Analysis and experiment of compression wave generated by train entering tunnel entrance hood

An analysis and a model experiment are performed on the compression wave generated by a train entering a tunnel with an entrance hood, which is a prevailing countermeasure for reducing the micro-pressure wave emitted from a Shinkansen tunnel portal. The tunnel entrance hood is a structure for extending a tunnel and has openings on its side walls or roof for decreasing the pressure gradient of the compression wave generated by train entry. The hood design has principally been performed through model tests since the three dimensionality of flow field is generally important. Thus, a more efficient design method is required. In this paper, an analytical method based on the aeroacoustic theory developed by Howe is applied to a short "acoustically compact" hood having a window on its side wall. Analytical results are in good agreement with experimental results including the effect of train offset in a double-track tunnel. It is also clarified by analysis that the performance of the entrance hood is greatly affected by the relative length of the train nose to the distance between the window and the hood entrance.