Laminar flow

Design of Fuselage Shapes for Natural Laminar Flow

    • dodlithr
    • January 18th, 2009

    Lot of great links. I’ll check them.

    I have been looking the effects of aft vortex generators to the laminar flow over the wing. It seems to give a small reduction of the drag, but is the benefit large enough to install them.

    There are lot of sources telling that vortex generators easily give 5% fuel savings, but is that really so?

    • Karoliina Salminen
    • January 18th, 2009

    Vortex generators don’t help on laminar flow, they actually cause turbulence. The idea is to energize the turbulent boundary layer with rotating vortexes on the wing surface. Vortex generators can be used after the laminar-turbulent transition point, but not before that. Before that they just add drag.

    On planes where you see these on the leading edge (usually STOL), the airfoil is turbulent flow to begin with. In case of laminar flow, you must not obstruct the flow with anything, and vortex generators would just kill the laminar flow and prematurely transition the flow into turbulent flow.

    In case of turbulent flow airfoils, the drag penalty caused by the vortex generators is small, but the increase in the Cl can be high and the flow can be attacted to a higher angles of attack. In Finland one example I have seen is a Maule that has vortex generators attacted to its leading edge.

    Someone in Cozy builders list attached vortex generators to his canard (which is the laminar flow part of the plane), and his plane became something like 20 km/h or so slower than without the vortex generators. He essentially tripped the flow of the Roncz canard so that it does not achieve laminar flow. Because the airfoil was designed so that it is not very sensitive to rain and bugs, it maintains its lift coefficient even if it functions with lower efficiency with the vortex generators attached.

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