ransition location moved to upstream when wall cooling was applied It is also found that the boundary layer is much more receptive to fast acoustic wave (by almost a factor of 50). When simulations performed using the same forcing frequency growth of the second mode disturbances are delayed with wall cooling and they attained values two times higher than that of adiabatic case. In 0.20*T(sub aw) case the transition Reynolds number is doubled compared to adiabatic conditions. The receptivity coefficient for adiabatic wall case (804 R) is 1.5225 and for highly cooled cones (241, and 161 R); they are in the order of 10(exp -3).

Kara, K.↗
NASA NTRS2008

Aeroacoustic Simulations of Tandem Cylinders with Subcritical Spacing

Tandem cylinders are being studied because they model a variety of component level interactions of landing gear. The present effort is directed at the case of two identical cylinders with their centroids separated in the streamwise direction by 1.435 diameters. Experiments in the Basic Aerodynamic Research Tunnel and Quiet Flow Facility at NASA Langley Research Center have provided an extensive experimental database of the nearfield flow and radiated noise. The measurements were conducted at a Mach number of 0.1285 and Reynolds number of 1.66x10(exp 5) based on the cylinder diameter. A trip was used on the upstream cylinder to insure a fully turbulent flow separation and, hence, to simulate a major aspect of high Reynolds number flow. The parallel computational effort uses the three-dimensional Navier-Stokes solver CFL3D with a hybrid, zonal turbulence model that turns off the turbulence production term everywhere except in a narrow ring surrounding solid surfaces. The experiments exhibited an asymmetry in the surface pressure that was persistent despite attempts to eliminate it through small changes in the configuration. To model the asymmetry, the simulations were run with the cylinder configuration at a nonzero but small angle of attack. The computed results and experiments are in general agreement that vortex shedding for the spacing studied herein is weak relative to that observed at supercritical spacings. Although the shedding was subdued in the simulations, it was still more prominent than in the experiments. Overall, the simulation comparisons with measured near-field data and the radiated acoustics are reasonable, especially if one is concerned with capturing the trends relative to larger cylinder spacings. However, the flow details of the 1.435 diameter spacing have not been captured in full even though very fine grid computations have been performed. Some of the discrepancy may be associated with the simulation s inexact representation of the experimental configuration, but numerical and flow modeling errors are also likely contributors to the observed differences.

Lockard, David P.↗
NASA NTRS2001

Design and Integration of a Rotor Alone Nacelle for Acoustic Fan Testing

A brief summary of the design, integration and testing of a rotor alone nacelle (RAN) in NASA Glenn's 9'x 15' Low Speed Wind Tunnel (LSWT) is presented. The purpose of the RAN system was to provide an "acoustically clean" flow path within the nacelle to isolate that portion of the total engine system acoustic signature attributed to fan noise. The RAN design accomplished this by removing the stators that provided internal support to the nacelle. In its place, two external struts mounted to a two-axis positioning table located behind the tunnel wall provided the support. Nacelle-mounted lasers and a closed-loop control system provided the input to the table to maintain nacelle to fan concentricity as thermal and thrust loads displaced the strut-mounted fan. This unique design required extensive analysis and verification testing to ensure the safety of the fan model, propulsion simulator drive rig, and facility, along with experimental consistency of acoustic data obtained while using the RAN system. Initial testing was used to optimize the positioning system and resulted in concentricity errors of +/- 0.0031 in. in the horizontal direction and +0.0035/-0.0013 in, in the vertical direction. As a result of successful testing, the RAN system will be transitioned into other acoustic research programs at NASA Glenn Research Center.

Shook, Tony D.↗