AOE 3054 Flow Visualization
• Relevant to experiments 1, 4 and 7.• General background to one of the most
basic techniques of wind tunnel testing • Reading: Lab manual, experiment 1. Also
Barlow, “Low Speed Wind Tunnel Testing” (on reserve).
What is flow visualization?
• The art of making an invisible flow visible.
•
• A key diagnostic tool for engineers.
This Class
• An overview of a few of the many flow visualization techniques– How do you use them?– What is seen?– Advantages, disadvantages?– Examples– Variations
What are the various techniques?
• Methods for visualizing flow fields1. 2.
• Methods of visualizing surface flows3. 4.
Methods for Visualizing Flow Fields1. Smoke or Dye Injection
Smoke (for air flows)
Dye (for water flows)
How?
(add labels)
1. Smoke or Dye Injection
Dye in water - NACA 65A015, Re = 7000, zero degrees angle of attack.
What is seen?
Note
1. Smoke or Dye Injection
Kerosine vapor in air. Sphere at 1.6m/s. (Experiment 1)
Advantages/Disadvantages••••
1. Smoke or Dye InjectionVariations
(a) …
(b) …
LEX vortex bursting on a 1/48th
scale F18 model visualized by injecting dye in water.
Spiral vortices formed on a 20cm-wide spinning cone at 2.9m/s. Boundary layer is revealed.
1. Smoke or Dye InjectionVariations
(c) …
Picture shows European Starling in 9m/s air flow. Filament lines are revealed.
http://www.biology.leeds.ac.uk/staff/jmvr/Flight/fvbzwjm.htm
Virginia Tech – Miami, 2003Crop spraying
Yachts in the Volvo Ocean Race in Cape Town
Methods for Visualizing Flow Fields2. Bubble Techniques(a) Air: Helium bubble technique
How?
What is seen?
(add labels)
2a. Helium bubble techniqueExamples
(b) Flow over a wing tip. Bubbles visualized using pulsed laser (note dotted paths)
Virginia Tech AOE Dept.
(a) Wind-tunnel test of a 1:20 scale model of the space shuttle
Sage Action Incorporated
2a. Helium bubble technique Example
Advantages/Disadvantages•
•
•
•
(c) Helicopter in forward flight
NASA
Methods for Visualizing Flow Fields2. Bubble Techniques
(b) Water: Hydrogen bubble technique
How?
What is seen? Depends on mode of operation:
Fluid line:
2(b) Hydrogen bubble technique
Examples
(a) Flow downstream of a circular cylinder
Cylinder
Platinum wire
Prongs supporting wire
(b) Flow in an inlet region of a circular pipe (water, flow velocity 6cm/s, 27mm pipe, Re=1600)
Japan Society of Mechanical Engineers: Visualized Flow, Pergamon Press, New York, 1988
Armfield Ltd. UK
2(b) Hydrogen bubble technique
Advantages/Disadvantages•••
Examples
(c) Turbulent flow in a rectangular duct (pulsed/insulated)
Armfield Ltd. UK
Methods for Visualizing Flow Fields2. Bubble Techniques
Variations
Turbulent separation over a rectangular block (water flow)
Methods for Visualizing Surface Flows3. Surface Oil Flow Visualization
How?
What is seen?
Skin-frictionlines
Separation ‘bubble’(Separation followed by Immediate reattachment)
Drips of oil!
Flow
3. Surface Oil Flow Visualization
Sep. Line
Sep. Line
(a) Flow over a stalled airfoilExamples
3. Surface Oil Flow Visualization
Advantages/Disadvantages••••
Examples(b) 50 c.c. Land Speed Record Vehicle Model Wind Tunnel Oil Flow Visualization (Sideslip Angle, β = 12°). Variation: use of dark pigment (not TiO2) Photo courtesy of
Eugene Heim
Methods for Visualizing Surface Flows4. Tufts
How?
What is seen?
Advantages/Disadvantages•••
4. Tufts
Examples
(a) Flow over a Clark Yshowing stalled and unstalled behavior.
(Experiment 7)
Flow
Flow
4. Tufts
(c) …
Flow over a transport aircraft wing.
University of Washington Aeronautical Laboratories
(b) Yarn tufts. Flow over the main sail of a model yacht
WB Sails Ltd.
Mast
Flow
4. Tufts(d) In flight tuft visualization
4. Tufts
Variations
Matt Orr, MS Thesis, Virginia Tech, 2000
