Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “prediction methods”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

A Tail Buffet Loads Prediction Method for Aircraft at High Angles of Attack

Aircraft designers commit significant resources to the design of aircraft in meeting performance goals. Despite fulfilling traditional design requirements, many fighter aircraft have encountered buffet loads when demonstrating their high angle-of-attack maneuver capabilities. As a result, during test or initial production phases of fighter development programs, many new designs are impacted, usually in a detrimental way, by resulting in reassessing designs or limiting full mission capability. These troublesome experiences usually stem from overlooking or completely ignoring the effects of buffet during the design phase of aircraft. Perhaps additional requirements are necessary that addresses effects of buffet in achieving best aircraft performance in fulfilling mission goals. This paper describes a reliable, fairly simple, but quite general buffet loads analysis method to use in the initial design phases of fighter-aircraft development. The method is very similar to the random gust load analysis that is now commonly available in a commercial code, which this analysis capability is based, with some key modifications. The paper describes the theory and the implementation of the methodology. The method is demonstrated on a JSF prototype example problem. The demonstration also serves as a validation of the method, since, in the paper, the analysis is shown to nearly match the flight data. In addition, the paper demonstrates how the analysis method can be used to assess candidate design concepts in determining a satisfactory final aircraft configuration.

Pototzky, Anthony S.↗
NASA NTRSDate not supplied

Time Domain Boundary Element Method Prediction of Noise Shielding by an NACA 0012 Airfoil

As aircraft noise constraints become more stringent and the number/mixture of aircraft configurations grows, the need for improved aircraft noise reduction technologies becomes more evident. To achieve more aggressive noise reduction goals, it becomes more important to not only understand individual aircraft noise sources, but their interaction with nearby aircraft structures as well. For example, the mutual interaction of multiple propulsors and the airframe structure can lead to increased system noise levels. However, these interactions may also offer opportunities for noise reduction. Understanding these interactions and exploring possible approaches to mitigate or exploit their acoustic impact is important for overcoming key noise barriers. This paper presents further validation of a time domain approach for the prediction of the aforementioned interactions between incident noise sources and nearby aircraft structures. Specifically, predictions using a time domain\ boundary element method1, 2 are compared with measured data from a fundamental shielding experiment.3, 4 The test facility and associated measurements are described in Section II. The computational model is then presented in Section III. Comparisons of the predictions with measured data are provided in Section IV. Finally, concluding remarks regarding some of the more significant results and further areas of interest are presented in Section V.

Acoustic scattering↗
NASA NTRSDate not supplied

Time Domain Boundary Element Method Prediction of Noise Shielding by a NACA 0012 Airfoil

As aircraft noise constraints become more stringent and the number/mixture of aircraft configurations grows, it becomes more important to understand the interaction of individual aircraft noise sources with nearby aircraft structures. Understanding these interactions and exploring possible approaches to mitigate or exploit their acoustic impact is essential for overcoming key noise barriers. This paper describes the further validation of a time domain boundary element approach for the prediction of the interactions between incident noise sources and nearby aircraft structures. Predictions were completed for multiple source locations and comparisons of these results with measured data are presented. Overall, very good agreement between the predicted and measured quantities was obtained in both the pressure time histories and pressure spectra. The effects of surface mesh resolution and source waveform are also presented. The very promising results demonstrate the capabilities of the time domain methodology employed in this study and provide further confidence in its continued development and application in future studies.

TD-FAST↗
NASA NTRS1984

An analytical method to predict efficiency of aircraft gearboxes

A spur gear efficiency prediction method previously developed by the authors was extended to include power loss of planetary gearsets. A friction coefficient model was developed for MIL-L-7808 oil based on disc machine data. This combined with the recent capability of predicting losses in spur gears of nonstandard proportions allows the calculation of power loss for complete aircraft gearboxes that utilize spur gears. The method was applied to the T56/501 turboprop gearbox and compared with measured test data. Bearing losses were calculated with large scale computer programs. Breakdowns of the gearbox losses point out areas for possible improvement.

Anderson, N. E.↗
NASA NTRS1984

An analytical method to predict efficiency of aircraft gearboxes

A spur gear efficiency prediction method previously developed by the authors was extended to include power loss of planetary gearsets. A friction coefficient model was developed for MIL-L-7808 oil based on disc machine data. This combined with the recent capability of predicting losses in spur gears of nonstandard proportions allows the calculation of power loss for complete aircraft gearboxes that utilize spur gears. The method was applied to the T56/501 turboprop gearbox and compared with measured test data. Bearing losses were calculated with large scale computer programs. Breakdowns of the gearbox losses point out areas for possible improvement.

Anderson, N. E.↗
NASA NTRS1975

Development and evaluation of a new method for predicting aircraft buffet response

The buffet prediction method uses rigid wind tunnel model fluctuating pressure data to form a buffet forcing function. The response is then calculated with a mathematical dynamic model of the airplane developed for gust response analysis. By including the extremes of phasing and contribution of symmetric and antisymmetric airplane responses, the upper and lower bounds are established for buffet response. F-111A flight test data show good agreement with predicted bounds for a variety of flight conditions.

Cunningham, A. M., Jr.↗
NASA NTRS1977

Assessment of existing analytic methods for prediction of high angle-of-attack loads on delta wings at supersonic speeds

An assessment of the applicability of four loading prediction methods to high angle-of-attack conditions for simplified wing-body configurations is provided. The methods are: The tangent wedge approximation, the linear theory methods of Middleton and Woodward, and a shock-fitting finite-difference technique. Estimates obtained by these methods were compared with experimental pressure data on delta wings to examine the effects of Mach number, camber, sweep angle, and angle of attack. Results indicate that all of the methods provided reasonable estimates at moderate angles of attack. At these moderate angles of attack, the methods of Middleton and Woodward provided good estimates at Mach numbers higher than those usually associated with linear theory. Only the finite-difference method provided reasonable load estimates at high angles of attack.

Landrum, E. J.↗
NASA NTRS1979

Evaluation of methods for prediction of propulsion system drag

The results of a study directed toward compilation of a theoretical and experimental data base covering inlet/airframe and nozzle/afterbody integration are described, with the major emphasis on the evaluation of the adequacy for preliminary design purposes of the data base for afterbody/propulsion system interference effects. Prediction methods that exist for afterbody/airframe interference effects are evaluated with respect to the requirements of breadth, ease of application and accuracy that are important for preliminary design.

Kuhn, G. D.↗
NASA NTRS1987

Aerodynamic characteristics of cruciform missiles at high angles of attack

An aerodynamic prediction method for missile aerodynamic performance and preliminary design has been developed to utilize a newly available systematic fin data base and an improved equivalent angle of attack methodology. The method predicts total aerodynamic loads and individual fin forces and moments for body-tail (wing-body) and canard-body-tail configurations with cruciform fin arrangements. The data base and the prediction method are valid for angles of attack up to 45 deg, arbitrary roll angles, fin deflection angles between -40 deg and 40 deg, Mach numbers between 0.6 and 4.5, and fin aspect ratios between 0.25 and 4.0. The equivalent angle of attack concept is employed to include the effects of vorticity and geometric scaling.

Lesieutre, Daniel J.↗
NASA NTRS1992

Stagnation-point heat-transfer rate predictions at aeroassist flight conditions

The results are presented for the stagnation-point heat-transfer rates used in the design process of the Aeroassist Flight Experiment (AFE) vehicle over its entire aeropass trajectory. The prediction methods used in this investigation demonstrate the application of computational fluid dynamics (CFD) techniques to a wide range of flight conditions and their usefulness in a design process. The heating rates were computed by a viscous-shock-layer (VSL) code at the lower altitudes and by a Navier-Stokes (N-S) code for the higher altitude cases. For both methods, finite-rate chemically reacting gas was considered, and a temperature-dependent wall-catalysis model was used. The wall temperature for each case was assumed to be radiative equilibrium temperature, based on total heating. The radiative heating was estimated by using a correlation equation. Wall slip was included in the N-S calculation method, and this method implicitly accounts for shock slip. The N-S/VSL combination of projection methods was established by comparison with the published benchmark flow-field code LAURA results at lower altitudes, and the direct simulation Monte Carlo results at higher altitude cases. To obtain the design heating rate over the entire forward face of the vehicle, a boundary-layer method (BLIMP code) that employs reacting chemistry and surface catalysis was used. The ratio of the VSL or N-S method prediction to that obtained from the boundary-layer method code at the stagnation point is used to define an adjustment factor, which accounts for the errors involved in using the boundary-layer method.

Gupta, Roop N.↗