An investigation of the hysteresis of vortex breakdown over pitching-up deltawings is presented. Based on experiments, there are two main reasons which can be usedto explain the hysteresis of vortex breakdown. One is the time or phase lag due to the ini-tial suPerPOsition of linearized small disturbance, which enlarges the range of the incidenceof keeping attached flow and postpones the initial incidence of vortex breakdown. Theother is the reduction of adverse pressure gradient due to the periphery centrifugal instabil-ity after the concentrated vortex has come into being, which is the key reason of hystere-sis of vortex breakdown- The structure of vortex over a pitching up delta wing can be di-vided into three layers, which is not a significant a1teration compared with that of vortexover a static delta wing.
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