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Journal ArticleDOI

Control of the Periodic Turbulent Flow over a Semicircular Airfoil with the Use of the Slot Suction of the Air from a Circular Vortex Cell at Small Angles of Attack

23 Nov 2016-Journal of Engineering Physics (Springer US)-Vol. 89, Iss: 6, pp 1500-1504
TL;DR: In this paper, it was shown that, in the case of a semicircular airfoil with an angle of attack of 5°, a vortex cell of diameter 0.2 in fractions of the air-foil chord is built in and the mean-mass rate of slot suction of air from this cell is larger than 0.15 of the incident-flow velocity.
Abstract: It is shown that, in the case where, into the back wall of a semicircular airfoil with an angle of attack of 5°, a vortex cell of diameter 0.2 in fractions of the airfoil chord is built in and the mean-mass rate of slot suction of the air from this cell is larger than 0.15 of the incident-flow velocity, the pattern of the turbulent flow over the airfoil is transformed, and, at an optimum suction rate of 0.75, the lift coefficient of the airfoil reaches a maximum value of the order of 1.7 at an aerodynamic efficiency of 10.
Citations
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Journal ArticleDOI
TL;DR: In this article, the galloping energy harvester, a curved blade oriented perpendicular to the flow, is capable of producing self-sustained oscillations at uncharacteristically low wind speeds.
Abstract: Aeroelastic energy harvesters are a promising technology for powering wireless sensors and microelectromechanical systems. In this letter, we present a harvester inspired by the trembling of aspen leaves in barely noticeable winds. The galloping energy harvester, a curved blade oriented perpendicular to the flow, is capable of producing self-sustained oscillations at uncharacteristically low wind speeds. The dynamics of the harvesting system are studied experimentally and compared to a lumped parameter model. Numerical simulations quantitatively describe the experimentally observed dynamic behaviour. Flow visualisation is performed to investigate the patterns generated by the device. Dissimilar to many other galloping harvester designs, the flow is found to be attached at the rear surface of the blade when the blade is close to its zero displacement position, hence acting more closely to aerofoils rather than to conventionally used bluff bodies. Simulations of the device combined with a piezoelectric harvesting mechanism predict higher power output than that of a device with the square prism.

17 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the control of a throttling air jet produced by a gas generator and of the energy sources positioned at the walls of an axisymmetric channel, which models the combustion-chamber unit of a ramjet in which a gas flow is decelerated, on the shock-wave structure of a supersonic gas flow in the channel for the purpose of formation of a lengthy transonic region.
Abstract: The control action of a throttling air jet produced by a gas generator and of the energy sources positioned at the walls of an axisymmetric channel, which models the combustion-chamber unit of a ramjet in which a gas flow is decelerated, on the shock-wave structure of a supersonic gas flow in the channel was investigated for the purpose of formation of a lengthy transonic region in it. A heat energy was supplied to the gas flow in the indicated channel in the pulse-periodic regime, and the pressure in the gas generator was also changed periodically. The range of energies corresponding to a stable transonic flow regime in the channel was determined on the basis of solution of the nonstationary Euler equations in dimensionless variables. For comparison, the combustion of a gaseous fuel inflowing to the channel through a slot in the channel wall upstream of the control air jet was considered. A nonstationary gas flow in the channel was calculated on the basis of the Reynolds-averaged Navier–Stokes equations with the use of the k–ω SST model of turbulence. It is shown that a controllable energy release in the channel, providing the obtaining of a transonic flow regime in it analogous to that obtained on the basis of solution of the Euler equations, can be realized with the use of a control transverse air jet.
References
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Patent
13 Oct 1992
TL;DR: In this article, a method and apparatus for boundary layer control by sucking air off the vortex chambers established in the trailing-edge portion of an aircraft aerodynamic surface is presented, where the rate of air bleed is controlled first by increasing it until the boundary layer is attached to the airstreamed surface, then by decreasing the rate for air bleed until the pressure in the aircraft portion starts decreasing.
Abstract: A method and apparatus for boundary layer control by sucking air off the vortex chambers established in the trailing-edge portion of an aircraft aerodynamic surface. The rate of air bleed is controlled first by increasing it until the boundary layer is attached to the airstreamed surface, then by decreasing the rate of air bleed until the pressure in the trailing-edge aircraft portion starts decreasing. The aircraft equipped with the boundary layer control system, including a number of vortex chambers accommodating streamlined bodies and communicating, through a common passage and a receiver, with a low-pressure source.

34 citations

Journal ArticleDOI
TL;DR: In this article, an unsteady flow around a NACA 0012 airfoil at a fixed Reynolds number of 40,000 is performed using several multi-block overlapping grids of different scales and densities, which cover settlement areas of various extents, including the near and far wakes.
Abstract: Parametrical calculations of an unsteady flow around a NACA 0012 airfoil at a fixed Reynolds number of 40,000 are performed using several multi-block overlapping grids of different scales and densities, which cover settlement areas of various extents, including the near and far wakes. The solutions found by Menter’s shear stress transport model, the Spalart–Allmaras vortex viscosity transport model, and the method of vortical domains, are compared with available estimated and experimental data. Verification of the two-dimensional model is performed by comparison of the numerical predictions for a cross flow over a thick plate with Igarashi’s experimental data.

13 citations