Under the hood of a car, or any other vehicle, space is finite and there are an increasing number of subsystems. Ensuring air flow is sufficient for the cooling system and all heat exchangers is a major concern for many engineers. System simulation can help you to predesign heat exchangers or fans, assess the air flow rates and temperatures and in fine reduce the number of prototypes and physical tests.
In Simcenter Amesim, the Heat Exchanger Assembly Tool (HEAT) library enables you to design the complete under hood system including heat exchangers stack and to perform rapid simulations. Depending on the available data and expected accuracy, different types of simulation can be used to simulate the external air flow:
- Set a homogeneous air velocity on each heat exchanger
- Set velocity maps on each heat exchanger
- Assume straight air flow channels and let Simcenter Amesim calculate the corresponding air flow distribution
- Define customized air paths and let Simcenter Amesim calculate the corresponding air flow distribution
- Use co-simulation with Star CCM+ using embedded CFD in steady state mode
- Use co-simulation with Star CCM+ using embedded CFD in transient mode
One demonstrator per feature is available within Simcenter Amesim. In this article I will explain the content of the demo and show how to customize the air paths through the following steps:
- What is the engine cooling system architecture?
- What is the air flow configuration through the different heat exchangers of the stack?
- How to perform modification on the airflow path system?
- How to get accurate and detailed results?
- Going further with CFD co-simulation
- Watch the video: Assessing thermal management under the hood in Simcenter Amesim
Underhood air flow model in Simcenter Amesim
What is the engine cooling system architecture?
As you can see in the Simcenter Amesim sketch above, we use in this model a standard cooling system architecture with the following subsystems:
- Centrifugal pump
- Heat exchange with engine block thermal masses
- Expansion tank
- Heater core
The coolant fluid is a mixture of ethylene and water we take directly from the thermal hydraulic library database of Simcenter Amesim. This allow us to identify where we can optimize our thermal management system
What is the air flow configuration through the different heat exchangers of the stack?
The different heat exchangers and other elements interacting with the air flow are placed in 3D. Using the HEAT Assistant, we can visualize in this 3D environment the arrangement of the different elements and the air paths. In this demo, the manual air path feature is used and the air flows through:
- Three front grilles accounting for the pressure drop
- Charge-air-cooler and radiator, accounting for the pressure drop and the heat exchange
- Fan accounting for the pressure increase with characteristic maps
- Engine block accounting for the pressure drop given available space around it and heat transfer with walls
A robot composed of three arms able to handle small objects at up to 300 movements per minute. This ensures excellent throughput for the manufacturer that requires packaging within industries such as pharmaceuticals or foods …
HEAT assistant showing the air paths
How to perform modification on the airflow path system?
In this example, all the air is merged after the radiator (in the orange node in the image above) and then goes through the fan. We therefore simulate a case where a shroud covers the space between the radiator and the Fan.
We can however wonder what would be the behavior without such a shroud. Here, air going through the top part of the radiator could go directly to the engine without passing through the fan. Using the manual air path feature, we can make this modification:
HEAT assistant showing the air paths (modified)
Going further with CFD co-simulation
For more complex flow and more predictability, embedded co-simulation between Simcenter Amesim and CFD 3D software Simcenter StarCCM+ can be used where the strengths of system simulation (low run time) and 3D CFD (accuracy) are combined for maximum efficiency.