Module 2 - Airflow Visualization

Question 1

assumed to neglect the effects of friction in tackling situations involving fluid dynamics

Answer 1

inviscid

Question 2

can either be compressible or incompressible

Answer 2

inviscid

Question 3

the property of a fluid to resist shearing stresses and a tendency to adhere to solid surfaces

Answer 3

viscous

Question 4

a measure of a fluid’s resistance to flow

Answer 4

viscosity

Question 5

viscosity of water

Answer 5

1.0 centipoise

Question 6

viscosity of honey

Answer 6

12,200.0 centipoise

Question 7

the lower the centipoise, the _______ the viscosity

Answer 7

lower

Question 8

is one way to measure a fluid’s resistance to flow when an external force is applied

Answer 8

dynamic viscosity

Question 9

is another way to measure a fluid’s resistance to flow when no external force is applied except for gravity

Answer 9

kinematic viscosity

Question 10

D’Alembert’s paradox in 1752 states that

Answer 10

both drag and lift are zero in potential flow with the following characteristics: incompressible, inviscid, irrotational, and stationary

Question 11

properties involved in D’Alembert’s paradox of 1752

Answer 11

incompressible, inviscid, irrotational, stationary

Question 12

it is the air flow that is closest to and in contact with the aircraft surface

Answer 12

boundary layer

Question 13

it is a very thin layer of air lying over the surface of the wing and all other surfaces of the airplane

Answer 13

boundary layer

Question 14

Why does the boundary layer tend to stick to the wing?

Answer 14

because air has viscosity

Question 15

grows as the flow moves over the aerofoil

Answer 15

boundary layer thickness

Question 16

The boundary layer thickens as more and more friction affect the flow as the distance along the surface increases. The surface of the aerofoil also contributes to the _________ at the surface.

Answer 16

shear stress

Question 17

______ has dimensions of F/A and acts in a direction tangential to the surface.

Answer 17

Shear stress

Question 18

Shear stress gives rise to a drag force called _________.

Answer 18

skin friction drag

Question 19

What do you call when the fluid moves in parallel layers?

Answer 19

Laminar Flow

Question 20

What do you call when the fluid moves chaotically with irregular fluctuations?

Answer 20

Turbulent Flow

Question 21

Factors that affect the type of flow in the Boundary Layer

Answer 21

• flow quality
• shape
• texture
• pressure gradient
• Reynolds Number
• heating of the fluid

Question 22

Reynolds Number was named after?

Answer 22

Osborne Reynolds

Question 23

If the Reynolds number is small then the flow is __________.

Answer 23

laminar

Question 24

If the Reynolds Number is high, then the flow is _________.

Answer 24

turbulent

Question 25

Osborne Reynolds noticed that if the fluid velocity or diameter of the stream are _____ and the viscosity of the fluid is _____, the Reynolds number will be small.

Answer 25

small, large

Question 26

Symbol for Reynolds Number

Answer 26

Re

Question 27

formula of Reynolds Number

Answer 27

Re = ρVl / μₒ = Vl / v

Question 28

On the boundary layer, the fluid’s interaction with the wall induces a ________ boundary condition and increases continuously to its value of V2 on the _____ of the boundary layer.

Answer 28

no-slip, outer edge

Question 29

zero velocity at the wall condition in a boundary layer

Answer 29

no-slip

Question 30

Because high skin friction drag results to a turbulent flow, designers who want to reduce skin friction drag always try to ___________.

Answer 30

extend the point at the aerofoil’s surface with which laminar flows exist

Question 31

Formula of Laminar Boundary Layer Thickness

Answer 31

δ = 5.2x / sqr of Reₓ

Question 32

symbol for laminar local skin friction

Answer 32

Cfₓ

Question 33

Formula of Turbulent Boundary Layer Thickness

Answer 33

δ = 0.37x / 5th root of Reₓ

Question 34

a point in the flow where it changes or “transitions” from laminar flow to turbulent flow

Answer 34

transition point

Question 35

The transition point’s location in the chord is indicated by the ________ derived from the critical Reynolds Number.

Answer 35

critical chord xcr

Question 36

Friction also causes this phenomenon which in turn creates another source of aerodynamic drag due to separation.

Answer 36

flow separation

Question 37

the drag caused by the flow separation is called _______

Answer 37

pressure drag or form drag

Question 38

Two major consequences of the flow separating over an aerofoil

Answer 38

* drastic loss of lift * major increase in drag caused by pressure drag due to separation

Question 39

Viscous Effects on Drag

Answer 39

* skin friction drag * pressure drag or form drag

Question 40

symbol of skin friction drag

Answer 40

Df

Question 41

symbol of pressure drag or form drag

Answer 41

Dp

Question 42

Formula of total drag caused by viscous effects

Answer 42

D = Df + Dp