Design of a tunnel entrance hood for high-speed trains

Abstract Micro-pressure waves (MPWs) are radiated from tunnel exits when trains enter the tunnels at high speeds. Because MPWs produce infrasound and audible noise around the tunnel portal, they should be suppressed to mitigate its environmental impact. Hood installation at the entrance portal of tunnels is a common MPW suppression method. However, an increase in train speed mandates a corresponding increase in hood length. This paper reports the development of a tunnel entrance hood that allows a decrease in the extension required at high speeds. Calculations based on the acoustic theory were used to investigate an economical hood-extension method, and model experiments were performed to validate predictions. Results revealed that increasing the cross-sectional area of the extended part of the hood over that of existing hoods can effectively shorten the overall hood length. As a result, the first optimum cross-sectional area of the hood was greater than that of the tunnel by a factor of 3.9, and the second optimum value demonstrated a corresponding factor of 3.2. Based on this finding, the proposed hood design can be more economical than existing hoods.