| This study focuses on the formation of the vortex breakdown over the wings. The objective of this study is twofold: (1) to propose the new physical mechanism of the formation of the vortex breakdown, and based on this, (2) to control and suppress the vortex breakdown over the delta wings. The self-induction mechanism proposed here seeks the explanation of the vortex breakdown to the spiraling structure of the vortex emanating initially from the apex of the delta wing. The self-induction among the spiraling vortex filaments comprising the apex vortex transforms it to the vortex breakdown. In self-induction, two key ingredients, the initial straightness of the apex vortex and the existence of the vorticity gradient, are found to trigger the formative process of vortex breakdown. From an analytical model and numerical simulation, several observable features during the transient course have been identified. Transient experiments using different techniques were conducted and compared with the theory, the results of which are found to be favorable. We applied the theory to the occurrence of steady-state vortex breakdown over flat plate wings with straight leading edge. It was found that vortex breakdown can form even over swept wings at the certain conditions. Also in this special case, the new semi-empirical scaling parameter ‘swirl angle’ is introduced to correlates the position of vortex breakdown. Finally, based on the theory, we successfully employed various means to control and suppress vortex breakdown over the delta wings. |
