Wing Theory Chapter 2

Symmetric vs. Cambered Airfoils

Camber Line

camber line bisects any line the perpedicular to the upper and lower surface of the airfoil

Sharp Trailing Edge vs. Blunt Trailing Edge

Some trailing edges are designed to be blunt

• Even sharp trailing edges are technically blunt, sharp corner is not physically possible and is—even is quite small—blunt on the trailing edge

Potential Flow

Also known ideal flow

• Ideal flow is irrotational and incompressible

Ideal flow is used as an approximation of what flow may actually be around objects—neglects many of the complicated effects (viscosity, density fluctuations) in order to have a mathematical model that gives approximations for the flow profile

Irrotational Flow

Essentially an idealized (approximation) type of flow where the viscous effects are negligible (inviscid flow)

Boundary Layer

Concentration of the viscous effects within a thin layer

• Viscous effects only manifest in boundary layer and in the wake

• Outside of the boundary layer, no viscous effects are felt

Incompressible Flow

An idealized (approximate) type of flow where fluid density is constant in space and time

• Flow is actually incompressible when M = 0 (flow is stationary)

IN PRACTICE - flow is ~essentially incompressible when Mach is small

• Ma ~= 0.2 - 0.3

Mach Number

Ma = speed of flow/speed of sound

• speed of sound is a function of fluid density (often atmospheric implications)

Potential Flow Solutions

Solution to is a velocity flow field

• Solution achieved by solving the Laplace equation for velocity potential

Solving Laplace equation includes satisfying boundary conditions:

1. No flow through BC

2. Infinity BC

No-flow-through Boundary Condition

Known as:

• Wall Boundary Condition

• Zero Normal Flow Boundary Condition

Essentially, flow normal to solid surface is zero perpendicular to the surface. —> does not flow into the body

Infinity Boundary Condition

Ensures freestream velocity remains unaltered far upstream from the body

• Ensures body’s effect on local airflow does not affect the upstream free stream velocity

Done in practice mathematically by adding sinks and vortices that are far upstream