In a nutshell, the answer depends on the nature of unsteady flow event, and I am assuming here you have a one-dimensional system. If you have a fast transient (definition follows below) in a single-phase (homogeneous) flow, you need a solution approach that accounts for water/pipe wall/system elasticity in the formulation, such as numerical models based on the traditional Method of Characterstics. Slow transients (which occur within times much larger than the time scale L/a - pipeline length divided by the acoustic wavespeed of pressure waves in the pipe) can be modeled/described with lumped inertia models. Finally, if you are looking into other types of surges (air/water compression), you may have to investigate deeper into modeling alternatives accounting for air-water interactions.
In a nutshell, the answer depends on the nature of unsteady flow event, and I am assuming here you have a one-dimensional system. If you have a fast transient (definition follows below) in a single-phase (homogeneous) flow, you need a solution approach that accounts for water/pipe wall/system elasticity in the formulation, such as numerical models based on the traditional Method of Characterstics. Slow transients (which occur within times much larger than the time scale L/a - pipeline length divided by the acoustic wavespeed of pressure waves in the pipe) can be modeled/described with lumped inertia models. Finally, if you are looking into other types of surges (air/water compression), you may have to investigate deeper into modeling alternatives accounting for air-water interactions.
Dear Vipin: I agree with Jose. You need first to define clearly the type of pressure surge you have (water hammer?), if you have a single phase or a multiphase flow, the characteristics of the fluids, and the geometry and remaining frontier conditions. Although the elastic model is more general, it still requires frequently some approximations.
There are many good books written on the subjec matter. However, I will list here two of them due to time constraints. I hope you will find them useful.
1) Fluid Transients in Systems by E. Benjamin Wylie and Victor L. Streeter
2) Applied Hydraulic Transients by M. Hanif Chaudhry