Greetings dear experts,
I am solving a turbulent flow, inside a tube twisted tape. I was wondering provided that the boundary conditions are set as constants, could it be possible that the flow behaves as a transient or periodic flow?
In what circumstances a partial differential equation can have periodic or transient solutions?
Thank you all in advance
Yes, a time-dependent flow can develop also in a problem having steady BC.s. This is in the nature of the NSE.
Of course, I am talking about the time-dependent formulation while if you set the steady state equations, that is no longer possible.
Hello dear Filippo Maria Denaro .
Thank you for your response.
How about a periodic flow?
Consider a turbulent flow over a cylinder. By assuming a constant velocity inlet and a known pressure outlet while solving the equation as a steady-state flow. In reality, the flow has a periodic behavior, the question is whether our solution provides the same behavior or not? If it does, how is it possible to identify the same thing for other geometries and problems?
Kind Regards,
Mahyar Seyd Eshaghi
you are making a lot of confusion between different issues.
1) Turbulence is physically always unsteady and 3D. The steady state for a turbulent flow is possible to be assumed but only in case of an energy equilibrium and for the statistically averaged variables, not for the total variables.
2) The steady state for the statistical mean field implies you can never see a vortex shedding but only the mean steady part of the separated flow. Thus, the flow over a cylinder produces two statistically steady separated regions of the flow behind the cylinder.
3) The steady state flow for the statistically averaged equations produces in your flow problem a 2D field.
4) The way to produce a time-dependent flow and resolve the vortex sheding is to solve the 3D unsteady equations in DNS or LES formulation.
Dear Filippo Maria Denaro ,
Thank you for enlighting me.
I am currently solving a 3D turbulent flow inside a tube with a twisted-tape. I was wondering what kind of behavior in the residuals implies the existence of vortex shedding or other kinds of periodic behavior if a steady-state method is chosen.
Thank you in advance,
You cannot see vortex shedding in your steady formulation, but only steady separated regions of the flow. The residuals are numerical errors in the solver and should be driven under a small threshold to ensure the convergence.
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