Fluent中湍流强度(Turbulence Intensity)的基本定义和理解

2022-12-29  by:CAE仿真在线  来源:互联网

关于的基本公式是这样的:

稍微解释一下就是

1、他是一种比值,衡量的是湍流的程度,所以fluent后面给他带了个单位是%,百分比的单位

2、他是用来衡量湍流的程度的,所以并不是两个速度的比值,而是速度波动程度相对于平均速度的比值。而速度波动描述的就是湍流的特征。

这个值会因为采用模型不同而有不同,一般10%一下算是较小的,而20%算是较大的,但是也有300%及其以上的,比如流速变化剧烈的局部区域,这也不奇怪。

下面是具体来源和官方的解释:

https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v181/en/flu_ug/x1-4300008.63.2.html

文档位置:help/flu_ug/x1-4300008.63.2.html

7.4.2.1.3. Turbulence Intensity
The turbulence intensity, , is defined as the ratio of the root-mean-square of the velocity fluctuations, , to the mean flow velocity, .

A turbulence intensity of 1% or less is generally considered low and turbulence intensities greater than 10% are considered high. Ideally, you will have a good estimate of the turbulence intensity at the inlet boundary from external, measured data. For example, if you are simulating a wind-tunnel experiment, the turbulence intensity in the free stream is usually available from the tunnel characteristics. In modern low-turbulence wind tunnels, the free-stream turbulence intensity may be as low as 0.05%.

For internal flows, the turbulence intensity at the inlets is totally dependent on the upstream history of the flow. If the flow upstream is under-developed and undisturbed, you can use a low turbulence intensity. If the flow is fully developed, the turbulence intensity may be as high as a few percent. The turbulence intensity at the core of a fully-developed duct flow can be estimated from the following formula derived from an empirical correlation for pipe flows:

At a Reynolds number of 50,000, for example, the turbulence intensity will be 4%, according to this formula.

The default value for turbulence intensity is 5% (medium intensity).

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