5 votes
Accepted

Deriving the turbulent kinetic energy equation

The two terms are equal due to the product rule and continuity equation. The use of the continuity equation might not be obvious, however. In their notation, the Reynolds decomposition is $u_i = \...
4 votes
Accepted

Ideal funnel design for powders

The problem you have is more complicated than you think. Any industry that deals with the storage and movement of granulated/powdered materials has to deal with this and most have unique solutions. ...
  • 9,542
4 votes

How safe is this assumption for turbulence modelling in porous media?

It is just saying that since there is no turbulence or dissipation being computed; your solution will be less accurate for lower and lower permeability. As I read it; eddy currents in this model will ...
  • 7,559
3 votes
Accepted

How do I select an appropriate turbulence model?

Disclaimer: As you requested general guidelines here they are. After having a converged solution, you need to investigate it thoroughly and look for clues that the choice of the turbulence model ...
  • 1,202
2 votes

What is a non-equilibrium boundary layer?

For the equilibrium boundary layer, the local skin friction coefficient is independent of two parameters, both the streamwise distance and the Reynolds number, based on the momentum thickness, and the ...
  • 95
2 votes
Accepted

Is inviscid flow necessarily turbulent?

No, inviscid flows are not necessarily turbulent. If there is nothing to "trip" the turbulence, then the flow will remain laminar. Features which could trip the turbulence include vibration, small ...
2 votes

Ways to reduce turbulence in internal flows

Dolphin skin seems to have properties that limit drag, also by reducing turbulence: In the late 1950s the aerodynamicist Max Kramer claimed that a dolphin ensured a low level of friction drag by ...
  • 4,661
2 votes

Ways to reduce turbulence in internal flows

I think you have a pretty comprehensive list. Some things could be more general such as flow straighteners could also include airfoils for correcting flow around obtuse geometry. Other geometry which ...
  • 7,559
2 votes
Accepted

Best way to get rid of turbulent flows?

Assuming you are wanting to minimize turbulence in the region of the pump, you would probably need to use flow straighteners somewhere upstream of the pump. You would have to study the optimal ...
  • 493
2 votes

Best way to get rid of turbulent flows?

In wind tunnels usually meshes and/or honeycombs are used to reduce turbulence. However, to really achieve low turbulence it's probably not enough to add a single component to your facility. I rather ...
  • 679
2 votes

Von Karman mixing length $l=k \frac{du/dy}{d^2u/dy^2}$

I am not entirely sure I follow your derivations, specifically I'm not sure where you get the equation for the Von Karman mixing length, and why the equivalence of tau and $\tau_0$ give you the ...
  • 314
2 votes

How to measure turbulence parameters experimentally?

One method is to use a hot wire anemometer. This (about 50 pages, ignoring the product-specific stuff at the end) is a good read. In principle, a hot wire anemometer is simply a metal wire (often ...
  • 12.6k
2 votes
Accepted

Why does the standard $k-\epsilon$ model use zero equation models?

There are two ways of "wall treatment" both feature two layers but at different $y^+$. The general idea is that the velocity gradients in the boundary layer are so high that one would need a very high ...
  • 1,202
1 vote
Accepted

What is 'wavelength' with reference to turbuence?

Wavelength is with reference to Kolmogorov's theory of turbulence. Kolmogorov postulated a theory for how turbulence is conveyed from large to small scale eddies, as you described. The wavelength and ...
  • 513
1 vote

Does turbulent river flow classify as uniform?

I'm not sure if there is any further context to this meme, but I would have chosen B) Unsteady Uniform Flow. Since almost all real flows are unsteady and non-uniform, it is really an application of ...
  • 513
1 vote

Turbulence model for low reynolds problem

I solved my problem. I refined the mesh. Part of the problem was the high aspect ratio of my cells, because my tube is very thin in comparison to the length. I have solved the problem laminar and then ...
  • 93
1 vote

Direction of rotation of turbulent eddies in channel flow

Non-laminar flow is often hard to characterize with much mathematical rigor (though in certain special cases and geometries may be done with a little limitation). The phenomena depends heavily on ...
1 vote
Accepted

How safe is this assumption for turbulence modelling in porous media?

Short answer: The FLUENT approach is trivial. Many information are lost due to the space-averaging process - over a representative elementary volume - of the governing equations (which is the essence ...
  • 2,149
1 vote

Ways to reduce turbulence in internal flows

Adding to these above ideas&techniques, In flexible pipes, along with the flexibility we can have filaments(flagellum ) on the walls. These could dissipate the turbulence kenetic energy for the ...
  • 486
1 vote

Is inviscid flow necessarily turbulent?

The simple answer Reynolds number can be more simply defined as the ratio of Inertial forces to Viscous forces. viscous >> inertial = Laminar viscous << inertial = Turbulent This is why ...
  • 386

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