Hi I was wondering if anybody know what is a physically and mathematically way to estimate that the convergence of an unsteady flow field is over . I mean just from flow field pictures taken at certain time steps that shows a periodicity of the flow field? or is it possible to estimate that from watching the residual convergence or something else?

Thx

(1). Convergence is related to a mathematical process, such as the iterative method. (2). So, within that definition, it is fairly straight forward. (3). Unsteady flow is a physical process and it is not related to the convergence of a method used. (4). Even in the periodic flow, there is no guarantee that the numerical solution or even the physical solution will be perfic periodic. (5). So, in this case, you will have to use statistical approach to identify the global periodic flow structures. (6). Still, within the same time step, the iterative solution must converge in order to have meaningful solution. (using transient approach to obtain the steady-state solution is a different thing. in that case, there is no need to have time-accurate converged solution)