Real-time Diagnosis of Flow by Using Pressure Wave

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The puropose of the present research is to defvelop a flow diagnosis method on the basis of the numerical calculation on the computer. The flow diagnosis means detecting and identifying obstacles or cavities included in the flow field of pipes or fluid machines. At first, basic research wag performed for* a simple-shaped closed tank filled with water before general flow passage is treated. A small electric discharge with high energy was generated in two kinds of rectangular tanks, i. e., one made of acrylic resin and the etlier made of brass, and impulsive pressure wave was generated by sudden generation of a bubble due to the discliarge. Stable generation of the bubble, correct synchronization of a discharge circuit and a sensing circuit, receiving of signal having very high frequency, and high speed data access to the computer using A/D converter were achieved and highly accurate measurement of flow was possible. According to the results calculated from the data, it was shown that a one-dimensional method gives a satisfactory solution for an obstacle of simple shape (e. g., sphere). Although the actual shape of pressure wave front is unsteady and complex, the one-dimensional geometric - acoustics gives a solution with high accuracy if the wave fronts are considered of passing through, refracting on and diffracting around the obstacle body. However, in calculating the reflection wave from the wall boundar the one - dimensional solution was not adequate but, the reflection property due to acoustic impedance of the wall should be considered correctly., On the other hand, in the case of obstacle body of complex shape, three-dimensional inverse solution. to the wave equation must be calculated. In the present research, we proposed a three-dimensional boundary element method which gives high accuracy solution to the wave equation. The rail-time identification of three-dimensional obstacles is under development and we plan to report the results.