> > > 1) You have way too many Newton steps. Newton is quadratically >convergent, so if > you have 100+ steps, it means you are very very far from the >solution when you > begin. In this region, Newton is a really bad algorithm and can >be very very > sensitive to perturbations. I would never expect it to be >reproducible. From the > well-known fracint demo, it can be chaotic. >
The initial solution from which Newton's algorithm is started is obtained using a fixed point iterative scheme in which the turbulence transport eqn is solved de-coupled from the mean-flow eqns. This de-coupled solution strategy usually stalls (in terms of residual decrease) after a residual drop of a few orders of magnitude. At this stage Newton is invoked. From a qualitative view-point (say at plotting level) the initial solution is close to the fully converged one, but I will try to quantify this and check how mutually far or close are the two. Even for the 2D RANS eqns we have noticed a fairly "long" plateau in terms of residual convergence history before quadratic convergence occurs. This is also in line with the few references on the subject I have in mind. 3D Euler is far more benign in our experience. > 2) I would also question whether the system is actually stable. >Instability can result > in occasional divergence based upon small perturbations. > We know this might occur. At this stage we are still trying to make sure there are no implementation bugs in our code. Aldo -- Dr. Aldo Bonfiglioli Dip.to di Ingegneria e Fisica dell'Ambiente (DIFA) Universita' della Basilicata V.le dell'Ateneo lucano, 10 85100 Potenza ITALY tel:+39.0971.205203 fax:+39.0971.205160
