DRAG COEFFICIENT FOR CARS. by SANDHYA

Transcription

1 DRAG COEFFICIENT FOR CARS by SANDHYA

2 Concept of Drag Drag is the retarding force exerted on a moving body. It attempts to slow down the moving body. It is a function of the speed of the body, the size (and shape) of the body, and the medium through which it is moving

3 Drag Force Due to Air The drag force due to wind (air) acting on an object can be found by: F D = ½ ρ C D V 2 A where: F D = drag force (N) kg/m 3 } C D = drag coefficient (no units) V = velocity of object (m/s) A = projected area (m 2 ) ρ = density of air (kg/m 3 ) {1.2

4 Generally the size of a vehicle and its frontal area is determined by the design requirements. Consequently efforts to reduce drag are concentrated on reducing the drag coefficient by proper shaping of the body..

5 Drag Coefficient: C D The drag coefficient is a function of the shape of the object and the Reynolds Number (Re) Re = (velocity * length-scale) / (kinematic viscosity) For a full-size truck, a change in drag coefficient of 0.01s approximately equal to an improvement in fuel economy of 0.1 mpg on the combined city/highway driving cycle. The same drag coefficient reduction can improve a car's fuel economy by approximately 0.2 mpg.

6 Typical drag coefficients The average modern automobile achieves a drag coefficient between 0.30 and SUVs(sport utility vehicle), with their typical boxy shapes and larger frontal area, typically achieve a C d of A very gently inclined windshield gives a lower drag coefficient but has safety disadvantages, including reduced driver visibility. Certain cars can achieve figures of , although sometimes designers deliberately increase drag to reduce lift. Some "high performance" models may actually have higher drag, due to wider tires and extra spoilers.

7 Drag coefficient Cd Old Car like a T-ford Modern Car like Toyota Prius 0.26 Sports Car, sloping rear Convertible, open top Common Car like Opel Vectra (class C) 0.29

8 Drag coefficient Make Model Year Cd Acura CL Acura CL Acura Integra Acura NSX Acura RSX Acura TSX

9 Make Model Year Cd Audi A Audi A Audi A Audi A Make Model Year Cd BMW Compact BMW 3-series BMW 5-series BMW 7-series

10 Make Model Year Cd Mercedes-Benz C-class Mercedes CL Mercedes-Benz E-class Mercedes-Benz G-class Mercedes-Benz S-class Mercedes SL Mercedes-Benz Vito Fiat Bravo Fiat Cinquecento Fiat Punto Fiat Ulysse

11 Make Model Year Cd Ford Aspire Ford Escort (Euro) Ford Escort Ford Explorer II Ford F-150 Lightning Ford Fiesta Ford Galaxy Ford Ka Ford Maverick Ford Mondeo Ford Mondeo Turnier Ford Ranger Ford Scorpio Ford SVT Mustang Cobra Ford Thunderbird

12 Make Model Year Cd Honda Accord Ex Coupe Honda Civic Honda Civic Hatch Honda Civic Coupe Honda Civic Honda Civic Coupe Honda Civic Del Sol Honda Civic Hatch Honda Civic Hatch Honda Civic Sedan Honda Civic Hybrid Honda Civic Hybrid Honda Civic SI Honda CRX Honda CRX Honda CRX HF Honda Insight

13 Make Model Year Cd Volkswagen 1L Concept 0.15 Volkswagen Beetle Volkswagen Beetle Volkswagen Caravelle/Transpo rter Volkswagen Golf Volkswagen Golf Variant Volkswagen Jetta Volkswagen Jetta Volkswagen Jetta sedan Volkswagen Jetta Volkswagen Jetta wagon Volkswagen Passat Volkswagen Passat Wagon Volkswagen Polo Volkswagen Sharan Volkswagen Vento/Jetta

14 Make Model Year Cd Jeep Cherokee Jeep Grand Cherokee Jeep Jeep Wrangler TJ- Hardtop Wrangler TJ-Soft Top Mazda Mazda Xedos 9/Millenia Mazda MX Nissan Cube Nissan Leaf Nissan Maxima Škoda Felicia Škoda Octavia Toyota Prius Toyota Sienna Toyota Supra General Motors EV

15 To improve Cd To improve Cd, designers may make the following changes: Round the edges of the front end Tune the grille and fascia openings Tune the wheel openings Place spats (small spoilers) in front of the tires to reduce turbulence Tune the size and shape of the outside mirrors and their attachment arms Add side skirts Tune the deck height, length and edge radius Install a rear spoiler Adjust the angle of the rear window Tuck up the exhaust system Use a diffuser to tune air coming off the underside Install "belly pans," underbody panels that cover components and smooth airflow

16 THANK U