Modelagem computacional do fechamento dinâmico de válvulas de retenção em regime de transitório hidráulico

Abstract

The analysis of dynamic check valve closure constitutes a problem of great relevance, since closure under reverse flow can generate significant pressure surges. The numerical modeling of this phenomenon is complex and requires the definition of a large number of input parameters. The objective of this study was to model the dynamic closure of a check valve during hydraulic transients, incorporating the Cavitation Method with Voids and Wave Damping (CMVWD), and to propose a simplified boundary condition based on dimensionless characteristic curves. Three boundary conditions were implemented: the complete dynamic closure model based on the resolution of the momentum equation; the instantaneous closure condition at the onset of flow reversal; and the simplified boundary condition, based on the general orifice equation with determination of the maximum reverse velocity from characteristic curves. The comparison between the three conditions demonstrated that, under direct flow, the discharge and pressure results were identical. The differences were manifested in the closure instant and in the pressure variation resulting from this phenomenon. The simplified boundary condition proved capable of adequately reproducing the results of the complete dynamic closure model, provided that the characteristic curve used is representative of the operational conditions and type of valve simulated, and was validated against experimental data from Himr et al. (2017). A sensitivity analysis was subsequently performed for the CMVWD parameters, specifically the initial void fraction and the damping coefficient, which demonstrated significant influence on flow deceleration at the check valve, as well as on the maximum reverse velocity and the pressure response associated with check valve closure. A dimensionless correlation approach for characteristic curves from different experimental sources was also proposed for the swing check valve, aiming at generalization for different nominal diameters and operating conditions. The correlation obtained had a preliminary character, with a fit compatible with the intended scope of the methodology.