# Reynolds-number effects in turbulent boundary layers around wing sections

## TL;DR

This study uses large-eddy simulations to analyze how Reynolds number influences turbulent boundary layers around a wing, revealing that adverse pressure gradients have a stronger impact at lower Reynolds numbers, energizing the outer flow region.

## Contribution

It provides new insights into Reynolds number effects on turbulent boundary layers around wings, highlighting the increased influence of adverse pressure gradients at lower Re.

## Key findings

- Adverse pressure gradient effects are more intense at lower Reynolds numbers.
- Outer region energization by APG is stronger at low Re, with increased wall-normal velocities.
- Wall-normal velocities are 40% and 20% larger at Re=200,000 and 400,000 compared to Re=1,000,000.

## Abstract

Four well-resolved LESs of the turbulent boundary layers around a NACA4412 wing section, with Rec ranging from 100,000 to 1,000,000, were performed at 5 degree angle of attack. By comparing the turbulence statistics with those in ZPG TBLs at approximately matching Re_tau, we find that the effect of the adverse pressure gradient (APG) is more intense at lower Reynolds numbers. This indicates that at low Re the outer region of the TBL becomes more energized through the wall-normal convection associated to the APG. This is also reflected in the fact that the inner-scaled wall-normal velocity is larger on the suction side at lower Reynolds numbers. In particular, the wing cases at Rec = 200,000 and 400,000 exhibit wall-normal velocities 40% and 20% larger, respectively, than the case with Rec = 1,000,000. Consequently, the outer-region energizing mechanism associated to the APG is complementary to that present in high-Re TBLs.