Controlling heat transport and flow structures in thermal turbulence using ratchet surfaces

TL;DR

This study demonstrates how asymmetric ratchet surfaces can control flow structures and heat transport in thermal turbulence, enabling orientation locking and tuning of large-scale circulation with implications for engineering and geophysical applications.

Contribution

It introduces a novel method of controlling thermal turbulence flow structures and heat transport using asymmetric ratchet surfaces, combining experimental and numerical approaches.

Findings

Ratchet surfaces lock LSCR orientation even when leveled

Small tilts can tune LSCR orientation

Heat transport efficiency depends on LSCR direction

Abstract

In this combined experimental and numerical study on thermally driven turbulence in a rectangular cell, the global heat transport and the coherent flow structures are controlled with an asymmetric ratchet-like roughness on the top and bottom plates. We show that, by means of symmetry breaking due to the presence of the ratchet structures on the conducting plates, the orientation of the Large Scale Circulation Roll (LSCR) can be locked to a preferred direction even when the cell is perfectly leveled out. By introducing a small tilt to the system, we show that the LSCR orientation can be tuned and controlled. The two different orientations of LSCR give two quite different heat transport efficiencies, indicating that heat transport is sensitive to the LSCR direction over the asymmetric roughness structure. Through a quantitative analysis of the dynamics of thermal plume emissions and the orientation of the LSCR over the asymmetric structure, we provide a physical explanation for these findings. The current work has important implications for passive and active flow control in engineering, bio-fluid dynamics, and geophysical flows.