Technical article: Why real-time climate models are the future of vehicle interior simulation
The demands placed on the interior climate of modern vehicles are constantly increasing: maximum comfort with minimum energy consumption is now a key development goal. Air zone cabin models make it possible to precisely evaluate and optimise the thermal behavior of the passenger compartment as early as the virtual concept phase. This reduces the necessary tuning effort on the physical vehicle to a final fine calibration. The resulting shortening in development cycles lowers costs, accelerates decision-making processes and increases competitiveness in the international market. Multi-air zone cabin models make it possible to precisely evaluate and optimize the thermal behavior of the passenger compartment as early as the virtual concept phase. This reduces the necessary tuning effort on the physical vehicle to a final fine calibration. The resulting shortening of development cycles lowers costs, accelerates decision-making processes and increases competitiveness in the international market.
Physically consistent simulation with minimized CFD computing effort
Conventional transient CFD simulations provide detailed flow and temperature fields but are unsuitable for early concept phases due to high computing times. The multi-air zone model in the Theseus-FE software from ARRK Engineering GmbH offers a novel approach here, as shown in Fig. 1: It divides the cabin volume into discrete air zones and links these to data that provides the model with time-dependent air exchange variables via an AI-supported ventilation matrix. To create this matrix, the relevant operating conditions in the cabin are first identified. Stationary CFD calculations ranging from a few dozen to a few hundred simulations are then performed for these conditions. In this way, the dominant physical mechanisms are retained, while changes in the ventilation situation in the cabin can be simulated without the need for new CFD calculations, drastically reducing the computing time required for the investigations.
The model maps temperature, humidity and air exchange between zones, enabling a predictive assessment of thermal comfort. Validations show deviations of less than 1 K in most areas of the occupants' bodies – a level of accuracy that is ideal for concept studies. In poorly ventilated zones, where greater inhomogeneities and temperature deviations tend to occur, these can be specifically taken into account through more detailed modelling.
Rapid climate strategy development instead of CFD marathon
The development of efficient climate control strategies is caught between the conflicting priorities of comfort, safety requirements such as windscreen de-icing, and energy consumption. However, real prototypes are often lacking in early development phases, while fully coupled CFD/FE models can take several days to weeks of computing time, limiting the possibility of iterative optimization.
The multi-air zone model presented here offers decisive advantages:
- Automatic or manual zoning for relevant areas
- CFD-based heat transfer coefficients for convection
- AI-supported ventilation matrix for changing operating conditions
- Coupling with a thermophysiological human model according to Fiala
This interaction enables near real-time simulations of thermal interior behavior with high physical validity. Typical scenarios such as defrosting, rapid heating strategies or comfort comparisons can be simulated within about an hour – instead of several days with conventional approaches.
Validation: High accuracy with drastically reduced computing time
An exemplary defrost operating case over 30 minutes with dynamic air volume, distribution and temperature progression demonstrates the performance of the model. A cabin mock-up with air conditioning unit and 21 thermocouples as well as the ARRK comfort dummy were used for validation. The temporal progression of air temperatures at the measurement points of the comfort dummy (see Fig. 2) corresponds very well with the simulation results in most areas of the body:
- < 1 K deviation in the head and upper body area
- up to 2.8 K deviation in the footwell due to local inhomogeneities
- Realistic comfort response of the Fiala model for different body segments
The comfort model shows rapid thermal relief in the head area, while lower body regions react with a delay, whereby the quality of the results is currently still being optimized. The combination of the multi-air zone model and thermophysiological calculation enables a reliable assessment of the interior climate and comfort. The high degree of consistency proves that physical consistency is maintained, even though the calculation times are orders of magnitude shorter than for fully coupled CFD/FE simulations.
Summary
The real-time capable multi-air zone climate model in Theseus-FE enables, for the first time, a fast, physically sound assessment of the interior climate already in the early stages of vehicle development. The combination of zonal modelling, CFD-based parameterization, AI-supported ventilation matrix and thermophysiological comfort assessment allows climate strategies to be designed efficiently without relying on real prototypes. The drastic reduction in computing times, high model accuracy and the ability to quickly analyze variants lead to significant time and cost savings. This not only increases the efficiency of the development process – companies also gain a noticeably higher level of competitiveness on the international market.