Effects of distributed leading-edge roughness on aerodynamic performance of a low-Reynolds-number airfoil: an experimental study

Distributed leading-edge (LE) roughness could have significant impact on the aerodynamic performance of a low-Reynolds-number (low-Re) airfoil, which has not yet been fully understood. In the present study, experiments were conducted to study the effects of distributed hemispherical roughness with different sizes and distribution patterns on the performance of a GA (W)-1 airfoil. Surface pressure and particle image velocimetry (PIV) measurements were performed under various incident angles and different Re numbers. Significant reduction in lift and increase in drag were found for all cases with the LE roughness applied. Compared with the distribution pattern, the roughness height was found to be a more significant factor in determining the lift reduction and altering stall behaviors. It is also found while the larger roughness advances the aerodynamic stall, the smaller roughness tends to prevent deep stall at high incident angles. PIV results also suggest that staggered distribution pattern induces higher fluctuations in the wake flow than the aligned pattern does. Results imply that distributed LE roughness with large element sizes are particularly detrimental to aerodynamic performances, while those with small element sizes could potentially serve as a passive control mechanism to alleviate deep stall conditions at high incident angles.