Considered are the transitional instabilities of the flow inside three‐dimensional rectangular
cavities that are differentially heated over two opposing vertical walls. The horizontal and
lateral walls are adiabatic. Emphasis is on (though not restricted to) the air‐filled, cubical
cavity. For this configuration, it was found that the occurrence of unsteady oscillations in the
flow was preceded by a steady instability (ie an instability resulting in a steady solution of the
Navier–Stokes equations for large time) which originated in an internal, stratified shear layer …