Early-stage dynamics in the onset of free-convective reversal flow in an open-ended channel asymmetrically heated

• An experimental analysis from PIV in the early transient is conducted.
• Instabilities and topological features are highlighted.
• War boundary layer beating is evidenced before a reversal flow takes place.

An experimental study from PIV in an open-ended vertical channel is carried out in order to describe the fluid dynamics during the early stage regime of free convection inside a vertical channel asymmetrically heated at 445 W/m2 and 1550 W/m2 uniform heat fluxes. The analysis allowed to detect a complex topological behavior in the internal flow leading to numerous instabilities whose topological features are described. Vortex formation and shedding, vortex splitting, separation and beating of the boundary layer from one wall to another are identified, leading to an imbalance in the outlet pressure field which is certainly at the origin of a large-scale reversal flow.