PRESSURE MEASUREMENTS AND FLOW VISUALIZATION J. JAGODA MK – 321-5 jeff.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? Constant cross-section along span

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

Pressure vs. Stagnation Pressure 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

Maintain different pressure need solid body (e.g., wing or shock) 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

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

Smoke Tunnel

Streamline Pathline Streakline Timeline Fluid Lines 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

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

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, Visualize displacement (velocity) Wire Wall

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

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

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

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)

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

Pressure Measurement Setup