Tunnel ventilation fans, classically, must have the ability to both supply and extract air from a tunnel system, with the operator�s\r\nchoice dependent on the tunnel ventilation system�s operating mode most appropriate at any given point in time. Consequently,\r\ntunnel ventilation fans must incorporate a reversible aerodynamic design which limits the maximum fan pressure rise. This paper\r\npresents three high pressure reversible fan concepts. These comprise a two-stage counter rotating fan, a single-stage high speed\r\nfan, and a two-stage fan with a single motor and impeller on each end of the motor shaft. The authors consider the relative merits\r\nof each concept. The third concept offers the most compact fan, transform, silencer, and damper package size. The authors discuss\r\nthe mechanical design challenges that occur with a two-stage fan with a single motor and impeller on each end of the motor shaft.\r\nThey present and consider a selected motor bearing arrangement and casing design for maintainability. Finally, the authors present\r\nboth prototype fan and full-scale package aerodynamic and acoustic performance, before discussing the challenges presented by\r\nhigh temperature certification in accordance with the requirements of EN 12101-3: 2012.
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