The most common and most likely answer to this crossword clue is the 10 plus 4 letter word PREVAILING WIND
I've seen this crossword clue in The Times
P
R
E
V
A
I
L
I
N
G
W
I
N
D
Buddy explains!
The straight part
We know that "the dominant flow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case the dominant flow = prevailing wind.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.