Evaluating the performance of a non-oscillatory TPA approach in mixed flow analysis of sewer pipes with different shapes

Two-Component Pressure Approach (TPA) is utilized to calculate transient mixed flow in sewer pipe systems. However, this method gives rise to spurious numerical oscillations when the flow is changed from open channel to pressurized flow. The induced numerical oscillations intensify as the acoustic speed of the pipe increases and come to corrupt the results when the acoustic speed exceeds a limit that is found to be between 300-400 m/s. In some cases, however, the real pipe acoustic speed is far above this limit, and any attempt to apply reduced acoustic speeds would severely distort the transient responses of the system.

The authors recently proposed a non-oscillatory TPA model, which is free of spurious numerical oscillations even in high acoustic speed conditions that are usually encountered in practice. Nevertheless, the performance of the proposed model was justified just for circular and box shape pipes, while a variety of pipe shapes are still utilized in real sewer systems.

To this end, this research tends to justify the performance of the proposed TPA in capturing transient mix flow in a variety of pipe shapes covered by the most popular off-the-shelf-software such as SWMM. Due to the lack of experimental data, some hypothetical examples for which analytical solutions exist are employed to verify the obtained results. The results reveal that for all pipe shapes considered, the model provides oscillation free solution even at a high acoustic speed of 1400 m/s. It is also observed that the numerical results are in perfect agreement with the analytical solution. The obtained results conclude that the proposed model can correctly capture transient responses of sewer systems with any pipe shape.