Fidelity CFD for Coupled CHT Simulation in ICEV

Introduction

The focus areas for thermal management in an internal combustion engine vehicle (ICEV) are the underhood/underbody, HVAC, and cabin comfort. Thermal management strategies such as thermal soak, zoned cooling, and automatic climate control technologies aim to balance passenger comfort, safety (in terms of brakes, to ensure stable friction for smooth stopping), critical peak temperatures (for example, reliability and durability), and fuel consumption.

The heat from the engine, the exhaust system, the radiator, and the condenser, as well as the fans attached to it, along with the surrounding terrain and weather, all need to be considered while designing an ICEV thermal management system. Coupled conjugate heat transfer (CHT) simulation using Cadence's Fidelity CFD software uses computational fluid dynamics technology to provide an accurate prediction of heat transfer between solid and fluid domains for advanced thermal management of the entire vehicle.

Challenges in Thermal Management of ICEV

The heat exchanger (HE) is the heart of vehicle thermal management, a complex system consisting of the radiator, oil cooler, fuel cooler, evaporators, charge coolers, etc. A typical internal combustion (IC) engine is composed of at least two or more HEs; hence by reducing the size of a HE, the weight is considerably reduced, contributing to improved aerodynamics, and fuel economy. A compact HE model with a faster response to changing operating conditions reduces fluid inventory expenses while simultaneously reducing the environmental impact.

Figure 1. Counter-rotating fans in front of the radiator of an ICEV.

Heat transfer fluids such as ambient air, coolant, fuel, engine oil, refrigerant, etc., are used in vehicle thermal management systems and exhibit relatively low thermal conductivity. Hence, a CHT model that optimizes the thermal components of an ICEV for engine cooling and an improved HVAC system performance is substantial.

Managing thermal transients after a vehicle has stopped running (also known as key-off and soak), is one of the critical concerns during the design phase in the automotive industry because the rising temperatures can cause under hood damage or premature failure of the parts.

User Benefits of Fidelity CFD

Fidelity CFD offers advanced geometry healing, meshing, and scale resolving simulations to meet customer requirements for innovative CFD solutions on a single interface, saving time spent on switching between platforms.

The gaps and holes in the vehicle's computer-aided design (CAD) geometry can be automatically sealed using the AutoSeal technology in Fidelity CFD, reducing preprocessing time from days to hours and; delivering a watertight body that is ready for meshing. Fidelity CFD includes automated mesh generation technology for a conjugate heat transfer model, which predominantly uses unstructured full-hex or hexahedral dominant mesh for both solid and fluid domains. Moreover, Fidelity CFD has industry-compliant repeatable templates for common models.

Figure 2. Half-body mesh of Honda-CRV model (left), cut section of the meshed engine block with air inside the exhaust manifold and the external air, where the mesh is fully conformal, including the connection between fluid and solid domains (right).

Easily identify hotspots in the underhood or underbody systems, predict external aerodynamic performance and capture real-world scenarios such as key-off and soak, and hill climbs by running transient and steady-state simulations, including radiation from hot components with Omnis.

                                                   

Figure 3. Temperature of the engine surface (left), Static temperature of the exhaust system, and the underbody flow field (right).

Conclusion

A fully coupled CHT simulation provides more realistic results for both the aerodynamic and thermal performance of a vehicle. From computing the radiation components to capturing the physics involved in heat transfer across the solid and fluid domains, Fidelity CFD does it all with minimal user intervention. With shorter design cycles in the automotive industry, a multi-faceted simulation platform like Fidelity CFD rises to the challenge of predicting the thermal behavior of a vehicle in a shorter time frame.