Starting vortex

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

An inviscid model for vortex shedding from a deforming body

Abstract: An inviscid vortex sheet model is developed in order to study the unsteady separated flow past a two-dimensional deforming body which moves with a prescribed motion in an otherwise quiescent fluid. Following Jones (J Fluid Mech 496, 405-441, 2003) the flow is assumed to comprise of a bound vortex sheet attached to the body and two separate vortex sheets originating at the edges. The complex conjugate velocity potential is expressed explicitly in terms of the bound vortex sheet strength and the edge circulations through a boundary integral representation. It is shown that Kelvin's circulation theorem, along with the conditions of continuity of the normal velocity across the body and the boundedness of the velocity field, yields a coupled system of equations for the unknown bound vortex sheet strength and the edge circulations. A general numerical treatment is developed for the singular principal value integrals arising in the solution procedure. The model is validated against the results of Jones (J Fluid Mech 496, 405-441, 2003) for computations involving a rigid flat plate and is subsequently applied to the flapping foil experiments of Heathcote et al. (AIAA J, 42, 2196-2204, 2004) in order to predict the thrust coefficient. The utility of the model in simulating aquatic locomotion is also demonstrated, with vortex shedding suppressed at the leading edge of the swimming body.

Three-dimensional vortex structure on a rotating wing

Abstract: The three-dimensional structure of the leading-edge vortex on a rotating wing is addressed using a technique of particle image velocimetry. Organized patterns of chordwise-oriented vorticity, which exist within the vortex, arise from the spanwise flow along the surface of the wing, which can attain a velocity the same order as the velocity of the wing at its radius of gyration. These patterns are related to the strength (circulation) and coherence of the tip and root vortices. The associated distributions of spanwise-oriented vorticity along the leading-edge vortex are characterized in relation to the vorticity flux and downwash along the wing.

Lift evaluation of a two-dimensional pitching flat plate

Abstract: Several previous experimental and theoretical studies have shown that a leading edge vortex (LEV) on an airfoil or wing can provide lift enhancement. In this paper, unsteady two-dimensional (2D) potential flow theory is employed to model the flow field of a pitching flat plate wing. A multi-vortices model is developed to model both the leading edge and trailing edge vortices (TEVs), which offers improved accuracy compared with using only single vortex at each separation location. The lift is obtained by integrating the unsteady Blasius equation. It is found that the motion of vortices contributes significantly to the overall aerodynamic force on the flat plate. A Kutta-like condition is used to determine the vortex intensity and location at the leading edge for large angle of attack cases; however, it is proposed to relax this condition for small angle of attack cases and apply a 2D shear layer model to calculate the circulation of the new added vortex. The results of the simulation are then compared with classical numerical, theoretical, and experimental data for canonical unsteady flat plat problems. Good agreement with these data is observed. Moreover, these results suggested that the leading edge vortex shedding for small angles of attack should be modeled differently than that for large angles of attack. Finally, the results of vortex motion vs. lift indicate that the slow convection of the LEV creates less negative lift while the rapid shedding of the TEV creates more positive lift. The difference between these two contributions of lift results in a total positive lift that lasts for about two chord-length travel of the plate. It is therefore concluded that the lift enhancement during the LEV “stabilization” above the wing is a combined effect of both the LEV and TEV motion. This also provides the insights for future active flow control of micro aerial vehicles (MAVs) that the formation and shedding process of LEVs and TEVs can be manipulated to provide lift enhancement.

Coupling of shear flow and pressure gradient instabilities

Abstract: The nonlinear dynamics of a shear flow and its subsequent evolution in the equatorial plane of the inner plasma sheet is studied. A linear analysis of the ideal MHD equations reveals a hybrid vortex instability which appears because of the coupling of Kelvin-Helmholtz (KH) and Rayleigh-Taylor instabilities. The hybrid vortex mode grows faster than a KH mode, extracts ambient potential energy, and leads to vortex cells that have a larger spatial extent than a simple KH vortex. In the nonlinear stage, vortices become surge-like and may destroy the shear flow region. The relevance of this model to vortex generation and auroral arc intensifications at the inner edge of the plasma sheet is discussed.

Experimental and numerical investigation of free surface vortex

Abstract: An experimental model was set up to investigate the formation and evolution of the free surface vortex. A Particle Image Velocimetry (PIV) was used to measure the free surface vortex flow field at different development stages. Flow visualization was used to locate the vortex position and find its structure. Empirical formulas about the critical submergence and the whole field structure were obtained. It is found that the tangential velocity distribution is similar to that of the Rankine vortex and the radial velocity changes little in the vortex functional scope. Vortex starts from the free surface and gradually intensifies to air entrainment vortex. The vortex core moves during the formation and evolution of the free surface vortex. Based on the experimental model, the vortex position and structure were predicted by numerical simulation combined with a vortex model and compared with that of the experiments, which shows satisfactory agreement.