Vortex Characterization and Parametric Study of Miniature Vortex Generators and Their Near-Field Boundary Layer Effects

Abstract

Delaying the onset of laminar-turbulent transition is an attractive method in reducing skin friction drag, especially on streamlined bodies where Tollmien–Schlichting instabilities are the dominating mechanism for transition. Miniature Vortex Generators (MVGs) offer an effective approach to attenuate these instabilities by generating counter-rotating vortex pairs. They are placed in pairs within an array and resemble small-winglet-type elements. The conventional methodology involves adjusting the MVG parameters and conducting computationally expensive DNS and/or downstream stability analyses to assess their effectiveness. However, analyzing the vortex parameters of MVG-generated vortices can potentially guide a more targeted approach to modifying the MVG parameters and identifying the critical factors for transition delay. Therefore, this study investigates the changes in three primary MVG parameters, namely inner distance, periodicity, and height, and utilizes computational fluid dynamics (CFDs) analysis to create a dataset that examines the characteristics of the generated counter-rotating vortex pairs and their potential in drag reduction. The objective is to establish correlations among these parameters and their influence on delaying transition. The results show that there is an optimal ratio between the MVG height and boundary layer thickness. Higher MVGs cause a decrease in the vortex radius and an increase in the amount of circulation, raising the likeliness of bypass transition. The derived correlations between the different MVG parameters show that the vortex radius is the most critical one and is hence an important parameter in the drag reduction potential.

Keywords

• drag reduction
• boundary layer interaction
• miniature vortex generator
• transition delay