Assessment of Transient CFD Techniques for Virtual Thermal Manikins’ Breathing Simulations

Abstract

A qualitative cross-analysis of three different computational fluid dynamics transient modelling techniques (“Unsteady Reynolds Averaged Navier Stokes - URANS”, “Detached Eddies Simulations - DES” and “Large Eddies Simulations - LES”) for flow simulation with virtual thermal manikins is presented. The interaction between the free convection flow, resulting from the heated manikin’s surface, and the exhalation/inhalation flow is modelled, under controlled room conditions. It has been shown in recent studies of the authors, that the steady-state simulations lead to over-prediction of the resultant velocity and temperature fields. For this reason, the implementation of transient simulation methods is recommended and implemented in the presented study, however, without validation with measured data. The comparison of temperature and velocity fields is the basis for the qualitative analyses made between the different simulation techniques. The achieved results in this qualitative assessment provide novel and valuable information on the integration of numerous simulation techniques. This is supported by the fact that these virtual thermal manikins represent complex assessment tools for virtual design of the human thermal comfort, as well as for virtual analyses of indoor air quality. In general, the numerical results showed a good correlation between the different techniques, especially for the exhalation stage from the breathing cycle, in the breathing zone of the manikin. Furthermore, in both DES and LES methods, significant flow similarities were demonstrated in the zones dominated by the manikin’s free convection, while, for the URANS simulations, a sensible refraction of the thermal plume was observed in the zone above the head with shifting of almost 0.4 m.