Entropy production analysis in thermodynamic cavitating flow with the consideration of local compressibility

Abstract

The objectives of this research are to apply entropy production theory into cavitating flows and investigate dynamic characteristics of entropy production rate (EPR). A thermodynamic cavitation model and a density corrected turbulence model was adopted to this simulation around NACA0015 hydrofoil. Entropy production as a new method for evaluating energy performance is applied on thermodynamic cavitating flows. Cavitation effects on entropy production are firstly derived and revealed. Different entropy production terms by direct dissipation (EPDD), turbulent dissipation (EPTD), wall shear stress (EPWS), mean and fluctuating temperature gradients (EPMT and EPFT) were established in unsteady cavitating flow at 343 K to understand the interactions between cavitation and entropy. The results indicates that entropy production has strong association with cavitation. And entropy production rate by cavitation (EPRC) was derived firstly to evaluate the effects of phase change on entropy production rate. The entropy production rate by cavitation mainly focuses on the interface of cavity where there has intensive mass transfer procedure. Total entropy production rate (TEPR) mainly focuses on leading edge of hydrofoil, rear of attached cavity, detached cavity. Direct and turbulent entropy production rate are two main part in thermal cavitating flows. Direct entropy production can better reflect how total entropy production is distributed. Velocity gradients and phase change are two dominate factors controlling entropy change. In one cycle, total entropy production firstly decreases to its minimum and keeps stable to the inception stage of detached cavity collapse, then increases and fluctuates with cavity collapse.