Abstract: Experiments of flow visualization and dynamic unsteady pressure measurement with pitchingup delta wings are carried out in a water channel and a wind tunnel, respectively in order to study the flow and frequency characteristics of the leading-edge vortices over a delta wing undergoing pitching upstop motions. The result of the flow visualization test shows that in the case of pitching upstop movement the vortex breakdown position is dependent on the range of incidence at which the wing is subject to pitching upstop and the reduced frequency k. Analysis of the pressure signal measured in the wind tunnel shows that when the delta wing is subject to pitching up, the nondimensional spiral wave frequency at nominal incidence in postbreakdown is higher than that at the corresponding static state, and that the larger the kis, the higher the nondimensional spiral wave frequency will be. The same conclusion is obtained with different sweep delta wing configurations.

Key words: delta wing acrcraft, reduced frequency, pitchingup, vortex breakdown, frequency characteristics