Flow Control over Rough Surfaces: Investigations through High-Fidelity Simulations and Experiments

Frictional resistance between flowing fluids and solid surfaces leads to significant energy loss in engineering, particularly in maritime and water utility systems. We investigate the efficiency of two flow control strategies—spanwise opposed wall-jet forcing (SOJF) and steady modification of the mean velocity profile—under both smooth and rough wall conditions.

Hull roughness due to bio-fouling affects maritime energy efficiency. Using DNS, we compare drag reduction and energy consumption in smooth and rough channels at Re_τ=180. Results show that while maximum drag reduction is achieved at higher forcing amplitudes in rough channels (2.4% at A⁺= 0.035), it is significantly less than in smooth channels (18.6% at A⁺= 0.015). This discrepancy arises because SOJF cannot effectively mitigate pressure-dominated drag.

Frictional losses in water pipes account for about 10% of global electricity consumption. Manipulating the mean velocity profile shows promise for reducing these losses. Techniques like annular injection and preconditioning have achieved up to 90% friction reduction in smooth pipes. Our research extends this investigation to rough pipes using both simulations and experiments.

Our LES findings with annular injection align with existing experimental trends, achieving relaminarization up to Re_b = 6000. Also, our study of preconditioners includes LDV and pressure measurements in both smooth and rough pipes, providing insights into the synergy of flow control and surface roughness.