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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.

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