進行方向と逆向きに浮力が作用する渦輪の並進速度

抄録

To investigate the change of translational velocity of negatively buoyant vortex rings, PIV measurement has been performed with four high-resolution cameras placed in a line in the direction of the ring movement in the range of Reynolds number based on a jet velocity, 10,000 < Re_Ujmax < 25,000 and Froude number, 3.0 < Fr < 16.8. It is found that the vorticity distribution in the core is nearly Gaussian to be the same as non-buoyant vortex rings and the decreasing rates of circulation and radius of rings with time are proportional to 1/Fr². The impact of the decrease of the translational velocity from the variation of circulation, radius of ring, and radius of core is discussed by using theoretical formula for a thin vortex ring.