Those two sentences are saying two completely different things:
Everyone gets to sing one or two songs, but sometimes our manager will sing for ages by himself until he runs out of steam.
This one is saying that, occasionally, the manager sings for a long time. It does not actually imply that this always occurs... the word sometimes is telling you that.
Everyone gets to sing one or two songs, because our manager will always sing for ages by himself until he runs out of steam.
This one is saying that the manager always sings for a long time and the because makes the first clause beg for the word only:
Everyone only gets to sing one or two songs,...
If you really want to simplify the sentence and keep the same meaning, the simplest thing to do is to remove the word will:
Everyone gets to sing one or two songs, but sometimes our manager sings for ages by himself until he runs out of steam.
From what you added in the comments, this may be a good way to word it, with some slight changes for what you're trying to say:
Everyone usually gets to sing one or two songs but sometimes our manager will sing (or sings) for ages by himself until he runs out of steam. When that happens, most of us only get to sing one song.
There are many ways to say the last part of the phrase based on what you're actually trying to say. You could say:
When that happens, most of us don't get to sing at all.
When that happens, we're lucky if we can sing even one song.
Just a couple of options in addition to what's in the example above.
'Because' is redundant. It lets the reader know that the next part of the sentence is the reason for the previous part, but the subject of the sentence is already identified as 'the reason', so it's unnecessary.
Including both sounds stilted, and is officially incorrect (though many people find it acceptable). This article (which I have shamelessly appropriated from this ELU answer to the same question) goes in greater detail.
Best Answer
A couple of issues before I address the question of "in order to ... because".
I would say "the tip leakage flow" and "the suction surface of the blade". "Flow" can be countable or uncountable, while "surface" is countable so I'd consider both countable. You could say "between tip leakage flow ... and the suction surface of the blade" but when listing two things I like to use the same structure, where possible.
It should be "one of the most important secondary flows in ..." The "one of ..." structure requires a plural.
Otherwise this sentence is fine, but you lose part of the meaning of the original sentence. The reason you are measuring tip leakage flow is because it is important. Without the because you're just adding descriptive detail without causation.