Prediction of the Behaviour of Large Vortex Drop Structures in Municipal Sewerage Systems

The physical model is a tool for producing technically, environmentally, and economically optimal solutions for engineering problems. However, frequently it is not possible to avoid scale effects if the prototype fluid — normally water — is used in the model studies. In such cases, it is necessary to use process functions to determine the magnitude of the scale effects and to inform the adjustment of measured flow properties in the model to reflect the true value of the flow properties in the prototype. Such functions have been used in the past to evaluate scale effects in, for example, full-pipe flows and flume calibrations and are described by Keller. The present paper extends the use of process functions to annular flows, such as occur in vortex drop structures, and plunge pools. It is shown that the process functions cannot be used to evaluate scale effects directly, but, instead, must be used in conjunction with the model data to develop an analytical model for the prediction of corresponding prototype behavior. In the paper, the techniques are developed and their use illustrated through application to a large physical model study of a vortex drop and plunge pool in a municipal sewerage system. It is shown, further, that ignoring the insight gained from the developed process functions would lead to large errors in the prediction of prototype flow behavior from measured model results.