Ordered roughness effects on NACA 0026 airfoil

[摘要] The effects of highly-ordered rough surface - riblets, applied onto the surface of a NACA 0026 airfoil, are investigated experimentally using wind tunnel. The riblets are arranged in directionally converging - diverging pattern with dimensions of height, h = 1 mm, pitch or spacing, s = 1 mm, yaw angle α = 0° and 10° The airfoil with external geometry of 500 mm span, 600 mm chord and 156 mm thickness has been built using mostly woods and aluminium. Turbulence quantities are collected using hotwire anemometry. Hotwire measurements show that flows past converging and diverging pattern inherit similar patterns in the near-wall region for both mean velocity and turbulence intensities profiles. The mean velocity profiles in logarithmic regions for both flows past converging and diverging riblet pattern are lower than that with yaw angle α = 0°. Converging riblets cause the boundary layer to thicken and the flow with yaw angle α = 0° produces the thinnest boundary layer. Both the converging and diverging riblets cause pronounced outer peaks in the turbulence intensities profiles. Most importantly, flows past converging and diverging pattern experience 30% skin friction reductions. Higher order statistics show that riblet surfaces produce similar effects due to adverse pressure gradient. It is concluded that a small strip of different ordered roughness features applied at a leading edge of an airfoil can change the turbulence characteristics dramatically.

[发布机构] Department of Mechanical and Materials, Universiti Kebangsaan Malaysia, Malaysia^1

[学科分类] 航空航天科学

[关键词] Adverse pressure gradient;Hot-wire anemometry;Hot-wire measurements;Logarithmic regions;Mean velocity profiles;Skin friction reduction;Turbulence characteristics;Turbulence intensity