A Savonius rotor (see Fig. 6.29b) can be approximated by the two open half tubes in Fig.

Question:

A Savonius rotor (see Fig. 6.29b) can be approximated by the two open half tubes in Fig. P7.96 mounted on a central axis. If the drag of each tube is similar to that in Table 7.2, derive an approximate formula for the rotation rate Ω as a function of U, D, L, and the fluid properties ρ and μ.