השפעה של מחוללי מערבולות זעירים על שכבת גבול טורבולנטית

צבי נדלר
עבודה לקראת תואר דוקטור תחת הנחייתם של פרופ' ג. יוסילבסקי ור. אריאלי
הפקולטה להנדסת אוירונוטיקה וחלל
טכניון - מוסד טכנולוגי לישראל

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 vortices 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 effect of a positive pressure gradient. In particular, it increases the shear stress at the wall and hence delays separation (which occurs 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.

הסמינר יינתן בעברית

רביעי, 29-10-2014, 16:30 (התכנסות בשעה 16:00)

כיתת הספריה, חדר 165, קומה ראשונה

כיבוד קל יוגש לפני תחילת הסמינר


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