抄録
Microgravity and normalgravity experiments were conducted in which a low-speed liquid jet issued from a circular hole. In order to eliminate the effects of the velocity distribution formed by a finite-length nozzle, a thin orifice plate was adopted. In addition to the evaluation of the nondimensional breakup length, the nondimensional wavelength of the unstable wave causing the breakup was estimated through the results of the image analysis. Under microgravity condition, the dominant breakup mode was smoothly changed from the short-wave mode to the long-wave mode as the issue speed increased. On the other hand, under normalgravity condition, due to gravitational acceleration of the baseline liquid jet, the jump in the nondimensional breakup length was observed around the transition of the dominant breakup modes. Gravitational acceleration also affected the behaviors of the unstable waves. In the case where the effect of gravity was large, the nondimensional wavelength was much larger than the value of the unstable wave with the largest amplification
rate. In such cases, the capillary waves propagating upward from the liquid jet tip was converted into the unstable waves before reaching the orifice exit. In other words, the gravity itself can make the unstable waves. The continuous extension of the nondimensional wavelength of the unstable wave led to the larger breakup length under normalgravity condition.
