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At least 253 records · Page 14

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NASA NTRS2006

A Sub-filter Scale Noise Equation far Hybrid LES Simulations

Hybrid LES/subscale modeling approaches have an important advantage over the current noise prediction methods in that they only involve modeling of the relatively universal subscale motion and not the configuration dependent larger scale turbulence . Previous hybrid approaches use approximate statistical techniques or extrapolation methods to obtain the requisite information about the sub-filter scale motion. An alternative approach would be to adopt the modeling techniques used in the current noise prediction methods and determine the unknown stresses from experimental data. The present paper derives an equation for predicting the sub scale sound from information that can be obtained with currently available experimental procedures. The resulting prediction method would then be intermediate between the current noise prediction codes and previously proposed hybrid techniques.

Goldstein, Marvin E.↗

NASA NTRS2011

Acoustic Prediction Methodology and Test Validation for an Efficient Low-Noise Hybrid Wing Body Subsonic Transport

This investigation was conducted to: (1) Develop a hybrid wing body subsonic transport configuration with noise prediction methods to meet the circa 2007 NASA Subsonic Fixed Wing (SFW) N+2 noise goal of -52 dB cum relative to FAR 36 Stage 3 (-42 dB cum re: Stage 4) while achieving a -25% fuel burned compared to current transports (re :B737/B767); (2) Develop improved noise prediction methods for ANOPP2 for use in predicting FAR 36 noise; (3) Design and fabricate a wind tunnel model for testing in the LaRC 14 x 22 ft low speed wind tunnel to validate noise predictions and determine low speed aero characteristics for an efficient low noise Hybrid Wing Body configuration. A medium wide body cargo freighter was selected to represent a logical need for an initial operational capability in the 2020 time frame. The Efficient Low Noise Hybrid Wing Body (ELNHWB) configuration N2A-EXTE was evolved meeting the circa 2007 NRA N+2 fuel burn and noise goals. The noise estimates were made using improvements in jet noise shielding and noise shielding prediction methods developed by UC Irvine and MIT. From this the Quiet Ultra Integrated Efficient Test Research Aircraft #1 (QUIET-R1) 5.8% wind tunnel model was designed and fabricated.

Kawai, Ronald T.↗

NASA NTRS1984

Synthesized airfoil data method for prediction of dynamic stall and unsteady airloads

The synthesized unsteady airfoil data method, which accurately describes the unsteady aerodynamic characteristics of stalled airfoils in the time domain, is expanded and improved. Nine sets of unsteady drag data are synthesized, providing a basis for the successful expansion of the method to include the computation of unsteady pressure drag of airfoils and rotor blades. An improved prediction model for airfoil flow reattachment is incorporated into the method. Application of the model results in a better correlation of analytic predictions with measured full-scale helicopter blade loads and stress data. The results show that it is feasible to generalize the empirical parameters embedded in the method over a range of angles of attack, Mach number, airfoil shape, and sweep angle.

Gangwani, S. T.↗

NASA NTRS1994

Experimental validation of finite element and boundary element methods for predicting structural vibration and radiated noise

This research report is presented in three parts. In the first part, acoustical analyses were performed on modes of vibration of the housing of a transmission of a gear test rig developed by NASA. The modes of vibration of the transmission housing were measured using experimental modal analysis. The boundary element method (BEM) was used to calculate the sound pressure and sound intensity on the surface of the housing and the radiation efficiency of each mode. The radiation efficiency of each of the transmission housing modes was then compared to theoretical results for a finite baffled plate. In the second part, analytical and experimental validation of methods to predict structural vibration and radiated noise are presented. A rectangular box excited by a mechanical shaker was used as a vibrating structure. Combined finite element method (FEM) and boundary element method (BEM) models of the apparatus were used to predict the noise level radiated from the box. The FEM was used to predict the vibration, while the BEM was used to predict the sound intensity and total radiated sound power using surface vibration as the input data. Vibration predicted by the FEM model was validated by experimental modal analysis; noise predicted by the BEM was validated by measurements of sound intensity. Three types of results are presented for the total radiated sound power: sound power predicted by the BEM model using vibration data measured on the surface of the box; sound power predicted by the FEM/BEM model; and sound power measured by an acoustic intensity scan. In the third part, the structure used in part two was modified. A rib was attached to the top plate of the structure. The FEM and BEM were then used to predict structural vibration and radiated noise respectively. The predicted vibration and radiated noise were then validated through experimentation.

Seybert, A. F.↗

NASA NTRS1983

A method of predicting the performance deterioration of a compressor cascade due to sand erosion

Performance deterioration due to sand erosion is a well known phenomena for aircraft engines operating in particulate flow environments. A method for predicting this performance deterioration is developed and applied to a two dimensional compressor cascade. The locations of the particles impacts are computed by analyzing the trajectories of the individual particles. From this analysis, the material removed, the changes in the airfoil shape, and the roughness development over the surface are estimated as a function of time. The resulting airfoil profiles are analyzed for predicting performance by using an inviscid-viscous interaction technique. The analytical solution is compared with experimental results.

Balan, C.↗

NASA NTRS1990

A simple parcel method for prediction of cumulus onset and area-averaged cloud amount over heterogeneous land surfaces

A set of PBL data selected from the Wangara experiment is used to examine the relationship between cumulus amount and the calculated relative humidity of rising parcels. The Wilde et al. (1985) method is compared to two explicit parcel methods. It is shown that predictions using parcel methods, in which surface air is lifted to its equilibrium level while being diluted by a defined amount of mixed layer air, are superior for cloud amount, especially during periods of rapid cloud onset when the mean boundary layer top is swiftly rising through a near-neutral layer. Pending independent verification, it appears that an rms error in instantaneous cloud amount of + or - 10 percent may be achievable.

Wetzel, Peter J.↗

NASA NTRSDate not supplied

TPSAS-NF1676L-27686-DND

Accurate flight prediction methods are critical for all aspects of vehicle performance, handling characteristics, and structural integrity. The first NASA/Industry/DoD workshop on wind tunnel/flight correlation was held in 1981, when discrepancies arising from Reynolds number effects, aeroelastic effects, and tunnel wall and sting interference effects posed significant barriers to experimentally-based prediction methods in use at that time. Significant advances in ground-based experimental capabilities and facilities, CFD methods, and flight test technology in the next 20 years significantly improved the tools available for predictions. In addition, numerous new production and experimental military and civil aircraft completed flight testing, offering an unprecedented experience base and data for assessing the accuracy of current prediction methods and practices. Thus, the first Flight Prediction Workshop (FPW) was held in 2002. The objective of the 2002 workshop and the current 3 day workshop for technical specialists is to provide a forum for the exchange of: experiences and lessons learned, critical assessments of the state of the art, and recommendations for further developments in flight prediction methodology. Information and opinions provided by the workshop will be incorporated in R&T planning for future government activities in aerodynamics, aeroelasticity, aeroacoustics, propulsion/air frame integration, etc.

Joseph H Morrison↗

NASA NTRS1983

A method of predicting flow rates required to achieve anti-icing performance with a porous leading edge ice protection system

A proposed method of analytically predicting the minimum fluid flow rate required to provide anti-ice protection with a porous leading edge system on a wing under a given set of flight conditions is presented. Results of the proposed method are compared with the actual results of an icing test of a real wing section in the NASA Lewis Icing Research Tunnel.

Kohlman, D. L.↗

NASA NTRS1975

Theoretical and experimental study of a new method for prediction of profile drag of airfoil sections

Theoretical and experimental studies are described which were conducted for the purpose of developing a new generalized method for the prediction of profile drag of single component airfoil sections with sharp trailing edges. This method aims at solution for the flow in the wake from the airfoil trailing edge to the large distance in the downstream direction; the profile drag of the given airfoil section can then easily be obtained from the momentum balance once the shape of velocity profile at a large distance from the airfoil trailing edge has been computed. Computer program subroutines have been developed for the computation of the profile drag and flow in the airfoil wake on CDC6600 computer. The required inputs to the computer program consist of free stream conditions and the characteristics of the boundary layers at the airfoil trailing edge or at the point of incipient separation in the neighborhood of airfoil trailing edge. The method described is quite generalized and hence can be extended to the solution of the profile drag for multi-component airfoil sections.

Goradia, S. H.↗

NASA NTRS1996

Improved NASA-ANOPP Noise Prediction Computer Code for Advanced Subsonic Propulsion Systems

Recent experience using ANOPP to predict turbofan engine flyover noise suggests that it over-predicts overall EPNL by a significant amount. An improvement in this prediction method is desired for system optimization and assessment studies of advanced UHB engines. An assessment of the ANOPP fan inlet, fan exhaust, jet, combustor, and turbine noise prediction methods is made using static engine component noise data from the CF6-8OC2, E(3), and QCSEE turbofan engines. It is shown that the ANOPP prediction results are generally higher than the measured GE data, and that the inlet noise prediction method (Heidmann method) is the most significant source of this overprediction. Fan noise spectral comparisons show that improvements to the fan tone, broadband, and combination tone noise models are required to yield results that more closely simulate the GE data. Suggested changes that yield improved fan noise predictions but preserve the Heidmann model structure are identified and described. These changes are based on the sets of engine data mentioned, as well as some CFM56 engine data that was used to expand the combination tone noise database. It should be noted that the recommended changes are based on an analysis of engines that are limited to single stage fans with design tip relative Mach numbers greater than one.

Kontos, K. B.↗

NASA NTRS1993

Predictive sensor method and apparatus

A microprocessor and electronics package employing predictive methodology was developed to accelerate the response time of slowly responding hydrogen sensors. The system developed improved sensor response time from approximately 90 seconds to 8.5 seconds. The microprocessor works in real-time providing accurate hydrogen concentration corrected for fluctuations in sensor output resulting from changes in atmospheric pressure and temperature. Following the successful development of the hydrogen sensor system, the system and predictive methodology was adapted to a commercial medical thermometer probe. Results of the experiment indicate that, with some customization of hardware and software, response time improvements are possible for medical thermometers as well as other slowly responding sensors.

Cambridge, Vivien J.↗

NASA NTRS1993

A sublaminate analysis method for predicting disbond and delamination loads in composite structures

A method is proposed for assessing the forces that can delaminate composite laminates and bonded structures. The approach employs a higher-order plate theory to represent portions of the laminate. The ply properties are integrated through the thickness in a manner that is consistent with the displacement assumptions in the plate theory, thus providing for accurate representation of the stacking sequence effects. In addition to stress analysis, the method also provides the strain energy release rate for the growth of existing delaminations. The analysis has been incorporated into a computer code, TTSS (through thickness stretching and shear). Application examples, including a double cantilever beam and a curved laminate, are examined.

Flanagan, G.↗

NASA NTRS1982

Approximate method of predicting heating on the windward side of Space Shuttle Orbiter and comparisons with flight data

An approximate method is developed for predicting laminar and turbulent heating rates on the windward side of the Space Shuttle Orbiter for both the wind-tunnel and flight environments. The method is based on a 'local infinite swept cylinder' analysis and includes both equilibrium-air chemistry and variable boundary-layer-edge entropy. The method is validated by comparing with data from wind-tunnel experiments and from the first and second Space Shuttle flights both along the windward-symmetry plane and in a lateral direction off the symmetry plane. Agreement with the flight data is good from approximately 67 km (peak heating) downward.

Hamilton, H. H., II↗

NASA NTRS1979

Propagation predictions for the HF-range by the Research Institute of the Deutsche Bundespost

Long term and short term HF propagation prediction service is described. The long term prediction method is computer based. The short term prediction method is still a manual method which relies mainly on a number of continuous field strength recordings and on the forecaster's ability to interpret the recordings and to combine this information with all available solar-geophysical data. Examples of the predictions are given and are compared with actually observed HF propagation conditions.

Damboldt, T.↗

NASA NTRS1995

A review of propeller noise prediction methodology: 1919-1994

This report summarizes a review of the literature regarding propeller noise prediction methods. The review is divided into six sections: (1) early methods; (2) more recent methods based on earlier theory; (3) more recent methods based on the Acoustic Analogy; (4) more recent methods based on Computational Acoustics; (5) empirical methods; and (6) broadband methods. The report concludes that there are a large number of noise prediction procedures available which vary markedly in complexity. Deficiencies in accuracy of methods in many cases may be related, not to the methods themselves, but the accuracy and detail of the aerodynamic inputs used to calculate noise. The steps recommended in the report to provide accurate and easy to use prediction methods are: (1) identify reliable test data; (2) define and conduct test programs to fill gaps in the existing data base; (3) identify the most promising prediction methods; (4) evaluate promising prediction methods relative to the data base; (5) identify and correct the weaknesses in the prediction methods, including lack of user friendliness, and include features now available only in research codes; (6) confirm the accuracy of improved prediction methods to the data base; and (7) make the methods widely available and provide training in their use.

Metzger, F. Bruce↗

NASA NTRS2017

Multimodel Ensemble Methods for Prediction of Wake-Vortex Transport and Decay Originating NASA

Several multimodel ensemble methods are selected and further developed to improve the deterministic and probabilistic prediction skills of individual wake-vortex transport and decay models. The different multimodel ensemble methods are introduced, and their suitability for wake applications is demonstrated. The selected methods include direct ensemble averaging, Bayesian model averaging, and Monte Carlo simulation. The different methodologies are evaluated employing data from wake-vortex field measurement campaigns conducted in the United States and Germany.

Korner, Stephan↗

NASA NTRS1975

Method of predicting radiation heat transfer in turbine cooling test facilities

A method is presented for calculating the average net radiation heat flux to turbine vanes and blades. The net radiation heat flux at a vane leading edge calculated by this method was compared with heat flux values independently determined from experimental tests on a vane in a cascade. The spectral emissivities of the turbine vane and the cascade wall were also measured.

Gladden, H. J.↗

NASA NTRS1989

A numerical method for predicting hypersonic flowfields

The flow about a body traveling at hypersonic speed is energetic enough to cause the atmospheric gases to chemically react and reach states in thermal nonequilibrium. The prediction of hypersonic flowfields requires a numerical method capable of solving the conservation equations of fluid flow, the chemical rate equations for specie formation and dissociation, and the transfer of energy relations between translational and vibrational temperature states. Because the number of equations to be solved is large, the numerical method should also be as efficient as possible. The proposed paper presents a fully implicit method that fully couples the solution of the fluid flow equations with the gas physics and chemistry relations. The method flux splits the inviscid flow terms, central differences of the viscous terms, preserves element conservation in the strong chemistry source terms, and solves the resulting block matrix equation by Gauss Seidel line relaxation.

Maccormack, Robert W.↗