Aerodynamics and CFD at Volvo Car Corporation

Transcription

1 Aerodynamics and CFD at Volvo Car Corporation KTH April 2010 Johan Ljungberg Volvo Car Corporation Issue date: , Security Class: Public Page 1 Graduated from KTH 2005 Scania AB Volvo Cars Present at the CFD group: 12 employees KTH, Johan Ljungberg, jljungb3 Issue date: , Security Class: Public Page 2

2 Overview Background Influence of Aerodynamics Why is aerodynamics important Development Facilities Test Techniques Moving Ground Page 3 Influence of Aerodynamics Drag (fuel consumption, top speed, acceleration) High-speed stability (lift) Cross-wind stability (side force and yawing moment) Passenger comfort (cabriolets) Cooling Performance Dirt deposition (visibility) Aero acoustics (limiting the strength of sources) Body deformation (Door frames etc) Page 4

3 Road Load 2500 Load, N The aerodynamic drag increases as a function of speed Rolling resistance Aero Drag Total N km/h Page 5 Sources of drag on a modern car 45% 30% 25% Page 6

4 Aerodynamics part of total fuel consumption EU Combined cycle NEDC (Note! Average speed 33km/h) Electrical systems 16% Transmission losses 8% Drag 26% Lost kinematic energy during braking 29% Rolling resistance 21% Page 7 Aerodynamics part of total fuel consumption Constant speed 90km/h Electrical systems 8% Transmission losses 9% Rolling resistance 30% Drag 53% Page 8

5 Aerodynamics part of total fuel consumption EU Combined cycle NEDC (Note! Average speed 33km/h) Rule of thumb: 26% Electrical systems 16% Transmission losses A 10% reduction of CdxA will reduce Lost kinematic energy Dragthe NEDC fuel consumption by 1,5% during braking Assuming that the performance changes, ie keeping the same gearbox ratios Rule of thumb: 8% Rolling resistance A 10% reduction of CdxA will reduce the NEDC 21% fuel consumption by 2,5% If the gearbox ratios are changed to keep the same performance 29% Page 9 Aerodynamics On the C30 DRIVe Page 10

6 C30 DRIVe: Aerodynamic parts Cooling air intake Front undershield Front wheel deflectors Page 11 C30 DRIVe: Aerodynamic parts Roof wing Cover plate Diffusor panel Floor panels Rear bumper Page 12

7 C30 DRIVe: Cd reduction -0,007-0,008 Page 13 C30 DRIVe: Cd reduction (-0,002) (-0,002) -0,012 (-0,003) -0,008 (-0,002) Page 14

8 C30 DRIVe: Aerodynamic parts Special wheels (Libra) delta Cd (compared to steel rims) -0,002 (standing still) -0,005 (rotating) Lowered chassis delta Cd -0,005 Page 15 Aerodynamic drag reduced more than 10% compared to standard car Fuel consumption reduced by: 0,12 l/100km or 3g CO 2 /km (EU Combined) (this corresponds to an equivalent weight reduction of approx. 80kg) 0,3 constant 90km/h Page 16

9 Challenges facing Aerodynamicists Styling Manufacturing Parts Assembly Packaging Visbility Other attributes (eg Thermo, dirt, handling ) Carry-over content Cost!!! Page 17 Aerodynamics through the ages Year Cd PV ,50 Amazon ,48 Cd v Year P ,48 P1800ES , , , , , , , , ,34 S ,31 V ,33 XC ,40 V ,35 S40N , ,39 480ES ,38 S ,34 V ,36 0,60 0,55 0,50 0,45 0,40 0,35 0,30 0, Page 18

10 Aerodynamics through the ages Year Cd PV ,50 Amazon ,48 P ,48 CdxA v Year P1800ES , , , , , , , , ,34 S ,31 V ,33 XC ,40 V ,35 S40N , ,39 480ES ,38 S ,34 V ,36 1,20 1,10 1,00 0,90 0,80 0,70 0, Page 19 Aerodynamics through the ages Year Cd PV ,50 Amazon ,48 Frontal Area v Year P ,48 P1800ES , , , , , , , , ,34 S ,31 V ,33 XC ,40 V ,35 S40N , ,39 480ES ,38 S ,34 V ,36 2,90 2,70 2,50 2,30 2,10 1,90 1,70 1, Page 20

11 Development process Concept study Generic shape studies Evaluate styling proposals Define underfloor concepts Analysis and research of previous models and competitors Simple scale model tests (parameter studies) Semi-detailed CFD (parmeter studies) Create guidlines to design and engineering Create aerodynamic hard points Page 21 Development process Prestudy Develop frozen design Develop underfloor solutions Analyse and suggest improvements to many designs (CFD and models) Give recommendations when choosing design Develop and improve chosen design using full-scale clay model and fully detailed CFD modelling Confirm and approve the chosen design s predicted characteristics Page 22

12 Development process Fine tuning of pre-production prototypes Confirm and approve all characteristics Follow up any late design changes Confirm production car Project Detail optimization Verification Page months Concept study Generic shape studies Evaluate styling proposals Define underfloor concepts Prestudy Develop frozen design Develop underfloor solutions Project Detail optimization Verification Page 24

13 Wind tunnel facilities at Volvo In-house testing in three wind tunnels, Gothenburg PVT Test section 27m2 (6.6mx4.1m, length 15.8m) Max speed 250 kph Temp. +20 to 60 C Chassi dyn. load 150 kw Sun sim. max 1200 W/m2 MWT 1:5 scale of PVT Test section 1.1m2 Max. speed 200 kph Climatic Test section/nozzle 11.2m2 Max. speed 200 kph Temp range -40 to +50 C Chassi dyn. load 280 kw Sun sim. max 1200 W/m2 Issue date: , Security Class: Public Page 25 Conventional aerodynamic testing Balance measurements Effect of configuration changes on aero coefficients Investigate sensitivity to flow angle, vehicle attitude and wind speed Turn table Wheel Drive Units Centre belt Supporting struts Issue date: , Security Class: Public Page 26 Measuring frame

14 Methods to increase the knowledge gained from aerodynamic testing Flow visualization (smoke, surface paint, tufts) Page 27 Methods to increase the knowledge gained from aerodynamic testing Pressure Measurements Page 28

15 Methods to increase the knowledge gained from aerodynamic testing Wake measurements = 2 2 D ( P + ρu P U ) dydz ρ 2 Seven-hole probe rake Floor traverse Page 29 Wake analysis Wake measurements 100 mm downstream of a notchback Total pressure Microdrag Identify regions that can be improved Page 30

16 Why Moving Ground is Neccessary Provides correct relative movement between the car body and tunnel floor Provides correct relative movement between the car body and wheels Influences flow under and around car Page 31 How: Stationary Floor and Wheels Wind Page 32

17 How: Moving Ground and Rotating Wheels Wind Road/Floor Page 33 Optimisation affected Roof and boot Wheel Design Front-end and deflectors Underbody design Page 34

18 Thank you for your attention Page 35