题目

英语翻译
Because the vortex rope appearing in the draft
tube is a common phenomenon for most Francis
turbines in the part load zone,and the rotating
frequency of the rope is about 1/4 to 1/3 multiple of
runner rotation frequency
,it may be concluded
that the low-frequency component of vibration,
oscillation and pressure fluctuation existing in the
investigated turbine is induced by draft tube vortex
rope.Generally,it could not be avoided completely in
this part load zone.Some technical means should be
applied to control the unsteady features.This content
will be included in another article in the future.
In addition to the above low frequency,another
characteristic frequency,1.25 Hz (or 1.0f),was found
in the frequency spectrum of vibration and pressure
fluctuation,as shown in Figs.3 and 7.It is very
possible to correlate this frequency and the runner
passing frequency.
Considering the 5.7 Hz (or 4.56f) charact

提问时间：2020-12-28

答案