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Aeronautical Laboratory > Module 2 - Airflow Visualization > Flashcards

Module 2 - Airflow Visualization Flashcards

1
Q

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

A

inviscid

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2
Q

can either be compressible or incompressible

A

inviscid

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3
Q

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

A

viscous

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4
Q

a measure of a fluid’s resistance to flow

A

viscosity

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5
Q

viscosity of water

A

1.0 centipoise

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6
Q

viscosity of honey

A

12,200.0 centipoise

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7
Q

the lower the centipoise, the _______ the viscosity

A

lower

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8
Q

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

A

dynamic viscosity

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9
Q

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

A

kinematic viscosity

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10
Q

D’Alembert’s paradox in 1752 states that

A

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

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11
Q

properties involved in D’Alembert’s paradox of 1752

A

incompressible, inviscid, irrotational, stationary

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12
Q

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

A

boundary layer

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13
Q

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

A

boundary layer

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14
Q

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

A

because air has viscosity

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15
Q

grows as the flow moves over the aerofoil

A

boundary layer thickness

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16
Q

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.

A

shear stress

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17
Q

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

A

Shear stress

18
Q

Shear stress gives rise to a drag force called _________.

A

skin friction drag

19
Q

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

A

Laminar Flow

20
Q

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

A

Turbulent Flow

21
Q

Factors that affect the type of flow in the Boundary Layer

A
  • flow quality
  • shape
  • texture
  • pressure gradient
  • Reynolds Number
  • heating of the fluid
22
Q

Reynolds Number was named after?

A

Osborne Reynolds

23
Q

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

A

laminar

24
Q

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

A

turbulent

25
Q

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.

A

small, large

26
Q

Symbol for Reynolds Number

A

Re

27
Q

formula of Reynolds Number

A

Re = ρVl / μₒ = Vl / v

28
Q

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.

A

no-slip, outer edge

29
Q

zero velocity at the wall condition in a boundary layer

A

no-slip

30
Q

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

A

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

31
Q

Formula of Laminar Boundary Layer Thickness

A

δ = 5.2x / sqr of Reₓ

32
Q

symbol for laminar local skin friction

A

Cfₓ

33
Q

Formula of Turbulent Boundary Layer Thickness

A

δ = 0.37x / 5th root of Reₓ

34
Q

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

A

transition point

35
Q

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

A

critical chord xcr

36
Q

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

A

flow separation

37
Q

the drag caused by the flow separation is called _______

A

pressure drag or form drag

38
Q

Two major consequences of the flow separating over an aerofoil

A
  • drastic loss of lift
  • major increase in drag caused by pressure drag due to separation
39
Q

Viscous Effects on Drag

A
  • skin friction drag
  • pressure drag or form drag
40
Q

symbol of skin friction drag

A

Df

41
Q

symbol of pressure drag or form drag

A

Dp

42
Q

Formula of total drag caused by viscous effects

A

D = Df + Dp

Aeronautical Laboratory (3 decks)

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