However, this small increase in TVC performance is also accompanied by a drag 



increase approximately double that of the smaller bulb. On this basis, the smaller 



bulb appears to be the more acceptable bulb shape. The data for the small bulb with 



roughness show substantial increases in TVC inception speed for the lower values of 



C . However, U„/U falls off rather rapidly for the larger C^ values. This trend 

 i-' P P L 



is also present in the data for the roughness alone (no bulb) in Figure 26. In 

 addition, comparison of the data for the bulb with roughness and the corresponding 

 data for roughness alone (Figure 26 — diamond symbols) show that, for C < 0.32, the 



bulb provides no substantial increases in U„/U . However, for C, > 0.32, the bulb 



B p L 



provides an additional 10 percentage points in U„/U . 



P P 



2.1 

 2.0 

 1.9 



3 

 O 

 P 1.7 



< 



iu 1.6 



1 1 



Rg = 5(10)^ 



O LARGE BULB 



O SMALL BULB 



<S SMALL WITH ROUGHNESS- 

 600 tl, 12.7 mm STRIP 

 PRESSURE SIDE TIP 



1.3 



1.2 



0.16 



0.20 



0.24 



0.28 



0.32 

 LIFT COEFFICIENT C, 



0.36 



0.40 



Figure 30 - Tip Vortex Cavitation Inception Speed Ratio as a Function 

 of Lift Coefficient for the Bulbous Tip Foils 



42 



