Numerical study of the blockage length effect on the transient wave in pipe flows

Abstract

A pipeline with an extended blockage is modelled as a system of three pipes in series. A computational fluid dynamics approach using the ADINA software is adapted to solve the slightly compressible turbulent flow problem with complex geometry. Two-dimensional axisymmetric computational results are validated by several examples. In practice, the water hammer wave generated by rapid valve closure usually exhibits wave front smearing. The numerical analysis shows that for a blockage length larger than the wave front thickness, the magnitude of the incident wave may be significantly suppressed as a result of the interaction between the blockage and the wave front. By reflecting negative pressure waves toward the incident wave before its maximum pressure arrives at the blockage, the maximum transient pressure may be considerably reduced. Consequently, the blockage behaves as a discrete blockage. However, if the blockage length is large compared with the thickness of the wave front, the incident wave conserves its initial amplitude, and the blockage behaves as an extended blockage. Therefore, the occurrences of discrete and extended blockages depend on the thickness of the wave front and thus on the rapidity of the manoeuvre that generates the transient.