Exit pathway is as critical as entry. Exit pathway should be smooth so the spent cooling air rejoins the slipstream as parallel to ambient flow as possible.
Think: Fish gill, with entry at the nose stagnation point (highest pressure) and exit at the point of lowest dynamic pressure along the side or bottom, with flow virtually parallel to the slipstream. That way, the slipstream sucks air through the gill (radiator).
NACA did a lot of studies of engine cowlings in the WWII era, much of which was forgotten in the dawning jet age. Unfortunately.
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