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

Sammanfattning

Swing check valves are used throughout piping networks to prevent sustained backflowfollowing abnormal events such as a pipe break. System-level simulations haveshown that pressure waves originating from such events can induce rapid clatteringof check valves even far from the initiating disturbance, where the fluid is otherwisestationary. This thesis investigates the dynamic response of one such valve,comparing predictions from the 1D system code RELAP5 against compressible 3Dcomputational fluid dynamics (CFD) simulations in STAR-CCM+.The results show that RELAP5 predicts substantially faster and more aggressivevalve motion than STAR-CCM+: while STAR-CCM+ reaches a single full openingbefore settling into a damped oscillation around a partial opening angle, RELAP5repeatedly cycles between open and closed throughout the simulation. This discrepancywas traced to three contributing factors: an underestimation of the valve’seffective inertia due to the absence of added mass and other hydrodynamic effectsin the 1D model; an overestimated hydraulic force arising from RELAP5’s pressureextrapolation and area assumptions; and a deviation between the loss coefficient predictedby RELAP5’s angle-dependent scaling and that obtained from STAR-CCM+at intermediate opening angles. As a result, RELAP5 likely overpredicts the severityof the associated water hammer effect, though the present results do not allow adefinitive conclusion on the validity of the originally predicted clattering behavior.As a secondary objective, torque coefficients required to implement an alternativeRELAP5 check valve model were extracted from steady-state and transient 3D CFDsimulations. The resulting model, however, was found to be poorly constrainedoutside the conditions explicitly simulated, and could not be meaningfully evaluatedagainst the 3D results within the scope of this thesis.