Results 1 - 10 of 1844
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[en] A series of radio-controlled glider models was constructed by duplicating the aerodynamic shape of soaring birds (raven, turkey vulture, seagull and pelican). Controlled tests were conducted to determine the level of longitudinal and lateral-directional static stability, and to identify the characteristics that allowed flight without a vertical tail. The use of tail-tilt for controlling small bank-angle changes, as observed in soaring birds, was verified. Subsequent tests, using wing-tip ailerons, inferred that birds use a three-dimensional flow pattern around the wing tip (wing tip vortices) to control adverse yaw and to create a small amount of forward thrust in gliding flight.
[en] This paper deals with the flow calculation in a thermal countercurrent centrifuge at total reflux. Matched asymptotic expansions are used to find approximate solutions of Navier-Stokes equations which are assumed to be valid in the whole domaine. Convection and viscous dissipation disappear because of linearization, but compressibility is taken into account. Let epsilon be the Ekman number. The equations are solved in the inviscid core, in the horizontal Ekman layers of thickness 0 (epsilonsup(1/2) and in the Stewartson layer of thickness 0 (epsilonsup(1/3)), parallel to the axis. As the thermal convection is neglected, the Stewartson layer of thickness 0 (epsilon sup(1/4)) does not occur. The results show the importance of the recirculating mass-flow rate of order 0 (epsilonsup(1/3)) in front of the countercurrent mass-flow rate of order 0 (epsilonsup(1/2)). The temperature profile rules the pattern and the intensity of the recirculating flow
[fr]Dans cette etude, on calcule l'ecoulement dans une centrifugeuse a contre-courant thermique pur et a rejet nul. La methode appliquee est celle des developpements asymptotiques raccordes, les equations de Navier-Stokes etant supposees valables dans l'ensemble de l'ecoulement. Si la convection et la dissipation visqueuse disparaissent dans la linearisation des equations, par contre les effets de compressibilite sont pris en compte. Designant pas epsilon le nombre d'Ekman, nous avons calcule les grandeurs caracteristiques de l'ecoulement dans le coeur, dans la couche d'Ekman d'epaisseur epsilonsup(1/2) sur les plateaux de la centrifugeuse et dans la couche de Stewartson d'epaisseur epsilonsup(1/3) le long des parois. En l'absence de convection la couche parietale d'epaisseur epsilonsup(1/4) disparait. Les resultats obtenus montrent l'importance du flux de recirculation d'ordre epsilonsup(1/3) par rapport au flux de contre-courant d'ordre epsilonsup(1/2) cree par les couches d'Ekman dans la couche parietale. Le profil axial de temperature agit quantitativement et qualitativement sur la recirculation parietale
[en] Author considers the formulation and algorithms of the nonstationary problem for calculation of temperature fields of shell of revolution in high-temperature aerodynamic flow with known temperature. The physical model and calculation of temperature fields in the frontal part and in circle sections of the shell of revolution are also proposed
[ru]В работе рассматриваются постановка и алгоритмы решения нестационарной задачи расчета температурных полей оболочки вращения в высокотемпературном аэродинамическом потоке с заданной температурой. Предлагаются физическая модель и алгоритмы расчета температурных полей в лобовой части и в окружных сечениях оболочки
[en] The size of sports fields considerably varies from a few meters for table tennis to hundreds of meters for golf. We first show that this size is mainly fixed by the range of the projectile, that is, by the aerodynamic properties of the ball (mass, surface, drag coefficient) and its maximal velocity in the game. This allows us to propose general classifications for sports played with a ball. (paper)
[en] The requirements on the use of titanium alloys used as thermal protection in hypersonic airplanes are considered. The ignition of titanium alloys in aerodynamic heating is analyzed. A mathematical model is proposed for the surface oxidation of the alloys in a high-temperature air flux.
[en] An aerodynamic window for high power gaseous lasers having a plurality of blades mounted on the periphery of a circular disc outside the aperture in the laser cavity is described. The downwash of the blades as they move before said aperture provide a component directed into the cavity and away from the aperture to inhibit escape of the lasing medium. (auth)
[en] Highlights: • A combined thermal control approach for preventing serious aerodynamic heating is proposed. • The thermal control effect of the proposed method is simulated and analyzed. • The engineering practicability is evaluated by a mass penalty method. A 5 mm-wide gap of a shaft connected to the rudder in a hypersonic vehicle is exposed without any heat insulation bearing serious aerodynamic heating. A new thermal control approach combining CO2 flow forced convection in the central inner channel with copper-plating on the outer surface is proposed to prevent the temperature of the gap from exceeding the material’s highest tolerance temperature. Based on the integrated thermal management, CO2 first cools the electronic equipment after being gasified from a high-pressure cylinder, and then moves into the shaft for active thermal control. The thermal control performance is simulated, and the results show the proposed method could satisfy with the thermal control requirements, however, the thermal control requirements could not be fulfilled if the forced CO2 flow convection or the copper-plating was used alone. The mass penalty was estimated within a weight of 11 kg which is quite feasible for engineering applications.
[en] The purpose of this feasibility study was to conduct preliminary modeling to elucidate the mechanisms responsible for the effects observed in the Air Force Research Laboratory (AFRL) shock tube experiment. It was assumed that the plasma is simply a region of gas in the shock tube that has a higher gas temperature. Computational fluid dynamics (CFD) calculations were performed to simulate the propagation of a shock wave through the tube, using the same parameters in the experiment. Both 1- D and 3-D CFD calculations were performed to determine which effects can be explained simply by axial temperature gradients and which effects require the presence of radial temperature gradients. Discharge plasma physics calculations of a longitudinal glow discharge were then used to establish if the electrical currents used in the experiment are consistent with the gas temperature distributions that are necessary to explain the observed effects
[en] When driving high-speed electric locomotives, the aerodynamic component can no longer be neglected. This component influences the interaction between the pantograph and the catenary by further loading or unloading the downforce of the pantograph on the contact wire. The paper aims to determine the additional forces required by the pantograph and to determine the effects of these demands on the dynamic behaviour of the pantograph. This analysis is important because the aerodynamic stresses exerted on the pantograph can cause the contact force to drop on the contact wire, which may result in the detachment of the catenary current collector. The effects of the loss of contact between the pantograph sleeve and the contact line has direct consequences on the operation of the electrical circuits on the locomotive, especially the force circuits, given their capacitive and inductive loads. Through this study we aim to determine if negative effects cannot be converted into positive effects through a constructive solution of the current collector. (paper)