1. PRESSURE MEASUREMENTS AND FLOW VISUALIZATION
J. JAGODA
MK – 321-5

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. 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

4. 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

5. 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

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. 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

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

16. Pressure Measurement Setup