Fundamentals Flashcards
Define the Chord of an aerofoil
distance from leading edge to trailing edge
Define the Camber of an aerofoil
maximum distance between the mean camber line and the chord line.
Define the thickness of an aerofoil
the distribution of the aerofoil along the camber line
Whats the equation for a wing aspect ratio AR with varying chord?
b^2/S
wing span squared over wing area
Whats the equation for the standard mean chord in a varying chord wing?
S/b
or
b/AR
What 3 aspects do Tensors cover?
Magnitude, Direction and Orientation
Define vorticity
Vorticity is the microscopic measure of rotation at any point in a fluid. This relates to the average angular momentum of a fluid particle.
If vorticity is zero everywhere, how is the flow described?
Irrotational
What vector operation is used to find vorticity?
Curl of the Velocity vector
Define Circulation
Circulation is 2D scaler vorticity that gives a macroscopic measure of rotation within a flow.
What is a potential flow?
A simplified flow in which a scalar function can be used to represent a velocity vector field. V = grad fi (velocity potential)
What are the constraints of a potential flow?
Flow must be irrotational and incompressible
Fi must meet continuity equation (laplace equation)
Why is a potential flow always irrotational ?
Becasue a curl of a gradiant is always ZERO
Why must potential flow be incompresssible?
Because in incompressible flow the divergence of the velocity field is ZERO, this then means the laplacian of the scalar is also ZERO.
What makes the laplacian of potential flow significant?
potential flow solutions to the laplace equation can be superimposed and so problems can be broken down into smaller ones. eg source + sink = doublet
What are the issues with using potential flow to solve problems?
They are not real flows
Cannot be used near solid bodies that have boundary conditions
Cannot be used where vorticity is expected
What does it mean if the Coefficient of pressure is positive?
p > p(inf)
V < V(inf)
What does it mean if the Coefficient of pressure is negative?
p < p(inf)
V > V(inf)
What are the two aerodynamic forces and what are they casued by?
Pressure forces - caused by interactions (collisions) with a body surface
Shear forces - caused by viscocity in fluid
The resultant aerodynamic force can be split into two pairs of components, what are these?
Lift and Drag (lift is perpeducular to motion)
Normal and Axial (normal is perpedicular to chord)
Define the centre of pressure
The location of average pressure, moves with angle of attack and lift. Moment is always ZERO
Define the aerodynamic centre
The location where the moment remains constant no matter the angle of attack
What are the 3 aerodynamic moments and their corresponding axes?
Pitch - y
Roll - x
Yaw - z
In this module what do upper and lower case letters stand for?
Upper case - 3D
Lower case - 2D
Define the Reynolds numbers
Ratio between inertial forces and viscous forces.
The higher the number the more complex aerodynamic calculations
Define Mach number
Ratio of velocity over characteristic speed of sound
What is the local mach number and why can it be important
The local mach number (the one corresponding to air around wings) can be diffrerent to the free stream M number due to differing velocities. In the transonic region compressibiity effects may appear on the top surface of aerofoil.
