Buoyancy-driven flow across a vertical vent/window. 

In this study, we study the effect of buoyancy or the density difference in a flow configuration where a heavier fluid is placed next to the lighter fluid separated by a vertical barrier. The barrier consists of a small opening in comparison to the cross section size of the barrier. The small opening is supposed to simulate a window. The flow is allowed to start when a plate covering the opening is slid out using a piston mechanism. 

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The flow is studied in the chamber initially containing the lighter fluid. The figure to the right is a PLIF image, where the heavier fluid is seeded with higher concentration of a fluorescent dye (Rhodamine 6G in this case). The flow exhibits interesting characteristics, where as the heavier fluid enters the chamber, undergoes KH instability and vortices form. These vortices then pair with other vortices, eventually transitioning to turbulence.

 

The interesting phenomenon that we found is that the KH instability forms only on the top interface of the flow. This interface is characterised by a stable stratification. Whereas at the bottom interface due to unstable stratification, the vortex formation (KH instability) is counteracted by the RT instability.