Effect of the duct and the pre-swirl stator on the wake dynamics of a pre-swirl pumpjet propulsor

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

“…16 In the study of Qin et al, 2 this form of oscillation is called short-wave instability of PJP, caused by the stator blades. Qin et al 2 compared the vortex structure of a normal PJP with the PJP without stator (contains rotor and duct), and it is found that the tip vortex of PJP presents a standard spiral shape without stator, which confirms the conclusion. This short-wave instability originates from the definition of Saffman, 28 in which the smooth-sinuous-wave-type mode of tip filaments is called as shortwave instability mode.…”

“…The spatial evolution process of rotor trailing wake [see Figs. 13(c) and 13(d)] is usually called the roll-up process (the upper part of the trailing edge vortex undergoes a progressively increasing angular displacement and a radial rise 2 ).…”

“…1 Therefore, since the birth of the PJP, it has received extensive attention, and research of PJP has grown rapidly. 2 The experimental test is an essential means to study the flowfield characteristics of PJP. In 1963, McCormick and Elsenhuth 3 pointed out that PJP has apparent advantages in efficiency and cavitation performance with respect to other traditional propellers through experimental data analysis.…”

“…14 Furthermore, the effect of the duct and the pre-swirl stator on the wake dynamics of a pre-swirl PJP (with an eight-bladed stator and six-bladed rotor) is numerically studied based on the IDDES. 2 In addition, the wake of this pre-swirl PJP and the vortex morphology is investigated using stress-blended eddy simulations. 15 Until now, most of the research works are focused on the hydrodynamic performance and the wake dynamics of the pre-swirl pumpjet propulsor with a fixed number of blades, and less attention has been paid to the study of different rotor/stator blades numbers, especially the odd and even numbers.…”

“…The PJP is always designed as an odd number of rotor/stator blades (such as 21, 15, 11, 9 stator blades and 15, 11, 9, 7 rotor blades) to avoid possible frequency resonance between rotor and stator. 2 However, what are the conditions for the occurrence of resonance phenomenon? Is an even number of blades necessarily a poor solution?…”