| Summary: | 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.
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