Nowackt and Sharma 
ferent methods of averaging. The measured nominal wake is conven- 
tionally averaged over the disk on a volume flux basis, while the 
mean effective wake is measured by the propeller as a calibrated 
thrust (or torque) generating device which tends to put maximum 
weight near the radii where the circulation is a maximum, The follow- 
ing table, a by-product of our calculations, is likely to shed some 
light on the relative importance of these two effects. 
Effective 
Speed-length Measured Corrected 
parameter nominal nominal wake 
wake wake 2 
Simu-| Meas- 
lated | ured 
~ 
Ww w 
w etl 
4.0 [0.354 | 0.208] 0.230 | 0.704|/ 0.146| 0.162 |0.153| 0.145 
7.0|0.267 | 0.291| 0.322 |0.892 | 0.259) 0.287 |0.291 | 0.285 
12.5 |0.200 | 0.304| 0.370 | 0.933 | 0.284] 0.346 | 0.377 | 0.360 
First, note that the wake corrector k is a measure of the 
true physical difference between nominal and effective wake since, as 
explained earlier, it was determined by trial and error as the requir- 
ed multiplier of the measured nominal wake in the computer program 
to ensure that the simulated and measured thrusts were equal. This 
difference is here seen to vary from -7% at the lowest Froude 
number to -30% at the highest. That it is strongly negative, suggests 
that the viscous effect mentioned above was probably dominant in this 
case. Second, the residual difference (up to +33%) between the cor- 
rected volume average wake kw and the thrust average wake wer 
must be attributed to the difference in the methods of averaging. Note 
that this spurious effect is greatest at the lowest Froude number 
where the concentration of bound circulation over the inner radii was 
also the most pronounced. Third, the good agreement between the 
computer simulated and the experimentally measured mean effective 
wake is rather encouraging. Fourth, note that the effective wake is 
much better approximated by the corrected nominal wake at 0.7 
radius, kw(. 7Rp): than by its disk average, kw. This observa- 
tion has direct relevance to the design of wake-adapted propeilers. 
Finally,asa word ofcaution, it should be noted that the relative ma- 
gnitudes of the nominal and effective wakes as well as the quantitative 
rankings of the different effects found here may be peculiar to this 
model and therefore should not necessarily be generalized. 
To complete the discussion of wake, Fig. 28 shows the meas- 
ured versus calculated wake as.a function of Froude number. The fol- 
lowing quantities are plotted: 1) The disk average of the measured 
1866 
