Design Of A Dynamic Calibration System For Large-caliber Shock Tube

With the development of high-tech weapons and various types of ammunition, shock wave testing is more and more important and the accuracy requirements are also rising. The transducer shape and structure can change the waveform fluidity of the shock wave during the test of shock wave overpressure in free field, which will inevitably affect the measurement. In order to simulate the real testing environment, it is necessary to place the whole transducer in the calibration facility to perform an overall calibration. Because of its good step-pressure signal, shock tubes are chosen as the pressure calibration device, especially the main device for shock wave pressure dynamic calibration. According to the technical indicators required in the key laboratory improvement project, this paper has been focused on the following work involving the length of large caliber shock tube, the roughness of the tube internal wall, the calibration uncertainty and the acquisition system of the calibration system.(1) Based on the basic theory of flow in a shock tube, from the longest fitted steady- flow duration time both after reaching the incident shock and after the contact surface, we derived the relation of the incident shock Mach number and the length ratio of high and low pressure segments in the shock tube, subsequently worked out the optimal length ratio.(2) Based upon the theory of fluid mechanics numerical simulation, a three-dimension solid model of the shock tube was established. Simulation analysis was conducted on the flow in the shock tube by applying the turbulence model RNG and model. The simulation result is consistent with the theoretical value under the ideal breakage of the diaphragm. We also compared the flow field in the high- and low-pressure segments in the shock tube under different roughness of the shock tube internal wall, thus drew a conclusion that the roughness of the shock tube wall has little impaction the flatness of the shock wave front but great impact on the shock wave decay.(3) Based on the measurement of the uncertainty source, we analyzed the influence of each uncertainty component of the incident step pressure on the whole uncertainty and put forward corresponding measures to reduce the uncertainty.(4) Considered that the data acquisition system of the shock tube velocity transducer in a certain extent influences the accuracy of the calibration system, this paper designed a specified data acquisition system, which mainly includes the data collection and storage circuit design and a host computer software for display and processing based on Lab VIEW.