As Doomer perfectly explained, a lot of Ukrainians are able to speak normal Russian. But in some parts (Western Ukr) thanks to the russophobic propaganda some are embarrassed to speak it (while they actually CAN) as well as there are some that are embarrassed to speak pure Ukrainian... so they begin to "russify" Ukrainian words which is called "surzhik" (Brainwashing effects).
But if you as a tourist visit even western parts of Ukraine and speak Russian, Most of them will understand you. They have a lot of visitors/tourists and in order to not lose them, they usually hide their a bit "nationalistic" sentiments. I mean if you are a foreigner, that's ok. National tensions exist only between Ukrainian citizens themselves. It has no connection with tourists. Also they are hospitable.