Physicist who studied supersonic flow (4)

I believe the answer is:

mach

(Other definitions for mach that I've seen before include "Ratio of the speed of a moving body to the speed of sound" , "Number referring to speed of sound" , "-- Number relates to speeds" , "Ratio of a body's speed to the speed of sound" , "Ratio used to measure high speeds" .)

I've seen this clue in The Washington Post.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.