(Solved): Air flows steadily through a circular, constant-diameter duct. The air is perfectly inviscid, so the ...

Air flows steadily through a circular, constant-diameter duct. The air is perfectly inviscid, so the velocity profile is flat across each flow area. However, the air density decreases as the air flows down the duct. Is this is 1-D, 2-D or 3-D flow? Why?