To date, there is no other international research association with a specific representation on hydraulic transients. The aim of the newly created working group on Transient Flows is to provide a framework to the transient group community within IAHR. Its aim is to organize IAHR symposiums and conferences on transients and to ensure that transient flow issues are included in future IAHR congresses.

Fluid transients are generated in closed conduits or open channels whenever a rapid flow change is imposed onto the system. There are numerous interesting aspects of fluid transients that have driven continued research and developmental interest in this field. For instance, stormwater sewer systems are hydraulic structures designed to function under unsteady conditions. Yet many aspects of their hydraulic behavior remain poorly understood, such as the transition from open-channel to fully pressurized flow, and how air-water interactions relate to the induced transient pressure. Furthermore, the high pressure wave speed of pipeline systems means that small changes in the fluid velocity lead to large pressure variations that can damage the pipes. The kinetic energy variation caused by water hammer is dissipated by straining and expanding the pipeline. Often, the pressures are sufficient to result in permanent distortion of pipeline supports and in severe cases, this can lead to failure of pipe walls, pumps and turbines. Thus, further research is required to develop cost effective and efficient means of fluid transient suppression, especially since pipeline failures from transients continue to occur around the world.

Although they were initially assumed to be one dimensional, recent research has demonstrated that three-dimensional shear and turbulence effects produce significant changes in the nature of the pressure waves generated during transients. The mechanisms for wave propagation are also frequency and mode dependent, creating a myriad of complexities that have driven fundamental research in this area and the development of efficient solution schemes capable of predicting the evolution of these waves in conduit flows networks.

Ultimately, improved understanding of the behavior of pressure waves has opened up exciting technological possibilities that could lead to means of fault detection in pipe systems in the future. In fact, they can be used to transmit information across the pipeline system for the collection of consumer usage information as well as network monitoring and control.

Focus areas of the working group include: 

• Transient wave theory in hydro-systems.

• Hydro-system diagnosis by means of transient waves.

• Waves-structure interaction in hydro-systems.

• Geysers in stormwater and combined sewer systems.

• Computational transient flow modelling (in closed or opened conduit flows).

• Transient-turbulent flows (in closed or opened conduit flows).

• Field work: case studies, practical applications and projects.