Evaluation of Skin Friction Drag Reduction in Turbulent Boundary Layer Using Riblets

摘要

Turbulent boundary layer characteristics for a riblet surface in relation to the skin friction drag were examined by wind tunnel experiments with hot-wire anemometry. The riblet surface was fabricated using aviation paint-based material and was attached on a flat-plate model. The geometry was three-dimensional to maximize alteration of the turbulent structure near the wall. A unique approach was taken for evaluation of skin friction drag reduction by putting emphasis on the turbulent scales. Hot-wire anemometry was implemented at a sampling frequency of 20 kHz in the turbulent boundary layer. The turbulent statistics obtained for the riblet surface were compared to those obtained for a smooth flat plate without riblets. Profiles of integral scales and turbulent Reynolds numbers in the boundary layer were identified based on the temperature-corrected freestream-velocity data from the hot-wire anemometry. Results indicated that the riblet surface increased the turbulent Reynolds numbers and integral scales which indicated that the turbulent structure became favorable for reducing skin friction drag. The three-dimensional riblet surface fabricated by the paint-based material showed successful reduction of skin friction drag of approximately 6.3% at a location 67% downstream of the model leading edge and at a freestream velocity of 42 m/s.