Questions tagged [turbulence]
The turbulence tag has no usage guidance.
25
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Why are Reynolds Stresses time-varying?
The time-averaging operator definition gives us
$$\overline{u_iu_j}=\lim_{T\rightarrow\infty}\frac{1}{T}\int_{0}^{T}u_i(x,t)u_j(x,t)dt.$$
From my understanding, this should mean that the Reynolds ...
- 123
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19
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Turbulent flow, fluctuating part of velocity
Let's say we have a fully developed turbulent flow on x axis (simple shear flow). Time-averaged components of velocity on y and z axis are 0. If a lump of particles is moving upwards, then the ...
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Why is the turbulent kinetic energy $k=\overline{v_1'^2}+\overline{v_2'^2}+\overline{v_3'^2}$ even in 2D cases?
I'm writing an essay which partly includes writing about the Reynolds stress model where the dissipation term $\varepsilon_{ij}$ is assumed to be isotropic (since dissipation mostly occurs at small ...
- 11
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Help with friction factors for non-newtonian fluids
I've been researching about friction factors for non-newtonian fluids and I've found quite inconsistent results. The power-law model correlations I've tested do not agree (within some interval) as to ...
- 133
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2
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159
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Imposing/ensuring a constant mass flow rate in turbulent flow simulation
I'm trying to simulate using Finite Elements (non commercial software) the Tube Bundle benchmark problem:
http://cfd.mace.manchester.ac.uk/ercoftac/doku.php?id=cases:case078&s[]=tube&s[]=...
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346
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What is 'wavelength' with reference to turbuence?
When reading about turbulent flows and turbulence spectrum I frequently come across the terms 'wavelength' 'wavenumber'. I understand that the energy is transferred from larger eddies to smaller ones ...
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Does turbulent river flow classify as uniform?
I found this meme in a facebook group on engineering concepts:
I selected A (steady and uniform). In selecting A I assumed the width of the river to remain constant along its path and no parameters ...
- 443
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450
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Ideal funnel design for powders
I'm designing a funnel/bottle for a powder. My goal is to have all of the bottle's powder contents come out when inverted. However, the powder has a tendency to stick to itself (like flour or brown ...
- 363
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Distribution of turbulent energy dissipation in a stirred tank
Is detailed experimental information on the distribution of energy dissipation in a stirred tank(45o Pitch blade) available? I require this variation in all directions in a standard stirred tank ...
- 11
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552
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Von Karman mixing length $l=k \frac{du/dy}{d^2u/dy^2}$
In a fully developed turbulent flow of an in-compressible fluid inside a pipe of radius $R$, velocity at the center is $U_m$. If we define $U^*=\sqrt{\tau_0/\rho}$, where $\tau_0$ is the wall shear ...
- 159
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110
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Turbulence model for low reynolds problem
I'm simulating the flow in a capillary with a sudden expansion. The small capillary has a diamater of 250 µm. The big capillar has a diamater of 1000 µm. My flow rate ist $ 1\frac{ml}{min} $. Using ...
- 93
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266
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Why Taylor's microscale gives us information about the smallest scales of the flow?
So I understand the principles of two-point time correlations (covariance) and how you can just normalise that to get the autocorrelation. I also understand the integral time scale which is quite ...
- 241
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101
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Direction of rotation of turbulent eddies in channel flow
Suppose we have a isotropic homogeneous turbulent channel flow. We know that this flow is associated with many swirling eddies of different length and time scales. I need to know the direction of ...
2
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263
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Obtaining the correct flat plate turbulent boundary layer thickness in a CFD simulation
I used a commercial CFD software to simulate incompressible turbulent flow of air over a flat plate. I setup a 2D domain 1.5m long in the x direction and .2m in the y direction. The boundary ...
- 2,539
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544
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How to measure turbulence parameters experimentally?
When running CFD simulations with turbulence on, I often need to specify inlet parameters such as the turbulent intensity, turbulent viscosity ratio and/or the turbulent length scale. If these ...
- 2,539
4
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466
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How should I set the turbulent prandtl number in a turbulent compressible flow simulation?
I'm working on simulating compressible fluid flow over a flat plate with turbulence. The energy equation for compressible flow with turbulence requires modeling a turbulent heat flux of the form
$$...
- 2,539
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Deriving the turbulent kinetic energy equation
I'm trying to understand the derivation of the turbulent kinetic energy equation, as described in this link: Evaluation of RANS turbulence models for flow problems with significant impact of boundary ...
- 2,539
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2
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346
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Best way to get rid of turbulent flows?
I am making a testing facility for pumps. This facility has to be able to handle 500 m3/h with at little turbulence as possible. The basin itself is 5 meters long, 2,5 meters wide and 2 meters tall. ...
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2
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673
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How safe is this assumption for turbulence modelling in porous media?
I am studying the performance of volumetric solar receivers (specifically ceramic foams) versus the change of many parameters: solar flux, surface temperature, porosity, pore diameter, flow pressure ...
- 2,160
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4
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Ways to reduce turbulence in internal flows
Often it's desirable to reduce the turbulence level in an internal flow without changing the Reynolds number or fluid. This could be measured by the turbulence intensity, though other measures might ...
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322
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Wall functions and separation in turbine blade simulation
I am simulating a turbine and I have some question about standard wall function in FLUENT.
Standard wall function requires $y^+$ value between 30 to 60 on the blade. but the following quote states:
...
- 899
8
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1
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364
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How do I select an appropriate turbulence model?
Turbulent flow involves extremely small scale fluctuations which are usually too small to resolve by using the Navier-Stokes equations directly. To overcome this, we model each transient variable $\...
- 2,539
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What is a non-equilibrium boundary layer?
I studied a manual of Ansys CFX about turbulence models and I came across the term "non equilibrium boundary layer". What does this term mean?
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Is inviscid flow necessarily turbulent?
The Reynolds Number is defined as $Re = \frac{\rho v L}{\mu}$, where $\rho$ is the density, $v$ is the fluid velocity, $L$ is the characteristic length, and $\mu$ is the dynamic viscosity. By ...
- 2,539
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Why does the standard $k-\epsilon$ model use zero equation models?
According to Hoffman, the standard $k-\epsilon$ turbulence model incorporates a two-layer approach (inner region and outer region formulations to reperesent mixing length) when it comes to regions ...
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