Example of propeller blade forces measurement due to cavitation and ventilation. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n°233896.
the 3 forces and the 3 moments. Because every calibration term has its contribution to the overall accuracy of the balance only the significant terms of the 6 by 12 calibration matrix are selected. One could say: less is more.
After the calibration several check loads are applied to the balance. These check loads are based on the expected measured values during the tests. If the accuracy of the check loads’ measurements is of the same magnitude as the accuracy of the calibration it confirms that a good calibration matrix has been determined with a high degree of certainty (see table).
Applications We have applied this special balance in several projects on podded propulsors. We found that propeller loads in off-design conditions can be considerably higher than in design condition. This can have an impact on the maintenance interval and the maintenance cost of the drive train of the propeller. Therefore, these measurements provided highly relevant information.
Currently this balance is being used to measure the dynamic propeller blade loads in the TT JIP, which is focusing on the development of low noise tunnel thrusters. Due to the irregular flow in the thruster tunnel and cavitation, the hydrodynamic blade loads have a dynamic character. This balance, in combination with the propeller blade, has a high stiffness, so these high frequency loads can be measured.
Percentage accuracy based on the maximum applied calibrated loads Fx Fy Max load range U95 2 RMSE 275 N 0.17% 245 N Fz 245 N Mx My Mz 10 Nm 15 Nm 15 Nm 0.06% 0.11% 0.13% 0.09% 0.11%
Measuring setup with balance (1) and bypass (2)
report
19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28
