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A numerical and experimental investigation was undertaken to assess the accuracy and sensitivity of a commercial CFD code when predicting the effect of changes to a car fascia on radiator airflow. The Fluent CFD software program was used to model the external and underhood airflow for the front half of a car allowing the mass flow rate of air through the radiator to be calculated. These CFD predictions were compared with experimental measurements of radiator Specific Dissipation (SD) made after CFD predictions were completed. Twenty-two cases were run with five different fascias possessing air inlets that varied in size and shape. The experimental and numerical results obtained showed a 98.4% correlation coefficient with standard deviation of 2.1% on the difference between the techniques and a prediction interval of ±4.2%. Fourteen of the twenty-two cases were ranked correctly giving a Spearman Rank Coefficient of 0.992.

In this paper, a theoretical model for the calculation of Specific Dissipation (SD) was developed. Based on the model, the effect of ambient and coolant radiator inlet temperatures on SD has been predicted. Results indicate that the effect of ambient and coolant inlet temperature variation on SD is small (less than 2%) when ambient temperature varies between 10 and 50°C and coolant radiator inlet temperature between 60 and 120°C. The effect of coolant flowrate on SD is larger if there is a larger flowrate variation. Experimental results indicate that a 1 % variation at 1.0 L/s will cause about ±0.6% SD variation. Therefore the flowrate should be carefully controlled.