| Abstract: | This paper describes a finite element implementation of an operator-splitting algorithm for solving transient/steady turbulent flows and presents solutions for the turbulent flow in an axisymmetric 180° narrowing bend, a benchmark problem dealt with at the 1994 WUA-CFD annual meeting. Three k–? based models are used: the standard linear k–? model, a non-linear k–? model and an RNG k–? model. Flow separation after the bend, as observed in the experiment, is predicted by the RNG model and by both the linear and non-linear k–?ε models with van Driest mixing length wall functions. Good agreement with experimental data of pressure distribution on bending walls is obtained by the present numerical simulation. Results show that there is very little difference between the linear and non-linear k–?ε models in terms of predicted velocity fields and that the non-linearities mainly affect the distribution of turbulent normal stress and pressure, in analogy to the effect of second-order viscoelastic fluid models on laminar flow. Both the linear and non-linear k–?ε models fail to predict any flow separation if logarithmic wall functions are used. |
