"certain fluctuations" is a correct and usable phrase in written English.
You can use it to refer to changes or variations in something, or a situation that is not stable. For example, "The stock market is subject to certain fluctuations which can impact the value of investments."
If we have certain fluctuations in the coolant temperature, reactor pressure or load, any of these can damage a certain amount of tubes.
The measured signals contained certain fluctuations, which indicate that the process of corrosion initiation is not a smooth one, but consists of a sequence of several events.
There were, however, certain fluctuations left up to chance, as in the maps where the ocean is pink rather than blue.
Obviously, the waveform of r[n] still has certain fluctuation.
There is, however, a certain fluctuation in 'Abd al-Latif's attempt to establish a perfect conformity between the First Cause as presented in the Liber de causis and the First Principle presented in his chapters devoted to the paraphrase of Metaphysics Lambda.
Such small energy difference indicates that the delocalized cluster geometry varies easily under certain thermal fluctuations.
The energy barrier is quite small in comparison with the F−(H2O) cluster, which indicates the frequent changes of cluster geometry under certain thermal fluctuations.
Worse still, some cosmologists regard it as a genuinely chancy matter whether our universe is open or closed (apparently certain quantum fluctuations could, in principle, tip it one way or the other), yet whatever it is, it is 'single-case' in the strongest possible sense.
Once considered to be simply "physiological noise," certain characteristic fluctuations in the fMRI signal during rest have been shown to be associated with specific neuronal networks.
According to statistics, raw coal output increased from 70.3% in 1978 to 76.5% in 2012 and showed a dominant part in China's energy supply structure despite the occurrence of certain amplitude fluctuations during this period.
If a company is buying and selling a very specific kind of product with a narrow group of specialists spread around the world, a specialized industry currency could be a tool to mitigate currency fluctuations, certain legal issues, and other risks.
