The operation of heavily loaded diesel locomotives in long tunnels is a problem due to the inability to provide adequate air flow into the annulus between the train and tunnel walls. The existing solutions are expensive, sometimes ineffective and prone to damage. To understand the dynamics of the air flow in a 2 mile long tunnel, measurements were taken of the flow ahead and behind the train and in the annulus between the train and tunnel walls. Air flow measurements were taken from a cross section at each end of the tunnel 50 feet in from the portals. Air flow instruments were mounted on a swing arm on the tunnel wall to record data while the train was in the tunnel. Flow, temperature and flow direction were measured near the tunnel wall to measure the annulus air properties as the train passed the instrumentation. Results from these tests show that for freight trains the annulus air flow in the direction opposite the train is small, resulting in little flow of fresh air past the locomotive. For more aerodynamic trains such as a passenger train there is a definite annulus air flow that is opposite the train direction. The flow pattern ahead of the train is a well developed parabolic pattern whereas the flow behind the train is essentially uniform across the cross section of the tunnel. The momentum of the air after the train exits the tunnel and the natural draft of the air through the tunnel greatly affect the speed at which the exhaust gases are purged from the tunnel. These data are being used to develop a model to predict air flow patterns in a tunnel.
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