Abstract
We present large-eddy simulations of the turbulent compressible flow at a low Mach number in curved ducts. The aim is to investigate the influence of the curvature radius R c on the flow. Three simulations are carried out at R c = 3.5 D h , 6.5 D h and 10.5 D h (D h hydraulic diameter). We first validate our computations by comparison with the incompressible experiments performed by Chang et al. (1983, Turbulent flow in a strongly curved U-bend and downstream tangent of square cross-sections. Physico-chemical Hydrodynamics, 4(3), 243–269). We observe that the decrease of the curvature radius is accompanied by a strong intensification of the secondary transverse flows : a rise of 100% of the maximum of their intensity is obtained between the smaller and the higher values of R c . We show that the secondary flows strength is directly related to the radial pressure gradient intensity. We observe a significant modification of the near-wall laws in the vicinity of each curved walls in correlation with the favourable or the adverse streamwise pressure gradient depending on the nature of the curvature. The influence of R c on the coherent vortices is also estimated.
Highlights
Turbulent flows on curved walls play an important role in many engineering applications such as turbines, heat exchangers or cooling channels of rocket engines
We first consider the turbulent flow for the duct with the strongest curvature (Rc = 3.5Dh)
This constitutes the lowest limit which can be reached with our numerical code which is conceived for compressible flow and which uses explicit numerical methods
Summary
Turbulent flows on curved walls play an important role in many engineering applications such as turbines, heat exchangers or cooling channels of rocket engines. In closed duct of a small-aspect ratio, experiments have brought to light the development of an intense cross-stream flow due to the unbalance between the radial pressure gradient and the centrifugal forces, taking the shape of two large counter-rotating vortices of Ekman-type. This three-dimensional character has motivated several numerical works able to take into account the flow unsteadiness: curved boundary layers or curved channels have been studied by Moser and Moin [7], Lund and Moin [8], Silva Lopes and Piomelli [11]
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