In many flow case, something like pipeflow or external flow over body, there is always effort to estimate reattachment length. I know a recirculation by separating flow results the bad effect like energy loss, nosie and increasing darg.
what i want to know the reason for estimate a reattachment length.
if reattachmen lengt is longer, is it mean more bad effect ??
Is it means to know that the amount of bad effect by calculating reattachment length??
The size of the separation cell could be considered as a "dead zone" respect to the main flow. For example, in a contact tank, as plug-flow conditions are useful for the best performance of the tank, separation/recirculation regions should be reduced as much as possible.
On the principle of independence of the boundary conditions of structure direction of turbulence
Lu Panming
Abstract
This is an introduction to the turbulence modeling theory of the present author, which can take the boundary conditions of turbulence structure into consideration ( the main contents have either not been published in normal journals or only published in chinese papers). It is included that： (I)。Difficulty Problems Encountered in “Second-Moment-Closure” turbulence modelling ，i.e. “Gao-Ge Anomaly” ; (II)。The improvement to the ”Second-Moment-Closure” turbulence modelling in order to allows the boundary conditions of turbulence structure direction could be prescribed; (III)。An explanation to the principle of independence of the boundary conditions of
turbulence structure direction ; (IV)。Six suggestions to the possible future work directions; (V)。 An explanation to the ”Gao-Ge Anomaly”.
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4. The principle of the independence of the boundary conditions is not only to the turbulence modelling, but also suitable to the other subject, because it is frequently meet the equations are not easy to solve, so there is often a need of modelling or predigestion. For example, both the D‘Alembert anomaly (~1752) and the Stokes anomaly (~1856), are due to breach the principle of independence of the boundary conditions, according to today`s point of view .This is because, first, by using the inviscid potential flow`s dynamic equations it is not possible to affiliate the slip-less condition of the real fluid at the wall, and second, using the Stokes equation it is not possible to affiliate the boundary conditions both at the wall of cylinder and at the infinite to the cylinder. The first anomaly lead to the discovery of the Prandlt`s boundary layer theory（1904）, and the second anomaly was solved by Oseen（1910）with introducing a modification. All these reflect the scientific worthiness and broad latency of the present principle of the independence of the boundary conditions.
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Dear sir:
above is an example paragraph,for more details or need the full text, please go to the end of this letter, where will be an web address （or entrance ）existed.
http://staff.ustc.edu.cn/~pmlu/
or http://staff.ustc.edu.cn/~pmlu/%C2%C0%D6%F8%D5%D5%C6%AC%BB%E3%B1%E0/
or http://staff.ustc.edu.cn/~pmlu/%C2%C0%D6%F8%D5%D5%C6%AC%BB%E3%B1%E0/On%20the%20principle.pdf
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BTW:
my question is that does anyboby can find any other examples of this kind ?(that is any other anomaly due to breach the principle of independence of the boundary conditions.)
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