Visualization of a FourVortex Wake

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Visualization of a Four-Vortex Wake

• Dr Robert C. Nelson Brian M. Babie
• rnelson_at_nd.edu, bbabie_at_nd.edu
• Hessert Laboratory for Aerospace Research
• Department of Aerospace Mechanical Engineering
• University of Notre Dame
• Notre Dame, Indiana 46556

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Motivation for Research

• Aircraft trailing vortex wakes can be a hazard to
  other aircraft
• In flight wake vortex encounters cause control
  problems for aircraft
• Roll excursions
• Increased structural loading factors
• Wake hazard limits airport capacity due to
  aircraft spacing
• Two methods for addressing the wake encounter
  problem
• Wake prediction and avoidance
• Influence of wake vortex stability
• Focus of this research is to excite wake
  instabilities such that a rapid attenuation of
  the wake is achieved
• Need to understand flow physics of vortex decay
• How can vortex instability mechanisms be
  enhanced?

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Research Program Objectives

• To obtain a qualitative understanding of the
  configurations that are conducive to rapid
  amplification of instabilities
• Based on ?2/ ?1 and b2/b1
• Identification of instability types/modes that
  are responsible for wake vortex attenuation
• Identify wavelength, core size, vorticity
  distribution, circulation strength
• Attempt to actively perturb experimental wake
• Plasma actuation
• Control surface oscillation
• Relate experimental results directly to aircraft
  variables
• Calculate induced rolling moment

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Aircraft Wake at Cruise Altitude
Photo taken from http//www.airliners.net
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Wake Upset Video
Video clip courtesy of the Boeing Corporation
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The Four-Vortex System

• Why study a four-vortex wake?
• A four-vortex model is selected as it represents
  an aircraft wake in a high-lift configuration

TIP VORTEX
FLAP VORTEX
Photo taken from http//www.airliners.net
Counter-rotating configuration
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Large Subsonic Wind Tunnel Facility
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Four-Vortex Wake Experiment
Artist rendition of wake facility at Notre Dame
Near-field Helium bubble visualization
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Four-Vortex Wake Visualization
Wing models
Outer core
Inner core
Vortex cores

• Further details on experimental results presented
  in publications
• 23rd AIAA Applied Aerodynamics Conference, AIAA
  2005-4852, Toronto, ON, June 2005.
• 11th Intl Symposium on Flow Visualization, paper
  103, Notre Dame, IN, August 2004.

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Summary

• An experimental apparatus has been developed to
  generate a wake consisting of four vortices
• A four-vortex model was selected as it represents
  a simplified model of an aircraft during take-off
  and landing
• The apparatus permits the control of the
  circulation strength of each vortex as well as
  the spacing between vortices
• The facility may be used to study both
  co-rotating and counter-rotating configurations
• The large subsonic tunnel allows for
  visualization of the wake up to 30 spans
  downstream of generation
• Helium bubbles are excellent for marking wake
  vortices
• Symmetric instability modes were observed in the
  far-field of the wake

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Proposed Future Experimentation

• Identify dominant instability types/modes
  responsible for wake dynamics
• Flow visualization
• Wavelength/Amplitude measurements
• Use of PIV for detailed flow-field surveys
• Knowing the dominant instability modes, it should
  be possible to actively perturb the wake
• Frequency and location of perturbations known a
  priori
• Methods for perturbing wake include
• Plasma actuation
• Oscillating control surfaces
• Use of PIV to measure velocity for actively
  controlled wakes
• Relation of measurements to aircraft variables
• Calculation of rolling moment induced on
  following wing model
• Compare results to uncontrolled case

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Questions?
Photo taken from http//www.airliners.net