Numerical investigation of the unsteady flow characteristics of human body thermal plume

Abstract

Human thermal plume is quite important to the study of airflow organization in the indoor environment, especially in the micro-environment research such as personalized ventilation, infectious disease transmission through air, etc. In order to investigate the unsteady fluctuation of the thermal plume around human body, a series of transient numerical simulations are conducted in this study. Numerical simulation based on 9.7 million grids and 0.02 s time step is performed to obtain the detail quantitative data of flow field. The obvious fluctuation and separation are captured in the upper flow region of human body based on the high resolution grids. The maximum time-averaged velocity of the thermal plume is found to be 0.25 m/s while the maximum fluctuate velocity is about 0.07 m/s. The further analysis of frequency spectrum shows that the thermal plume around the body is mainly dominated by the low frequency fluctuation which is lower than 1 Hz and the principal frequency is around 0.1 Hz. In order to overcome the drawback of the high computation cost for application of the engineering simulation, a new numerical simulation method combining a modified k-ε turbulence model and coarse grids is presented. This modified k-ε model can reduce the calculation error of Reynolds stress in the flow region of natural convection through redefining the turbulence viscosity coefficient segmentally and avoid a high numerical viscosity appeared due to the central difference scheme. It can reasonably predict the general fluctuation velocity and the frequency distribution during simulation process in coarse grids and show a huge potential to be applied to the engineering application.

A modified turbulence model for simulating airflow aircraft cabin environment with mixed convection

“…The line y = 1.35 is quite uniform due to the boundary layer effect, which is rather stable on the surface of the manikin. For the frequency, it is observed that the thermal plume oscillates with a low frequency and the dominant frequency is around 0.1 Hz which matches the result in Liu et al (2016).…”

“…(5) and further obtain the initial condition for the unsteady simulation. Liu et al (2016) found that the dominant frequency of thermal plume from human body is less than 1 Hz. Thus, the physical unsteady time step is set as 0.04 s. To prevent the initial flow conditions, the first 400 time steps were removed from the results.…”

“…When considering the thermal plume in an aircraft cabin, one needs to properly control the turbulence viscosity in the thermal plume region while keep it in the forced convection region. Here, we refer to the method proposed by Liu et al (2016) to redefine the turbulence viscosity.…”

“…In Liu et al (2016), the flow field is divided into three parts depending on the velocity magnitude. When the velocity is less than 0.3 m/s, the region is dominant by thermal plume and the turbulence viscosity is modified.…”

A simple method for differentiating direct and indirect exposure to exhaled contaminants in mechanically ventilated rooms

“…Fig. 5(d) shows another scenario related to the thermal plume generated by the target person, which has been proven to be important in the near-body airflow field and contaminant transport (Liu et al 2016;Yan et al 2017). When the exhaled air penetrates the lower zone of the thermal plume boundary layer, the contaminants may move upward with the vertical airflow driven by the thermal plume and enter the breathing zone.…”