The ANSYS CFX Solver Manager is demanding to reduce time step while I am running a steady state simulation.
In transient simulation setup, there is an explicit option to define the time steps?
How can I achieve time step control in a steady state simulation defined in ANSYS CFX?
By steady sate there is no change with time, all parameters at all points remain constant. Your computations are to execute sufficient number of iterations to reach convergence for all the set residuals.
Kheng Ka Tan , so, we can not control time step size in steady state simulations, right?
In a steady state flow problem, the time derivatives are all zeros. You can solve the transient equation until a steady state is reached. Otherwise, the time derivatives do not appear at all in your solver and you do not have any time step. The residuals of the equations must be driven to zero to get convergent solution.
Maybe you read about something like pseudo-transient?
Thank You Filippo Maria Denaro
I did not know about pseudo-transient, maybe I will read about it.
Thank You.
ANSYS CFX as well as ANSYS Fluent are using pseudo-transient solution approach for steady-state computations. Here the timescale of the pseudo-transient solution method can easily be changed from automatic timescale selection (where CFX and/or Fluent decide by some heuristics about what might be an appropriate timescale for the method) to a user specified timescale. In CFX this is done in the solver control panel. There you can swith the "Fluid Timescale Control" to "Physical Timescale". Here you can set whatever timescale you desire for the pseudotransient solution method. Very large timescales might lead to numerical instability and divergence. Too small timescales take long time for a steady-state solution to converge or the solution might not converge in strict sense at all, because from one pseudo-timestep to the next some small scale turbulent changes to the flow are getting resolved in time, so that the residuals do not drop to very small values. So, a parametric study with this parameter might be suggested.
Hopefully this helps.
Regards, Th. Frank.
Hello Soumitra,
we can have control over time step in steady state simulation in cfx as it uses pseudo-transient approach to solve the problem.
There are different ways of it.
1. By selecting auto time scale in solver control and using time scale factor as 1e-4 which makes the time step very small. Here we can provide the constrain on the maximum time step. Selected time scale factor can be dynamically changed during run in solver manger of cfx.
2. we can select physical timescale in solver control by providing time step from user side.
Regards,
Rajdeep
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