Time-dependent features of the wall static pressure field beneath vortices modeled in a Ward-type vortex simulator have been investigated with emphasis on measurements of maximum surface pressure deficit. A pressure-measuring system was devised for this purpose which is capable of resolving important transient features of the surface pressure field in an essentially undistorted form, and measurement techniques were employed which reduced the influence of vortex wander. Measurements of maximum surface pressure deficits and their dependence on flow rate and geometry are presented, as well as a detailed study of the magnitudes of the maximum surface pressure deficits as a function of swirl ratio. Also presented are surface pressure distributions in individual subsidiary vortices in a multiple vortex flow.
The greatest deficit pressures are found to be associated with the penetration of the vortex breakdown to the surface. The magnitude of the surface pressure deficit is closely related to the. square of the mean vertical velocity of the upflow and also is dependent on swirl ratio. The pressure deficits in the subsidiary vortices presented are variable but range up to three times that found at the center of the “parent” vortex.