Water column separation during pipeline rapid filling is explored numerically. A shock fitting based model is utilized in order to conduct numerical experience. The model applies the well-known method of characteristic on a dynamic computational network whose number of cell increases during the simulation. DGCM (discrete gas cavity mode) is used to treat the column separation in the model. Extensive numerical experience has led to the identification of three new sources under which column separation could be induced during pipeline filling. In the first source a 'V' shape profile following a knee point of the pipeline gives rise to column separation. Following the formation of cavitating flow at knee point, the descending leg of the profile causes expansion of the cavity at knee point while the ascending leg of the profile is responsible for cavity contraction and collapse. The resulting cavity collapse can generate huge water hammer pressures that can detrimentally affect the whole length of connected pipeline. Numerical experience also shows that the magnitude of the overpressure directly depends on the geometrical configuration of the 'V' shape profile. Deeper inverted siphon or 'V' shape profiles allows the formation of larger cavities which in turn produces more severe pressurization events. In the second source of water column separation is sometimes induced during rapid filling by a flow restriction such as a partially closed valve. As the water column passes the partially open valves the negative pressure is induced in front of the valve and may result in the formation cavitating flow. Then the descending pipe leg in downstream side of the valve assists in the expansion of cavity in front of valve. An ascending pipe leg or even another clogging in the system gives rise to cavity contraction and collapse. The magnitude of the water hammer pressure following the cavity collapse depends on the shape of profile and the local head losses at the valve or restriction. The numerical results reveals that both steeper descending pipe leg and lesser opening percentage of the valve give rise to bigger cavity in front of the valve which in turn produce more severe water hammer pressures. In the third source column separation occurs as the overpressures induced in the two aforementioned cases are reflected at the water column front. As the pressure spikes are reflected at the front, they suddenly push the water column forward where the empty pipe exerts no resistive force. Intense driving force makes the water column front rapidly accelerate and can gain high velocity. However the preceding water column however is too massive to be simultaneously accelerated and this result in negative pressure and consequent column separation behind the column front. Effectively the stresses cause the water column to break apart. Surprisingly in this case column separation occurs in the straight portion of pipeline rather than knee points and deed ends which have been traditionally thought to be the suspected places for column separation occurrence. Finally the numerical results show that the physics of column separation during rapid filling is too complex to be intuitively understood. The physical insight obtained by the numerical model can be now assisted in designing a test rig for exploring the phenomena with more detail and accuracy. However without such a physical insight it seems to be impossible to configure a test rig capable of the capturing the events explored by the model. This implies that the numerical study should essentially precede physical model study.


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    Titel :

    Rapid filling in pipe systems with column separation


    Beteiligte:
    Malekpour, A. (Autor:in) / Karney, B. (Autor:in)


    Erscheinungsdatum :

    2012


    Format / Umfang :

    13 Seiten, 14 Bilder, 18 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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