Investigation of passive flow control over an airfoil using leading edge tubercles

TL;DR

This study uses numerical simulations to analyze how leading-edge tubercles on an airfoil can passively delay flow separation, improve stall behavior, and enhance aerodynamic performance at transitional Reynolds numbers.

Contribution

It introduces a detailed numerical investigation of leading-edge tubercles on an airfoil using DDES, including flow analysis and optimization of tubercle parameters.

Findings

Tubercles delay turbulent separation and improve stall behavior.

Modified airfoil shows more gradual stall compared to unmodified.

Flow analysis reveals vortex structures responsible for performance gains.

Abstract

The present paper numerically investigates flow control over NACA0021 (National Advisory Committee for Aeronautics) airfoil by applying a leading-edge tubercle as a passive flow control device at transitional Reynolds number (Re) regime. The study includes simulations over the unmodified airfoil and modified airfoil operating at Re=120000 using kT-kL-{\omega} based Delayed Detached Eddy Simulation (DDES) model. The calculations include both the pre-stall and post-stall regions, while the performance of the mean flow aerodynamic properties like pressure, lift, skin-friction, and drag coefficients are also investigated in the presence of tubercles. The spanwise flow over the modified airfoil interacts with the primary flow. The turbulent separation gets delayed compared to the unmodified airfoil, thereby significantly improving the stall behavior and flow behavior in the post-stall region. The modified airfoil provides the gradual stall behavior against the steep stall behavior for the unmodified airfoil. To optimize tubercle configuration, the study considers two modified airfoils with different combinations of amplitude and wavelength. The unsteady analysis, including the reduced-order modeling, i.e. 3D Proper orthogonal decomposition (POD), characterizes the dominant vortical structure of the flow to evaluate the improvement in the aerodynamic performance of the modified airfoil. The model decomposition for flow over airfoil helps to provide a deeper understanding of the flow control phenomenon.