Introductory Concept

Question 1

Mean Free Path

Answer 1

The average distance a molecule travels before it collides with another molecule.

Question 2

Continuum

Answer 2

Fluid is continuously distributed along the region of interest.

Question 3

Fluid Particle

Answer 3

A relatively small mass of the fluid, containing a large number of molecules that will provide a meaningful statical average.

Question 4

Pressure

Answer 4

Force acting per unit area.

Question 5

Shear stress and Normal Stress

Answer 5

Shear stress, is stress component acting tangential to area.
Normal stress is stress component acting normal to area.

Question 6

Eularian

Answer 6

Fixed in the flow field and you observe the variation of properties at the point (spatial description).

Question 7

Lagrangian

Answer 7

Identified fluid particles are followed in the course of time.

Question 8

Density

Answer 8

mass per unit volume

Question 9

Incompressible Fluid

Answer 9

Density = constant, Mach < 0.3

Question 10

Compressible Fluid

Answer 10

Density is not constant, and has a time variable. Mach >= 0.3

Question 11

Viscous Flow

Answer 11

if the viscosity (frictional effect) is important

Question 12

Inviscid Flow

Answer 12

If viscosity (frictional friction) is NOT important.

Question 13

Steady Flow

Answer 13

V, P, T constant in time.
func(x,y,z)

Question 14

Unsteady Flow

Answer 14

V = V(t), P = P(t), T= T(t),
func(x,y,z,t) :has a function of time.

Question 15

Pathline

Answer 15

A trajectory traced out by a fluid particle moving in a flow field (Lagranian).

Question 16

Streakline

Answer 16

A line connecting fluid particles that has passed from the same point (Eulerian).

Question 17

Streamline

Answer 17

Imaginary lines, which are tangent to flow direction at a given instant of time.

Question 18

Velocity define in 2D flow, equation:

Answer 18

dy/dx = v/u

Question 19

How are 3D flow represented

Answer 19

Uppercase i.e. F, C

Question 20

How are 2D flow represented

Answer 20

lowercase or hyphen i.e. F’ or c (per span)

Question 21

Lift, L

Answer 21

Component of R (resultant force) perpendicular to free stream velocity.

Question 22

Drag, D

Answer 22

Component of R (resultant force) parallel to free stream velocity.

Question 23

Axial Force, A

Answer 23

Component of R (resultant force parallel to c (chord).

Question 24

Normal Force

Answer 24

Component of R (resultant force) perpendicular to c (chord).

Question 25

dN’(u) and dA’(u) Equation, brackets represent subscript. u = upper surface

Answer 25

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)

Question 26

What does s normally represent?

Answer 26

The curve path along an aerofoil.

Question 27

dN’(l) and dA’(l) Equation, brackets represent subscript. u = leading surface

Answer 27

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)

Question 28

L’? Lift equation and D’? Drag equation.

Answer 28

L’ = N’cos(alpha) - A’sin(alpha)
D’ = N’sin(alpha) + A’cos(alpha)

Question 29

Centre of Pressure xcp

Answer 29

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.

Question 30

Aerodynamic Centre

Answer 30

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.

Question 31

Dimensional Homogeneity

Answer 31

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.

Question 32

Non - Dimensionalisation

Answer 32

Removing dimensional dependence.

Question 33

Laminar Flow

Answer 33

Organised, well defined, defined by Re number.

Question 34

Reynold Number

Answer 34

Re = (rholengthvelocity)/ viscosity
Re = Inertial force(force due to change in momentum) / Viscous forces (force due to shear).

Question 34

Turbulent Flow.

Answer 34

Essentially unsteady, random in time and space, mean quantities are deterministic. Defined by Re Number.

Question 34

Geometric Similarity

Answer 34

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.

Question 35

Kinematic Similarity

Answer 35

Flow fields in the protype and model must have geometrically the same set of streamlines.

Question 36

Dynamic Similarity

Answer 36

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.