Starting vortex

About: Starting vortex is a research topic. Over the lifetime, 4785 publications have been published within this topic receiving 100419 citations.

Single-Particle Motion and Vortex Stretching in Three-Dimensional Turbulent Flows.

Abstract: Three-dimensional turbulent flows are characterized by a flux of energy from large to small scales, which breaks the time reversal symmetry. The motion of tracer particles, which tend to lose energy faster than they gain it, is also irreversible. Here, we connect the time irreversibility in the motion of single tracers with vortex stretching and thus with the generation of the smallest scales.

A Systematic Presentation of the Theory of Thin Airfoils in Non-Uniform Motion

Abstract: The basic conceptions of the circulation theory of airfoils are reviewed briefly, and the mechanism by which a "wake" of vorticity is produced by an airfoil in non-uniform motion is pointed out. After a calculation of the induction effects of a wake vortex, it is shown how the lift and moment acting upon an airfoil in the two-dimensional case may be calculated directly from simple physical considerations of momentum and moment of momentum. Formulae for the lift and moment are then obtained which are applicable to all cases of motion of a two-dimensional thin airfoil in which the wake produced is approximately flat; i.e., in which the movement of the airfoil normal to its mean path is small. The general results are applied first to the case of an oscillating airfoil, and vector diagrams giving the magnitudes and phase angles of the lift and moment are obtained. The results of a sudden change of angle of attack are then determined, and a general method for handling transient cases is set up. This method is applied to the calculation of the lift and moment acting on an airfoil entering sharp-edged and graded gusts. The case of a series of sinusoidal gusts is also considered. A method of calculating the distribution of forces over the airfoil chord is then shown, and it is applied to the steady-state oscillation. The paper concludes with a discussion of the applicability of certain results to the explanation of observed phenomena beyond the stall.

Effect of Regular Surface Perturbations on Flow Over an Airfoil

Abstract: This paper presents an investigation on the effect of introducing large-scale roughness through static curvature modifications on the low speed flow over an airfoil. The surfaces of a standard Eppler 398 airfoil have been modified with regular perturbations or “bumps” of the order of 2%c for this purpose. While the actual E398 airfoil is not a suitable candidate for low Re cases due to extensive prevalence of boundary layer separation, it is expected that the bumps would exercise passive flow control by promoting early transition to turbulence, thereby reducing the extent of separation and improving the performance. The fluid dynamic mechanism behind this separation control methodology is not clearly understood, however. Smoke-wire flow visualization is performed for qualitative observation of the separation region in both the perturbed and unmodified airfoil geometry cases. At higher Re values, pressure probe measurements are made to quantify the wake momentum deficits. Unsteady 2D PIV measurements are employed to understand the near-wall flowfield behavior . The size and strength of vortical structures formed in the separating shear layer are examined, along with measurements on the laminar separation bubble. All the experiments are conducted for chord based Re values ranging from 25,000 to 500,000.

The effect of a bevelled trailing edge on vortex shedding and vibration

Abstract: Experiments using a wind tunnel and a flow visualization technique in a towing tank were conducted to investigate the mechanism of vortex shedding from bevelled trailing edges. These reveal an important difference between the wake structures generated by heaving and steady motion. The suppression of vortex-excited vibration by means of bevelled trailing edges is attributed to the intermittency and rapid decay of the vortex trail resulting from an asymmetric circulation distribution in the vortex formation region.

Visualization of pulsed vortex generator jets for active control of boundary layer separation

Abstract: The interaction of pulsed vortex generator jets with a zero pressure gradient turbulent boundary layer has been studied from the perspective of vorticity dynamics. The improved performance of the pulsed vortex generator jets is attributed to the formation, stretching and bending of the starting vortex ring in these jet flows. The shear in the boundary layer amplifies the vorticity of the starting ring and re-directs it into the streamwise direction. The pitching and skewing of the jet is necessary to create the initial tilt of the starting vortex ring with respect to the mean flow. The source of the supplementary streamwise vorticity is the jet boundary layer fluid, which rolls up into the starting vortex in the initial phase of jet ejection. Flow visualization experiments confirmed that the extra benefits obtained from pulsing the vortex generator jets stems from the alteration of flow structure. The pulsed VGJs create vortex ring-like structures that are inclined with respect to the freestream.