Effects of Low-Profile Vortex generators on a turbulent Boundary layer

Zvi Nadler
Work towards Ph.D. degree under the supervision of Profs. Iosilevskii and Arieli
Faculty of Aerospace Engineering
Technion – Israel Institute of Technology

Separation of the boundary layer from aerodynamic surfaces limits aircraft performance. It is long since known that separation can be delayed by a suitable installation of vortex generators. Recent studies suggest that miniature vortex generators, smaller than the thickness of the boundary layer in which they are placed, can be practically as effective as the larger generators, with less drag. The mechanism by which these generators delay separation is unclear. This study aims to describe and explain the flow phenomena associated with the miniature vortex generators. Research methods included wind-tunnel experiments, CFD simulations and analytical analysis.

Both the wind tunnel experiments and the CFD simulations were based on a flat-plate turbulent boundary layer flow with no stream-wise pressure gradient. The generator had slender trapezoidal planform; its span (height) was 30% of the local thickness of the boundary layer.

It was observed that the generator leaves a complex array of vortices, similar to those behind a slender delta wing. These induce mixing, and supply momentum into the lower regions of the boundary layer. The overall “filling” effect of the boundary layer velocity profile resembles the positive pressure gradient effect. In particular, it increases the shear stress at the wall, hence delaying separation (occurring when the shear stress vanishes).

The lecture will show the differences in the flow field in the wake of a miniature vortex generator placed in the boundary layer and a slender wing in a free flow.  It will also show that the mixing is essentially a non-viscous phenomenon.

The talk will be given in Hebrew

Wed, 29-10-2014, 16:30 (Gathering at 16:00)

Classroom 165, ground floor, Library, Aerospace Eng.

Light refreshments will be served before the lecture

Effects of Low-Profile Vortex Generators on a Turbulent Boundary Layer