-
7/30/2019 Intro Fluid Forces
1/14
Chapter 11: Flow over bodies;
Lift and Drag
Eric G. PatersonDepartment of Mechanical and Nuclear
Engineering
The Pennsylvania State University
Spring 2005
-
7/30/2019 Intro Fluid Forces
2/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
2
Objectives
Have an intuitive understanding of the various
physical phenomena such as drag, friction and
pressure drag, drag reduction, and lift.
Calculate the drag force associated with flow
over common geometries.
-
7/30/2019 Intro Fluid Forces
3/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
3
Motivation
-
7/30/2019 Intro Fluid Forces
4/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
4
Motivation
-
7/30/2019 Intro Fluid Forces
5/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
5
External Flow
Bodies and vehicles in motion, or with flow over them,
experience fluid-dynamic forces and moments.
Examples include: aircraft, automobiles, buildings,.
These problems are often classified as External Flows.
-
7/30/2019 Intro Fluid Forces
6/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
6
Fluid Dynamic Forces and Moments
Ships in waves present one of the most
difficult problems.
Airplane in level steady flight: drag =
thrust and lift = weight.
-
7/30/2019 Intro Fluid Forces
7/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
7
Drag and Lift
Fluid dynamic forces aredue to pressure and
viscous forces acting on
the body surface.
Drag: componentparallel to flow direction.
Lift: component normal
to flow direction.
-
7/30/2019 Intro Fluid Forces
8/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
8
Drag and Lift
Lift and drag forces can be found byintegrating pressure and
wall-shear stress.
-
7/30/2019 Intro Fluid Forces
9/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
9
Example: Automobile Drag
Scion XB Porsche 911
CD = 1.0, A = 25 ft2, CDA = 25ft
2 CD = 0.28, A = 10 ft2, CDA = 2.8ft
2
Drag force FD=1/2V2(CDA) will be ~ 10 times larger for Scion
XB
-
7/30/2019 Intro Fluid Forces
10/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
10
Friction and Pressure Drag
Fluid dynamic forces are
comprised of pressure and
friction effects.
Often useful to decompose,
FD = FD,friction + FD,pressure
CD = CD,friction + CD,pressure
Friction drag
Pressure drag
Friction & pressure drag
-
7/30/2019 Intro Fluid Forces
11/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
11
Streamlining
-
7/30/2019 Intro Fluid Forces
12/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
12
Streamlining via Active Flow Control
Pneumatic controlsfor blowing air from
slots: reduces drag,
improves fuel
economy for heavy
trucks (Dr. Robert
Englar, Georgia
Tech ResearchInstitute).
-
7/30/2019 Intro Fluid Forces
13/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
13
Effect of Roughness in Pipe flow
Similar to MoodyChart for pipe flow
Laminar flow
unaffected by
roughness
-
7/30/2019 Intro Fluid Forces
14/14
Chapter 11: Flow over bodies; lift and dragME33 : Fluid Flow
14
End Effects of Wing Tips
Tip effects can bereduced by attaching
endplates orwinglets.
Trade-off between
reducing induceddrag and increasing
friction drag.
Wing-tip feathers onsome birds serve the
same function.
