{"id":10269,"date":"2017-12-11T00:00:07","date_gmt":"2017-12-11T00:00:07","guid":{"rendered":"https:\/\/www.simscale.com\/?p=10269"},"modified":"2026-02-16T23:44:05","modified_gmt":"2026-02-16T23:44:05","slug":"turbulence-cfd-analysis","status":"publish","type":"post","link":"https:\/\/www.simscale.com\/blog\/turbulence-cfd-analysis\/","title":{"rendered":"Turbulence: Which Model Should I Select for My CFD Analysis?"},"content":{"rendered":"\n

\u201cTurbulence is the most important unsolved problem of classical physics.\u201d (Richard Feynman, American theoretical physicist, Nobel Prize in Physics in 1965)<\/p>\n\n\n\n

\u201cI am an old man now, and when I die and go to heaven, there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former, I am rather optimistic.\u201d (Horace Lamb, English applied mathematician, Advisor: George Gabriel Stokes)<\/p>\n\n\n\n

Even a few decades after these great scientists expressed these remarks, turbulence modeling is still no easy thing.<\/p>\n\n\n\n

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Fluid Flow: Laminar vs Turbulent<\/h2>\n\n\n\n

The idea of using fluid to extract or deliver energy is not recent. In the 17th century, Leonardo Da Vinci conducted various experiments to visualize fluid flow, talking about vortex flow, vorticity, swirls, and eddies.<\/p>\n\n\n\n

\"Experimental<\/a>
Figure 1: Experimental visualization conducted by Osborne Reynolds [1] (Source: By Osborne Reynolds (Scan from book) [Public domain], via Wikimedia Commons)<\/figcaption><\/figure>\n\n\n\n

Fluid flow is classified into two main categories\u2014laminar or turbulence\u2014regarding the driven forces (inertial, viscous, etc.), and also a transition regime between them. Notably, being laminar or turbulent is a property of fluid flow under dynamic conditions, not a property of being fluid.<\/p>\n\n\n\n

Laminar Flow: A fluid flows through a smooth path with no disruption between adjacent paths. It is quite compatible to examine laminar flow both numerically and experimentally.<\/p>\n\n\n\n

Turbulent Flow: A fluid flows through a chaotic path that comprises eddies, swirls, and flow instabilities. It is uneasy, almost impossible in some cases, to examine turbulent flow both numerically and experimentally.<\/p>\n\n\n\n

Earlier, the determination of the type of fluid flow numerically was hard to realize. Irish scientist Osborne Reynolds (1883) discovered the dimensionless number that predicts fluid flow based on static and dynamic properties such as velocity, density, dynamic viscosity, and length:<\/p>\n\n\n\n

Re=(inertial force)\/(viscous force)=\u03c1VL\/\u03bc<\/strong><\/p>\n\n\n\n

Where \u03c1 (kg\/m3<\/sup>) is the density of the fluid, V (m\/s2<\/sup>) is the characteristic velocity of the flow, L (m) is the characteristic length scale of flow, and \u03bc (Pa*s) is the dynamic viscosity of the fluid.<\/p>\n\n\n\n

\n

Type<\/strong><\/p>\n<\/td>

Flow type<\/strong><\/td>\n

Reynolds Number<\/strong><\/p>\n<\/td><\/tr>

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 <\/strong><\/p>\n

Internal<\/strong><\/p>\n<\/td>

\n

Laminar regime<\/p>\n<\/td>

up to Re=2300<\/td><\/tr>
\n

Transition regime<\/p>\n<\/td>

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2300<Re<4000<\/p>\n<\/td><\/tr>

Turbulent regime<\/td>\n

Re>4000<\/p>\n<\/td><\/tr>

External<\/strong><\/td>Laminar to Turbulence<\/td>\n

Re>3×105<\/sup><\/p>\n<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Table 1: Flow types according to the Reynolds number<\/p>\n\n\n\n

If the inertial forces\u2014which resist a change in velocity of an object and cause of the fluid movement\u2014are dominant, the flow is turbulent. On the contrary, if the viscous forces, defined as the resistance to flow, are dominant, the flow is laminar. It is common to generate turbulence for a fluid with low viscosity, though it is rare for fluids with high viscosity. A detailed description of the Reynolds number can be obtained from the SimWiki: What is the Reynolds number?<\/a><\/p>\n\n\n\n

Aside from laminar behavior, turbulence encompasses several hurdles, and thus requires rigorous effort during experimental and numerical examinations. Turbulence is a type of fluid flow which is unsteady, enormously irregular in space and time, three-dimensional, rotational, dissipative (in terms of energy), and diffusive (transport phenomenon) at high Reynolds numbers. Due to those divergences in turbulent flow, extremely small-scale fluctuations emerge in velocity, pressure, and temperature. Despite the fact that direct implementation of fluctuated values into the Navier-Stokes equation is possible, called a Direct Numerical Solution (DNS), it requires an extreme amount of resources in terms of hardware, software, and human effort. Therefore, an appropriate numerical model should be implemented when modeling turbulent flow.<\/p>\n\n\n\n

\"Figure
Figure 2: The velocity fluctuation in turbulent flow [2]<\/figcaption><\/figure>\n\n\n\n
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Turbulent Flow<\/span> Turbulence Modeling<\/strong><\/h2>\n\n\n\n

Which turbulence model is convenient for your CFD analysis<\/a> is a troublesome question. To select an appropriate model and simulate physical incident as accurately as possible, you must:<\/p>\n\n\n\n