ELMS 2017 second event at Monza circuit has offered the opportunity to see LMP2 and LMP3 racing on the high speed circuit, low drag configuration, last opportunity to prepare Le Mans 24 Heures.
After first race at Silverstone where more downforce setting and configuration was used, this provide a more complete picture of actual performance of different cars.
Standard solution adopted on LMP cars to ensure proper rear brakes cooling is the use of internal duct, inside rear fender, feeding with fresh air caliper-disc assembly. External air scope contributes to drag, due to the air momentum variation associated with change in airflow direction and additionally to their shape.
Consolidated good practice is to have the air duct entry on high pressure coefficient area on external surface of the fender, so to negotiate drag contribution due to local pressure; normally locating the entry section on rear fender front “nose”, just above side pod top surface.
This is clearly visible on drawing of Oreca 05 LMP2 where the engine exhaust pipe location is also visible, in front of the rear wheel arc, on lateral side surface.
Oreca 05 - details of rear brake duct intake and engine exhaust tube at rear fender
A good example of constant development on all area of LMP cars, is shown on Oreca 07 drawing below.
Rear fender “nose” doesn’t locate any longer the rear brake air scope which is moved down on side pod .
Due to the local pressure coefficient a flow guide is needed in order to get external air flow into the internal duct.
Exhaust tube location and shape of surrounding part of rear fender shows the concept of using the high momentum of exhaust gases to condition and direct flow on external side pod in front of the very critical area of rotating wheel. Note also the two small triangular strakes.
Oreca 07 - details of new design of rear brake duct intake and very refined engine exhaust exit on rear fender
Trailing edge nolder clearly visible on front splitter. As discussed on previous articles this is a key part of the nose to create downforce, and topic of several interpretation of the technical rules that are intentionally putting constrains to limit the “airfoil design concept”.
Dallara - Nolder at trailing edge on front splitter
Refined design of raised underfloor in front of side pod entry. This solution permit to increase airflow under the floor in the area behind front wheel and within bottom plank and lateral parts of side pod.
Increased airflow grant better feeding of rear diffuser increasing downforce with good efficiency.
Dallara – Raised floor on entry of side pods
Flow behind rear wheel arc and inside fender is very complex due to vorticity caused by the wheel and interaction with flow running on side parts of the car. Low pressure behind car is used to extract air from inside fender and directing it upward contributing to downforce generation and less drag. Lateral slot on side cone and turning vanes are used to create ducts for the flow.
Dallara – Side bottom of rear fender with fence and duct to guide lateral flow
Typical turning vanes design located on front keel to diverge the flow laterally and push it on side pod duct and under the floor.
Ligier JSP 217 – Barge board on front keel behind nose