How & Why Bicamber Technology Works—In Depth

Fluid Dynamics and Airfoil Motion

Fluid Dynamics is the study of how objects in motion flow through fluids, water and air being the most prevalent of these. Also it concerns the flow of fluids in confined spaces like pipes, vents or buildings or how fluids are moved by fans or propellers. It is a broad discipline with universal application. Except for astronauts in space, we and our machines are always interacting with, moving in and moving air or water. All objects move quite easily through fluids, such as a thrown ball, an automobile, someone walking, riding a bicycle, a falling object, animals, boats, airplanes and so on.

Airfoils are special streamlined objects that are designed to move much more readily through air or water than those previously listed.

This discussion is confined to the motion of an airfoil such as a wing, fan or propeller blade, through air or water.

Aerodynamics Basics and Terminology

The goal of aerodynamics is to find shapes that approach as closely as possible a zero drag optimum. Improvements are possible by reducing the amount of energy the moving airfoil body gives up to the passing fluid. If we reduce the amount of air that is put into motion from the airfoil’s passing drag is minimized.

The second important job of an airfoil is to create “lift” so airplanes can fly, boats can be propelled, and large objects can be maneuvered through air or water. By turning an airfoil so it does not point straight forward the fluid causes pressure on one side, the “windward” side and a reduction of pressure on the other, “lee” side causing the airfoil to be deflected from the path it was traveling to a new path where the airfoil is now pointing. If another force counteracts this turning motion the airfoil will continue in a straight path, but tilted at an angle to the direction it is traveling. Gravity is the typical counteracting force; for instance, the weight of an airplane forcing its airfoil wing down as the air pushes it upward from the wing being tilted upward. This continued tilt upward is referred to as the airfoil’s “angle-of-attack.

In producing lift the airfoil’s resistance to movement through the fluid increases. Both drag and lift increase as angle-of-attack increases. The object of any airfoil is to maximize the amount of lift produced while reducing drag to the lowest possible amount.

If you were to design an airfoil, intuitively you would think that a thin, knife-like design would work well to move with least resistance. This is true when pointed directly forward, but presented at only a slight angle-of-attack thin designs lose lift and increase their drag because fluid cannot follow the lee side of the thin, flat airfoil. To modify the design so air can follow the surface, you might curve the thin airfoil, like the sail of a sailboat, or you could make it rounded in front and curved on both sides in a teardrop shaped profile such as an airplane wing or rudder or keel of a boat. This allows the fluid to gently turn to follow the now streamlined surface.

Air or water flow still can’t follow even the best traditional airfoils for their full surface length if the airfoil is turned more than about 16 degrees angle-of-attack to the flow. Forced to turn too quickly, pressure from above is less than the inertia of the fluid. Flow deviates away from the lee surface flowing straight back. At low angles-of-attack, air flow becomes turbulent with a thick boundary layer. As this condition increases fluid from the high pressure windward side moves up to the lower pressure lee side at the back of the airfoil. This condition, known as “trailing edge separation” begins at modest angles-of-attack on the rear portion of the airfoil, the “trailing edge” and gradually moves forward covering more and more of the upper, lee surface as angle-of-attack increases. At some point the flow cannot stay attached on the lee surface at all. Separation from the entire lee surface develops. At this point, (somewhere between 12 to 22 degrees angle-of-attack), the airfoil is “stalled”; that is, it is producing a large amount of drag and very little lift.

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