Passive Mass Injection Tip 



Passive Mass Injection (PMI) is a new concept and again, as in the case of the 

 roughness, the design was guided primarily by a basic knowledge of the tip flow. 

 This TVC delay mechanism is governed by the viscous interaction of the fluid flow 

 exiting from the PMI channel with the tip vortex flow. The mass flow through the 

 channel is dependent upon the differential pressure between the entrance and exit of 

 the channel, including the effective component of free stream stagnation pressure. 

 The channel exit was located on the tip suction side at the observed attachment point 

 of the tip vortex — Figure 15 — and aligned with the vortex core. The entrance of the 

 PMI channel was located on the tip pressure side to align the channel, within the 

 physical constraints of the foil tip geometry, with the free stream in such a manner 

 as to maximize the channel mass flow. Two channel diameters were investigated, PMI 

 1—0.125 in. (3.2 mm) and PMI 2—0.188 in. (4.8 mm). 



The effects of the PMI channels on the foil lift and drag were well within the 

 experimental accuracy. Again, this result is expected, considering the small size 

 of the channels. 



The cavitation characteristics of the PMI foil are given in Figure 31. For the 

 PMI 1 and the lower values of C , C < 0.2, the data indicate that the PMI offers no 

 improvement — the TVC inception data coincide with that of the parent foil. However, 

 for larger C , C > 0.2, the data show that the PMI is effective and the data again 

 agree with Equation (1) for k = 14.1, representing an increase in the TVC inception 

 speed of 12 percent relative to the parent. These results indicate that, for this 

 channel configuration, the mass flow through the channel is insufficient for C 

 < 0.2. The low a conditions for the PMI 2 were not achieveable; but as C increases, 

 the PMI 2 performance improves as compared to PMI 1. This indicates that PMI 2 

 provides larger mass flows into the vortex core as expected. The results from 

 Figure 31 also show some local cavitation associated with the PMI channels; for C 

 <_ 0.2, this cavitation was located inside the PMI channels and for C > 0.2, the 

 cavitation initiated at the downstream edge of the channel exit, on the foil suction 

 side. This problem may possibly be alleviated through refinements in the channel 

 geometry. 



The PMI was also evaluated with roughness. For this investigation, as with the 

 bulb, 600-micron roughness was applied to the PMI 2 pressure side tip over the area 



43 



