1. Aerodynamics of Flow Around a Cylinder
Group 2A:
Adya Ali
Andrew Parry
James Sizemore
Dwayne White

2. Overview Objective Theory Experimental Procedure
Results and Discussion
Error Analysis
Conclusion

3. Objective
To find the aerodynamic lift and drag forces on a circular cylinder placed in uniform free-stream velocity.
To find drag, lift and pressure coefficients using different methods:
Wake Measurements
Normal pressure distribution

4. Theory
Skin friction drag (Df): resultant viscous forces acting on a body
Pressure drag (Dp): due to unbalanced pressure forces caused by flow separation
Total drag = skin friction drag pressure drag
D = Df + Dp

5. Method 1- Wake Measurements
Determine the velocity profiles in the wake
Select two sections
Section 1 (imaginary)- to account for the pressure difference
Section 2 - to obtain wake measurements
*Courtesy of Dr. Alvi’s Lab Manual (exp 7)

6. Method 1- Equations Conservation of Momentum: W= width of body
u1,u2=velocities
Assume no pressure loss between sections 1 & 2.

7. Method 1- Equations (cont’d)
Total Pressure:
Drag Force:

8. Method 1- Equations (cont’d)
Dimensionless Drag coefficient, CD

9. Method 2-Pressure Distribution
For large Reynolds number (Re>103), skin friction drag is negligible.
Total drag  pressure drag
Image reproduced from “Aerodynamics for Engineers”, J. Bertin & M. Smith

10. Method 2-Pressure Distribution (cont’d)
For a cylinder,
Drag force:
Lift force:
r = radius of cylinder
p = pressure
 = angular position

11. Experimental Technique
Apparatus
Wind tunnel - airflow driven by a fan
Pitot-static tube - used to measure the velocity of the wind in the wake
Image reproduced from “Fundamentals of Aerodynamics” J. Anderson, Jr.

12. Experimental Technique
Cylindrical test model - with pressure ports along its circumference
Courtesy Dr. Alvi’s Lab Manual

13. Experimental Technique
Scanivalve and scanivalve digital interface unit
ADC Card on Pentium-based PC
Computer-controlled vertical drive

15. Experimental Technique
Procedure
Wake Measurement:
Select 2 locations,
Set wind tunnel speed counter at 550; (V=30.68 m/s)
Measure dynamic pressure upstream of the cylinder
Move pitot-static tube to the center of the cylinder

16. Experimental Technique
Measure output at vertical locations (4mm intervals)
Repeat procedure with the cylinder at x/D = 10
Normal Pressure Distribution
Set wind tunnel speed counter at 550 (30.68m/s)
Record the output gauge pressure at each port
Repeat the procedure for counter reading at 350 (17.83m/s)

17. Results
Wake Profile x/D=5

18. Results
Wake Profile x/D=10

19. Drag Coefficients: V= 30.68 (m/s)
X/D=5: Re = 53,649
CD = .76 (+/-) .39
X/D=10: Re = 54,034
CD = .67 (+/-) .013
Theoretical Drag Coefficient:
Re = 59,380
CD = 1
V =30.68 (m/s)

20. Pressure Coefficient

21. Drag Coefficients V=17.83 (m/s): Re = 35,000 CD = 1.26 (+/-) .54
V=30.68: Re = 60,000
CD = (+/-) .079
Theoretical Drag Coefficient:
CD = 1; CL = 0
Transition Re: 300, ,000
V =17.83 (m/s)
V =30.68 (m/s)

22. Lift Coefficients
Theoretical Lift Coefficient:
CL = 0

23. Error Analysis Instrument Integration Wind Tunnel Pitot-static tube
Center calibration for cylinder wake
Integration
Trapezoidal approximation
Wind Tunnel
Length of the wind tunnel
Width of wind tunnel

24. Conclusion Method 2 (pressure ports) seems more accurate.
Pressure differential inside the wake is unsteady.
Outside the wake the pressure differential is steady.
The pitot-static tube can measure turbulent fluctuations accurately.

25. THE END QUESTIONS?