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Questions tagged [turbulence]

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3
votes
1answer
67 views

What is the physical meaning of second moment of wind velocity?

I have been reading some documents about meteorological data and many of them mention the second moment of wind velocity. I guess it has to do with the way the wind is changing but in such case I ...
1
vote
0answers
21 views

Turbulence strength from turbulence intensity?

I do not have a lot of knowledge in aerodynamics but I need to be able to derive turbulence strength (Cv2 and Ct2 - so called turbulence structural parameters I think) from turbulence intensity. Does ...
2
votes
0answers
49 views

Reasons for choosing LES in stead of RANS models?

In oceanography, is there any particular reason why choosing large eddy simulations in stead of RANS (regardless of the type of flow)? In both cases, 2d simulations would be used (shallow water model)....
13
votes
1answer
161 views

Can Monin-Obukhov Similarity theory be generalized to tracers?

According to Monin-Obukhov similarity theory, Reynolds-averaged surface layer winds can be expressed by $$\frac{\partial \bar{U}}{\partial z}=\frac{u_*\psi_M(\frac{z}{L})}{kz}$$ The potential ...
7
votes
1answer
246 views

What is the physical meaning of the von Kármán constant?

I know that the von Kármán constant ($k\approx0.4$) is useful in turbulence modeling. Something that bothers me is my lack of understanding where $k$ comes from or the physical meaning behind it. If $...
11
votes
3answers
327 views

Wind profile below the aerodynamic roughness length

The vertical profile of horizontal windspeed is often given by the so-called "log-law": $$u(z)=(u^*/k)\ln(z/z_0),\ \mathrm{for}\ z>z_0,$$ which can be found here. As can be seen from the ...
10
votes
1answer
91 views

Does within-canopy wind direction correlate with wind above the planetary bounday layer?

Wind above the planetary boundary layer (PBL) tends to be fairly smooth and constant over short periods of time. Below the planetary boundary layer, the smoothness is broken by eddies caused by ...
17
votes
1answer
9k views

What are the differences between an LES-SGS model and a RANS based turbulence model?

I'm kind of new to the Large Eddy Simulation (LES) modeling world and I wondered what is the difference between an LES subgrid scale model like the Smagorinsky–Lilly model and a one-equation Reynolds-...
9
votes
1answer
290 views

Given the well known effects of the inverse turbulence cascade for 2D flow, does it make sense to use grid resolutions that resolve turbulence?

As is well known, 2D simulations of turbulent flows in the ocean follow an inverse energy cascade, as opposed to a forward energy cascade observed in fully 3D flows. Because in 2D fluid filamentation ...