Starting vortex

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

Effects of Vortex Generators on an Airfoil at Low Reynolds Numbers

Abstract: A low-speed wind-tunnel investigation is presented detailing the effects of vortex generators on an airfoil at low Reynolds numbers (80,000 and 160,000) Six different static vortex generator layouts were tested In addition, an oscillatory (or active) vortex generator was designed and tested Force balance measurements were recorded and interpreted with the aid of surface flow visualization The data suggest that the static vortex generators function similarly to those at higher Reynolds numbers; increasing the maximum lift coefficient and increasing the stall angle Different static vortex generator configurations appear preferable at the two tested Reynolds number ranges The oscillating vortex generator did not appear effective in its present configuration

Measurement of the Interaction Between a Rotor Tip Vortex and a Cylinder

Abstract: The transient interaction between a cylinder and the trailing vortex from a rotor in forward flight is studied. Phase-averaged laser velocimetry and surface pressure measurements made with flush-mounted microphones are used to study the velocity and pressure variations during such an interaction. Vorticity contours constructed from the velocity measurements exhibit the presence of a secondary structure with vorticity opposite in sense to that of the primary tip vortex. This structure moves rapidly around the tip vortex from upstream to downstream. The pressure variations caused by the tip vortex on the surface of the cylinder are smooth as the vortex core passes by, and no evidence is found of fine structure inside the vortex core region. After vortex interaction, the secondary structure causes large variations in the surface pressure before being dissipated. Calculations using measured vortex strength and speed data indicate that the distortions and deflections of the vortex immediately prior to impingement on the surface differ significantly from those computed using two-dimensional potential flow concepts. Nomenclature Cpu = unsteady pressure coefficient: difference between the instantaneous pressure and the local mean static pressure, normalized by the tunnel dynamic pressure R - rotor radius r = radial position along the rotor radius U = velocity component along the tunnel axis, positive going downstream Um = freestream velocity V = vertical velocity component, positive downward X = distance parallel to the tunnel axis, origin is at the rotor hub center Xb - distance parallel to the tunnel axis, measured from the nose of the cylinder Yb = distance along the lateral direction from the cylinder axis Zb = vertical distance from the cylinder axis, positive

A higher order panel method applied to Vortex sheet roll-up

Abstract: The paper describes a computational method for two-dimensional vortex sheet motion in incompressible flow. The procedure utilizes a second-order panel method, an adaptive panel scheme, and a concept for treating highly rolled-up portions of the vortex sheet. Results are presented for the roll-up of the wake behind an elliptically loaded wing, a ring wing (nacelle), a fuselage/part-span flap/wing combination, and a delta wing with leadingedge vortex sheets. The examples demonstrate that the method is capable of describing complicated vortex sheet motion in a reliable and stable manner. v \

Helical structure of longitudinal vortices embedded in turbulent wall-bounded flow

Abstract: Embedded vortices in turbulent wall-bounded flow over a flat plate, generated by a passive rectangular vane-type vortex generator with variable angle β to the incoming flow in a low-Reynolds-number flow (Re=2600 based on the inlet grid mesh size L =0.039 m and free stream velocity U ∞ = 1.0 m s -1 ), have been studied with respect to helical symmetry. The studies were carried out in a low-speed closed-circuit wind tunnel utilizing stereoscopic particle image velocimetry (SPIV). The vortices have been shown to possess helical symmetry, allowing the flow to be described in a simple fashion. Iso-contour maps of axial vorticity revealed a dominant primary vortex and a weaker secondary one for 20° ≤ β ≤ 40°. For angles outside this range, the helical symmetry was impaired due to the emergence of additional flow effects. A model describing the flow has been utilized, showing strong concurrence with the measurements, even though the model is decoupled from external flow processes that could perturb the helical symmetry. The pitch, the vortex core size, the circulation and the advection velocity of the vortex all vary linearly with the device angle β. This is important for flow control, since one thereby can determine the axial velocity induced by the helical vortex as well as the swirl redistributing the axial velocity component for a given device angle β. This also simplifies theoretical studies, e.g. to understand and predict the stability of the vortex and to model the flow numerically.

Experimental studies of vortex disconnection and connection at a free surface

Abstract: An experimental study is presented that examines the interaction of a vortex ring with a free surface. The main objective of this study is to identify the physical mechanisms that are responsible for the self-disconnection of vortex filaments in the near-surface region and the subsequent connection of disconnected vortex elements to the free surface. The understanding of those mechanisms is essential for the identification and estimation of the appropriate spatial and temporal scales of the disconnection and connection process. In this regard, the velocity and vorticity fields of an obliquely approaching laminar vortex ring with a Reynolds number of 1150 were mapped by using Digital Particle Image Velocimetry (DPIV). The evolution of the near-surface vorticity field indicates that the connection process starts in the side regions of the approaching vortex ring where surface-normal vorticity already exists in the bulk. A local strain rate analysis was conducted to support this conclusion. Disconnection in the near-surface tip region of the vortex ring occurs because of the removal of surfaceparallel vorticity by the viscous flux of vorticity through the surface. Temporal and spatial mapping of the vorticity field at the surface and in the perpendicular plane of symmetry shows that the viscous flux is balanced by a local deceleration of the flow at the surface. It is found that the observed timescales of the disconnection and connection process scale with the near-surface vorticity gradient rather than with the core diameter of the vortex ring.