[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] 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

[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

[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] Highlights: • Experimental investigation of a platoon of 2,3,4 vehicles. • PIV results indicate that the large vortex near the rear base is responsible for the wake pumping. • Platoon marching at small inter vehicle distances can lead to drag reduction as large as 35%. • Low order model to determine the number of vehicles to attain a given drag reduction. Platooning configurations of two, three and four commercial vehicles were tested at a Reynolds number based on the vehicle’s length ($L$) of$230000$. The platoon configurations were obtained using an instrumented model, and three wooden replicas located at different positions with respect to the instrumented one. The reference model presents a slant angle at the leading edge, which can produce, in principle, a significantly different flow field compared to the generally studied Ahmed body. Drag, static pressure distributions and pressure fluctuations measurements were carried out. Additionally, planar PIV measurements were performed to investigate the near wake of the two-vehicles platoon configuration. For the two-models platoon, drag reductions of 30% and 43% were evidenced for the front and for the rear vehicle, respectively, at an inter-vehicle distance ($d$) equal to half the vehicle’s length, and corresponding to an average drag reduction of 36.5%. For increasing distance, the benefit associated with the platooning configuration reduces, reaching an average drag reduction of 20% at$d/L$ = 3. We relate the vehicle’s drag to the flow field organization and to the distribution of the modal energy through Proper Orthogonal Decomposition of the microphonic probes located on the base of the instrumented vehicle. We also evidence that the key element that is responsible for the pumping of the wake is the large vortex that generates near the top edge of the vehicle’s base. We show that the slant angle does not affect the drag reduction of the leading vehicle of the platoon, whereas it can lead to larger differences in the case of the rear vehicle. For three and four-vehicles platoons, consistently larger values of the average drag reduction are experienced ($\approx$35%) and were also obtained for distances >1$L$. A simple model describing the overall drag reduction for a generic number of vehicles is presented and discussed.

[en] Highlights: • A TMS consisting of passive TPS and ACN is developed for a hypersonic launch vehicle. • The coupled design method of TPS and ACN is developed based on an equivalent thermal equilibrium model. • An equivalent HTC is proposed to indicate the overall capacity of ACN. -- Abstract: In this paper, a design method of thermal management system (TMS) for hypersonic vehicles is developed. The system consists of a passive thermal protection system (TPS) and an active cooling network (ACN) with coolant of kerosene. In most previous studies, the passive TPS and ACN are always designed separately and thus leads to over-conservative results that deviating from real engineering conditions. A coupled design method is developed in present work, and the process includes calculation of aerodynamic heat, determination of passive TPS concept distribution, computation of TPS and ACN scales, and iterative design. The coupled design is realized based on two keys, the active cooling is coupled in aerodynamic heating and heat transfer in TPS by an equivalent thermal equilibrium model, and the overall capacity of active cooling is indicated by an equivalent heat transfer coefficient. The model and the coefficient act as the rationale and the equivalent parameter of the whole process, respectively. The TMS of a reusable launch vehicle is established under a typical trajectory. The influences of equivalent heat transfer coefficient on aerodynamic heating, passive TPS and ACN are studied. The results show that the weight of passive TPS decreases, while the coolant mass flow rate increases with the enhancement of active cooling.

[en] Highlights: • Effects of side ratio on energy harvesting from galloping of rectangles are studied. • The onset galloping velocity decreases with increasing the side ratio. • A side ratio of ∼1.0 is good for energy harvesting at high reduced flow velocities. • Side ratios within1.62–2.0 is beneficial for harvesting at low reduced velocities. Rectangular cylinders have been identified as ideal bluff bodies for galloping-based energy harvesting, while a systematic study of the effects of the side ratio (i.e., the ratio between the cylinder width and the cylinder height) remains unavailable. This study investigates the influences of the side ratio on the piezoelectric energy harvesting from the transverse galloping of a rectangular cylinder based on a representative electro-aero-mechanical model, in which the aerodynamic force is calculated by the quasi-steady theory. The existing experimental aerodynamic coefficients for rectangular cylinders with side ratios of 0.62–3.0 are utilized as inputs of the quasi-steady aerodynamic force model. The influences of the side ratio and load resistance on the onset velocity, displacement, and power output of the galloping-based energy harvester are investigated. The results show that the onset velocity of galloping is dependent on the load resistance while this dependency becomes less significant with increasing the natural frequency. The onset galloping velocity of the energy harvester decreases with increasing the side ratio, and the lowest onset velocity is achieved by a rectangular cylinder with a side ratio of around 2.50. The largest vibration amplitude is achieved by the cylinder with a side ratio of 1.62 or 2.0 at low flow velocities, while the largest vibration amplitude is always achieved by the square cylinder at high flow velocities. Therefore, the side ratio of a galloping-based energy harvester should be designed according to its working environment: the optimal side ratio is around 1.0 if the harvester is expected to work at relatively high reduced flow velocities, while the optimal side ratio is around 1.62–2.0 if the harvester is expected to be effective at relatively low reduced flow velocities. These conclusions can provide references for designing galloping-based energy harvesters with rectangular cylinders as bluff bodies.

[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)

No abstract available