aoe 3054 flow visualization - virginia techaborgolt/aoe3054/classes/experimentsclass1... · aoe...
TRANSCRIPT
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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).
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What is flow visualization?
• The art of making an invisible flow visible.
•
• A key diagnostic tool for engineers.
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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
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What are the various techniques?
• Methods for visualizing flow fields1. 2.
• Methods of visualizing surface flows3. 4.
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Methods for Visualizing Flow Fields1. Smoke or Dye Injection
Smoke (for air flows)
Dye (for water flows)
How?
(add labels)
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1. Smoke or Dye Injection
Dye in water - NACA 65A015, Re = 7000, zero degrees angle of attack.
What is seen?
Note
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1. Smoke or Dye Injection
Kerosine vapor in air. Sphere at 1.6m/s. (Experiment 1)
Advantages/Disadvantages••••
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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.
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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
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Virginia Tech – Miami, 2003Crop spraying
Yachts in the Volvo Ocean Race in Cape Town
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Methods for Visualizing Flow Fields2. Bubble Techniques(a) Air: Helium bubble technique
How?
What is seen?
(add labels)
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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
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2a. Helium bubble technique Example
Advantages/Disadvantages•
•
•
•
(c) Helicopter in forward flight
NASA
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Methods for Visualizing Flow Fields2. Bubble Techniques
(b) Water: Hydrogen bubble technique
How?
What is seen? Depends on mode of operation:
Fluid line:
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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
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2(b) Hydrogen bubble technique
Advantages/Disadvantages•••
Examples
(c) Turbulent flow in a rectangular duct (pulsed/insulated)
Armfield Ltd. UK
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Methods for Visualizing Flow Fields2. Bubble Techniques
Variations
Turbulent separation over a rectangular block (water flow)
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Methods for Visualizing Surface Flows3. Surface Oil Flow Visualization
How?
What is seen?
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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
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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
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Methods for Visualizing Surface Flows4. Tufts
How?
What is seen?
Advantages/Disadvantages•••
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4. Tufts
Examples
(a) Flow over a Clark Yshowing stalled and unstalled behavior.
(Experiment 7)
Flow
Flow
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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
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4. Tufts(d) In flight tuft visualization
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4. Tufts
Variations
Matt Orr, MS Thesis, Virginia Tech, 2000