Parametric study on flow characteristics of air vortex ring supply using large-eddy simulation

Abstract

Air vortex-ring-based supply mode was proposed to deliver fresh air. The influence of air supply parameters on the entrainment and mixing of air vortex rings was investigated numerically. The air supply parameters, including the supply air velocity, formation time, and supply air temperature difference, were specified by theoretical analysis based on both the simple cylindrical-slug model and the application scenario. A large eddy simulation with a dynamic Smagorinsky–Lilly model was used to generate the data required for analysis. Sensitivity tests of the computational parameters and experimental validations were conducted to ensure the accuracy and applicability of the numerical method. The results showed that when the formation time was less than the formation number, increasing the formation time reduced the entrance gap width and consequently restricted the entrainment of the air vortex ring. When the formation time exceeded the formation number, the additional air appeared as a trailing wake and enhanced the diffusive entrainment. If the supply air velocity is too high, the entrainment and mixing process of the air diffused from the boundary of the vortex ring is accelerated. However, if the supply air velocity is too low, the air vortex ring collapses downstream, increasing the amount of pulsed air jet deposited behind the vortex ring. The non-isothermal pulsed jet caused more air from the pulsed jet to be deposited behind the vortex ring and accelerated the attenuation rate of the air vortex ring, indicating that the entrainment was enhanced.