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

Overview Objective Theory Experimental Procedure Results and Discussion Error Analysis Conclusion

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

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

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)

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

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

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

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

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

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.

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

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

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

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)

Results Wake Profile x/D=5

Results Wake Profile x/D=10

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)

Pressure Coefficient

Drag Coefficients V=17.83 (m/s): Re = 35,000 CD = 1.26 (+/-) .54 V=30.68: Re = 60,000 CD = 1.19 (+/-) .079 Theoretical Drag Coefficient: CD = 1; CL = 0 Transition Re: 300,000- 500,000 V =17.83 (m/s) V =30.68 (m/s)

Lift Coefficients Theoretical Lift Coefficient: CL = 0

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

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.

THE END QUESTIONS?