CHAPTER 6 LPV CLOCKING AERO-PERFORMANCE DATA
6.3.2 Reynolds Number Effects on Time-Averaged Data
Looking at a comparison of Mgroup 1 and MGroup 6 shows the effect due to Reynolds number. To be consistent, a subgroup of each will be used and only include positions C, D, and E since these are the only clock positions these groups share. The time-averaged values for the 50% span locations are plotted in Figure 6.12. One sees no observable effect on the HPV and HPB. One sees a small effect on the LPV, but before
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concluding that this is a Reynolds number effect, one should re-examine the data from Table D.6 and Table D.8, which shows that the corrected speed variation (on average) for these two groups varies from 357.7 to 364.6 rpm/K^.5. This is primarily due to the changes in the absolute value of the time window. Mgroup 1 varies from 357.7 to 363.7 RPM/K^.5 over the same time period variations. Looking only at the variation in Run 9 (clock D) over these same two periods (Figure 6.13), we see a variation similar in size over most of the airfoil (but not quite at the leading edge on the pressure side). For such a substantial change in Reynolds number, if this is a Reynolds number effect, it is quite small. Most likely this difference is due to a pressure ratio and incidence angle mismatch between the two data sets and not due to Reynolds number.
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0 0.2 0.4 0.6 0.8 1
-100 -50 0 50 100
Average of Time-Averages Normalized Pressures At Two Different Reynolds Numbers for HPV 50% Span
(Range Bars from STD of average)
Mgroup 1_TW P Re=4.6E6 MGroup 6_TW M Re=6.4E6 Time Average of Normalized Pressure
% WETTED DISTANCE Note: Only positions C, D, and E
are used in Avg.
0 0.1 0.2 0.3 0.4 0.5 0.6
-100 -50 0 50 100
Average of Time-Averages Normalized Pressures At Two Different Reynolds Numbers for HPB 50% Span
(Range Bars from STD of average)
Mgroup 1_TW P Re=4.6E6 MGroup 6_TW M Re=6.4E6 Time Average of Normalized Pressure
% WETTED DISTANCE Note: Only positions C, D, and E
are used in Avg.
0 0.05 0.1 0.15 0.2 0.25
-60 -40 -20 0 20 40 60
Average of Time-Averages Normalized Pressures At Two Different Reynolds Numbers for LPV 50% Span
(Range Bars from STD of average)
Mgroup 1_TW P Re=4.6E6 MGroup 6_TW M Re=6.4E6 Time Average of Normalized Pressure
% WETTED DISTANCE Note: Only positions C, D, and E
are used in Avg.
Figure 6.12 Reynolds Effect on Time-average Values for Airfoils at 50% span
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0 0.05 0.1 0.15 0.2 0.25
-60 -40 -20 0 20 40 60
Time-Averages Normalized Pressures for Run 9- Clock D At Two Different Time windows Numbers for LPV 50% Span
Average_Run 9_P Average_Run 9_M Time Average of Normalized Pressure
% WETTED DISTANCE
Figure 6.13 Effect of Time Window on Run 9, LPV 50% Span
The same data sets used in Figure 6.12 can be used to show if the Reynolds number has any effect on variations from the average. This will be done only on the LPV as shown in Figure 6.14. In these figures, the colors represent the same clock positions, and the solid symbols are the higher Reynolds number condition. There definitely seems to be a switch from clock D having the highest pressure at the low Reynolds number to Clock E at the high Reynolds number. This variation seems to be consistent across the different spans of the airfoil.
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-15 -10 -5 0 5 10
-50 0 50
Variation In Clocking Due to Reynolds Number LPV 10% Span
(Range Bars are Max Variation on clock D data)
Run 9_P-Clock D Run 10_P-Clock C Run 15_P-Clock E Run 32_M - Clock D Run 33_M - Clock C Run 34_M - Clock E
% Change from Average Time-Averaged Values
% WETTED DISTANCE
Note: Runs 9-15, Re= 4.6E6 Runs 32-34, Re = 6.4E6
-8 -6 -4 -2 0 2 4 6 8
-60 -40 -20 0 20 40 60
Variation In Clocking Due to Reynolds Number LPV 50% Span
(Range Bars are Max Variation on clock D data)
Run 9_P-Clock D Run 10_P-Clock C Run 15_P-Clock E Run 32_M - Clock D Run 33_M - Clock C Run 34_M - Clock E
% Change from Average Time-Averaged
Values
% WETTED DISTANCE
Note: Runs 9-15, Re= 4.6E6 Runs 32-34, Re = 6.4E6
-8 -6 -4 -2 0 2 4
-60 -40 -20 0 20 40 60 80
Variation In Clocking Due to Reynolds Number LPV 90% Span
(Range Bars are Max Variation on clock D data)
Run 9_P-Clock D Run 10_P-Clock C Run 15_P-Clock E Run 32_M - Clock D Run 33_M - Clock C Run 34_M - Clock E
% Change from Average Time-Averaged Values
% WETTED DISTANCE
Note: Runs 9-15, Re= 4.6E6 Runs 32-34, Re = 6.4E6
Figure 6.14 Cocking Effects of Time Averaged Data Due to Reynolds Number
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However, before making the conclusion that we are in fact seeing an effect due to Reynolds number on clocking, it is important to note that the observed differences between positions C, D, and E are not great, and that this variation may be due to slight changes in the blade incidence angle as mentioned above. Using a similar technique, as done with the low-pressure data, the total effect for the two groups will be shown in the following tables.
Time Avg Mgroup 1 Mgroup 6
Straight Avg D C E D C E
All spans 0.169 0.168 0.160 0.173 0.169 0.175
10% 0.159 0.157 0.147 0.164 0.157 0.165
50% 0.173 0.170 0.164 0.177 0.174 0.180
90% 0.178 0.181 0.174 0.180 0.180 0.182
Integral
10% (56% of airfoil) 0.150 0.148 0.140 0.155 0.148 0.156 50% (70% of airfoil) 0.172 0.169 0.163 0.176 0.173 0.179 90% (83% of airfoil) 0.178 0.181 0.176 0.180 0.180 0.182 Integral on Same Areas
10% (70% of airfoil) 0.187 0.184 0.174 0.193 0.185 0.195 50% (70% of airfoil) 0.172 0.169 0.163 0.176 0.173 0.179 90% (70% of airfoil) 0.183 0.187 0.181 0.185 0.186 0.188 Average (all spans) 0.181 0.180 0.173 0.185 0.181 0.187 Table 6.4 Integral Effect for Time-Averaged Data based on Reynolds Number Here the effect observed in the figures is a little easier to see. The maximum time- average pressure seems to have moved from position D to position E as the Reynolds number changes, but again the changes are not as significant as the spanwise distribution.
The same analysis done on the percentage variation does not seem to produce any clear results, which once again points out the benefits of using the raw data (as opposed to the percentage change) to look at these “total” effects. Currently we will reserve judgment on this Reynolds number effect and look for changes due to Reynolds number in other techniques to see if this trend is continued.
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% Var. of Time Avg Mgroup 1 Mgroup 6
Straight Avg D C E D C E
All spans 2.10 1.30 -3.40 0.35 -1.82 1.47
10% 3.33 1.66 -4.99 1.27 -2.97 1.71
50% 2.40 0.41 -2.81 -0.07 -1.86 1.93
90% 0.30 1.63 -1.93 -0.44 -0.34 0.78
Integral
10% (56% of airfoil) 2.96 1.35 -4.31 1.28 -3.06 1.78
50% (70% of airfoil) 2.16 0.72 -2.88 0.02 -1.61 1.59
90% (83% of airfoil) -0.09 1.53 -1.44 -0.58 -0.29 0.87 Integral on Same Areas
10% (70% of airfoil) 3.69 1.68 -5.37 1.59 -3.81 2.22
50% (70% of airfoil) 2.16 0.72 -2.88 0.02 -1.61 1.59
90% (70% of airfoil) -0.24 1.81 -1.57 -0.67 -0.24 0.92
Average (all spans) 1.87 1.40 -3.27 0.31 -1.89 1.57
Table 6.5 Integral Effect for Percent Variation of Time-Averaged Data based on Reynolds Number