Water hammer simulation by explicit central finite difference methods in staggered grids

Four explicit finite difference schemes, including Lax-Friedrichs, Nessyahu- Tadmor, Lax-Wendroff and Lax-Wendroff with a nonlinear filter are applied to solve water hammer equations. The schemes solve the equations ina reservoir-pipe-valve with an instantaneous and gradual closure of the valve boundary. The computational results are compared with those of the method of characteristics (MOC), and with the results of Godunov sscheme to verify the proposed numerical solution. The computations reveal that the proposed Lax-Friedrichs and Nessyahu-Tadmor schemes can predict the discontinuities in fluid pressure with an acceptable order of accuracy incases of instantaneous and gradual closure. However, Lax- Wendroff and Lax-Wendroff with nonlinear filter schemes fail to predict the pressure discontinuities in instantaneous closure. The independency of timeand space steps in these schemes are allowed to set different spatial grid size with a unique time step, thus increasing the efficiency with respect to theconventional MOC. In these schemes, no Riemann problems are solved; hence field-by-field decompositions are avoided. As provided in the results, this leads to reduced run times compared to the Godunov scheme.

Keywords:

Water hammer , Lax-Friedrichs , Nessyahu-Tadmor , Lax-Wendroff , Method of Characteristics , Godunov’s method