Research on the influence of wind tunnel background pressure interference effects on sonic boom measurement and its suppression techniques

Wind tunnel test is a crucial means for evaluating the low sonic boom characteristics of supersonic civil aircraft and validating related design prediction methods. Investigating the influence of wind tunnel background pressure (WBP) on sonic boom measurement and developing suppression techniques are essential for establishing reliable wind tunnel test methodologies for sonic boom measurement. This study focuses on the unique spatiotemporal distribution and coupling characteristics of WBP. Through theoretical analysis and experimental verification, the mechanism of its influence on sonic boom measurement is explored. The independent effects of WBP distribution in the time and spatial domains under approximate decoupling conditions are successfully revealed. A fine-control strategy for the settling chamber total pressure is proposed, which employs a composite control method combining feedforward and PID feedback to suppress temporal influences. This strategy improves the total pressure control accuracy from 0.2%～0.3% to better than 0.15%, significantly reducing the temporal non-uniformity of WBP. By integrating specific test arrangements, selecting the region with minimal fluctuations as the test section and applying spatial averaging data processing, a comprehensive strategy is formed. This effectively enhances the ability to distinguish and extract weak sonic boom signals in environments with high spatial disturbances. Applying this methodology to low sonic boom supersonic civil aircraft benchmark model tests in a 2 m supersonic wind tunnel shows that the near-field sonic boom measurement results are in good agreement with those obtained from continuous wind tunnels of similar scale internationally. The deviation of the head shock peak is less than 3%, validating the effectiveness of the proposed framework in mitigating the influence of wind tunnel background pressure on sonic boom measurement.