Uncertainty analysis method of skin friction balance measurements in shock tunnel

Skin friction balance (SFB) is an important means to evaluate the wall shear stress. Analyzing its measurement uncertainty has engineering value. The current SFB measurement error analysis methods have some deficiencies, so they need to be further optimized and improved. The SFB measurement uncertainty includes calibration uncertainty, measurement uncertainty caused by the SFB structure, and signal uncertainty. The error sources in the calibration uncertainty analysis are identified and analyzed. In the analysis of measurement uncertainty caused by an SFB structure, the commonly neglected lip force error is discussed, and its estimated value is given through simulation. The estimated value is applicable to the flow with non-dimensional pressure gradient of |Pgn = (dp/dx)·D/τ| ≤ 5.2. In addition, an integrated processing scheme for eliminating the misalignment error is proposed. The calculation method and key problems of signal uncertainty are discussed. The uncertainty analysis method is applied to the skin friction measurement experiments in JF-12 shock tunnel. The measurement uncertainties of the assembled SFB and the integrated SFB are ±9.4%R and ±8.9%R at 95% confidence (R is Reading value), respectively, indicating the advantage of the integrated SFB in measurement.