Surface roughness

Skin-friction drag due to turbulent boundary layers is one of the sources of energy consumption in transport vehicles. For a large passenger aircraft around 50% of the drag experienced is caused by skin-friction drag, for a large ship such as a Very Large Crude Carrier (VLCC) it can be up to 80%-90%. ​This issue is exacerbated when the surface of an aircraft or ship is rough due to ​construction irregularities such as welding, rivets, painting, and bio-fouling (in ships). Here we intend to study of how much does  skin-friction drag from actual ship's hull roughness increases compared to hydronomically smooth wall.

AIM
To understand  skin friction drag due to turbulent boundary layers over rough wall to achieve lower emission and operating costs for air and naval transport.

METHOD
An imprint of rough surface from the base of a recently cleaned ship hull is obtained and scanned using laser. The  scan is reconstructed digitally and scaled appropriately to match the wind tunnel's Reynolds number. The digitally reconstructed roughness is then manufactured using a CNC-Machine and replicated via moulding and casting techniques. The plates are laid into wind tunnel and measured using Hot-Wire Anemometer.

RESULTS
B. Nugroho,  J. P. Monty, I. K. A. P. Utama,  B. Ganapathisubramani, N. Hutchins. (2021) Non k-type behaviour of roughness when in-plane wavelength approaches the boundary layer thickness. Journal of Fluid Mechanics. 911 A1-1

 I. K Suastika, , M. L Hakim, B. Nugroho, A Nasirudin, I K A P Utama , J P Monty and B Ganapathisubramani (2021) Characteristics of drag due to streamwise inhomogeneous roughness. Ocean Engineering. 223, 108632
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Z. Harun, A. A. Abbas, B. Nugroho, L. Chan, S. Mat (2018) Surface Roughness Effects Studies in Transportation Industries. Jurnal Kejuruteraan SI 1(7):87-90 

Experiment figures