摘要
In this study,the unsteady flow and heat transfer characteristics of a laminar slot jet at low Reynolds numbers impinging on an isothermal plate surface in a two-dimensional confined space are numerically investigated.The investigations are performed at Reynolds numbers of 120,150 and 200 based on the nozzle width and mean inlet velocity of the jet.Results show that the Reynolds numbers of 120,150 and 200 correspond to different flow features,namely,a steady flow,an intermittent flapping motion of jet column and a continuous sinusoidal flapping state,respectively.Based on some time snapshots of the flow field,the dynamic characteristics and driving mechanism of the intermittent flapping motion of the jet column and the continuous sinusoidal flapping state are explained.When the jet flaps at the Reynolds number 150 and 200,there are other Nusselt number peaks outside the stagnation zone,which are related to the interference between the vortices shedding on both sides of the jet and the boundary layers of the plate surface.Furthermore,the dynamic mode decomposition is implemented to accurately extract flow modes with characteristic frequencies.For a Reynolds number of 150,there is a flapping mode,which describes the lateral flapping motion of the jet column.When the Reynolds number is 200,there are multiple modes related to the flapping motion of the jet,as well as a low-frequency mode,which reflects the periodic changes of the boundary contour and position of the recirculation zone.
基金
the support for the research from the National Key R&D Program of China(2018YFB0604404)。
