Abstract
An extensive range of conventional, vane-type, passive vortex generators (VGs) are in use for successful applications of flow separation control. In most cases, the VG height is designed with the same thickness as the local boundary layer at the VG position. However, in some applications, these conventional VGs may produce excess residual drag. The so-called low-profile VGs can reduce the parasitic drag associated to this kind of passive control devices. As suggested by many authors, low-profile VGs can provide enough momentum transfer over a region several times their own height for effective flow-separation control with much lower drag. The main objective of this work is to study the variation of the path and the development of the primary vortex generated by a rectangular VG mounted on a flat plate with five different device heights h = δ, h1 = 0.8δ, h2 = 0.6δ, h3 = 0.4δ and h4 = 0.25m, where 5 is the local boundary layer thickness. For this purpose, computational simulations have been carried out at Reynolds number Re = 1350 based on the height of the conventional VG h = 0.25m with the angle of attack of the vane to the oncoming flow β = 18.5°. The results show that the VG scaling significantly affects the vortex trajectory and the peak vorticity generated by the primary vortex.
Highlights
Due to large energy losses associated with boundary-layer separation, flow separation control has become a very important issue for several industrial applications in the field of fluid mechanics
The main objective of this work is to study the variation of the path and the development of the primary vortex generated by a rectangular vortex generators (VGs) mounted on a flat plate with five different device heights h = δ, h1 = 0.8δ, h2 = 0.6δ, h3 = 0.4δ and h4 = 0.2δ, where δ is the local boundary layer thickness
The results show that the VG scaling significantly affects the vortex trajectory and the peak vorticity generated by the primary vortex
Summary
Due to large energy losses associated with boundary-layer separation, flow separation control has become a very important issue for several industrial applications in the field of fluid mechanics. The most important reason of flow-separation is the lack of momentum in the boundary layer, usually the primary option in trying to control the flow separation is the installation of vortex generators because they have the advantage of being cost-effective and simple to set-up and manufacture. Flow control devices can be used to increase both free-shear and wall-bounded flows by extending the effective area through which transport occurs, by setting off resonant flow instabilities, by advancing laminar to turbulent transition and by enhancing the turbulence once the shear flow is already turbulent, Gad-el-Hak [1]. Many models for the generated vortices have been presented over the years. Theoretical models include, for example, the one by Smith [2] and a model presented by Velte et al [3] that was developed and applied to show the helical symmetry of the vortices generated by a passive rectangular vane-type vortex generator.
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