This research focuses on a desensitization method to develop a wide-range FBG sensor for extra-large strain monitoring, which is an essential requirement in large scale infrastructures or for some special occasions. Under appropriate hypotheses, the strain transfer distribution of wide-range FBG sensor based on the shear-lag theory is conducted to improve the accuracy of extra-large strain measurements. It is also discussed how the elastic modulus of adhesive layer affects the strain transfer rate. Two prototypes in different monitoring ranges are designed and fabricated by two layers of steel pipe encapsulation. The presented theoretical model is verified by experimental results. Moreover, it is demonstrated that experimentation in regards to the calibration of the wide-range FBG sensor, improved the amplification coefficient up to 2.08 times and 3.88 times, respectively. The static errors are both calculated and analyzed in this experiment. The wide-range FBG strain sensor shows favourable linearity and stability, which is an excellent property of sensors for extra-large strain monitoring.
In order to obtain the cold flow structures inside a model scramjet combustor, direct-connected experiments have been conducted on the inlet Mach number of 2.0. The length to height ratio of the isolator is 6 and 8. The static pressure along the wall is measured with varied back pressure. The Schlieren technique is employed for visualizing the typical shock train structures in the model. The results indicate that the flowfield in the scramjet combustor is rather complicated because of shock wave/boundary layer interaction. The first shock of the normal shock train is bifurcated at the foot, while the subsequent shocks are seen to be of nearly normal shock. Each successive shock is weaker. The shock train moves towards the isolator entrance as back pressure increases. The position of the leading edge of shock train is sensitive to the pressure variation. The isolator of Liso/ h=8 can sustain pressure rise better than Liso/ h=6.
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