Direct numerical simulation of a turbulent jet impinging on a heated wall

Abstract

Direct numerical simulation (DNS) of an impinging jet flow with a nozzle-to-plate distance of two jet diameters and a Reynolds number of 10 000 is carried out at high spatial resolution using high-order numerical methods. The flow configuration is designed to enable the development of a fully turbulent regime with the appearance of a well-marked secondary maximum in the radial distribution of the mean heat transfer. The velocity and temperature statistics are validated with documented experiments. The DNS database is then analysed focusing on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall. A phenomenological scenario is proposed on the basis of instantaneous flow visualisations in order to explain the non-monotonic radial evolution of the Nusselt number in the stagnation region. This scenario is then assessed by analysing the wall temperature and the wall shear stress distributions and also through the use of conditional averaging of velocity and temperature fields. On one hand, the heat transfer is primarily driven by the large-scale toroidal primary and secondary vortices emitted periodically. On the other hand, these vortices are subjected to azimuthal distortions associated with the production of radially elongated structures at small scale. These distortions are responsible for the appearance of very high heat transfer zones organised as cold fluid spots on the heated wall. These cold spots are shaped by the radial structures through a filament propagation of the heat transfer. The analysis of probability density functions shows that these strong events are highly intermittent in time and space while contributing essentially to the secondary peak observed in the radial evolution of the Nusselt number.

Database of Near-Wall Turbulent Flow Properties of a Jet Impinging on a Solid Surface under Different Inclination Angles

“…The authors provided turbulence statistics of the velocity and temperature, turbulent heat fluxes, local Nusselt numbers, budget terms of turbulent kinetic energy among other turbulent quantities. Recently, DNS of impinging jet flows at Re = 10,000 and Re = 8000 were performed with high spatial resolution and high order numerical methods by Dairay et al [27] and by Wilke and Sesterhenn [28], respectively. The first study focused on the role of unsteady processes to explain the spatial distribution of the heat transfer coefficient at the wall, while the latter analyzed the influence of Mach number, Reynolds number and ambient temperature on the mean velocity and temperature fields.…”

Lagrangian wall shear stress structures and near-wall transport in high-Schmidt-number aneurysmal flows

“…WSS patterns have been demonstrated to affect the heat transfer in impinging jets. As examples, the heat transfer coefficient has been shown to have similar distribution as WSS with a phase shift (Hadžiabdić & Hanjalić 2008), and Dairay et al (2015) showed that the secondary vortex resulting from flow impingement creates negative WSS regions that correspond to heat transfer augmentation.…”

Study of an array of two circular jets impinging on a flat surface

“…The outlet boundary is placed at a sufficiently large radial distance, so that the error from applying the outlet-pressure condition will not affect the region of interest. According to Dairay et al [17], the radial expansion of the flow domain was chosen at 12 . The mesh has 198000 cells, and was built with special attention in the region close to the impingement plate, where a further refinement was done.…”