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10 May 2006 Detect nozzle deformation by JTFA pattern of jet noise: assessment of the procedure
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As the deformation in nozzle will cause thrust miss aligned and other problems which would degrade the performance of rocket severely, deformation detection will help to correct the ballistic parameters for control and guide of the rocket. Prior or real time detection is important for calculate the ballistic parameters. Rocket noise in active period during rocket launch has close relationship with core length in the exhausted jet flow. The core length depends on the nozzle structure and the combustion situation inside chamber. If the parameters inside chamber are fixed, the core length could be determined by nozzle structure. Thus the jet noise would reflect the change in nozzle structure. Experiments with cold jet flow were conducted to explore the relationship between nozzle deformation and the spectrum pattern of jet noise. Three groups of nozzles with different expansion ratio, length of expand segment, and throat structure were used in the experiment. The spectrums of jet noise for each nozzle under different chamber pressure were obtained as a reference to detect the deformation in nozzles. Then the nozzle was deformed artificially and the jet noise was analyzed by joint time-frequency analysis (JTFA) method. Several JTFA algorithms are used to process the noise data. The joint time-frequency distribution pattern reflects the change in nozzle structure.
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Qiang Xu "Detect nozzle deformation by JTFA pattern of jet noise: assessment of the procedure", Proc. SPIE 6222, Sensors for Propulsion Measurement Applications, 62220P (10 May 2006);

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