3D Airflow and Vortices Flashcards
how are vortices generated?
at the wingtip, the air is free to move between upper and lower surfaces. At the wing tips the air moves from high pressure to low pressure.
The low pressure moves inboard and down to the high pressure.
counter-rotating vortices develop at the wing tips.
What is the affect of vortices on lift?
vortices produce induced drag and downwash.
Vortices is a by-product of lift and this energy must be used to create it and thus creates an induced drag.
the vortex downwash has an upstream influence at the leading edge which inclines the airflow downward, artifically reducing the angle of attack (known as effective AOA) and thus reducing the lift co-efficient.
affect is stronger at wing tips than wing root.
therefore, vortices = induced drag and reduced lift co-efficient.
What can we do/add to reduce vortices?
Winglets Sharklets Tiptanks Chamber? EDIT Geometric twist Aerodynamic twist
What is a geometric twist and what does it do?
A geometric twist is a reduction of the angle of incidence along the wingspan from root to tip.
The reduction of AOI means less lift and thus less induced drag from wingtip vortices is generated.
What is an aerodynamic twist and what does it do?
An aerodynamic twist is the reduction or ‘flattening out’ of the chamber line from the wing root to wing tip.
This generates less lift towards the wing tips and thus reduces vortices generation and induced drag.
Describe the span wise airflow of a 3D wing?
The high pressure air under the lower surface tries to escape to the upper surface to equalise the pressure. The easiest way is by moving towards and over the wing tip.
The lower pressure on the upper surface escapes by moving toward the wing root.
What is the difference between Ai and Ae
Induced angle of attack is the difference between free airflow AOA and the artificially generated airflow/AOA
Effective AOA is the difference between the chord line and new artificial AOA.
Ae = A - Ai
