Starting vortex

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

Characteristics of Tornado-Like Vortices as a Function of Swirl Ratio: A Laboratory Investigation

Abstract: The investigation of tornado vortex dynamics by means of a laboratory simulation is described. Based on observations from nature and an examination of the Navier-Stokes equations, a laboratory simulator of the Ward type has been constructed. This simulator generates various vortex configurations as a function of swirl ratio, radial Reynolds number and aspect ratio. Configurations which are described are 1) a single laminar vortex; 2) a single vortex with breakdown bubble separating the upper turbulent region from the lower laminar region; 3) a fully developed turbulent core, where the breakdown bubble penetrates to the bottom of the experimental chamber; 4) vortex transition to two intertwined helical vortices; and 5) examples of higher order multiple-vortex configurations that form in the core region. Hot-film anemometry measurements of the magnitude of the velocity vector and inflow (swirl) angle have been obtained in a sequence of flows characterized by progressively increasing values of swirl...

Parametric and internal study of the vortex tube using a CFD model

Abstract: A computational fluid dynamics (CFD) model is used to investigate the energy separation mechanism and flow phenomena within a counter-flow vortex tube. A two-dimensional axi-symmetric CFD model has been developed that exhibits the general behavior expected from a vortex tube. The model results are compared to experimental data obtained from a laboratory vortex tube operated with room temperature compressed air. The CFD model is subsequently used to investigate the internal thermal-fluid processes that are responsible for the vortex tube's temperature separation behavior. The model shows that the vortex tube flow field can be divided into three regions that correspond to: flow that will eventually leave through the hot exit (hot flow region), flow that will eventually leave through the cold exit (cold flow region), and flow that is entrained within the device (re-circulating region). The underlying physical processes are studied by calculating the heat and work transfers through control surfaces defined by the streamlines that separate these regions. It was found that the energy separation exhibited by the vortex tube can be primarily explained by a work transfer caused by a torque produced by viscous shear acting on a rotating control surface that separates the cold flow region and the hot flow region. This work transfer is from the cold region to the hot region whereas the net heat transfer flows in the opposite direction and therefore tends to reduce the temperature separation effect. A parametric study of the effect of varying the diameter and length of the vortex tube is also presented.

On the Formation of the Counter--Rotating Vortex Pair in Transverse Jets

Abstract: Among the important physical phenomena associated with the jet in crossflow is the formation and evolution of vortical structures in the flow field, in particular the counter-rotating vortex pair (CVP) associated with the jet cross-section. The present computational study focuses on the mechanisms for the dynamical generation and evolution of these vortical structures. Transient numerical simulations of the flow field are performed using three-dimensional vortex elements. Vortex ring rollup, interactions, tilting, and folding are observed in the near field, consistent with the ideas described in the experimental work of Kelso, Lim & Perry (1996), for example. The time-averaged effect of these jet shear layer vortices, even over a single period of their evolution, is seen to result in initiation of the CVP. Further insight into the topology of the flow field, the formation of wake vortices, the entrainment of crossflow, and the effect of upstream boundary layer thickness is also provided in this study.

Vortex evolution in a round jet

Abstract: A study has been made of the varicose instability of an axisymmetrical jet with a velocity distribution radially uniform at the nozzle mouth except for a laminar boundary layer at the wall. The evolutionary phenomena of instability, such as the rolling up of the cylindrical vortex layer into ring vortices, the coalescence of ring vortex pairs, and the eventual disintegration into turbulent eddies, have been investigated as a function of the Reynolds number using smoke photography, stroboscopic observation, and the light-scatter technique.Emphasis has been placed on the wavelength with maximum growth rate. The jet is highly sensitive to sound and the effects of several types of acoustic excitation, including pure tones, have been determined.

The vortex wake of a ‘hovering’ model hawkmoth

Abstract: Visualization experiments with Manduca sexta have revealed the presence of a leading-edge vortex and a highly three-dimensional flow pattern. To further investigate this important discovery, a scaled-up robotic insect was built (the 'flapper') which could mimic the complex movements of the wings of a hovering hawkmoth. Smoke released from the leading edge of the flapper wing revealed a small but strong leading-edge vortex on the downstroke. This vortex had a high axial flow velocity and was stable, separating from the wing at approximately 75 per cent of the wing length. It connected to a large, tangled tip vortex, extending back to a combining stopping and starting vortex from pronation. At the end of the downstroke, the wake could be approximated as one vortex ring per wing. Based on the size and velocity of the vortex rings, the mean lift force during the downstroke was estimated to be about 1.5 times the body weight of a hawkmoth, confirming that the downstroke is the main provider of lift force.