Abstract: The precise measurement of skin friction is crucial for the aerodynamic performance optimization of hypersonic vehicles, and the measurement accuracy directly affects the accurate evaluation of the aerodynamic characteristics of aircraft and the engine thrust. In order to solve the problem of skin friction measurements in high-speed and high-enthalpy flows, three types of skin friction balance (SFB) were developed, namely the type I SFB, type II-A SFB and type II-B SFB. A processing scheme for integrated SFB using additive manufacturing technology was proposed and applied to the type II-A and type II-B SFBs. The integrated SFBs can be polished integrally with the test surface, eliminating the misalignment error inherent in traditional assembled SFBs. Therefore, the traditional uncertainty analysis method considering the misalignment in the performance evaluation of SFB measurement is not applicable. An improved uncertainty analysis method was proposed, which systematically identifies the calibration error, structure errors, and signal error, and provides a calculation approach for the combined uncertainty. The previously neglected lip force error was quantified through numerical simulation, and conservative estimates of the structure error were given. To verify the reliability of the above technical approach, the flat plate skin friction measurement experiments were conducted in the JF-12 shock tunnel with the type I and type II-A SFBs. The nominal Mach number of the incoming flow was 7, and the unit Reynolds number was 10^6 m-1. At the 95% confidence level, the calibration uncertainties of the type I and type II-A SFBs are both below 0.2% FS (Full Scale). The measurement uncertainty of the type II-A SFBs is 8.9%R (Reading), outperforming the 9.4%R of the type I SFBs, demonstrating the measurement advantage of the integrated SFBs. In response to the technical demand for direct wall shear stress measurement in supersonic combustion flow environments, the type II-B SFB with both large range and miniaturization characteristics has been developed based on the type II-A SFB, which can be directly adapted to the embedded installation requirements of the internal flow channel of scramjet engine. The first-order natural vibration frequency of this balance is approximately 165 Hz, with a static calibration uncertainty of 0.81%FS at 95% confidence level. It exhibits excellent dynamic response performance and measurement accuracy. Based on this balance, systematic wall shear stress measurement research was conducted in a rectangular scramjet combustor test piece. The measurement results under cold-flow conditions are in good agreement with numerical and classical empirical formula prediction results. The total measurement uncertainty is stably within the range of 5.8%R to 11.4%R at 95% confidence level, verifying the reliability of the measurement system. Under hot-flow conditions, the sudden change in skin friction caused by boundary-layer combustion was directly captured, and the variation pattern is consistent with theoretical expectations. This verifies the feasibility of using the type II-B SFB for direct skin friction measurement in supersonic combustion environments, providing key sensor technology support for the detailed study of skin friction characteristics in supersonic combustion flow channels. The development and engineering verification of specialized SFBs capable of adapting to various extreme flow conditions provide a core sensor technology foundation and credible experimental data support for high-precision measuring of wall shear stress in high-speed, high-enthalpy extreme flow environments.

Key words: integrated skin friction balance, high-speed and high-enthalpy flow, wind tunnel experiment, wall shear stress measurement, uncertainty analysis