Numerical and Experimental Assessment of Dual-Surface Triangular Roughness on the Aerodynamic Performance of a CR001SM Airfoil

Abstract

Passive flow-control techniques are crucial to enhancing the performance of airfoils at low Reynolds numbers, where boundary-layer separation and related aerodynamic losses are a problem. This study examines the aerodynamic performance of a CR001SM airfoil with both upper and lower surface triangular roughness elements at low Reynolds numbers. Two modified configurations were tested: M1 (roughness elements at 5% and 80% of the chord) and M2 (roughness elements at 10% and 70% of the chord). Experimental wind-tunnel measurements and numerical simulations were carried out in ANSYS Fluent 2021 R1 with the transient Transition SST model to compare the aerodynamic characteristics of these configurations with that of the smooth baseline airfoil. Freestream velocities of 1.25 m/s, 2.25 m/s and 3.0 m/s and angles of attack between 0⁰ and 18⁰ were investigated. The lift, drag and aerodynamics are strongly affected by the roughness configuration. The maximum lift coefficient of M1 is around 1.19, 1.24 and 1.28 at 1.25, 2.25 and 3.0 m/s respectively. The smooth airfoil, on the other hand, has a lower drag and thus better lift-to-drag ratio at low and moderate angles of attack. The roughened configurations have relatively good lift retention at higher angles of attack, and at some angles of attack, lower drag than the smooth airfoil. The overall average absolute percentage deviation obtained from the numerical validation is around 8.79% with experimental lift coefficients. The aerodynamic effects of triangle roughness are influenced by the angle of attack, freestream velocity, and chordwise location of the triangle. The M1 configuration is beneficial in situations where high angle of attack lift retention is important.