Airfoil thickness effects on flow and acoustic characteristics

The present study numerically, investigates the aerodynamic characteristics of low speed flow past symmetric NACA airfoils, for various t/c values of 0.10, 0.15, 0.18, 0.21 and 0.24 at chordwise Reynolds numbers of 2 x 10(5) and 4 x 10(5), where t is the airfoil thickness and c is the airfoil chord. The presence of laminar separation bubble is indicated by oscillatory behaviour of pressure coefficient on the suction surface beyond peak pressure. The fluctuations in lift/drag are seen at smaller t/c values of 0.10 and 0.15, whereas no fluctuations are seen at a higher t/c value of 0.21. An empirical expression is developed to predict the mean lift, viscous as well as total drag coefficients for symmetric airfoils as a function of t/c only, which varies linearly for both the Reynolds numbers studied. The velocity vectors show the flow separations phenomenon only at smaller t/c values of 0.10 and 0.15, while at a higher t/c value of 0.21, well behaved and steady flow field is seen, which might be the reason for the absence of lift/drag fluctuations. The far-field acoustic measurements of symmetric NACA airfoils for various thickness ratios reveal that thicker airfoil (NACA0021, t/c = 0.21) radiates lower acoustic emissions (i.e., about 2 dB) as compared to the thinner (NACA0010, t/c = 0.10) ones. (C) 2021 THE AUTHORS. Published by Elsevier BV on behalf of Faculty of Engineering, Alexandria University.

Automated summary

This study numerically investigates the aerodynamic characteristics of symmetric NACA airfoils at various thickness ratios, revealing lift/drag fluctuations at lower thickness ratios and proposing an empirical expression to predict lift and drag coefficients. The far-field acoustic measurements show that thicker airfoils emit lower acoustic emissions compared to thinner ones.