The aeroacoustic noise caused by pantographs is one of the dominant wayside noises of high speed trains to make an obstacle for further speed-up. In particular, the panhead significantly influences the aeroacoustic characteristics of pantograph. The purpose of this study is to visualize the dipole noise source distribution around the panhead and clarify how the shape of the panhead affects its characteristics. The dipole noise source distribution is estimated by Howe's vortex sound theory from flow field quantities obtained through numerical simulation. This paper describes the result of visualizing the dipole noise source distributions around three types of panheads, which show that the size of separation region and the existence of reattachment strongly influence the aeroacoustic characteristics of panhead.

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The advanced CT (computerized tomography) reconstruction technique for measuring an instantaneous three-dimensional distribution of chemiluminescence of a turbulent premixed flame is accomplished. In the technique, first, instantaneous two-dimensional images (projections) of an objective flame are simultaneously taken from forty horizontal directions with a forty-lens camera. Next 550 horizontal CT images, which are reconstructed from the projections by MLEM (maximum likelihood expectation maximization) algorithm, are vertically accumulated, resulting in an instantaneous three-dimensional distribution of flame-chemiluminescence. Results for a propane-air fuel-rich-premixed turbulent flame are as follows. The flame front is observed to be a thin wrinkled luminous region of 0.6 mm in thickness. The three-dimensional result clearly shows that the cusps observed in horizontal cross-sections correspond to ridges of the three-dimensional flame front. The luminosity is quenched at the ridges by Lewis number effect. Finally, various types of display of three-dimensional distribution are performed to demonstrate the three-dimensionality of data acquisition.

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