[求助]离心力引起的二次留问题

午夜流星

在一般的资料文献中，一般认为弯管处外侧压力大，内侧压力小，相应的也就是外侧速度小，内侧速度大。但是在下面情况下，纯粹的环型管道，刚好相反，U型管道只有在直管与圆弧过渡处是这样，90度管道也是如此，不知道应该如何解释。

午夜流星

环型管道

午夜流星

U型管道

flowermoon

To 午夜流星:

1. U型管道
You may explain the velocity distribution based on the vorticity conservation (zeta = constant):
zeta = @V/@R + V/R
where R is the radius that may vary along flow. The first term is called shear vorticity and the second term is called curvature vorticity.  Before entering the U-section, vorticity is zero (zeta=0). To maintain a zero vorticity at the U-section where V/R>0, the velocity distribution needs to be @V/@R<0, that is, the velocity decreases with the radius.

2. 环型管道
You may explain the velocity distribution based on the balance between the pressure gradient (force) and the centrifugal acceleration. ........