Thermal Management

With PowerFLOW® version 4.0 Exa now offers a complete capability for thermal management simulations for the automotive and ground transportation industries. Capabilities range from cooling airflow simulations – the analysis of the flow through the cooling module of the car (both air and coolant sides) – to thermal protection – the calculation of air and component surface temperatures in the underhood and underbody regions.

PowerFLOW’s thermal management capabilities are enabled by:

• Extended temperature range: all thermal calculations are fully coupled to the momentum calculations in PowerFLOW, i.e. density and temperature are coupled in a physically consistent manner. This enables PowerFLOW to handle temperature ranges fully sufficient for all automotive applications.
• PowerCOOL™: the simulation of the coolant side of heat exchangers such as radiators or charge air coolers is possible with PowerCOOL. PowerCOOL simulations are performed in a fully integrated and closely coupled way with PowerFLOW simulations.
• Radiation and conduction are handled in Exa PowerTHERM. PowerTHERM simulations are performed in a closely coupled and fully integrated manner – providing unmatched ease of use and accuracy.

With these extensions PowerFLOW is capable of detecting and analyzing critical flow situations impacting the thermal performance of a vehicle – grille openings too small to provide sufficient cooling airflow, coolant temperatures exceeding operating limits, or component temperatures higher than allowed for the materials used. Once a problem is identified a remedy can be quickly tested – an enlarged grille opening created with PowerCLAY, a fan moved to a different location by changing a single positioning parameter in PowerCASE, or a heat shield added or removed with a few mouse clicks.

Cooling Airflow

The goal of cooling airflow simulations with PowerFLOW is to ensure sufficient airflow through the cooling module – resulting in coolant temperature distributions within acceptable operating limits – while not negatively affecting the aerodynamic performance of the vehicle. A fully detailed geometric representation of the cooling module is typically used in PowerFLOW, and can be set up with the same ease of use our customers are accustomed to for pure aerodynamics simulations. In fact, almost all customers now include cooling airflow details for all aerodynamic simulations as closed grille models create an unrealistic situation. The airflow through heat exchangers is handled with PowerFLOW’s flexible porous media capability, and the coupling to PowerCOOL provides coolant temperature predictions as one of the key outputs of PowerFLOW cooling airflow simulations. Fans are modeled with a Multiple Reference Frame (MRF) model which takes the detailed geometry and operating condition of the fan into account.

Cooling airflow simulations can be performed for any vehicle operating point – from maximum velocity to idle. Leakage flows resulting in recirculation under idle or low speed conditions, which lead to hot air circulating back to the front of the radiator and a corresponding increase in top tank temperature can be exactly located and corrected with PowerFLOW.

Thermal Protection

The prediction of component surface temperatures under various vehicle operating conditions is another important thermal application of PowerFLOW. The ability to predict the temperature of heat sensitive components – for example engine mounts in the vicinity of hot exhaust system components – early in the design process can help avoid costly redesigns at a later point.

With air temperatures exiting the cooling module correctly predicted through the coupling to PowerCOOL, and radiation and conduction effects handled through the two-way coupling with PowerTHERM, PowerFLOW can accurately predict the air and surface temperatures at any location in the underhood and underbody regions of the vehicle.

Coupling to Aerodynamics

Thermal management problems of vehicles are closely coupled to aerodynamic characteristics in reality: the flow through the open grille changes the aerodynamics of a vehicle and vice versa, and underbody flow characteristics have a significant influence on component surface temperatures. In PowerFLOW this interdependence of aerodynamics and thermal management is preserved since both types of flow regimes can be handled with a single geometry, a single set of physics, and in fact in a single simulation. Interdisciplinary questions which can not be sufficiently answered in today’s typical development process – for example, How does an increased grille opening affect drag and lift? or, How does an added front spoiler influence top tank temperature? – can now be answered simultaneously and early in the development process, this avoiding the need for costly fixes at a later stage of the development.

Validation

A combination of validation cases ranging from simple academic cases to full vehicles with true CAD geometry detail has allowed us to fully ensure the correct modeling and implementation of thermal management capabilities in PowerFLOW. A representative sample of well documented results for both cooling airflow and thermal protection is available to all customers on Exa’s user center.

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