In a centrifugal fan (Fig. 1.118(a)), the air at any point is subjected to an impulse each

Question:

In a centrifugal fan (Fig. 1.118(a)), the air at any point is subjected to an impulse each time a blade passes the point, as shown in Fig. 1.118(b). The frequency of these impulses is determined by the speed of rotation of the impeller $n$ and the number of blades, $N$, in the impeller. For $n=100 \mathrm{rpm}$ and $N=4$, determine the first three harmonics of the pressure fluctuation shown in Fig. 1.118(b).

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