In hydraulic turbines, why shouldn't the number of wicket gates share a common denominator with the number of runner blades?

In the textbook it says :

Note that in a good design, the number of wicket gates does not share a common denomi- nator with the number of runner blades. Otherwise there would be severe vibration caused by simultaneous impingement of two or more wicket gate wakes onto the leading edges of the runner blades. For example, in Fig. 14–87 there are 17 runner blades and 20 wicket gates. These are typi- cal numbers for many large reaction hydroturbines, as shown in the pho- tographs

I really can't understand how having the same number for both would cause severe vibration.

Can anyone help clarify it ?

Thanks in advance.

submitted by /u/theflyingegyptian
[link] [comments]

from The ME Hang Out https://ift.tt/37CuS1y https://ift.tt/eA8V8J