Abstract:
Detailed measurements, including surface-pressure distributions, shock-wave photographs and observations of boundary-layer separation, have been made over a wide range of incidence in the National Physical Laboratory 20-in. x 8-in. High-Speed Wind Tunnel on the Goldstein 1442/1547 aerofoil NPL 177, previously tested at lower incidences in this tunnel. The tests have shown that with standard models of 5-in. chord the stall can be covered for Mach nmnbers up to nearly 0.8 unless it is delayed beyond the usual incidence range, as for Mach numbers above 0.7 for the present section. For these cases, however, it should still be possible to cover the useful range of CL which is often limited by other considerations, e.g., pitching-moment coefficients. The observations enable the effects of compressibility on CL max and on the nature of the stall to be studied in detail for the two-dimensional case. The pitching-moment coefficients, also, can be integrated from the pressure distributions. Since the main purpose of experiments of this type is to provide qualitative explanations of the compressibility effects, the limitations on the accuracy of the results due to tunnel interference and the fairly low Reynolds numbers (1.0 to 1.8 x 10power6) are not likely to detract seriously from their value.
