Diffuser (automotive)
A diffuser, in an automotive context, is a shaped section of the
Overview
When a diffuser is used, the air flows into the underbody from the front of the car, accelerates and reduces pressure. There is a suction peak at the transition of the flat bottom and diffuser. This transition is where the lowest pressure generally is located and is called the throat of the diffuser. The diffuser then eases this high velocity air back to normal velocity and also helps fill in the area behind the car making the whole underbody a more efficient downforce producing device by reducing drag on the car. The diffuser also imparts upward momentum to the air which further increases downforce.
The trailing or leading edge of a diffuser may receive a nolder—a precise small lip, protuberance or wing to enhance its performance.
Operation (rear diffuser)
The aft part of a car underbody is where a rear diffuser is usually located. It works by accelerating the velocity of the airflow underneath the car. At the diffuser exit station the air flow is at the same pressure and speed of the ambient. Since its geometry is expanding the rear region, the exit area is much bigger than the inlet, so for the conservation of mass principle the air flow will have a much bigger speed at the diffuser inlet and as a consequence under the whole car underbody. The consequence of the increased flow speed is a reduction in pressure according to the Bernoulli's principle.[1] Since the pressure below the car is lower than on the side and above the car, downforce is produced if implemented correctly.
Front diffusers also exist (especially on
Injecting the exhaust into the rear diffuser can also help extract the air from below the car. The exhaust gasses effectively energize the boundary layer, helping to raise the pressure of the low-pressure, fast-moving airstream back to the ambient atmospheric pressure at the exit of the diffuser. This fast-moving air helps evacuate the diffuser more quickly, which helps drop the pressure at the underbody. However, this makes the diffuser rather sensitive to engine speed. When the driver lifts off the throttle, the exhaust flow is greatly reduced, which makes the diffuser less effective, robbing the vehicle of downforce. Thus, handling is negatively affected.
The car's bodywork also interacts with the flow through the diffuser. In addition to creating downforce, the front wing and nose try to keep "clean air" flowing around, and more importantly under, the car.
Multi-deck diffusers
In 2009, the
Splitters
As the front of the car slows down the air without a diffuser, this is the ideal place for an inlet. A splitter is commonly used here, serving to increase the amount of downforce at the front of the car. The airstream is brought to stagnation above the splitter by an air dam, causing an area of high pressure. Below the splitter, the air is redirected away from the stagnation zone and is accelerated, causing the pressure to drop. This, combined with the high pressure over the splitter, creates downforce. The larger the area of the splitter, the more downforce is generated. In most closed-wheel race cars, the underside of the splitter smoothly integrates with the undertray, creating one large flat plane that is driven by the rear diffuser. Some race cars, such as the Toyota GT-One, use an additional diffuser immediately behind the splitter to help create more downforce.[7] The air extracted by this diffuser is exhausted through vents in the sidepods or above the car around the cockpit.
Examples of diffusers and splitters
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Rear diffuser protruding from below bumper on a Chevrolet Corvette C6.R. Note the strakes for keeping out tyre wake.
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Double Decker diffuser of a Formula One car (Toyota TF109). Note channels above the main diffuser on either side of the light.
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Rear diffuser visible below the license plate on aPorsche 918 Spyder.
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Large front splitter below nose on an Audi R10 TDI
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Front splitter visible below the nose on an Aston Martin DBR9
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Front splitter integrated into bumper of a Lotus Exige S.
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Small front splitter below the bumper of Subaru Impreza WRX.
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Two-tier rear wing, with lower profile mounted to enhance diffuser airflow.
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Front view of a splitter on a NASCAR car (white)
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Side view of a splitter on a NASCAR car (white)
See also
- Aerodynamics
- Ground effect in cars
- Racing car
- Venturi effect
References
- from the original on 2022-08-28. Retrieved 2020-10-04.
- ^ "EzCarbon - EzCarbonfiber". EzCarbon. Archived from the original on 2022-04-09. Retrieved 2022-04-09.
- ^ "Shell Motorsports: Front Wing Profiles". Archived from the original on 2010-02-26. Retrieved 2010-02-01.
- ^ "Mulsanne's Corner: WFO; Ward, FUJIMORI, and others". www.mulsannescorner.com. Archived from the original on 2010-01-07. Retrieved 2010-02-01.
- ^ "The row that has split F1". April 17, 2009. Archived from the original on April 21, 2009. Retrieved February 1, 2010 – via news.bbc.co.uk.
- ^ "ITV F1: Double diffusers to be banned for 2011". Archived from the original on 2010-01-27. Retrieved 2010-02-01.
- ^ "Mulsanne's Corner: 1998-1999 Toyota GT-One". www.mulsannescorner.com. Archived from the original on 2008-06-24. Retrieved 2008-07-08.
- Katz, Joseph (2006), Race Car Aerodynamics: Designing for Speed, Bentley Publishers, ISBN 0-8376-0142-8
External links
- Mulsanne's Corner: What is a Diffuser?
- Pressure Images
- Airflow Patterns
- Airflow bottom view Archived 2008-03-08 at the Wayback Machine
- Airflow side view Archived 2007-10-13 at the Wayback Machine
- Rear diffuser Archived 2007-10-24 at the Wayback Machine
- Formula 1 Multi-Deck Diffusers