Influence of Fluid–Structure Interaction on Pressure Fluctuations in Transient Flow

Sudden changes in operating conditions of a piping system induce a fluid hammer with cyclic pressure fluctuations that moves back and forth and finally dies out. Although one-dimensional continuity and momentum equations can predict the maximum pressure in a fluid hammer accurately, the simulated flow characteristic, viz., the pressure wave, deviates from the measured one, in subsequent cycles. In many instances, this deviation in the modeling is reduced by incorporating the concepts such as variable unsteady friction, artificial viscosity and diffusive terms, in the governing equations. The current study demonstrates that proper accounting of fluid-structure interaction (FSI) in the transient analysis in a three-dimensional computational fluid dynamics (CFD) model can predict the damping of a pressure wave with reasonable accuracy. The CFD-FSI model couples the Navier-Stokes equation with structural equations for axial, radial, flexural, and torsional motions, to represent the effect of FSI. Numerical simulations of three different problems from two different experimental setups were used for assessing the effect of FSI on the damping of the pressure wave. It is found that the incorporation of FSI into the three-dimensional (3D) CFD model leads to better prediction of the damping of the pressure wave in a quasi-rigid piping system. In contrast, such incorporation is not required for the prediction in a fully rigid system such as pipe buried in concrete.