The following page contains brief introductions of essential aerodynamic terminologies. Meanwhile, it includes a majority of Phase 1 and Phase 2 of Experimental Aerodynamics & Flow Visualization Design Project.

## Section 1

Chord length c is the distance from the front to the rear of the airfoil.

Angle of attack α, is the angle between the airfoil chord and incoming velocity u.

- Lift force L is a force exerted on the object by the fluid flow around the body in the direction perpendicular to the flow direction.
- Drag force D is a force exerted on the object by the fluid flow around the body in the direction parallel to the flow direction.
- Resultant aerodynamic force R is the resultant body force due to the excepted drag force D and lift force L.
- Normal force N is the component of resultant force R normal to chord c.
- Axial force A is the component of resultant force R parallel to chord c.

The physical meaning of Reynolds Number, according to *Fundamentals of Aerodynamics* (Anderson), is the ratio of inertia forces to viscous forces in a flow. It is a crucial parameter in Aerodynamics used to describe the property of the flow.

It also plays a crucial role in the analytical and design part of the project, to determine the velocity of the fluid flow.

Dimensionless numbers are numbers such as lift force, drag force, normal force, normalized by the surrounding fluid and subject properties. It can greatly simplify the analytical process.

In 2D case, forces can be normalized as follows.

Slat is a device installed on the leading edge of the wing to extend when needed. It increases the stall angle and therefore produces higher lift.

Flap is installed at the trailing edge of the wing and could be extended when needed to increase the camber or the curvature of the wing to raise the maximum lift (lift coefficient) and drag (drag coefficient).

## Section 2

As we know, lift and drag are forces acting on the airfoil (or any other interested subject), and force is directly related to pressure and area. As a result, in order to calculate lift and drag, it is essential that we know the pressure (acting normal to the surface) and shear stress (acting parallel to the surface) distribution over the subject surface.

Consider flow over a flat plate at 0 degree angle of attack, the lift and drag forces can be calculated as shown below.

__Things to consider: __

– Why there is one of the terms in the lift equation has a negative sign, but the drag equation does not?

– How would you calculate these two forces with an angle of attack?

In Fluid Dynamics, fluid flow can be divided into two types. One is laminar, and the other one is turbulent. The easiest way to determine the flow type is by Reynold number. By definition, the flow is laminar when the Reynolds number is below 2300. In contrast, the flow becomes turbulent when its Reynolds number is above 4000.

Flow acts very differently at different Reynolds Numbers, even with the same subject. (The following visuals are collected by Professor Donald Bliss at Duke University and the original authors are mentioned below the visuals)