Laboratory investigation of nominally two-dimensional anabatic flow on symmetric double slopes

TL;DR

This study used particle image velocimetry and thermocouple measurements to analyze highly turbulent, thermally driven anabatic flows on symmetric double slopes, revealing their complex three-dimensional behavior and challenging simplified models.

Contribution

It provides new experimental insights into the three-dimensional and unsteady nature of anabatic flows over slopes, highlighting features previously unaccounted for in models.

Findings

Flow exhibits B-shaped velocity and flux profiles.

Flow contains helical vorticity structures and vortices.

Flow cannot be accurately modeled as two-dimensional or steady.

Abstract

We investigated the dynamics of highly turbulent thermally driven anabatic (upslope) flow on a physical model inside a large water tank using particle image velocimetry (PIV) and a thermocouple grid. The results showed that the flow exhibited pronounced variations in velocity and temperature and, importantly, could not be accurately modeled as a two-dimensional quasi-steady flow. Five significant findings are presented to underscore the three-dimensional nature of the flow. Namely, the B-shaped mean velocity profiles, B-shaped turbulent flux profiles, synthetic streaks that revealed particles flowing perpendicular to the laser sheet, average vorticity maps revealing helical structure splitting, and identified vortices shooting away from the boundary towards the apex plume. Collectively, these findings offer novel insights into the flow behavior patterns of thermally driven complex terrain flows, which influence local weather and microclimates and are responsible for scalar transport, e.g., pollution.