Investigation of flow over rough surfaces

• Main Author: Ong, Yee Seng
• Other Authors: Chan Weng Kong
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/76241
• Institution: Nanyang Technological University

Frictional forces due to fluid flows are encountered by many everyday objects. From flows within ducts to the air resistance encountered by cars and aircrafts, energy is often expended to work against these frictional forces. The ability to reduce drag directly translates to costs savings. However, the process of optimising daily objects to minimise drag becomes a tedious process of constant fine-tuning. Researchers have adopted nature’s designs such as the hierarchical structures on superhydrophobic lotus leaves and riblets on sharks’ skin to reduce drag. In this study, riblets will be fabricated using a relatively less costly method; carbon steel shims will be cut and assembled to form riblet patterns. Thereafter, the riblet samples will be tested for its pressure drop characteristics in a square macro-channel, with air as the fluid. Pressure drop reduction of up to 10.8% was achieved. In addition, the complications involved in the fabrication technique used in this study will also be discussed. In the second part of this study, a less commonly explored aspect of testing superhydrophobic surfaces for its air drag properties will be investigated. Surfaces will be fabricated by various chemical etching process, as well as sandblasting. The different processes used will be analysed for its effectiveness in producing superhydrophobic surfaces. Pressure drop reduction of up to 9.9% was observed, highlighting a possible trend between contact angles and pressure drop characteristics for air. Other surface parameters such as fractal dimension and profile amplitude computed using the roughness-length method will be evaluated for their relationship with contact angles as well. This study will also discuss the challenges involved in obtaining accurate surface parameters, and the steps taken to alleviate inaccuracies in data acquisition.