Turbulent length scale

MissCFD · February 22, 2017, 18:33

Can somebody confirm me that the turbulent length scale that we need to input as a inlet condition (with the turbulent intensity) corresponds well to integral scale

which is the size of the largest eddies and which is also to be found in this formula:

$\eta/l=Re^{-3/4}$ where $\eta$ is the Kolmogorov scale.

The reason I ask is that there is a lot of notation for turbulent length scale:

,

,

, etc.

Thank you for your help !

piu58 · February 23, 2017, 01:12

is the length of the large eddies. It should not be larger than

(the size of the problem) of course.

can be guessed.

For pipe flows:

is the hydraulic diameter, which is identical the diameter for round pipes. For rectangular ones:

$d = 2 \frac{ab}{a+b}$

For flow around / past bodies:

is the size of the problem, for cylinders and spheres the diameter, for other bodies the diameter of the flow directed area.

February 22, 2017, 18:33	Turbulent length scale	#1
MissCFD Senior Member Join Date: Aug 2014 Posts: 160 Rep Power: 12	Can somebody confirm me that the turbulent length scale that we need to input as a inlet condition (with the turbulent intensity) corresponds well to integral scale which is the size of the largest eddies and which is also to be found in this formula: $\eta/l=Re^{-3/4}$ where $\eta$ is the Kolmogorov scale. The reason I ask is that there is a lot of notation for turbulent length scale: , , , , etc. Thank you for your help !

February 23, 2017, 01:12		#2
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	is the length of the large eddies. It should not be larger than (the size of the problem) of course. can be guessed. For pipe flows: is the hydraulic diameter, which is identical the diameter for round pipes. For rectangular ones: $d = 2 \frac{ab}{a+b}$ For flow around / past bodies: is the size of the problem, for cylinders and spheres the diameter, for other bodies the diameter of the flow directed area. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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