A constrained vortex model with relevance to helicopter vortex ring state

Sandham, N.D. (2005) A constrained vortex model with relevance to helicopter vortex ring state. Southampton, UK, University of Southampton, 14pp. (Aerodynamics and Flight Mechanics Internal Report Series, (AFM 05/05) ).


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A planar model of a lifting surface descending into its own wake is constructed with the aim of demonstrating some underlying mechanisms of the ‘vortex ring’ state that may be entered
by a rotary wing aircraft during a vertical descent. The model uses line vortices that are periodically released from a point in space and then allowed to evolve in a constrained manner. For low descent velocities the model reproduces a hover state, where the wake vortices move downwards relative to the lifting plane. A critical descent speed is reached after which the model produces a quasi-periodic shedding of vortex agglomerations. This state is reached via a Hopf bifurcation of the steady state and persists until another critical descent velocity after which a steady windmill brake state is possible, in which vortices travel upwards in a regular manner. Unconstrained simulations reveal a more chaotic vortex pattern, but frequency analysis reveals an underlying structure similar to that shown for the constrained model. Besides offering a qualitative understanding of possible mechanisms of vortex ring state, the analysis suggests some dimensionless parameters that collapse the
model data.

Item Type: Monograph (Technical Report)
Keywords: vortex ring state, helicopter aerodynamics
Subjects: T Technology > TJ Mechanical engineering and machinery
T Technology > TL Motor vehicles. Aeronautics. Astronautics
Divisions: University Structure - Pre August 2011 > School of Engineering Sciences > Aerodynamics & Flight Mechanics
ePrint ID: 64136
Date Deposited: 05 Jan 2009
Last Modified: 27 Mar 2014 18:45
Publisher: University of Southampton
URI: http://eprints.soton.ac.uk/id/eprint/64136

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