Abstract
A microfiber coating having a hair-like structure is investigated as a passive flow control device of a bluff body. The effect of microfiber length is experimentally studied to understand the impact of the coating on drag on a cylinder. A series of microfiber coatings with different lengths are fabricated using flocking technology and applied to various locations over the cylinder surface under the constant Reynolds number of 6.1 × 104 based on the diameter of the cylinder. It is found that the length and the location both play important roles in the drag reduction. Two types of drag reduction can be seen: (1) when the relative length of the microfiber, k/D, is less than 1.8%, and the coating is applied before flow separates over the cylinder; and (2) k/D is over 3.3%, and the coating is applied after the flow separation location on the cylinder. The maximum drag reduction for the former type is 59% compared to that from the cylinder without the microfiber coating. For the latter type, the maximum drag reduction is 27%.
Highlights
Flow control over a bluff-body, especially drag reduction over a circular cylinder, is an engineering interest for broad applications in ground objects such as buildings, towers, bridges, or transportation systems like cars, trucks, rail, and airplanes [1,2,3,4]
A microfiber coating having a hair-like structure was introduced as a passive flow control device for
A microfiber coating having a hair-like structure was introduced as a passive flow control device bluff-body drag reduction
Summary
Flow control over a bluff-body, especially drag reduction over a circular cylinder, is an engineering interest for broad applications in ground objects such as buildings, towers, bridges, or transportation systems like cars, trucks, rail, and airplanes [1,2,3,4]. Drag can be reduced actively or passively using a flow-control device. Passive devices, which do not require external energy, will be a practical option because of broader possible applications using engineered surfaces, materials, and coatings. A drag reduction was not shown by the microfiber coating in the flow separation region. Further studies in microfiber length are necessary to reveal: (1) the correlation between microfiber length and coating location, and (2) the impact on drag by the microfiber coating in the separation region.
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