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 Dan April 22, 2008 23:26

Could someone give me a explanation of how a quasi-steady solution differs from the unsteady solution? Thanks!

 davoche April 23, 2008 08:45

From a physical point of view, a quasi steady solution refers to phenomena for which each temporal states of the evolution of your system can be found independantly from a steady state (by applying the same conditions). A contrarion, unsteady phenomena cannot.

 Ananda Himansu April 23, 2008 15:08

I would say that a non-steady-state flow viewed in a given reference frame is considered quasi-steady if the time-average (over a suitable time scale or period) of the flow quantities at each reference spatial location in the flow is independent of time. This would seem to imply that quasi-steady flows are periodic flows, though I think some authors would include in the quasi-steady category turbulent flows in which the turbulent quantity time-averaged statistics are independent of time.

I think what davoche describes is in thermodynamics referred to as quasi-static states of a thermodynamic system.

 davoche April 24, 2008 05:34

I don't understand how you could obtain a time dependant solution from an time average operation ?

 davoche April 24, 2008 06:14

Or maybe you think about phase average operation ?

 ganesh April 24, 2008 13:32

Dear Himanshu,

"..........is considered quasi-steady if the time-average (over a suitable time scale or period) of the flow quantities at each reference spatial location in the flow is independent of time". I thought the definition looked more appropriate for stationary flows. A flow is said to be quasi steady if temporal variations at a spatial location are much smaller (they would be zero if the flow was steady) ompared to spatial variations for any quantity.

Regards,

Ganesh

 Ananda Himansu April 24, 2008 15:02