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To guarantee the function of today's passenger cars, it is necessary to ensure that all components with thermal loads are sufficiently cooled. This is usually realized by extracting air from the flow around the vehicle, guiding it through heat exchangers mounted within the vehicle and returning it back into the external flow. This leads to a change in the aerodynamic properties of the vehicle.The purpose of this work is to present a first analysis of the cooling air drag based on detailed generic model. Due to the design of the hardware model, a number of uncertainties which occur in full scale testing like deformations of sealing lines, leakage flows and geometric uncertainties can be excluded. STATE OF THE ARTThe following section gives a short introduction to cooling air flow and corresponding research work on reference models.A cooling air flow system is the sum of all components which contribute to the task of delivering cooling air to the place where it is needed, including cooling air inlets, ducting, heat exchangers and fans. There are a large number of parameters, which can influence the performance of such a system e.g. the size and location of the cooling air inlets, the performance curve of the heat exchangers including pressure loss, the package of the underhood compartment and the location of the cooling air exits. A study of the effect of such parameters on the aerodynamic performance can be found in [1]. ABSTRACTCooling air flow is an important factor when it comes to vehicle performance and operating safety. In addition, it is closely linked to vehicle aerodynamics. In recent years more and more effort is being spent to optimize the losses generated by the flow through the vehicle. Grille shutters, better sealing and ducting are only some examples for innovations in this field of work, resulting in a lower contribution of the cooling air flow to overall drag.When investigating those effects, both experiments and numerical simulations are commonly used in the automotive environment. Still, when comparing the results from both methods, differences in the effect of cooling air flow can often be observed.To better understand the effects of cooling air flow, the ECARA Subgroup CFD decided to establish a common design for a generic open source vehicle model with a detailed underhood compartment to lay the foundation for a common investigation model. The DrivAer-model, developed at the TU Munich, was chosen as the baseline vehicle, due to its high level of detail and the good acceptance in the community in recent years.Based on the input of the members of the group, FKFS designed a baseline version of the underhood compartment including a radiator package with fan and a representation of the engine in close cooperation with TU Munich. Since the majority of DrivAer models built are for scale model testing, the engine features a simplified design to be used as a starting point for CFD validation. This simplified design fits well to the level of detail of the original model. The underhood flow can both exi...

As the automotive industry strives to increase the amount of digital engineering in the product development process, cut costs and improve time to market, the need for high quality validation data has become a pressing requirement. While there is a substantial body of experimental work published in the literature, it is rarely accompanied by access to the data and a sufficient description of the test conditions for a high quality validation study. This paper addresses this by reporting on a comprehensive series of measurements for a 25% scale model of the DrivAer automotive test case. The paper reports on the measurement of the forces and moments, pressures and off body PIV measurements for three rear end body configurations, and summarises and compares the results. A detailed description of the test conditions and wind tunnel set up are included along with access to the full data set.