Comparing two bodies with the same streamlined longitudinal shape, and the same cross-sectional area, one with a circular cross-sectional shape, the other with a quadratic cross-sectional shape, which one of these two bodies would create more aerodynamic drag?
My prediction would be that it is the one with quadratic cross-sectional shape. As around the sharp edges where the two straight surfaces meet, flow interference would occur, which increases the total aerodynamic drag.
Note that these two bodies have 0 angle of attack relative to the incoming flow.
Related question: Why is the fuselage on an airliner circular-shaped?