7 - External Forced Convection Flashcards
Define free-stream velocity
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.
Define upstream/approach velocity
The velocity of the approaching fluid far ahead of the body.
Define drag
The force a flowing fluid exerts on a body in the flow direction.
Define lift
The sum of the components of the pressure and wall shear forces in the direction normal to the flow.
What is the drag force dependent on?
Density of the fluid Upstream velocity Size of body Shape of body Orientation of body
What is (skin) friction drag?
The part of drag that is due directly to wall shear stress.
What is the pressure drag?
The part of drag that is due directly to pressure.
At low Reynolds numbers, what is most drag due to?
Friction drag
Relationship between friction drag and surface area
Directly proportional
What is pressure drag proportional to?
Frontal area
Difference between the pressures acting on the front and back of the immersed body
What is a separated region?
The low-pressure region behind the body recirculating and causing backflows to occur.
What happens to the pressure drag with a larger separated region?
Larger pressure drag
Define wake
The region of flow trailing the body where the effects of the body on velocity are felt.
Where are viscous and rotational effects most significant?
Boundary layer
Separated region
Wake
What does the transition from laminar to turbulent flow depend on?
Surface geometry Surface roughness Upstream velocity Surface temperature Type of fluid
