7 - External Forced Convection Flashcards

1
Q

Define free-stream velocity

A

The velocity of the fluid relative to an immersed solid body sufficiently far from the body.
Taken to be equal to the upstream/approach velocity.

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2
Q

Define upstream/approach velocity

A

The velocity of the approaching fluid far ahead of the body.

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3
Q

Define drag

A

The force a flowing fluid exerts on a body in the flow direction.

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4
Q

Define lift

A

The sum of the components of the pressure and wall shear forces in the direction normal to the flow.

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5
Q

What is the drag force dependent on?

A
Density of the fluid
Upstream velocity
Size of body
Shape of body
Orientation of body
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6
Q

What is (skin) friction drag?

A

The part of drag that is due directly to wall shear stress.

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7
Q

What is the pressure drag?

A

The part of drag that is due directly to pressure.

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8
Q

At low Reynolds numbers, what is most drag due to?

A

Friction drag

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9
Q

Relationship between friction drag and surface area

A

Directly proportional

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10
Q

What is pressure drag proportional to?

A

Frontal area

Difference between the pressures acting on the front and back of the immersed body

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11
Q

What is a separated region?

A

The low-pressure region behind the body recirculating and causing backflows to occur.

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12
Q

What happens to the pressure drag with a larger separated region?

A

Larger pressure drag

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13
Q

Define wake

A

The region of flow trailing the body where the effects of the body on velocity are felt.

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14
Q

Where are viscous and rotational effects most significant?

A

Boundary layer
Separated region
Wake

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15
Q

What does the transition from laminar to turbulent flow depend on?

A
Surface geometry
Surface roughness
Upstream velocity
Surface temperature
Type of fluid
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16
Q

How do the local friction and heat transfer coefficients differ between turbulent and laminar flow?

A

Higher in turbulent flow.