同軸二重円管噴流の渦周波数成分に及ぼす内側ノズル噴流の影響

抄録

This paper describes the results of an experimental study concerning the frequency components of flow fluctuation in double coaxial pipe jets. We examined the effects of velocity ratio, outer pipe length and lip thickness of the inner nozzle on the flow structure and velocity frequencies. It was found that, for velocity ratios u^^-_i/u^^-_o ≲ 0.5, the velocity fluctuation is mainly composed of the frequency of the vortex street whose excitation depends on the outer pipe length, and the values of the Strouhal number St_Lbased on the outer pipe length are constant at 0.64N (N=1, 2, 3...). u^^-_i/u^^-_o ≳ 0.5, however, the velocity fluctuation frequency is due to the alternate shedding of lip wake vortices in the inner mixing regions, and behaves in such a way that the Strouhal numbers St_bi, based on the lip thickness of the inner nozzle are constant at about 0.2 for any outer pipe length of the jets.