Part 4: Boundary Layer Concepts and Flow over Immersed Bodies

Question 1

What is an External Flow?

Answer 1

a flow field for which the object is completely surrounded by the fluid. Ex. Submarine, plane, building

Question 2

A body interacts with the surrounding fluid through..

Answer 2

pressure and shear stresses

Question 3

What is Drag?

Answer 3

the resultant force acting on a body due to the pressure and/or shear stresses acting in the direction of the approach velocity

Question 4

What is Lift?

Answer 4

the resultant force acting on a body due to pressure and/or shear stresses acting perpendicular to the direction of the approach velocity.

Question 5

T or F: Both Re and body shape have significant effect on the Cd?

Answer 5

True

Question 6

What plays a dominant factor on the lift coefficient?

Answer 6

Body Shape

Question 7

What is the Boundary Layer?

Answer 7

The region adjacent to the surface of a body in which viscous effects are important.

Question 8

T or F: Flow within the boundary layer is only laminar?

Answer 8

False, flow within the boundary layer can be turbulent or laminar.

Question 9

How low must the Re be so that a boundary layer does not occur?

Answer 9

Re<1000

Question 10

What is the Transitional Range of Re?

Answer 10

2x10^5 to 3x10^6

Question 11

True or False: Outside the boundary layer the flow behaves as it were inviscid?

Answer 11

True

Question 12

The boundary layer is response to…

Answer 12

fluid viscosity

Question 13

Where does the no-slip condition occur?

Answer 13

at a solid boundary

Question 14

How is the edge of the boundary layer defined?

Answer 14

By velocity, once U reaches 99%U

Question 15

The flow outside of the boundary layer is classified as the “ “

Answer 15

free stream

Question 16

T or F: Flow posses vorticity inside the boundary layer?

Answer 16

True

Question 17

T or F: Flow posses vorticity outside the boundary layer?

Answer 17

False, only within the boundary layer

Question 18

What type of mixing/rotation occurs in the laminar layer?

Answer 18

simple mixing`

Question 19

What type of mixing/rotation occurs in the turbulent layer?

Answer 19

random mixing

Question 20

What is the displacement thickness?

Answer 20

It is used to describe the “outward shift” from edge of body to account for velocity deficit relative to free stream.

Question 21

True or False: Shear stress decreases as x increases

Answer 21

True, as you move further down the pipe you have less shear stress

Question 22

True or False: The drag on a flat plate is not related to the momentum deficit within the boundary layer?

Answer 22

False, it is

Question 23

” “ is the dimensionless wall shear stress

Answer 23

local friction coefficient

Question 24

Laminar Flow is characterized by

Answer 24

-Viscous, flowing in layers, random motion is on a molecular level, velocity at a point is constant

Question 25

Turbulent flow is characterized by

Answer 25

-Non-viscous, eddies, mixing, random motion occurs at a macroscopic scale, velocity at a point is fluctuating