Abstract
A unique approach to evaluate the reduction of skin friction drag by riblets was applied to boundary layer profiles measured in wind tunnel experiments. The proposed approach emphasized the turbulent scales based on hot-wire anemometry data obtained at a sampling frequency of 20 kHz in the turbulent boundary layer to evaluate the skin friction drag reduction. Three-dimensional riblet surfaces were fabricated using aviation paint and were applied to a flat-plate model surface. The turbulent statistics, such as the turbulent scales and intensities, in the boundary layer were identified based on the freestream velocity data obtained from the hot-wire anemometry. Those turbulent statistics obtained for the riblet surface were compared to those obtained for a smooth flat plate without riblets. Results indicated that the riblet surface increased the integral scales and decreased the turbulence intensity, which indicated that the turbulent structure became favorable for reducing skin friction drag. The proposed method showed that the current three-dimensional riblet surface reduced skin friction drag by about 2.8% at a chord length of 67% downstream of the model’s leading edge and at a freestream velocity of 41.7 m/s (Mach 0.12). This result is consistent with that obtained by the momentum integration method based on the pitot-rake measurement, which provided a reference dataset of the boundary layer profile.
Highlights
More and more people are traveling by air, so the demand for economical and environmentally friendly aircraft is increasing
This section discusses the insights gained from deriving turbulent integral scales and evaluating the reduction of Discussion skin friction drag by riblets and covers uncertainty analysis, characteristics of boundary
This section discusses the insights gained from deriving turbulent integral scales and evaluating the Uncertainty reduction of skin friction drag by riblets and covers uncertainty analysis, characteristics of Analysis boundary layer profiles and turbulent scales, and reduction of skin friction drag by riblets
Summary
More and more people are traveling by air, so the demand for economical and environmentally friendly aircraft is increasing Meeting these needs will require improvements in aerodynamic efficiency and in reduced drag. Riblets are one of the methods used to reduce aircraft surface drag [1,2,3,4] They are a passive means of turbulent flow control near the wall and were first used by the NASA Langley Research Center in the 1970s [3,5]. They imitate the fine structure of the skin of a shark, which is known for being able to swim long distances at high speed. Riblets are fine grooves aligned in the direction of a flow across a surface that induce a streamwise vortex, which reduces the turbulent flow in a boundary layer that causes surface drag, reducing skin friction drag
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