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PRESSURE MEASUREMENTS AND FLOW VISUALIZATION

PRESSURE MEASUREMENTS AND FLOW VISUALIZATION. J. JAGODA MK – 321-5 j eff.jagoda@ae.gatech.edu. PRESSURE MEASUREMENTS. Why does and airplane fly ?? Pressure below >pressure above What causes the asymmetry ? Angle of attack Camber (aided by flap) What is an airfoil vs. Wing?

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PRESSURE MEASUREMENTS AND FLOW VISUALIZATION

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  1. PRESSURE MEASUREMENTS AND FLOW VISUALIZATION J. JAGODA MK – 321-5 jeff.jagoda@ae.gatech.edu

  2. PRESSURE MEASUREMENTS • Why does and airplane fly ?? • Pressure below >pressure above • What causes the asymmetry ? • Angle of attack • Camber (aided by flap) • What is an airfoil vs. Wing? • Constant cross-section along span

  3. PRESSURE MEASUREMENT • Lift for an airfoil: • L’ = rVinfG • Cheat (faster, larger) • Normalization (unitless) • cL = L/1/2rVinf2c = L/qinf.c • cp = (p – pinf)/qinf

  4. PRESSURE MEASUREMENT • Pressure vs. Stagnation Pressure • P – local scalar quantity • P0 – local vector quantity normal to flow • Incompressible (Bernoulli) • Compressible P/P0 = fn(Mach#) {AE2010} • P0 constant for isentropic flow, i.e., NOT: • Boundary layer • Shock • Heat addition

  5. PRESSURE MEASUREMENT • How to measure ? • Pressure – don’t disturb flow • Stagnation (Total) Pressure – stop flow • Both simultaneously w/pitot static probe • Maintain different pressure need solid body (e.g., wing or shock) • Change P0 in isentropic flow through velocity

  6. PRESSURE MEASUREMENTS • No velocity at stationary surface (no slip condition) • Slow velocity increase to edge of b/l • Static pressure constant normal to surface • Boundary layers grow downstream • Join at the end to form wake • Blower up/downstream determines P & P0

  7. Smoke Tunnel

  8. Fluid Lines • Streamline • everywhere tangent to instantaneous velocity vector • Pathline • actual path traversed by a fluid packet • Streakline • locus of fluid packets that have all previously passed through a specific point in the flow • Timeline • set of fluid packets that form a line at some instant in time

  9. Hele-Shaw Flow • Creeping flow: water with dye lines (streaklines)

  10. Blausius Boundary Layer Profile • Fine tellerurium wire + few ms electrical impulse produces chemical reaction in water • Cloud of product drifts with tangential velocity • Time line, Visualizedisplacement (velocity) Wire Wall

  11. Airfoil Wake • 6:1 elliptical cylinder at zero angle of attack (Rechord=4000) • Drop of TiCl4 (liquid) on surface forms white smoke as it interacts with water vapor in the air • Laminar boundary layer separates, forms wake, sheds vortices

  12. Delta Wing Vortices • Thin wing, 15 semi-vertex at 20 angle of attack (Re=20,000) • Lines of colored fluid injected from wing

  13. Turbulent Distortion of Material Lines • Fine platinum wire in water tunnel behind turbulence grid • Periodic pulsing produces double lines of H2 bubbles

  14. Planar Visualization of 2-D Mixing Layer • 2-D flow in channel, higher velocity fluid on top • Low speed fluid contains dye that fluoresces when hit by vertical laser sheet (laser sheet visualization)

  15. Tanker Wake • Grounded tanker (Argo Merchant, 1976) • Oil spilling with current at 45 to ship

  16. Pressure Measurement Setup

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