Large eddy simulations in curved square ducts: variation of the curvature radius

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.

Acknowledgements

Some of the computations were carried out at the IDRIS (Institut du Développement et de Ressources en Informatique Scientifique, Paris). This work was supported by the CNES (Centre National d'Etudes Spatiales).