Hairpin vortices and heat transfer in the wakes behind two hills with different scales

TL;DR

This study uses numerical analysis to explore how hairpin vortices generated by two hills of different scales influence heat transfer in a laminar boundary layer, revealing effects of hill scale and spacing on vortex behavior and heat transfer efficiency.

Contribution

It provides new insights into the interaction of hairpin vortices and heat transfer around hills of varying scales and spacing in laminar boundary layers.

Findings

Interference of hairpin vortices is more intense with same-scale hills.

Narrower hill spacing increases vortex asymmetry and heat transfer.

Heat transfer is higher with same-scale hills due to vortex leg proximity.

Abstract

This study performed a numerical analysis of the hairpin vortex and heat transport generated by the interference of the wakes behind two hills in a laminar boundary layer. In the case of hills with the same scale, the interference between hairpin vortices in the wake is more intensive than in the different-scale hills. When the hills with different scales are installed, hairpin vortices with different scales are periodically shed. Regardless of the scale ratio of the hills, when the hill spacing in the spanwise direction is narrowed, the asymmetry of the hairpin vortex in the wake increases due to the interference between the wakes. At this time, the turbulence caused by the leg and the horn-shaped secondary vortex on the spanwise center side in the hairpin vortex increases, and heat transport around the hairpin vortex becomes active. In addition, the leg approaches the wall surface and removes high-temperature fluid near the wall surface over a wide area, resulting in a high heat transfer coefficient. These tendencies are most remarkable in the same-scale hills. In the case of hills with different scales, the heat transfer coefficient decreases because the leg on the spanwise center side in a small hairpin vortex does not develop downstream.