Tracking stall cell dynamics at high Reynolds numbers

TL;DR

This study investigates the behavior and dynamics of stall cells over a thick airfoil at high Reynolds numbers, revealing their spanwise organization, size, and coherent motion patterns.

Contribution

It provides new insights into stall cell dynamics at high Reynolds numbers, including their size, spanwise coherence, and motion characteristics, using surface pressure measurements.

Findings

Stall cell width increases linearly with angle of attack.

Coherent spanwise motion dominates stall cell dynamics at high Reynolds numbers.

Local pressure fluctuations correlate with stall cell presence, despite not affecting global lift.

Abstract

The spanwise organization of the flow over a thick airfoil is investigated using surface pressure measurements for a range of angles of attack around maximum lift and high Reynolds numbers (1 Million). Locally strong pressure fluctuations, which are not detected in the global lift coefficient, are shown to be associated with the presence of a stall cell. The stall cell width is of the order of the chord length and increases linearly with the angle of attack, with a weak dependence on the Reynolds number. Its dynamics at Reynolds numbers larger than 1 Million is dominated by a coherent motion in the spanwise direction with a characteristic velocity of order tenth of the freestream velocity. The motion can be decomposed into a large-scale, low-frequency sweep with a Strouhal number equal to 0.001 combined with faster, smaller-scale oscillations. The coherence of the stall cell makes it possible to track global dynamics from local measurements.