Thermal Zero Shift Correction of Strain-Gage Balance Output in the JAXA 2m X 2m Transonic Wind Tunnel

摘要

In the JAXA 2m x 2m Transonic Wind Tunnel, the thermal zero shift of strain-gage balance output caused by an unfavorable increase of flow temperature during a run influences the measurement accuracy of the balance. Temperature change in the balance and thermal gradients across the balance cause the thermal zero shift of the balance. Balance outputs for zero are conventionally corrected by the linear estimation from the no-wind data just before the run and the renewed no-wind data immediately after the run. In the correction method, the error increases at the beginning of the run, because the abrupt change in stagnation temperature causes balance outputs for zero to shift drastically. To reduce and correct the thermal zero shift of strain-gage balance output in force measurement, a preheating and checkpoint correction method is established. Variations of strain-gage balance output for zero are investigated during a run to confirm the effectiveness of the new method. Several series of wind tunnel tests with an ONERA-M5 calibration model and an AGARD-B calibration model are conducted to compare the new correction method with the conventional one. Results show that the error of the drag measurement from run to run is reduced to -2 drag counts. Moreover, the new correction method is improved by using a six component internal balance with strain-gages combined with thermocouples to be applied to various kinds of models and sequences of test conditions.