POF - Drag Flashcards
What are the two types of drag?
- Form Drag
2. Skin-Friction Drag
Why is it better to have a maximum thickness near the trailing edge?
- It delays the transition point.
- The surface maintains a laminar flow longer.
- It reduces skin friction drag.
What is the boundary layer?
It is the area that extends from the surface up to the flow speed that is 99% of the free stream flow
What is a pressure gradient?
It is when pressure moves from high pressure to low pressure.
What does a high Reynolds number mean?
A high Reynolds number means turbulent flows.
What are three factors that affect the transition point of a boundary?
- Speed of the airflow.
- Surface quality.
- Magnitude of adverse pressure gradient.
What does a low Reynolds number mean?
A low Reynolds number means laminar flows.
What is form drag?
When there is a pressure differential on the surface of the object.
What is the transition point?
It is the point on the surface when laminar flow changes to a turbulent flow.
If the aerofoil is thick towards the trailing edge, where would the transition point be?
The transition point would be further away from the leading edge.
What is profile drag?
Profile drag is form and skin-friction drag.
Where is the transition point on an aerofoil that’s thick near the leading edge?
The transition point is closer to the leading edge.
What are four key facts about the laminar boundary layer?
- It has a laminar flow.
- It is thin (mm).
- Slippery
- Has low kinetic energy.
What are four key facts about the turbulent boundary layer?
- It has turbulent flows.
- It is thick (cm).
- It is draggy.
- Has high kinetic energy.
What is the formula for Drag?
Drag Force = 1/2•rho•V^2•S•CD
