Skin-friction measurements in high-enthalpy hypersonic boundary layers

• Published in: Journal of fluid mechanics 2003-05, Vol.485 (25), p.1-32, Article S0022112003003975
• Main Authors: GOYNE, C. P., STALKER, R. J., PAULL, A.
• Format: Article
• Language: English
• Subjects: Air flow; Boundary layer; Boundary layers; Compressible flows; shock and detonation phenomena; Enthalpy; Exact sciences and technology; Fluid dynamics; Fluid mechanics; Friction; Fundamental areas of phenomenology (including applications); Heat transfer; Instrumentation for fluid dynamics; Physics; Reynolds number; Supersonic and hypersonic flows; Turbulent flow
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/S0022112003003975

Skin-friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4–6.7, 3–13 MJ kg$^{-1}$ and $0.16\times 10^{6}$–$21\times 10^{6}$, respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1–0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new skin-friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent skin-friction levels were measured to within a typical uncertainty of ± 7%. The systematic uncertainty in measured skin-friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the skin-friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent skin-friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the skin-friction coefficient may be applied.