Study on some breakdown forms and characteristics of leading edge vortex over delta wings

Since the discovery of vortex breakdown phenomenon, manytheoretical and experimental studies have been conducted. However, up todate the understanding of vortex breakdown is not enough or comprehensive.Vortex breakdown is an unsteady process and a breakdown vortex has verycomplex structure. The vortex breakdown phenomenon is concerned with afighter aerodynamic characteristics and buffeting. Farther investigation onthe vortex breakdown phenomenon is very important. It is well known thedominate vortex breakdown forms over delta wings are spiral and bubble form.However many other forms of vortex breakdown have been found in thevortex flow in a tube. A lot of flow visualization on vortex breakdown overdelta wings show that the spiral breakdown form is a dominant form. Othershave found that there are two new forms of vortex breakdown: one is doublespiral and another is filiform spiral form, which appears on delta wingswith smaller sweep angle. Recent years particle image velocimeter (PIV)technique is developed rapidly and applied in flow measurement. At certaindegree quantitative measurement of vortex breakdown phenomenon could beconducted.Based on experimental results of flow visualization and PIV measurement somebreakdown forms and characteristics of leading edge vortices over deltawings are analysed and discussed in this paper. It is shown that for spiralbreakdown the helix sense of the vortex core is opposite to the direction ofthe main vortex rotation and double spiral vorticity distributionperpendicular to the vortex axis is identified. Besides that different ideafrom existed explanation in lot of papers about spiral wave mechanism inbreakdown vortex flow is also presented.