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  • 1
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    Some after-dinner reflections on system identification (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The growth of the field of system identification is discussed along with changes in methodology which have taken place in recent years. The similarity between pattern recognition and system identification is pointed out, involving the modelling in the latter and the feature selection problem in the former. It is stated that once a model is formulated, including the disturbances and measurement errors, the parameter finding can be formulated as a statistical estimation problem. The various techniques and their application are discussed.
    Keywords: AERODYNAMICS
    Type: NASA. Flight Res. Center Parameter Estimation Tech. and Appl. in Aircraft Flight Testing; p 381-385
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  • 2
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    Real-gas flowfields about three-dimensional configurations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: AERODYNAMICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 46-53
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  • 3
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    A computational study of heat transfer for laminar hypervelocity flows (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Computational Fluid Dynamics (CFD) codes are routinely used to predict the flowfield and the heating environment around complex reentry configurations. At hypervelocities, where the velocity is greater than 3 km/sec, the AFWAL version of the blunt body code predicts the correct surface pressure distributions but underpredicts laminar wall heat fluxes. This study was performed to determine the reasons for the underprediction. The computer code chosen solves thin-layer Navier-Stokes equations in a time-asymptotic manner and assumes a constant isentropic exponent. Flowfields around a spherical configuration at various entry velocities are computed. The computed pressure distributions agree well with the tabulated, inviscid results of Lyubimov and Rusanov for entry velocities ranging from 0.6 to 5.92 km/sec. At hypervelocities, the calculated stagnation point heat transfer rates were lower by roughly fifty percent when compared to engineering correlations available in the literature. Good comparisons between heat transfer rates are obtained at hypervelocity entry conditions provided the CFD code is modified to include equilibrium air properties.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-2666
    Format: text
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  • 4
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    Radiation heat transfer in the wake of a hypersonic vehicle (1988)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Radiation heat transfer (RHT) from the wake of a hypersonic vehicle to its afterbody is evaluated from Gnoffo and Greene's (1987) calculated wake flowfield and the radiative properties of ionized high-temperature air with the calculated nonequilibrium composition. The 4.2-m aeroassisted flight experiment at an altitude of 75 km and velocity of 8900 m/s causes a 0.1-m-thick layer initially at T = 10,000 K and P = 1 kN/sq m to separate from the shoulder of the forebody heat shield and spread aft to form a wake at approximately T = 5000 K and P = 20 N/sq m. Gas in the separated flow region at approximately T = 3000 K and P = 10 N/sq m, recirculates about the afterbody. It is shown that the radiating layer, recirculating gases, and wake are optically thin for purposes of making engineering RHT calculations. Directional, spectral, and spatial variations of the radiation incident upon the afterbody are presented.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 88-2634
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  • 5
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    Viscous real gas flowfields about three dimensional configurations (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Laminar, real gas hypersonic flowfields over a three dimensional configuration are computed using an unsteady, factored implicit scheme. Local chemical and thermodynamic properties are evaluated by an equilibrium composition method. Transport properties are obtained from individual species properties and application of a mixture rule. Numerical solutions are presented for an ideal gas and equilibrium air for free-stream Mach numbers of 13 and 15 and at various angles of attack. The effect of real gas is to decrease the shock-layer thickness resulting from decreased shock-layer temperatures and corresponding increased density. The combined effects of viscosity and real gas are to increase the subsonic layer near the wall.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-1511
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  • 6
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    Calculation of the transient motion of elastic airfoils forced by control surface motion and gusts (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The time-domain equations of motion of elastic airfoil sections forced by control surface motions and gusts were developed for the case of incompressible flow. Extensive use was made of special functions related to the inverse transform of Theodorsen's function. Approximations for the special cases of zero stream velocity, small time, large and time are given. A numerical solution technique for the solution of the general case is given. Examples of the exact transient response of an airfoil are presented.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81351 , H-1125 , REPT-505-36-24
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  • 7
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    Aerothermodynamic environment for a Titan probe with deployable decelerator (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: It is pointed out that further exploration of Titan, Saturn's largest moon, is of current interest to the scientific community, particularly from the standpoint of the organic chemical evolution of its atmosphere. For a suitable study of this Saturnian satellite, a mission involving a Titan atmospheric entry probe is to be conducted. The probe is to employ a deployable decelerator with the aim to allow scientific measurements in the haze layer. The present investigation is concerned with an assessment of the aerothermodynamic environment for the considered probe during its hypervelocity, low-Reynolds-number entry. Attention is given to the employed computational method, the Titan probe configuration, the Titan probe trajectory, the viscous-layer regime of the aerothermodynamic environment, and the incipient merged-layer regime.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-1063
    Format: text
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  • 8
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    Radiative viscous-shock-layer analysis of Fire, Apollo, and PAET flight data (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Equilibrium, radiating viscous-shock-layer solutions are obtained for a number of trajectory points of the Fire II, Apollo 4, and PAET experimental flight vehicles. Convective heating rates calculated by a benchmark code agree well, except at high altitudes corresponding to low densities, with two engineering correlations. Calculated radiation intensities are compared with the flight radiometer data and with inviscid flow results. Differences as great as 70 percent are observed between measured data and the viscous calculations. Viscous effects reduce the intensity toward the wall, because of boundary-layer absorption, by as much as 30 percent, compared with inviscid intensities. Preliminary chemical and thermal nonequilibrium flow calculations along a stagnation streamline for a PAET trajectory predict enhancement of radiation owing to chemical relaxation. Stagnation point solutions are also presented for future air-assisted orbital transfer vehicle geometries with nose radii ranging from 0.3 to 15 m.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-1064
    Format: text
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  • 9
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    Application of a flux-split algorithm to chemically relaxing, hypervelocity blunt-body flows (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Viscous, nonequilibrium, hypervelocity flow fields over two axisymmetric configurations are numerically simulated using a factored, implicit, flux-split algorithm. The governing gas-dynamic and species-continuity equations for laminar flow are presented. The gas-dynamics/nonequilibrium-chemistry coupling procedure is developed as part of the solution procedure and is described in detail. Numerical solutions are presented for hypervelocity flows over a hemisphere and over an axisymmetric aeroassisted orbital transfer vehicle using three different chemistry models. The gas models considered are those for an ideal gas, for a frozen gas, and for chemically relaxing air consisting of five species. The calculated results are compared with existing numerical solutions in the literature along the stagnation line of the hemisphere. The effects of free-stream Reynolds number on the nonequilibrium flow field are discussed.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 87-1578
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  • 10
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    Numerical study of three-dimensional separation and flow control at a wing/body junction (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: The problem of three-dimensional separation and flow control at a wing/body junction has been investigated numerically using a three-dimensional Navier-Stokes code. The numerical code employs an algebraic grid generation technique for generating the grid for unmodified junction and an elliptic grid generation technique for filleted fin junction. The results for laminar flow past a blunt fin/flat plate junction demonstrate that after grid refinement, the computations agree with experiment and reveal a strong dependency of the number of vortices at the junction on Mach number and Reynolds number. The numerical results for pressure distribution, particle paths and limiting streamlines for turbulent flow past a swept fin show a decrease in the peak pressure and in the extent of the separated flow region compared to the laminar case. The results for a filleted juncture indicate that the streamline patterns lose much of their vortical character with proper filleting. Fillets with a radius of three and one-half times the fin leading edge diameter or two times the incoming boundary layer thickness, significantly weaken the usual necklace interaction vortex for the Mach number and Reynolds number considered in the present study.
    Keywords: AERODYNAMICS
    Type: NASA-CR-185819 , NAS 1.26:185819
    Format: application/pdf
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