Wavy Walls, a Passive Way to Control the Transition to Turbulence. Detailed Simulation and Physical Explanation

Abstract

Inducing spanwise motions in the vicinity of solid boundaries alters the energy, mass and/or momentum transfer. Under some conditions, these motions are such that drag is reduced and/or transition to turbulence is delayed. There are several possibilities to induce those spanwise motions, be it through active imposition a predefined velocity distribution at the walls or by careful design of the wall shape, which corresponds to passive control.In this contribution, we investigate the effect that wavy walls might have on delaying transition to turbulence. Direct Numerical Simulation of both planar and wavy-walled channel flows at laminar and turbulent regimes are conducted. A pseudo laminar regime that remains stable until a Reynolds number 20% higher that the critical is found for the wavy-walled simulations. Dynamic Mode Decomposition applied to the simulation data reveals that in these configurations, modes with wavelength and frequency compatible with the surface undulation pattern appear. We explain and visualize the appearance of these modes. At higher Reynolds numbers we show that these modes remain present but are not dominant anymore. This work is an initial demonstration that flow control strategies that trigger underlying stable modes can keep or conduct the flow to new configurations more stable than the original one.

Experimental Study of the Corrugation Profile Effect on the Local Heat Transfer Coefficient

“…Various geometries have been investigated, such as transversal grooved pipes [7], converging and diverging pipes [8], dimpled pipes [9], spirally corrugated pipes [10,11], internally corrugated pipes [12], and wavy channels [13,14]. When discussing the enhancement capabilities of corrugated tubes, the available scientific literature mainly focuses on the average heat exchange behavior across the pipe section or the entire heat exchange surface region [15][16][17].…”