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Thread: Car Grille Aerodynamics

  1. #1
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    Car Grille Aerodynamics

    I was wondering, since EVs like the Tesla Model S have solid front grilles, how much drag does the radiator behind an open grille in a normal ICE vehicle create? And is this drag so great that an open main grille with a radiator behind it is not an option in EVs?

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    Technical Fellow jboggs's Avatar
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    I have no idea how much drag the open grills in ICE cars create but I imagine it is significant. Regardless of how much it is, it's obvious that a properly designed closed front end would have less drag than one with holes and radiator fins. So, if efficiency is the name of the game for EV's, and cooling is not required, why would one even consider an open grill? Appearance?

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    Dear jboggs,I am doing a project on EVs and I was just wondering what impact an open grille would have on an EVs efficiency.Do you maybe know how the drag of an open radiator can be calculated? I have looked up some equations, but none are specific enough.

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    The significant effects of a grill on aerodynamic drag are strongly dependent upon the the overall contours of the front of a vehicle. A carefully designed bullet nose vehicle front shape without a front opening or grill is clearly superior to one with these features.

    As to your inquiry about being able to calculate the flow rate through a radiator, due to the design and density of the cooling fin structure, including the corregation in the fins, it would require an extremely sophisticated CFA program to provide even an approximate answer.

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    Technical Fellow jboggs's Avatar
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    I know the drag is significant enough that considerable engineering manhours have been consumed over the last few decades trying to optimize the airflow both at the grille and under the hood to the radiator and the combustion air intake. They might express the data in terms of BTU's of effective cooling per lb of drag force at a certain speed. If you research the car magazines and engineering journals, like Machine Design magazine, over that period you will see numerous articles in which that specific engineering task is mentioned.

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    Thanks for your contributions.
    What about sportscars, like the Lamborghini Huracan, that have those thin but long front air intakes? Does the longer & thinner grille create less drag than a big square grille?

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    Basically it is a simple matter of aerodynamics, the long thin grill opening allows improved front end streamlining. By looking at examples of modern supercars you are the right track in seeing how this issue has been addressed tom date.

    When it comes to the shape of the front end of a performance automobile, it is not as simple as just designing a wedge shape leading nose on the vehicle to provide a minimum frontal area and maximum flow streamlining because this must be balanced against the need to provide a front end design that does not create an excessively low pressure flow over the upper nose of the vehicle that will result in a lifting force on the front of the vehicle at high speeds; and, for race cars there is also the matter of providing adequate air cooling flow to the front brakes to prevent brake fade. The best design for providing the ideal combination of all of these elements is still a matter of ongoing continuous development.

    When comes specifically to grills and their shapes on standard production vehicles there are generally two factors that have historically controlled their addition and configuration and neither have anything to do with minimizing aerodynamic drag. First, they are primarily an appearance item that are used to define the cars heritage and manufacturer just as the same as car emblems; and second, from a more practical standpoint they act as a protective barrier to prevent large items from impacting and damaging the delicate radiator core needed for engine cooling.

    As for the design of radiators for standard production daily driven vehicles this is mostly focused on providing maximum heat transfer from the circulating coolant to the radiator fins and from the fins to the air flow through the radiator core to minimize the size and cost of the radiator. Providing engine cooling across a wide range of operating conditions from idling in stopped traffic to driving at highway speeds in both zero and hundred degree temperature conditions is more critical than minimizing air flow restrictions; and, the clear evidence that this cannot be determined strictly by radiator and front grill opening design is the universal application of cooling system fluid controlling thermostats and thermostat controlled electric cooling fans.

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