An experimental investigation of flow over riblets

• Main Author: Lim, Jonas Hong Xiang
• Other Authors: Chan Weng Kong
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Aeronautical engineering
• Online Access: http://hdl.handle.net/10356/77805
• Institution: Nanyang Technological University

Present research has concluded that a structured rough surface has potential drag reduction performance than a smooth surface for a fluid-body interface. Reducing the energy loss due to friction can have fuel saving benefits in various industrial applications. Semi-circular riblets of varying height-to-wavelength ratio and varying configuration were investigated for their viscous drag reduction characteristics. Turbulent air flow was passed through a closed channel with one side of the square duct as the sample surface. Their pressure drop values were measured and compared against the control pressure drop values as an indication of viscous drag. The results show that while most of the pressure drop values are greater than the control, the trends are in line with the findings of similar research which suggests a reduction in skin friction drag but increase in pressure drag. While varying Reynolds number in the turbulent flow region, the sample with angled configuration of h/λ ratio 0.02 yields pressure drop values closest to the control. Positive drag reduction was also observed for 6 out of the 15 samples at the lower range of the h/λ ratio and Reynolds number. Symmetrically configurated sample with h/λ ratio of 0.025 observed the greatest total drag reduction of 18%. Visualizing the flow and determining the average surface shear stress was a challenge encountered in this study. This study recommends establishing a velocity measurement system with a hot-wire anemometer probe for future research. Measuring the streamwise and vertical velocities can complement the pressure drop readings to present a clearer picture on the drag characteristics.