Comparing simulated and experimental hysteretic two-phase transient fluid flow phenomena
A hysteretic model for two-phase permeability (k)-saturation (S)-pressure (P) relations is outlined that accounts for effects of nonwetting fluid entrapment. The model can be employed in unsaturated fluid flow computer codes to predict temporal and spatial fluid distributions. Consideration is given to hysteresis in S-P relations caused by contact angle, irregular pore geometry, and nonwetting fluid entrapment effects and to hysteresis in k-Srelations caused by nonwetting fluid entrapment effects. An air-water flow experiment is conducted with a 72-cm vertical soil column where the water table is fluctuated to generate scanning S-P paths. Water contents are measured via a gamma radiation system, and water pressures are measured via pressure transducers connected to ceramic tensiometers inserted in the soil column. Computer simulations of the experiment employing the hysteretic k-S-P model and a nonhysteretic k-S-P are compared with measured water contents and pressures. Close agreement is found between experimental water contents and those predicted by a numerical code employing the hysteretic k-S-P relations. When nonhysteretic k-S-P constitutive relations are utilized, there is poor agreement between measured and predicted water saturations of the scanning paths. Only one more parameter is needed to model two-phase hysteretic fluid behavior than to model nonhysteretic behavior. Results of this study suggest that consideration should be given to effects of hysteresis in k-S-P relations to accurately predict fluid distributions.