Aerodynamic drag on trains in tunnels .2. Prediction and validation

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    Abstract

    The principal sources of aerodynamic drag on simple trains in tunnels are (a) surface skin friction and (b) stagnation pressure losses at the nose and tail. On sufficiently long trains, the first of these is dominant. On shorter trains, local losses can be more important.

    This paper seeks to provide a theoretical basis for predictions of the dependence of drag on the train/tunnel blockage ratio, attention being given to tunnel resistance as well as to train resistance. Hitherto, most predictions have relied on empirical formulae.

    It is shown that the train skin friction coefficient varies approximately linearly with the blockage ratio, beta(z). The dependence increases with increasing train roughness. The nose loss coefficient k(N) is shown to be smaller than 0.1 for reasonably streamlined noses. An approximate relationship between k(N) and beta(z) is hypothesized. The tail loss coefficient k(T) is shown to be approximately equal to beta(z)(2) for poorly streamlined tails. A tail shape coefficient is introduced for use with more streamlined tails.

    Original languageEnglish
    Pages (from-to)39-49
    Number of pages11
    JournalProceedings of the Institution of Mechanical Engineers Part F-Journal of Rail and Rapid Transit
    Volume210
    Issue number1
    Publication statusPublished - 1996

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