Introductory Concept Flashcards
Mean Free Path
The average distance a molecule travels before it collides with another molecule.
Continuum
Fluid is continuously distributed along the region of interest.
Fluid Particle
A relatively small mass of the fluid, containing a large number of molecules that will provide a meaningful statical average.
Pressure
Force acting per unit area.
Shear stress and Normal Stress
Shear stress, is stress component acting tangential to area.
Normal stress is stress component acting normal to area.
Eularian
Fixed in the flow field and you observe the variation of properties at the point (spatial description).
Lagrangian
Identified fluid particles are followed in the course of time.
Density
mass per unit volume
Incompressible Fluid
Density = constant, Mach < 0.3
Compressible Fluid
Density is not constant, and has a time variable. Mach >= 0.3
Viscous Flow
if the viscosity (frictional effect) is important
Inviscid Flow
If viscosity (frictional friction) is NOT important.
Steady Flow
V, P, T constant in time.
func(x,y,z)
Unsteady Flow
V = V(t), P = P(t), T= T(t),
func(x,y,z,t) :has a function of time.
Pathline
A trajectory traced out by a fluid particle moving in a flow field (Lagranian).
Streakline
A line connecting fluid particles that has passed from the same point (Eulerian).
Streamline
Imaginary lines, which are tangent to flow direction at a given instant of time.
Velocity define in 2D flow, equation:
dy/dx = v/u
How are 3D flow represented
Uppercase i.e. F, C
How are 2D flow represented
lowercase or hyphen i.e. F’ or c (per span)
Lift, L
Component of R (resultant force) perpendicular to free stream velocity.
Drag, D
Component of R (resultant force) parallel to free stream velocity.
Axial Force, A
Component of R (resultant force parallel to c (chord).
Normal Force
Component of R (resultant force) perpendicular to c (chord).
dN’(u) and dA’(u) Equation, brackets represent subscript. u = upper surface
dN’(u) = -P(u)ds(u)cos(theta) - tau(u)ds(u)sin(theta)
dA’(u) =-P(u)ds(u)sin(theta) + tau(u)ds(u)cos(theta)
What does s normally represent?
The curve path along an aerofoil.
dN’(l) and dA’(l) Equation, brackets represent subscript. u = leading surface
dN’(l) = P(l)ds(l)cos(theta) - tau(l)ds(l)sin(theta)
dA’(l) =P(l)ds(l)sin(theta) + tau(l)ds(l)cos(theta)
L’? Lift equation and D’? Drag equation.
L’ = N’cos(alpha) - A’sin(alpha)
D’ = N’sin(alpha) + A’cos(alpha)
Centre of Pressure xcp
location where resultant of a distributed load effectively acts on a body, i.e. centre of pressure is the point about which the total moment is 0.
Aerodynamic Centre
point at which the pitching moment of the aerofoil does not vary with the angle of attack, i.e. the point on the aerofoil about which the moment is independent of the angle of attack.
Dimensional Homogeneity
Dimensional analysis based on the fact that is an equation dealing with real physical world, each term of the equation must have the same dimension.
Non - Dimensionalisation
Removing dimensional dependence.
Laminar Flow
Organised, well defined, defined by Re number.
Reynold Number
Re = (rholengthvelocity)/ viscosity
Re = Inertial force(force due to change in momentum) / Viscous forces (force due to shear).
Turbulent Flow.
Essentially unsteady, random in time and space, mean quantities are deterministic. Defined by Re Number.
Geometric Similarity
States that the protype and model must be identical in shape and in size. The ratio of the corresponding linear dimensions in the model and the protype must be the same.
Kinematic Similarity
Flow fields in the protype and model must have geometrically the same set of streamlines.
Dynamic Similarity
Implies that the force distribution between the two flow fields is such that the type of forces are parallel and have the same ratio of magnitude.
