Numerical Computation of Turbulent Flow in a Square-Sectioned 180 Deg Bend

Abstract

Fine-grid computations are reported of turbulent flow through a square sectioned U-bend corresponding to that for which Chang et al. (1983a) have provided detailed experimental data. A sequence of modeling refinements is introduced: the replacement of wall functions by a fine mesh across the sublayer; the abandonment of the PSL approximation (in which pressure variations across the near-wall sublayer are neglected); and the introduction of an algebraic second-moment (ASM) closure in place of the usual k–ε eddy-viscosity model. Each refinement is shown to lead to an appreciable improvement in the agreement between measurement and computation. Direct comparisons with the measured rms turbulent velocity give further support to the view that the ASM scheme achieves a generally satisfactory description of the Reynolds stress field. Even with the most refined model some discrepancies between the experiment and computed development are apparent. It is suggested that their removal may require the use of a turbulent transport model in the semi-viscous sublayer in place of the van Driest (1956) mixing-length treatment used at present.