Experimental and CFD comparison of driver's thermal plume with classical air diffusers

Abstract

In confined spaces, such as vehicle cabins, airflow is one of the most critical factors affecting thermal comfort and pollutant dispersion. To develop innovative and energy-efficient HVAC systems, a deep understanding of the jet flows' interaction from air diffusers on the thermal plume became essential to improve our knowledge of airflow patterns for optimizing ventilation system design, thermal comfort, and indirectly, energy efficiency. We have developed a 1:1 scale mock-up with transparent walls, replicating a Renault Megane's interior in a climatic chamber and associated complex numerical models. PIV and IR measurements were firstly performed for the pure thermal plume with a thermal manikin in a driver's seat in this 1:1 scale mock-up. The experimental and numerical results showed good agreement regarding ranges and distributions. This paper presents experimental and numerical comparisons performed without and with ventilation systems to evaluate this interaction for classical air diffusers as a part of our larger project. The flow structure in the car cabin is complicated with existing large- and small-scale vortices. With an active ventilation system, the thermal plume is stronger in front of the head, the opposite of what has previously observed back the head. The airflow moves forward along the ceiling. The presence of the steering wheel distorts the flow direction at the thigh level. The additional velocity field on convective upward velocity in the shoulders' region is caused by impinging jets from diffusers. The Coanda effect caused by the central diffuser's flow creates a nonuniform and asymmetrical air distribution in the shoulders' region. A qualitative comparison of the jets' velocity distributions shows that the velocities are more uniform with innovative LAG diffusers than with the classical ones. This shows clearly the benefits of passive flow mixing to improve the thermal sensation.