Aerodynamics

Fluid particle

Fluid particle

A relatively small mass of the fluid, containing a large number of molecules that will provide a meaningful statistical averages

Kutta Condition

For a given airfoil at a given angle of attack, the circulation around the airfoil is such that the flow leaves the trailing edge smoothly.

Streakline

a line connecting fluid particles that has passed from the same point (Eularian)

Streamline

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

Pathline

a trajectory traced out by a fluid particle moving in a flow field (Lagrangian)

Reynolds number

a dimensionless number used in fluid mechanics to indicate whether fluid flow past a body or in a duct is steady or turbulent.

Kutta-Joukowski Theorem

the lift per unit length of a spinning cylinder is equal to the density (r) of the air times the strength of the rotation (G) times the velocity (V) of the air.

dynamic similarity

all forces in the model flow scale by a constant factor to corresponding forces in the prototype flow

Stagnation point

a point in a flow field where the local velocity of the fluid is zero

Boundary layer thickness

the distance normal to the wall to a point where the flow velocity has essentially reached the 'asymptotic' velocity

Separation

reduced lift and increased pressure drag, caused by the pressure differential between the front and rear surfaces of the object

Wall shear stress

expresses the force per unit area exerted by a solid boundary on a fluid in motion (and vice-versa) in a direction on the local tangent plane.

𝛁×𝑽

Curl

𝛁∙𝑽

Divergence

Dividing streamline

The part of the flow that separates the recirculating flow and the flow through the central region of the duct

Elementary flow

a collection of basic flows from which it is possible to construct more complex flows by superposition.

Buckingham Pi Theorem

Dimensional analysis is used to formulate a physical phenomenon as a relation between a set of nondimensional (unitless) groups

No-slip condition

assumes that at a solid boundary, the fluid will have zero velocity relative to the boundary

Circulation

the line integral of velocity around a closed curve in the flow

Vorticity

a region in a fluid in which the flow revolves around an axis line

Magnus effect

fluid pressure decreases at points where the speed of the fluid increases

d’Alembert’s Paradox

Body immersed in Fluid, There is no net drag, There is no net lift

Eularian

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

Lagrangian

Identified fluid particles are followed in \n The course of time

Source/sink

fluid moves radially inward/outward towards a point known as sink, and fluid disappear at sink/source at a constant rate.

Doublet

a result of construction of a flow field using the superposition of a source and a sink that are placed very close to each other

Mean free path

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

Continuum

Fluid (gas or liquid) is continuously distributed along the region of interest.

Wake

the region of disturbed flow (often turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body.