CFD Study of a Clattering Swing Check Valve During Sudden Pressure Transients: Comparison Between RELAP5 and STAR-CCM+

Abstract

Swing check valves are used throughout piping networks to prevent sustained backflow following abnormal events such as a pipe break. System-level simulations have shown that pressure waves originating from such events can induce rapid clattering of check valves even far from the initiating disturbance, where the fluid is otherwise stationary. This thesis investigates the dynamic response of one such valve, comparing predictions from the 1D system code RELAP5 against compressible 3D computational fluid dynamics (CFD) simulations in STAR-CCM+. The results show that RELAP5 predicts substantially faster and more aggressive valve motion than STAR-CCM+: while STAR-CCM+ reaches a single full opening before settling into a damped oscillation around a partial opening angle, RELAP5 repeatedly cycles between open and closed throughout the simulation. This discrepancy was traced to three contributing factors: an underestimation of the valve’s effective inertia due to the absence of added mass and other hydrodynamic effects in the 1D model; an overestimated hydraulic force arising from RELAP5’s pressure extrapolation and area assumptions; and a deviation between the loss coefficient predicted by RELAP5’s angle-dependent scaling and that obtained from STAR-CCM+ at intermediate opening angles. As a result, RELAP5 likely overpredicts the severity of the associated water hammer effect, though the present results do not allow a definitive conclusion on the validity of the originally predicted clattering behavior. As a secondary objective, torque coefficients required to implement an alternative RELAP5 check valve model were extracted from steady-state and transient 3D CFD simulations. The resulting model, however, was found to be poorly constrained outside the conditions explicitly simulated, and could not be meaningfully evaluated against the 3D results within the scope of this thesis.