Modelling unsteady annular downflow in vertical building drainage stacks

J. A. Swaffield, A. Thancanamootoo

    Research output: Contribution to journalArticlepeer-review

    11 Citations (Scopus)


    Annular water flow down building drainage stacks generates the air pressures that cause trap seal siphonage. Current steady flow based design practice avoids this by limiting annular flow thickness to 1/16th of the stack diameter. Annular stack flows are highly unsteady. Numerical modelling, via the method of characteristics solution of the continuity and momentum equations, results in flow capacity reassessment due to the attenuation of appliance discharges. Local annular flow thickness gradients necessitate the use of conformal transformation within the characteristics model. Model predictions were validated by laser measurement of annular flow velocities under representative unsteady flow conditions. © 1991.

    Original languageEnglish
    Pages (from-to)137-142
    Number of pages6
    JournalBuilding and Environment
    Issue number2
    Publication statusPublished - 1991


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