Circular Free Jets: CFD Simulations with Various Turbulence Models and Their Comparison with Theoretical Solutions

Abstract

The theory of turbulent free jet is fundamental for the design of comfort ventilation, as free jets frequently occur in mixing and personalized ventilation systems and their characteristics strongly influence the air quality in the breathing zone of an occupant. The aim of this research is to provide recommendations that help researchers and practitioners improve the accuracy and reliability of their computational models of ventilation systems involving circular free jets. To accomplish this, a review of existing theoretical calculation models is performed, and these models are subsequently investigated by computational fluid dynamics. The theoretical solutions of free jets are compared with CFD simulations using various turbulent models such as the standard k-epsilon model, the k-epsilon realizable model, the standard k-omega model, the shear stress transport (SST) k-omega model, and the Reynolds stress model (RSM). The simulated models are represented by profiles of the centreline velocity for a free jet emanating from a round nozzle, because such presentation of the data proved to be particularly helpful for the comparison of the turbulence models. The k-omega SST turbulence closure scheme with standard coefficients produced results of the centreline velocity closest to the average of theoretical solutions investigated, whereas the discrepancy between the simulations and the theoretical models was about 60 % with the k-epsilon standard turbulence model.The theory of turbulent free jet is fundamental for the design of comfort ventilation, as free jets frequently occur in mixing and personalized ventilation systems and their characteristics strongly influence the air quality in the breathing zone of an occupant. The aim of this research is to provide recommendations that help researchers and practitioners improve the accuracy and reliability of their computational models of ventilation systems involving circular free jets. To accomplish this, a review of existing theoretical calculation models is performed, and these models are subsequently investigated by computational fluid dynamics. The theoretical solutions of free jets are compared with CFD simulations using various turbulent models such as the standard k-epsilon model, the k-epsilon realizable model, the standard k-omega model, the shear stress transport (SST) k-omega model, and the Reynolds stress model (RSM). The simulated models are represented by profiles of the centreline velocity for a free jet emanating from a round nozzle, because such presentation of the data proved to be particularly helpful for the comparison of the turbulence models. The k-omega SST turbulence closure scheme with standard coefficients produced results of the centreline velocity closest to the average of theoretical solutions investigated, whereas the discrepancy between the simulations and the theoretical models was about 60 % with the k-epsilon standard turbulence model.