this one has received the greatest attention (see Table 1). Basically, 

 three mass ejection techniques are reported in the literature: linear or 

 axial mass ejection, directly into the vortex core, with either an (a) up- 

 stream or (b) downstream facing jet, and (c) spanwise mass ejection with an 

 outboard facing jet. These injection schemes are illustrated in Figure 4. 

 Linear mass ejection increases the core axial pressure and accelerates the 

 vortex decay through the viscous interaction of the two flows. Spanwise 

 mass ejection blocks or interrupts the vortex rollup as it forms along the 



tip chord and results in improved wing performance. 



22 23 

 Linear mass ejection studies ' have repeatedly demonstrated the 



concept effectiveness with regard to dissipation of the vortex core energy 



with little or no effect on performance. The results of some linear mass 



22 

 ejection wind tunnel studies are given in Figure 10 which shows the vari- 

 ation of vortex core relative vorticity intensity Q,/Q,^ as a function of jet 

 momentum coefficient C. with both an upstream and downstream facing jet, for 



various values of z/c. As indicated, for fixed values of C. the upstream 



J 

 facing jet appears to be more effective in reducing the vortex vorticity 



than the downstream one. However, the upstream configuration would require 



higher delivery pressures in order to overcome the opposing free-stream 



stagnation pressure. 



24 

 Spanwise mass ejection has been shown to be an effective means of 



altering tip vortex rollup and increasing wing performance. As shown in 



24 

 Figure 11, the spanwise ejection data indicate that, within one chord 



length downstream of the wing trailing edge, the peak rotational velocity 

 is reduced by approximately a factor of 5, and the vortex sheet wrapup has 

 been delayed beyond one chord length downstream. This is accompanied by an 

 induced drag reduction of approximately 15 percent at operational lift co- 

 efficients. Although these results are impressive, the spanwise mass 

 ejection rates are an order of magnitude higher than the corresponding 

 linear rates. 



There is little data on the correlation between the water mass 

 ejection rates required to delay tip vortex cavitation and the reported air 

 mass rates required to reduce vortex core vorticity. Nevertheless, tip 



22 



