| Dynamic pressure calibration is the key to guarantee the precision of dynamic pressure measurement. Shock tube is most widespread in dynamic pressure calibration technology and many countries have chosen shock tube as the recommended technique to accomplish dynamic pressure calibration. Therefore research to improve the calibration precision of shock tube is meaningful. This paper is to research a few key problems which affecting dynamic pressure calibration precision of the shock tube. The primary research methods used in this paper are theoretical analysis, experimental verification and numerical simulation. The major work and conclusions are as follows.First, the dynamic pressure calibration technique of shock tube and the method to obtain the dynamic characteristics of the pressure sensor were introduced. And then the derivation of the classical Rankine-Hugoniot overpressure formula for calculating the amplitude of the dynamic pressure signal was introduced. Then analyzed three factors lead to calculation error. They were the change of K value of medium specific heat ratio, energy loss in the propagation of shock wave and the non-ideal gas state of the medium after shock wave. And error caused by the non-ideal gas state was greatest. Choose the practical Virial equation which contains air humidity parameter to calculate the actual gas compression factor. Substituted compression factor in the modified overpressure formula and the result obtained.by the modified formula was more close to the measured values of the shock tube. The experimental results have showed that the modified overpressure formula was effective to calculate the actual gas overpressure.Use the finite element method to study some key flow-field problems of shock tube. With the commonly used fluid mechanics finite element software FLUENT as the platform, simulation study was carried out on the tube section shape, the opening size of the membrane rupture, the shock attenuation along the process and the installation of the sensor. The simulation results of tube section shape problem have provided reference for the design and manufacture of shock tube. The results of the opening size of membrane and the shock attenuation were of some reference value for the experimental setup of the shock tube. The simulation results of the sensor installation have provided help to analyze the measurement data and were helpful to analyze the abnormal data and find the possible reasons. Simulation of these key flow-field problems were of practical significance.Point at the stress wave interference generated in the shock tube experiment or the actual blast field shock wave test. Experimental study on stress wave effect of pressure sensor was carried out using the SHPB device. In the experiment, the pressure sensor was installed on the transmission bar laterally. Using the drop hammer loading, the stress wave could be input into pressure sensor laterally. When the hammer's releasing angle increases, the input stress amplitude and pressure sensor's output increase, the transmission rate of the two also increases. The maximum sensor's output value in the test was more than 10% of the full range of the sensor and it was very harmful to the sensor. The stress wave isolation base was manufactured by two kinds of high polymer materials, Nylon and Plexiglass. Experiments were carried out on SHPB and the results have showed that the Nylon isolation base could effectively isolate the interference caused by stress wave. The input stress amplitude, sensor's output signal amplitude and the transmission rate were significantly reduced. This stress isolation scheme was of reference value in practical measurement. At last, mathematical simulation was carried out using the constitutive model of polymer materials. Constructed stress wave signal was input in the constitutive model and the output was similar to the measured one. At the same time, the results had provided reference for the selection of isolation materials. |
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