Effects of swirl intensity on heat transfer and entropy generation in turbulent decaying swirl flow

• Accurate numerical model of anisothermal turbulent swirl flow was built and validated.
• The swirl number is directly and inversely proportional to Nusselt and Stanton numbers, respectively.
• Numerical simulations revealed that a critical swirl number exists Sn ≈ 0.278.
• A novel correlation for predicting entropy augmentation number in swirl flow is proposed.
• The entropy field in the flow core was found to be dominated by viscous irreversibilities.

In the present work, numerical simulations of turbulent incompressible nonisothermal pipe flows were conducted to investigate the effect of inlet swirl intensity and streamwise swirl decay on heat transfer and local entropy generation in the flow. The RANS, energy and entropy equations along with Shih's realizable k–ε turbulence model were numerically solved using second order finite volume upwind discretization scheme. The CFD model results showed very good agreement with established LDV measurements. The streamwise trends of Nusselt and Stanton numbers were studied at different inlet swirl intensities. A new CFD-based empirical correlation for predicting the entropy augmentation number as a function of swirl number was proposed. It is shown that the swirl number radically affects the local entropy generation due to viscous dissipation in the inner core of the Rankine vortex structure.