An investigation of the local receptivity of a Blasius boundary layer to a harmonic vortical disturbance is presented as a step towards understanding boundary-layer receptivity to free-stream turbulence. Although there has been solid experimental verification of the linear theory describing acoustic receptivity of boundary layers, this was the first experimental verification of the mechanism behind local receptivity to a convected disturbance. The harmonic wake from a vibrating ribbon positioned upstream of a flat plate provided the free-stream disturbance. Two-dimensional roughness elements on the surface of the plate acted as a local receptivity site. Hot-wire measurements in the boundary layer downstream of the roughness confirmed the generation of Tollmien–Schlichting (TS) instability waves by an outer-layer interaction between the long-wavelength convected disturbance and the short-scale mean-flow distortion due to the roughness. The characteristics of the instability waves were carefully measured to ensure that their behaviour was correctly modelled by linear stability theory. This theory was then used to determine the immeasurably small initial wave amplitudes resulting from the receptivity process, from wave amplitudes measured downstream. Tests were performed to determine the range of validity of the linear assumptions made in current receptivity theories. Experimental data obtained in the linear regime were then compared to theoretical results of other authors by expressing the experimental data in the form of an efficiency function which is independent of the free-stream amplitude, roughness height and roughness geometry. Reasonable agreement between the experimental and theoretical efficiency functions was obtained over a range of frequencies and Reynolds numbers.

Experiments conducted to determine the resistance of demountable HTS lap joints with variations in compressive stress are reported here. A joint fixture was constructed that enabled the simultaneous testing of multiple joints of different configurations. The joint fixture was installed in a loading facility, comprising a pneumatic press mounted in a vacuum bell jar and connected to a GM cryocooler. The resistance across each joint was measured by means of voltage taps over a range of compressive joint forces.The test results demonstrated that joint resistances less than 2 were possible with only light joint loading.

The development of semi-conductor sensors particularly aimed at gas turbine technology applications is outlined. Methods of manufacture and means of utilizing some of the inherent advantages of this type of sensor are discussed. A novel technique, where miniature sensors are attached directly to the surface where the measurement is required, is described. This technique combines a high surface density of measurement points with a high frequency response capability. Detailed tests of the sensor’s performance have been conducted and results obtained using this technology are presented. The performance tests include frequency response, base strain sensitivity, g sensitivity, and software temperature compensation schemes. Finally, possible future applications for these techniques in gas turbine technology are outlined.

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