I. D. Zverkov

Plasma Control Of Vortex Flow On Delta-Wing At High Angles Of Attack

Nomenclature AR = wing aspect ratio b = wing thickness Cp = pressure coefficient, (p-p0)/q+1 c = wing root chord length Cxa = drag coefficient Cya = lift coefficient Cza = side force coefficient K = lift-drag ratio, mxa = roll moment coefficient mza = pitching moment coefficients p = static pressure on the model surface Tu = free-stream turbulence level, % of U∞ U∞ = mean free-stream velocity q = dynamic pressure x = vortex breakdown position along the wing chord z = transversal direction along the wing span α = angle of attack χ = delta-wing leading edge sweep angle

Vortex structure of separated flows on model wings at low freestream velocities

Flow past model wings is experimentally investigated in a subsonic wind tunnel at large angles of attack at which the laminar boundary layer separates near the leading edge of the wing (flow stall). The object of the study was the flow structure within the separation zone. The carbon-oil visualization of surface streamlines used in the experiments showed that in the separation zone there exist one or more pairs of large-scale vortices rotating in the wing plane. Certain general properties of the vortex structures in the separation zone are found to exist, whereas the flow patterns may differ depending on the model aspect ratio, the yaw angle, and other factors.

Experimental and theoretical investigation of boundary layer perturbations on a low-aspect-ratio wing

Laminar-turbulent transition in a boundary layer of low-aspect-ratio wing was investigated. Experiments clarifying the flow structure, its mean and oscillatory characteristics were carried out accompanied by linear stability analysis of the wind tunnel data on the laminar flow velocity profiles. Theoretical results obtained in a parallel flow approximation are in a good agreement with the experimental data on disturbances evolution at the initial stage of transition to turbulence.

Alteration of separated-flow structure achieved through a local action

Results of an experimental study of a subsonic flow past a straight-wing model installed at fixed angle of attack in hysteresis range of flow velocity are reported. It was shown that, at the same angle of attack and at one and the same flow velocity, flows of two types are possible on the upper surface of the model, leading-edge flow stall and re-attached flow with laminar-turbulent transition in the vicinity of the leading edge. It was found that the wing flow could be transformed from stalled to re-attached one with the help of a local influence applied at one point on the model inside the stall zone. Visualization data for both flows, hot-wire anemometer measurements of flow velocity, and measurements of the amplitude and frequency spectra of flow pulsations in both flows, are reported.

Electric Discharge Control of Flow Separation on Oblique Airfoil

The possibility of controlling flow separation on an oblique airfoil using dielectric-barrier discharge has been experimentally studied. The experiments were performed at subsonic flow velocities in a broad range of the angle of attack. The results of measurements of the velocity and surface pressure fields and an analysis of the flow patterns show that the application of electric discharge allows the interval of the angles of attack for separation-free flow past the airfoil to be significantly increased. Various discharge regimes have been studied, including those with continuous activation by single voltage pulses with a frequency of 0.5–5 kHz and by pulse trains at a repetition rate of 1–100 Hz. The efficiency of the flow separation control has been studied as dependent on the electrical parameters, frequency characteristics, and position of the discharge relative to the flow separation line.

Development of laminar-separating-flow perturbations on a wavy wing

The development of velocity perturbations at laminar boundary-layer separation from a wing with wavy surface has been examined. Experiments were carried out to identify flow features displayed by the spatially periodic flow structure. An analysis of the linear stability of measured velocity profiles is performed. As a result of the analysis, the influence of surface waviness on the frequency range and growth rates of instability waves was investigated, with a good agreement between calculated and experimental data.

Influence of wind tunnel freestream turbulence level on boundary-layer separation

An investigation of aerodynamic performance for micro air vehicle (MAV) wing is performed. It is shown, what is a reason of significant wing performance difference between tests, which were carried out in different wind tunnels. New method for estimation of wind tunnel condition influence on experimental results is suggested.