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 October 2, 2006, 05:15 Re: How to determine whether flow is steady or uns #2 ganesh Guest   Posts: n/a Dear Maliya, In a strict sense, no flow can be aprioir judged to be steady or unsteady, when a computation is being performed, unless you have a knowledge of the same from experiments. The right thing to do is to run an unsteady flow solver on the problem, and the result will automatically emerge; either you get a steady converged solution or an unsteady oscillating solution. In fact, all FVM codes solve an unsteady problem, they march to steady state (if you are solving a steady state problem) by some time integration procedure. Hope this helps Regards, Ganesh

 October 2, 2006, 08:34 Re: How to determine whether flow is steady or uns #3 Jonas Holdeman Guest   Posts: n/a The numerical determination can be difficult. Near the transition from steady to unsteady, convergence can be rather slow. And apparent convergence or not to steady can depend on methods used. One mathematically-motivated method used by some authors is to generate a quasi-steady solution using a steady method. This can be done by a little smoothing of the convective velocity. Then introduce a series of perturbations and integrate in time with an unsteady solver and see if the perturbations grow or die away in time. Unsteadyness is likely to develop around irregularities in the boundary first, then spread to the whole domain as the Reynolds number increases.

 October 2, 2006, 12:11 Re: How to determine whether flow is steady or uns #5 prapanj Guest   Posts: n/a hi let me ask u something from the radical structure. when u iterate, what u do is u get a solution based on assumed solutions(which is not accurate) . Now let us look at the basic structure of an algorith of an unsteady scheme. u(some time-step) = u(previous time step) + the corrections now an iteration also has a similar structure u(more accurate) = u(less accurate) + the corrections. its just the names that we use are different. isnt it? doesn' this apply for implicit schemes too. Expecting edifications from Mr.Mani. (i am just a novice)

 October 2, 2006, 12:53 Re: How to determine whether flow is steady or uns #6 Renato. Guest   Posts: n/a The idea of a numerically steady flow can be based on a solution change tolerance, for example: if we say that a solution change (based on the magnitude of the time derivative, e. g.) of 10^-3 defines a steady condition, so, you'll have a reference to stop your *unsteady* computation and say: "My solver reached a steady state condition defined by some tolerance". In turbulent computations the term "steady in average" or quasi-steady can be used to define a condition when the solution fluctuations tends to become fix, but also bounded by some tolerance. Regards Renato.

 October 7, 2006, 02:26 Re: How to determine whether flow is steady or uns #8 msureshkumar Guest   Posts: n/a In the software CFDesign, transient only available for the turbomachinery where time is playing more role. Since there is no steady state, you can confirmedly move further.

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