Abstract: To study the characteristics of the microbubble flow and the drag reduction characteristics of the underwater vehicle in the pitching movement, the water tunnel experiments were conducted with a self-designed driving equipment, a high speed camera and a six-component force balance. The driving equipment can rotate the underwater vehicle around its head at a sinusoidal regular angular velocity.The characteristics of microbubble flow are analyzed based on the high-speed camera system, and the hydrodynamic characteristics of underwater vehicle and the variation of microbubble drag reduction characteristics in maneuvering process are analyzed based on the six-component force balance. The results show that the discrete microbubbles are always evenly distributed on the surface of underwater vehicle when the air injection rate is low. As the air injection rate increases, the density of the microbubble flow gradually increases and the transparency gradually decreases. The discrete microbubbles are eventually coalesced into transparent cavities. During the pitching movement, the axial and lateral force coefficients of the underwater vehicle are basically sinusoidal, and the periods are basically synchronous with the changing period of attack angle. The variation of the axial force coefficients at various air injection rates is basically the same, which are all sinusoidal. With the increase in the air injection rate, the axial force coefficient of vehicle under the same posture decreases gradually and eventually becomes constant. Key

Key words: underwatervehicle, pitchingmovement, microbubble, dragreductioncharacteristic, watertunnelexperiment