Zhang, C., Uddin, M., Song, X., Fu, C. et al., "Simultaneous Improvement of Vehicle Under-Hood Airflow and Cooling Drag Using 3D CFD Simulation," SAE Technical Paper 2016-01-0200, 2016, doi:10.4271/2016-01-0200.
The radiator is the key component of a vehicle’s cooling system. The cooling effectiveness of a radiator largely depends on the flow of fresh air through it. Thus, at high vehicle speeds, the mass flow rate and flow-distribution or flow-uniformity over the radiator surface are the major operating parameters influencing the performance of a radiator. Additionally, the mass of air coming from the front grille plays an important role on the total drag of the vehicle. This paper presents computational studies aiming at improving simultaneously the efficiency of a radiator and reducing the total drag of the vehicle; this is achieved using passive aerodynamic devices that alter the flow pattern approaching the radiator. The vehicle model considered is a Hyundai Veloster and all analyses were carried out using a commercial CFD code Star-CCM+ version 10.04 by CD-adapco. The baseline model used in this study has a vertical radiator with no air-duct where most of the incoming air from the grille blows over the bottom part of the radiator, which makes the upper part of the radiator ineffective. An air-duct introduced between the front grille and the radiator helps the airflow uniformity over the radiator surface by directing the flow towards the upper part of the radiator. This also resulted in an increased mass flow through the radiator due to faster flow induced by the air-duct. Since only the airflow going through the air-duct is useful for cooling the radiator, one could seal both sides of the front grille to remove excessive airflow going under the hood which reduces the cooling and total drag of the vehicle. Several design iterations involving a variety of air-duct geometries and front grille openings were investigated. The results were compared in terms of airflow uniformity, total mass flow rate through the radiator and total vehicle drag to determine the combination that gives the best performance.