[himanshu28]

hi,

i am trying so solve the flow through the varying cross-section duct transient analysis but as i come to the solver it again and again show me the error-255 the solver failure i am new to the software please help me... i have attached my .ccl file .. error-255.zip pl

[cdegroot]

Why do you want to do a transient analysis in a fixed duct when none of the BC's depend on time? Are you interested in the flow development?

What is the size of your duct? I am wondering if your timestep is too big and it is diverging because of that.

[himanshu28]

hi,
yes I am intrested in the flow development in the Duct and my duct length is 919.35 mm. since i want to anlaysis "unsteady" so i chooses ed transient analaysis.....

[cdegroot]

Okay so if I remember your CCL file, the time step was about the same as the characteristic time of the flow (object size divided by the flow speed). This might be a bit large. The solution could be unstable as a result. Try a time step 1/10th as large and see if there is a difference.

[himanshu28]

hi,
i entered the time step of 0.1 sec. but its still showing me the error... i caan't understand about how solver is taking this timesteps as....

[cdegroot]

I think you misunderstood. Your duct is about 1 m long and your inlet velocity is about 30 m/s. Thus it takes about 0.03 seconds for a fluid parcel to go though the duct. I am saying you should make you time step 1/10th of that, so 0.003 seconds. If it is still unstable you can go even smaller.

[cdegroot]

Maybe you could also post the output file to show the error.