Abstract
The concave curvature effect for an impinging jet flow is discussed in this paper. To do so, a submerged axisymmetric isothermal impinging jet at a Reynolds number (based on the nozzle diameter and the bulk velocity at the nozzle outlet) and for a nozzle to plate distance of two jet diameters is considered. This investigation is done numerically using a wall-resolved large-eddy simulation. Two geometrical arrangements are studied. These correspond to a jet impinging on a flat plate and a jet impinging on a hemispherical concave plate with a relative curvature , where is the concave plate diameter. A detailed comparison shows that both flow configurations are very similar in terms of flow dynamics and heat transfer behaviors. The same mechanisms, coming from the initial jet instability and driving the heat transfer at the wall, are found for both geometries. However, a reduction of the mean wall heat transfer is reported for the jet impinging on the concave surface when compared to the flat plate impingement. This reduction mainly comes from the alleviation of the secondary peak. The deterioration of wall heat transfer is shown to be caused by a reduction in the intensity of the intermittent cold fluid injections generated by the secondary structures. These weaker events are assumed to be the consequence of the stabilizing normal pressure gradient, in the outer layer of the wall jet, induced by the concave curvature of the plate. This result goes against the current consensus, inherited from boundary layer studies, that is to say, that concave curvature enhances the heat transfer rate at the wall due to the formation of Görtler vortices. In an attempt to explain the contradictory result of the present study, a discussion is proposed in this paper showing that the commonly used analogy with boundary layer results must be made with care owing to several inherent differences between impinging jet and boundary layer flows.
30 More- Received 13 July 2017
DOI:https://doi.org/10.1103/PhysRevFluids.2.114608
©2017 American Physical Society