I’ve often wondered this. My science professors have said “man-del-brawt” (as in bratwurst) but since Benoit Mandelbrot is a French person born in Poland(?) shouldn’t we pronounce his name more like “man-del-broe”(as in:how’s it goin’, bro’)?
The American Heritage Dictionary says brawt.
FactMonster says broe
I’m not sure how the Polish origins of the name tie in with him living in France and changing the spelling of his name (his uncles were named Mandelbrojt).