The flow development and behaviour of a fluid in a twodimensional cavity, heated and cooled periodically from one sidewall, with all other walls adiabatic, is investigated via numerical simulation. The heating and cooling on the sidewall produce alternating direction vertical natural convection boundary layers that entrain fluid from the cavity interior and discharge it at the top and bottom of the cavity. At start up and during a transition phase the heat content of the cavity, which is biased by the initial heating phase, has a non-zero mean. At full development the flow is quasi steady with the natural convection boundary layers maintaining a stable stratification in the cavity interior and the heat content oscillating around a zero mean value. The stratification strength is shown to be strongly dependent on the forcing frequency.
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