[rbarrett]

Hi all,

I am relatively new to CFX and I was just wondering if anyone could help me with a few problems that I have been having with a mesh deformation problem. I am modelling the compression of a piston within a cylinder. The actual geometry consists of two pistons within one cylinder, so there is a line of symmetry at mid chamber location. My model is also axisymmetric.

The problem that I am having is that the simulation deformation is over predicting the applied displacement and I was wondering if there is an issue with (i) my CEL expressions or (ii) my time step.

(i) The CEL expressions that I am using are ('WeightFunction' is a linear weighting function and 'Li' is the total length of the compression chamber):

Disp = sDisp*WeightFunction
Li = 0.178 [m]
WeightFunction = 1-((z-sDisp)/(Li-sDisp))
sDisp = velCV*t
velCV = 8 [m/s]

(ii) The time step that I am using is 5.2e-4 s for a total compression time of 16.6 ms.

Any help with this issue is greatly appreciated.