Study on Forms of Vortex Breakdown over Delta Wing

Abstract

Visualization test is performed at the water channel of BUAA. The vortex core is visualized by dye injection from a small tube located upstream the apex of a delta wing. The test results are recorded by a video camera connected to a computer and processed by Photoshop software. The test shows new findings in the following respects: (1)Besides the well known spiral and bubble forms of vortex breakdown, there are 3 other forms of vortex breakdown over delta wing found in the test. They are the frog-jump form, the double spiral form and the filiform spiral form.(2)It has also been found that there is a transition from the spiral form to the bubble form and then back to the spiral form in the test. Therefore it shows that the spiral form vortex breakdown over delta wing is often observed.(3)In a certain sense it can be said that the bubble form of vortex breakdown is a special case of the spiral form type. There is no essential difference between them. For the bubble form of vortex breakdown, there are branches of the vortex core and many elements carrying vorticity separated from the vortex core. However, there is at least one vortex filament that forms a spiral or a complex warping shape.