Effect of the odd and even number of blades on the hydrodynamic performance of a pre-swirl pumpjet propulsor

A numerical study based on detached eddy simulations is conducted to investigate the effects of the odd and even number of rotor/stator blades, that is, nr/ns, on the hydrodynamic performance of a pre-swirl pumpjet propulsor (PJP). In this paper, six PJPs, the PJP 6-4 (ns-nr), 8-6, 10-8, 7-5, 9-7, and 11-9, are created. The hydrodynamic performance, the unsteady force of blades, and the wake structure of the PJPs are compared. The results show that the frequency of the fluctuating force of the whole rotor highly depends on the number or, more specifically, the parity of nr. When the parameter nr is the even number, it can be found that the total unsteady force of the rotor blades will be strengthened at the k-order stator-blades-passing frequency (k = 1/2 n r). Moreover, it indicates that the superposition-enhancement coefficient (is defined as A*) at k = 1/2 n r equals to nr, at least from the present tests. In terms of both the rotor and stator numbers are even, a phenomenon of the rotor-stator resonance occurs at f = 1/2 n s n r f n, where fn represents the hub rotational frequency. This work is expected to give some insight in the design of a PJP.