![]() The wedges extend the linear part of the lift curve and raise the stalling incidence, say from 14° to 20°, increasing the maximum lift from 1♳3 to 1♸9. The wedge is useful for turbulent mixing, boundary layer attenuation between wedges, and discharge of the rest of boundary layer into the general flow. The effect of vortex generators and boundary layer wedges on the lift and drag of an NACA 63 3–018 airfoil The generator height should obviously be similar to the thermal boundary layer thickness for full effectiveness.įIG. Heat transfer will also be significantly improved by the thinning of the boundary layer downstream of the vgs, as has been shown experimentally by Fiebig (1995) and others. A small element of fin effect may be present on the fin. This will indirectly improve heat transfer by increasing the proportion of attached flow. The function of delayed separation is the feature most utilised to date in heat exchangers, as exemplified by the placing of vgs near the equator of tubes in a tube-fin exchanger to delay separation on the tubes (primary surface). The pressure distribution and boundary layer structure are significantly affected, and this delays separation in the adjacent flow. Low energy fluid is simultaneously removed from the surface of the outer side of the vortex cores. ![]() Vortex Generators Their Design and Their Effects on Turbulent Boundary Layers. Velocity contours at stations downstream of vortex generators showing striking reduction in thickness in a turbulent boundary layer, together with removal of low energy flow away from the wall. These data were selected because of the fine detail of velocity distributions.įig. 5.29, and their effect on a turbulent boundary layer flow is clearly displayed in Fig. The features of vortex flows generated (by a triangular generator in this case) are shown in Fig. An even further improvement was obtained by ‘biplane’ counter-rotating pairs. The rectangular counter-rotating vgs in an equi-spaced arrangement, as tested by Tanner et al. The vortices persist many tens of generator heights downstream, and the boundary layer is significantly thinned between the vortex cores in the ‘common down’ configuration, in which the bulk flow is ‘induced’ towards the surface by divergent pairs of vgs, that is, in the same way as aircraft trailing vortices. The vgs were typically of the height of the local boundary layer, and drew in high energy flow from outside the boundary layer. In these applications the boundary layers were relatively thick and it was found that the most effective kind were the delta-type winglet pairs, at incidence angles of between 10 and 15 degrees to the flow direction, inducing counter-rotating vortices. Vortex generators were originally studied in the late 1940s as a means of controlling (delaying) separation on aircraft wings and in wind tunnels.
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