A rapid water-filling analog model for entrapped air pockets based on the generalized Kelvin–Voigt model

ABSTRACT Pressurized water conveyance systems may contain entrapped air pockets during hydraulic transients. The rapid water–air interaction can induce severe pressure fluctuations, jeopardizing the safety and stability of hydraulic projects. Existing numerical models fail to accurately describe or account for energy dissipation caused by phenomena such as gas dissolution, heat transfer, and vortices at the water–air interface, as well as other uncertainties during the water–air coupling process. To address this, we develop a rapid water-filling analog model for entrapped air pockets based on the generalized Kelvin–Voigt model, aiming to accurately simulate water–air two-phase flow in viscoelastic pipelines. The optimized model analogized the compression and expansion process of the air pocket to the length variation of a spring-dashpot system, thereby representing energy dissipation from complex hydraulic phenomena as mechanical losses. Experimental validation demonstrates that the proposed model enables precise extrapolation and exhibits significant advantages in terms of simulation accuracy over traditional models. Overall, within a certain range (k ≤ 5), a higher hypothetical Voigt element number k generally yields higher inversion accuracy for creep compliance and more precise numerical simulations. Furthermore, the retardation time τ should be optimized to minimize the variation between the individual components of the retrieved creep compliance.