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Will "filling" areas with re-circulation always eliminate that flow separation |
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#1 |
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Michael Brooker
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Hi, i'm a new user here and a beginner to the field of fluid mechanics. In my little experience and human intuition when I've tried to design around flow separation I've found that "filling" these areas or essentially having the geometry follow where the natural flow wants to go seems to eliminate flow separation. For instance, in the example of a backward facing step, if you were to analyse how the flow separates and alter the geometry such that there was a transition following the natural path of the flow you would expect no separation.
My question is, is this always the case (with subsonic flows and standard conditions for air), and if not, what is the reason and could you give me some scenarios? Thanks, this is just for curiosity ![]() |
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#2 | |
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Filippo Maria Denaro
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#3 |
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Michael Brooker
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Thanks, I hadn't thought about this scenario. Is it possible that it might also work in this example? If the geometry of the flat plate started to follow the natural flow separation at that point I would imagine it would cause a locally higher pressure in that region therefore delaying flow separation due to less of an adverse pressure gradient?
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#4 | |
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Filippo Maria Denaro
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As different example, in flow over wing sections, it is quite common to work with geometries that tend to mantain a laminar condition, however separation is a quite common phoenomenon. Trying to prevent separation or to produce a delay is a hystorical issue in aerodynamics and fluid dynamics. Prevent separation for all types of geometries and flow conditions is not possible |
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#5 |
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duri
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Separation is not transition. Flat plate at zero angle of attack never separates. Flow separation can occur in laminar as well in turbulent boundary layers.
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#6 | |
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Filippo Maria Denaro
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Flow over flat plate a zero angle of attack has separation and reattachement, unsteady and three-dimensional, due to transition! What you are thinking about is in terms of the statistically averaged velocity field that shows no separation. |
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#7 | |
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duri
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#8 | |
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duri
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Vortex lift off during transition doesn't mean it is separated. It actually energize the boundary layer from main stream mixing. |
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#9 |
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Filippo Maria Denaro
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yes, I was not enough clear using the term "transition". I dont want to say that separation happens "in" the transitional region but that separation happens thereafter in the onset of turbulent region due to the previous transion.
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#10 |
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Michael Brooker
Join Date: Feb 2016
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Thanks for the info guys.
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Tags |
backward facing step, design, flow separation, recirculation |
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