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To get the useful information for a ventilation in tunnels, two-dimensional turbulence flow fields around trucks in tunnels are, as the first step, calculated numerically, while changing the vehicular gap and ejecting speed of gas exhausted from the rear of truck. In addition, to compare the calculated and measured results, the flow patterns in tunnel are visualized by an optical method of laser light sheet and pressure distributions along to center line of the truck are measured by a pressure transducer. Consequently, relationships between the flow and diffusion patterns of exhausted gas and aerodynamic characteristics around the truck are discussed for various vehicular gaps. Furthermore, the pressure coefficients and flow patterns obtained by calculation are found to be in reasonable agreement with those obtained from measurement.

For the past several years, construction of Japanese road network has maintained a rapid pace, but those roads, having many automotive tunnels, are affected by mountainous topography. The air pollution in tunnels by exhaust gases from cars, especially those from large-size vehicles, has become problematical in Japan. The purpose of this paper is to clarify the flow behavior, especially wake structure behind trucks, and their aerodynamics characteristics at overtaking in road vehicle tunnels with digital image processing technique and three dimensinoal numerical analysis.