Boundary Layers

Question 1

What is a boundary layer?

Answer 1

The layer where surface friction influences the speed between adjacent layer of air.

starting from zero at the wing surface, each layer increases upto free stream speed.

Question 2

What is a Laminar boundary layer?

Answer 2

Laminar flow is the area of smooth airflow across a surface (at the leading edge). The atoms travel in smooth parallel layers.

Question 3

What is a turbulent boundary layer?

Answer 3

Friction forces between air molecules and the surface reduce the local velocity to zero. The speed in each layer is gradually increased until it reaches free stream speed.
The atoms oscillate between layers transferring kinetic energy. Layer thickness and speed increases rapidly

Question 4

What are the properties of a turbulent flow?

Answer 4

> Greater thickness due to oscillating flow
higher speed and higher speed gradient closer to the surface (relative to laminar layer)
Higher kinetic energy due to speed (relative to laminar layer)

Question 5

What is airflow Separation?

Answer 5

A boundary layer is created due to skin friction and kinetic energy is diminshed.

after the greatest thickness, airflow decelerates, kinetic energy reduces but static pressure increases (adverse pressure gradient)

if kinetic energy does not surpass adverse pressure gradient. the flow can seperate.

the flow can also try to flow back upstream, diminishing lift.