bazanaius wrote:I believe there are a few threads discussing exhausts exiting into the diffuser area. I know Macca has done it a few times on their cars.
In general, I believe that the argument against this is that the exhaust gases are not a constant stream, but rather a series of pulses as the exhaust valves open/close. This could lead to an inconsistent level of downforce generated by the diffuser/floor and produce a rather unpredictable driver.
With the radiator, I'm not sure how fast the air would be going out of this area, and whether all you'd effectively be doing is unsealing your floor.
Ciro Pabón wrote:... Besides, the speed of the exhaust is not as high as the speed of the car.
Belatti wrote:Ciro Pabón wrote:... Besides, the speed of the exhaust is not as high as the speed of the car.
How can you be so sure?
Teams use the exhaust pipes exiting into the diffuser to “energise” the flow, there speed of the airflow through the diffuser can be sped up by the high velocity gasses exiting the exhaust pipes when the engine is revving. This apparently free increase in diffuser performance was very popular in the 90s and was encouraged by bodywork restrictions preventing the exhaust pipes routing over the gearbox. As the performance of the diffuser grew and it became a larger component of the cars rear downforce, it became a problem that the effect of the exhausts blowing was reduced when the driver lifted off the throttle and the speed of the flow reduced, teams found this made the cars handling very sensitive to engine speed and slowly the practice was dropped first by routing the exhausts into less effectual positions in the diffuser and then later through the top of the sidepods using the Ferrari inspired “periscope” exhausts.
Three teams still blow the exhausts into the diffuser, Williams and Minardi blow the exhausts over the inner side channel, in fact Minardi have shaped the ends of the exhaust pipes to form the top of the diffuser channel, Williams flattened the bottom of the pipes to merge the flow of the exhaust and out the top of the diffuser channel. McLaren blow their exhausts above the shadow plate in the centre of the diffuser, there may be a few reasons for this practice, one of the main reasons is to energise the flow coming from the transition area of step plane, McLaren use the exhausts blowing against a knife edge formed between the pipe and the vertical step, this speeds up the flow, improving the scavenging effect ton this area, it also adds t the downforce generated by the central diffuser tunnel.
F1_eng wrote:Averaging volumetric inlet air flow and assuming 100% vol eff @ 18,000 rpm, the average speed in a 60mm dia exhaust would be around 140mph
I am a huge fan of F1 and I have watched almost every race since 1989. I think there is less than 10 that I have missed since then
I am reading this forum for two years at lease and it was very helpful. I am currently building truck day car, mid-front engine with rear wheel drive, around 950kg with driver and 250hp engine and I need some help in terms of flat floor, exhausts and cooling. Car is equipped with flat floor and rear diffuser.
Can you explain me if there is any advantage/disadvantage of directing hot air from radiator under the floor. Radiator is about 50 cm after the front bumper and I can choose to direct hot air through the bonnet or under the floor.
The same question is for exhaust gasses. Should I put them under the floor or at the rear of the car above the diffuser?
Thanks for your help and understanding (I am not an engineer)
speedsense wrote:F1_eng wrote:Averaging volumetric inlet air flow and assuming 100% vol eff @ 18,000 rpm, the average speed in a 60mm dia exhaust would be around 140mph
Try this study on a rotary engine... the air flow through the intake and the exhaust is supersonic....
speedsense wrote:A airplane must use a higher top speed to become airborne on a hot day, as the heat causes less lift. However if you can increase the heat on the high velocity side of a wing and have a lesser temp on the low pressure side, you can actually increase lift.
When it comes to a diffuser, you would want the higher temp to be above the diffuser and not in it. IMHO
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