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4.1.6 Convergence Advice

A common cause of convergence difficulties is the use of inappropriate initial values for the turbulent normal stresses, e.g. zero. The user is referred to Section 4 above for advice on specifying initial values for these and other turbulence components.

The RSTM uses a collocated-variable arrangement and this may lead to decoupling of the mean-velocity and Reynolds-stress fields, and also the mean-scalar and Reynolds-flux fields. Eventually, this can lead to oscillatory solutions or even divergence of the solution. Thus far, experience has shown that the hydrodynamics is not susceptible to this problem, although on occasion the thermal and scalar fields are, especially when the generalised gradient-diffusion model is employed. However, in all cases encountered convergence could be secured by using sufficient false-time-step or linear relaxation.

The user is referred to the 'Advanced turbulence models' user library for examples of successful RSTM calculations, namely library cases T600-609.