Keeping Their Cool: Simulation-Based Thermal Design for Construction Vehicles
by Dave Mukutmoni
With their low velocity operation, frequent idle states, and increasing use of onboard technology, construction vehicles present design engineers with a unique thermal management challenge. On one hand, their safety and reliability depend on eliminating thermal issues in operation. On the other hand, thermal management can be a time-consuming and costly part of the engineering process because it requires evaluating a large number of variants to determine optimal cooling package configuration and ensure that no thermal issues will occur in the final design.
Using a simulation-based methodology for thermal design to reduce cost and time when compared to hardware testing is the subject of the technical paper “Thermal Design Evaluation of Construction Vehicles using a Simulation Based Methodology” (SAE 2015-01-2888). The paper addresses two cases that are especially challenging for typical thermal management approaches: electronic control units (ECUs) – the all-important brains of today’s increasingly high tech construction vehicles – and hot air recirculation, which is a common challenge considering these vehicles’ characteristically frequent idle states and low velocity operating conditions.
On the whole, thermal requirements for electronic components present a challenge to engineering teams. Their maximum allowable temperatures are low, but they are regularly exposed to high heat source temperatures when they’re a part of vehicle systems. This condition is complicated further when hot air that exits a heat exchanger recirculates, entering the heat exchanger inlets and leading to even higher overall temperatures.
During physical prototype testing, it’s nearly impossible to identify cases of hot air recirculation because air is by nature transparent. But using digital simulation, which leverages 3D visualization to apply color variation to temperature gradients, it is easy to see when hot air recirculation occurs, and to understand and manage its impact on vehicle systems.
The study confirmed that analysis performed using Exa PowerFLOW for flow simulations together with Exa PowerTHERM to evaluate conduction and radiation effects accurately predicted coolant temperatures and airflow recirculation around heat exchangers when compared with physical experimentation. Shown below are velocity magnitude and temperature snapshots of the transient flow around the vehicle.
The radiator surface temperture distribution in a vertical plane upstream of the radiator and comparison with test data is shown in the figure below. The red crosses indicate the location of the thermocouples in the experiment. As shown in the table, good agreement was observed between the experiments and simulation results. The difference in temperatures was within the experimental uncertainty of the measurements.
Using digital simulation to manage thermal conditions during construction vehicle design can reduce the cost and time associated with physical testing without sacrificing accuracy. Necessary design improvements can be identified and made earlier in the product lifecycle, when designs are still in work and changes are easier to make, thereby eliminating costly late-stage rework and resulting time delays and expenses. And 3D visualization in Exa is more effective than physical tests when it comes to helping engineers easily identify and address the effects of thermal issues – without adding time and cost to product development.
Reference: Mukutmoni, D., Donley, T., Han, J., Muthuraman, K. M., Campbell, P. D., & Mertz, T. (2015). Thermal Design Evaluation of Construction Vehicles using a Simulation Based Methodology (No. 2015-01-2888). SAE Technical Paper.