The theoretical development of vehicle engine cooling airflow models using incompressible flow methods

A one-dimensional incompressible flow model covering the mechanisms involved in the airflow through an automotive radiator-shroud-fan system with no heat transfer was developed. An analytical expression to approximate the experimentally determined fan performance characteristics was used in conjunction with an analytical approach for this simplified cooling airflow model, and the solution is discussed with illustrations. A major result of this model is a closed form equation relating the transient velocity of the air to the vehicle speed, pressure rise characteristics and speed of the fan, as well as the dimensions and resistance of the radiator. This provides a basis for calculating cooling airflow rate under various conditions. The results of the incompressible flow analysis were further compared with the computational results obtained with a previously developed one-dimensional, transient, compressible flow model. The effects of the ambient air temperature, pressure, and heat transfer in the radiator on the cooling airflow rate were analyzed, and the use of an empirical formula to estimate the variation of the flow rate corresponding to heating of the air is presented and discussed