Fluent中升力系数阻力系数定义

问题：圆柱绕流在fluent中如何得到阻力系数和升力系数？具体的设置是怎样的？是要监测得到阻力和升力吗？它们分别怎么设置来得到？

答：首先要在report－reference value里设置参考速度和长度

然后solve－monitor－force中设置监测drag，lift就可以了

阻力和升力是可以得到的，得到之后再除以1/2pV**2S就可以了

问题：fluent中升阻力系数如何定义？

答：升力系数定义：

FLUENT的升力系数是将升力除以参考值计算的动压 (0.5*density*(velocity**2)*area=0.5*1.225*

(1**2)*1=0.6125)，可以说只是对作用力进行了无量纲化，对自己有用的升力系数还需要动手计算一下，report一下积分的面积和力，自己计算。

其实本身系数就是一个无量纲化的过程，不同的系数有不同的参考值，就像计算Re数时的参考长度，是一个特征长度，反应特征即可

作为Cl、Cd也是具有特定含义的系数，参考面积的取法是特定的，比如投影面积等等，但是这个在Fluent 里是没有体现的

Fluent里面你不做设置，就是照上面的帖子这样计算出来的，

并不是你所期望的参考值，自己需要设定，对需要的参考值要做在里面设定

另外：参考值的改变不影响迭代计算的过程，只是在后处理一些参数的时候应用到

user guide 的相关内容

26.8 Reference Values

You can control the reference values that are used in the computation of derived physical quantities and nondimensional coefficients. These reference values are used only for postprocessing.

Some examples of the use of reference values include the following:

Force coefficients use the reference area, density, and velocity. In addition, the pressure force calculation uses the reference pressure.

Moment coefficients use the reference length, area, density and velocity. In addition, the pressure force calculation uses the reference pressure.

Reynolds number uses the reference length, density, and viscosity.

Pressure and total pressure coefficients use the reference pressure, density, and velocity.

Entropy uses the reference density, pressure, and temperature.

Skin friction coefficient uses the reference density and velocity.

Heat transfer coefficient uses the reference temperature.

Turbomachinery efficiency calculations use the ratio of specific heats.

26.8.1 Setting Reference Values

To set the reference quantities used for computing normalized flow-field variables, use the Reference Values panel (Figure 26.8.1).

You can input the reference values manually or compute them based on values of physical quantities at a selected boundary zone. The reference values to be set are Area, Density, Enthalpy, Length, Pressure, Temperature, Velocity, dynamic Viscosity, and Ratio Of Specific Heats. For 2D problems, an additional quantity, Depth, can also be defined. This value will be used for reporting fluxes and forces. (Note that the units for Depth are set independently from the units for length in the Set Units panel.)

If you want to compute reference values from the conditions set on a particular boundary zone, select the zone in the Compute From drop-down list. Note, however, that depending on the boundary condition used, only some of the reference values may be set. For example, the reference length and area will not be set by computing the reference values from a boundary condition; you will need to set these manually.

To set the values manually, simply enter the value for each under the Reference Values heading.

不同的Cd、Cl在各行业叫法一一致，如在汽车行业叫风阻系数

风阻系数：空气阻力是汽车行驶时所遇到最大的也是最重要的外力。空气阻力系数，又称风阻系数，是计算汽车空气阻力的一个重要系数。它是通过风洞实验和下滑实验所确定的一个数学参数, 用它可以计算出汽车在行驶时的空气阻力。

空气阻力是汽车行驶时所遇到最大的也是最重要的外力.风阻系数是通过风洞实验和下滑实验所确定的一个数学参数,用它可以计算出汽车在行驶时的空气阻力.风阻系数的大少取决于汽车的外形.风阻系数愈大,则空气阻力愈大.现代汽车的风阻系数一般在0.3-0.5之间.

下面是一些物体的风阻：

垂直平面体风阻系数大约1.0

球体风阻系数大约0.5