3D flow Flashcards
What factors affect span wise flow
Inertia of mass flow
Local pressure differences around aircraft
How are wing tip vortices formed
Air at bottom of wing (high Pressure) try’s to get to top. But wing tip moving rapidly. So mass of air left behind that rotates inwards. Occurs at both tips clockwise left anti righ
What factors affect intensity of wing tip vortices
Can only be produced when wings produce lift. If amount of lift increases intensity will be greater.
Slower speeds=Stronger vortices.
Wing aspect ratio increasing results in intensity decreasing. Low aspect ratio wing produces more intense vortices.
Effects of tip trailing vortices
Downwash
Drag
Wake turbulence.
Stronger tip trailing vortices stronger the effects.
Wake turbulence threat
Low speed and high AOA produce greatest wake turbulence.
Migrate downwards because of downwash. Only produced when wing produces lift. Can extend for several miles. Stabilise at 900ft.
How Trailing edge vortices form
Span wise flow cause air on upper surface to turn slightly inwards.
Air on bottom turns outwards.
At trailing edge the 2 air flows meet at an angle
Strength depends on angle they meet at.
What happens to upwash and downwash in 3D flow
Upwash decreases.
Downwash Increases.
What is Effective airflow
EAF is direction of airflow relative to the wing.
Pressure distribution and aerodynamic forces are determined by EAF.
Induced AOA
Angle between effective airflow and relative airflow.
Induced Drag
Whenever lift is generated induced drag is generated. depends on induced AOA and is proportional to induced AOA.
Angle of Attack in 3D Flow
AOA is the angle between aircrafts longitudinal axis and the relative airflow.
What affects Induced AOA
Induced AOA is large if aircraft is flying at lower TAS or if vortices are stronger therefore producing greater downwash.
What is effective AOA
Effective AOA is the angle between effective airflow and chord line of the wing.
AOA is now sum of Effective AOA and Induced AOA
Relationship between vortices and EAF/Induced AOA
Stronger vortices result in a smaller EAF and larger Induced AOA. This gives a lower proportion of lift to induced drag. So weaker vortices are better for lift.
Relationship between Rectangular wing and vortices.
For a rectangular wing vortex strength changes span wise. Stronger vortices and greater downwash occur close to the wingtips. Wing root vortices are weaker. This is because wing root has greater EAF and larger lift coefficient.
