In order to reveal the inner flow characteristics of cavity gyrating flow,the velocity characteristics of Gongboxia horizontal gyrating discharge tunnel were studied based on the numerical simulation and experimental results. The results indicated that with the increase of the radial,the tangential velocity increased at first，and then decreased, and had a distribution characteristics of combined vortex,while the axial velocity increased rapidly at first,and then changed slowly.The cavity gyrating flow in gyrating discharge tunnel was mainly tangential flow and axial flow,and changed from the tangential flow into the axial flow along the gyrating discharge tunnel,which was proved by the rotation angle.The freedom degree and energy loss of cavity gyrating flow were reflected by the combined vortex index,which decreased with the decrease of the radial in the range from -0.8 to 0.5.The variations of the combined vortex index indicated that the cavity gyrating flow changed from quasi forced vortex to quasi free vortex along the gyrating discharge tunnel.The computational formulas for pressure and discharge were established based on the motion rule of combined vortex,and the combined vortex motion law of the cavity gyrating flow was verified by the numerical datum.The results can provide a reference for the internal micro flow study of the cavity gyrating flow.
