Vortex formation on squared and rounded tip

The vortical flow originated from the tip of a NACA 0012 rectangular wing is described in its initial formation and development over a rounded and a squared tip. Smoke visualizations show the rolling-up kinematic and evolution of the vortical systems moving the plane towards the trailing edge. The presence of intense secondary vortices affects the primary vortex unsteadiness and shape during the formation and in the early wake. Stereoscopic Particle Image Velocimetry is used to describe vorticity, axial velocity and turbulent kinetic energy distributions of the vortex during the formation and in the early wake at different angles of attack of the wing. The rolling-up of the vorticity sheet around the vortex system is strongly influenced by the vortex shape and the intensity of secondary vortices. Turbulence coming from secondary structures and shear layers is wrapped into the roll-up of the vortex and high levels of turbulence are measured in the vortex core. However, a laminar vortex core is observed for the lower angle of attack in the early wake. Comparing the meandering of the vortex for the two wingtip geometries, two different sources of the vortex fluctuation in the wake are identified: the interaction of secondary vortices moving around the primary vortex and the rolling-up of the vorticity sheet. Lastly, measurements in the wake of the wing at zero incidence are also presented showing a distinctive counter rotating vortex pair

Rotor wake interactions with an obstacle on the ground

An investigation of the flow around an obstacle positioned within the wake of a rotor is described. A flow visualisation survey was performed using a smoke wand and particle image velocimetry, and surface pressure measurements on the obstacle were taken. The flow patterns were strongly dependent upon the rotor height above the ground and obstacle, and the relative position of the obstacle and rotor axis. High positive and suction pressures were measured on the obstacle surfaces, and these were unsteady in response to the passage of the vortex driven rotor wake over the surfaces. Integrated surface forces are of the order of the rotor thrust, and unsteady pressure information shows local unsteady loading of the same order as the mean loading. Rotor blade-tip vortex trajectories are responsible for the generation of these forces

Coupled thrust and vorticity dynamics during VRS

The focus is on the vortex ring state (VRS) observed at rapid descent rates. At VRS, the helical vortex filaments coming off the blades amalgamate around the rotor disk forming a vortex ring, which periodically detaches into the wake, causing extreme oscillations in thrust, with periods on the order of several tens of rotor revolutions. We discuss here the phase relation between the thrust cycle and vorticity distribution at the rotor disk. Maxima of the VRS thrust oscilla- tions correlate well with the maxima of circulation, enstrophy, and minima of enstrophy dispersion radius observed in the vicinity of the rotor disk

A Stepper Motor Based System For Rapid Pitching of Wind Tunnel Models. G.U. Aero Report 9402

This report describes the apparatus and computer codes for the unsteady aerodynamics flow visualisation rig in the Department of Aerospace Engineering's smoke flow visualisation wind tunnel. The purpose of the report is to archive the work done and provide information to those who may need to set up the apparatus or modify any of the running parameters. Loose descriptions of the structure of the Lab VIEW computer code are also given

Recent Developments in the 3' x 3' Flow Visualization Wind Tunnel. G. U. Aero Report 9717

This report presents a description of the modifications to the Aerospace Department’s "Smoke tunnel" that took place over the summer of 1997. These improvements were essential for research developments taking place. Also described are essential items of user information regarding programming, safety and use of the equipment

A Flow Visualization Study of a Pitching Delta Wing. G.U. Aero Report 9824

A series of flow visualization tests of a uniformly pitching, 60° sweep delta wing have been performed. Measurements of vortex position over the wing and vortex breakdown are then presented. For the pitch up case, the vortex forms further outboard and closer to the wing surface than in the steady case, and vortex breakdown occurs at higher incidence. Vortex breakdown is preceded by a distortion of the vortex core. The pitch down case is characterized by the restoration of the vortex, the main effect being that a broken down flow is observed at lower incidence than the static case

Observations of the Vortex Ring State

This paper considers the vortex ring state, a flow condition usually associated with the descent of a rotor into its own wake. The phenomenon is investigated through experiments on simple rotor systems, and a comparison is then made with observations of a flow generated by a specially designed open core, annular jet that generates a mean flow velocity profile similar to the mean flow in a rotor wake in hover. In an experimentally simulated descent, the jet flow generates a flow state that shares many features of the rotor vortex ring state

Investigation of the Orthogonal Blade-Vortex Interaction 1st Interim Report. G.U. Aero Report 0210

Steps towards the implementation of a stereoscopic particle image velocimetry (PIV) system for the investigation of the orthogonal blade-vortex interaction are described. The design of the stereo PIV system used is described, and details of the Scheimpflug camera mounts are provided. The necessary changes to the image capture and calibration procedures are described, and brief details of the stereo PIV analysis are given. This is essential preparatory work for the experimental study of the orthogonal blade-vortex interaction using stereoscopic PIV to take place later in this project

Investigation of the Orthogonal Blade-Vortex Interaction 2nd Interim Report. G.U. Aero Report 0103

Preliminary results from a PIV study of the orthogonal blade-vortex interaction are presented. This report presents a comparison of the details of the orthogonal BVI over the lower and upper surfaces of the blade. Detailed differences in the mechanics of these interactions have been noted. Features of the vortex behaviour in the wake of the blade are also presented together with the results obtained at very close proximity to the blade surface

Investigation of the Orthogonal Blade-Vortex Interaction 1st Interim Report. G.U. Aero Report 0210

Steps towards the implementation of a stereoscopic particle image velocimetry (PIV) system for the investigation of the orthogonal blade-vortex interaction are described. The design of the stereo PIV system used is described, and details of the Scheimpflug camera mounts are provided. The necessary changes to the image capture and calibration procedures are described, and brief details of the stereo PIV analysis are given. This is essential preparatory work for the experimental study of the orthogonal blade-vortex interaction using stereoscopic PIV to take place later in this project