I get the error "Newton's Method failed to converge in 100 iterations...." for "Temperature" with location "Vertices".

The error is displayed a few times and soon the solver stops.

How do I go about debugging this?

Newton's method ? sounds like a Finite Element problem, this is CFD site.

Hi Ogbeni,

I know this is a cfd site and CFX forum. I guess every cfx user must have encountered this error at some point when using the CFX Solver.

The exact error goes like: ****** Notice ****** | | Newtons method failed to converge in 200 iterations. This | | occured while computing the following variable: | | | | Variable Name : Temperature | | Location Name : FluidZone | | Mesh location : VERTICES | | Mesh entity : | | Last 3 Changes : 4.59189E+01 4.59189E+01 4.59189E+01 | | Tolerance : 1.0000E-02 | | | | The Newton iteration was either slowly converging or has stalled. | | The solver will continue with the variable set as it was on the | | final iteration. If this situation continues you might try | | increasing the number of iterations allowed for Newtons method. | | This can be changed by setting one of the parameters: | | | | Temperature : "Constitutive Relation Iteration Limit" | | Pressure : "Newton Pressure Iteration Limit" | | | | for your mixture using the definition file editor. | +----------------------------------------------------

The Newton iteration is used for calculation of thermodynamic properties of mixtures. How is your physical setup? What kind of fluid do you have? Without answers to that questions it is not possible to help you.

Thanks Joe. I had no idea that it is related to thermodynamic properties of mixtures.

Fluid: Mixture of 3 user-defined gases.(Variable Composition Mixture). [Cp(T),Thermal cond(T), Viscosity(T) have been defined as functions of temperature apart from the mol. wt. and other essential parameters]

The setup basically consists of a cylinder with 3 inlets, one for each of the gases and an outlet.

As I reduce the timestep(at the beginning of a run), the no. of iterations after which this error comes(and stops the solver) increases. However, for a very small timestep of the order of -5(approx. 1/10th of the autotimestep value) , this error seems to have vanished.

Could this be because of wrongly defining the properties of the gases? or anything to do with the timestep? or anything else?

Yes, it could be that there is a mistake in your property defintion. Especially the cp values, as the problem is related to temperature. I would check them. If you have a result file or backfile make a chart cp over T.

I also got this error message although I'm using CFX materials. A binary mixture of O2 and JetA. Cp is given in Nasa Format for both materials.

Does anybody have an idea what causes this error message?

JetA is that part of the cfx material properties data bases or is it your own data? If its your own data, check first the simple things like typos, dimensions etc.