Coupling of 1-D and 3-D CFD Models to Predict Transient Hydraulics in an Engine Cooling Circuit

In general, the solution of automotive cooling hydraulic networks requires the construction of two separate models. Initially a 3-dimensional CFD model is required to predict air flow patterns through the bumper apertures (and cooling pack heat exchangers) with the results being fed into a 1-dimensional hydraulic model. The 1-D model is then used to predict engine coolant temperatures based on measured (or predicted) heat exchanger performance and calculated radiator coolant flow rates. When predicting the transient temperature and flow rates produced within a circuit over a single drive cycle (where vehicle speed, engine load and cooling fan speeds are changing) such an approach can become extremely time consuming.

This document describes a technique for coupling the two methodologies in a manner which eliminates the need for repeated 3-D solutions to be provided for every vehicle operating condition. The resulting methodology allows a large number of rapid 1-D solutions to be performed based on relatively few 3-D simulations.

Using the technique a vehicle drive cycle was simulated. The drive cycle chosen was a cabin air warm-up test with the vehicle initially starting in an ambient of -18°C. The results presented herein show the high degree of accuracy possible by using such a coupled approach. The modelling approach is easily extendable to predict the effects of variations in any of the cooling system component strategies (such as changes to the cooling fan activation temperatures).