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Re: Blown Diffuser??
Posted: 08 Jul 2010, 19:00
by Richard
speedsense wrote:richard_leeds wrote:
I’d appreciate it is an aero person could explain how the temperature of the exhaust contributes to the enhanced flow compared to cold air.
F(thrust) ~ Area(air stream) * Density(air) * Average Velocityair2
That formula shows that the heat reduces the force, hot air is less dense.
My question is because comments on this topic often refer to the heat, not just the velocity.
Is the heat beneficial because less dense air helps with reducing pressure at the DDD exit?
Re: Blown Diffuser??
Posted: 08 Jul 2010, 19:35
by autogyro
Yes the Macca was faster on the straits with f-duct but that is not the same as high mass airflow on the RB allowing it to go through T8 flat.
I believe this was a result of better streamlining and better dealing with the airflow to generate better high speed DF. It may also be because of better ride height control.
The Macca may also get around slow and medium corners better with higher DF but the over all balance of aero seems better on the RB.
Re: Blown Diffuser??
Posted: 08 Jul 2010, 22:20
by ringo
The red bull has less thrust than the Mclaren, or any other car without a ebd.
Remember the engines all have virtually the same exhaust mass flow and all send this flow to the rear of the car, regardless of how high it is.
The redbull has less thrust because in the strict sense, thrust is taken as the longitudinal component of force.
Red bull takes away some of it's longitudinal thrust and directs this at the diffuser ramp, creating some of the down force. This reduces it's thrust, but increases the vertical component of force.
The portion of exhaust that it puts through the upper deck doesn't lose it's longitudinal component because of redirection, however it gives up it's internal energy to the low pressure low it drafts from the diffuser.
One thing that can be argued though, is that reb bull's exhuast remedies some of the aero inefficiency, since it's placed in an aerodynamic trouble spot, that ussually has separated flow and eddies.
Re: Blown Diffuser??
Posted: 08 Jul 2010, 23:15
by speedsense
richard_leeds wrote:speedsense wrote:richard_leeds wrote:
I’d appreciate it is an aero person could explain how the temperature of the exhaust contributes to the enhanced flow compared to cold air.
F(thrust) ~ Area(air stream) * Density(air) * Average Velocityair2
That formula shows that the heat reduces the force, hot air is less dense.
My question is because comments on this topic often refer to the heat, not just the velocity.
Is the heat beneficial because less dense air helps with reducing pressure at the DDD exit?
With regard to a generated vortex, a heated vortex would contain higher velocity, thus having more effect than one that is below ambient temp (non heated vortex). "Controlled" vortices are vital to increasing performance of the diffuser. For example, the slats in the diffuser, create counter rotating vortices at each 90 of the slat. One slat creates two vortices counter rotating, one on each surface of the slat. Any intensity increase in these vortices (heated) results in preventing higher pressures at the end (exit) of the diffuser by way of less expansion of the exiting air.
The question of the RB's use of exhaust gas around the outside of the diffuser and some inside, the vortices would be more intense and of higher velocities.
Personally, I don't believe that "thrust" is the result, except if the thrust is an acceleration of the vortex itself. IMHO
Re: Blown Diffuser??
Posted: 09 Jul 2010, 01:49
by autogyro
ringo wrote:The red bull has less thrust than the Mclaren, or any other car without a ebd.
Remember the engines all have virtually the same exhaust mass flow and all send this flow to the rear of the car, regardless of how high it is.
The redbull has less thrust because in the strict sense, thrust is taken as the longitudinal component of force.
Red bull takes away some of it's longitudinal thrust and directs this at the diffuser ramp, creating some of the down force. This reduces it's thrust, but increases the vertical component of force.
The portion of exhaust that it puts through the upper deck doesn't lose it's longitudinal component because of redirection, however it gives up it's internal energy to the low pressure low it drafts from the diffuser.
One thing that can be argued though, is that reb bull's exhuast remedies some of the aero inefficiency, since it's placed in an aerodynamic trouble spot, that ussually has separated flow and eddies.
+1 I believe the exhaust on the RB is used more to improve the flow of air rather than to directly influence the diffuser.
There is a thrust element (the RR Crecy aero engine developed 30 percent of the aircrafts thrust from the exhaust alone) but I do not believe this is very much in this application.
I think the RB is a smoother design where all the aero aspects are far better balanced than on the other cars resulting in better drivability and set up capability. They may lose this however as the other teams look to be catching up.
Re: Blown Diffuser??
Posted: 10 Jul 2010, 04:37
by godlameroso
Perhaps having the top mounted exhaust heats the air going to the rear aerodynamic elements of the car making the air that reaches those components less dense. If this is the case then it would make sense to move the air heaters known as exhausts away from these components. Cooler air = denser air, which means that denser air probably has some effect at creating more downforce when said air strikes said components. But this is just a guess, and have no proof to back it up.
Re: Blown Diffuser??
Posted: 10 Jul 2010, 10:34
by imightbewrong
Re: Blown Diffuser??
Posted: 10 Jul 2010, 12:01
by autogyro
I am coming round to this retarded ignition idea.
Scarbs article is fairly convincing.
It would have to be applied through mapping only during braking and cornering though IMO. The heat and fuel needed would not be acceptable for any longer use.
Does anyone have video of Vettel or Webber operating a map change under braking on a regular basis during a lap. Specificaly in Q3?
Re: Blown Diffuser??
Posted: 10 Jul 2010, 16:25
by donskar
Brilliant, absolutely brilliant. Typical Newey -- simple and elegant. The sort of thing that makes you say, "Why didn't [your favorite team here] think of that?"
Thank you for that link.
Re: Blown Diffuser??
Posted: 10 Jul 2010, 17:26
by xpensive
So Renault has developed a special engine-mapping-layout for their customer team only, not vey plausible that if you ask me?
Re: Blown Diffuser??
Posted: 10 Jul 2010, 17:42
by timbo
xpensive wrote:So Renault has developed a special engine-mapping-layout for their customer team only, not vey plausible that if you ask me?
I think RBR write their own code.
After all, they make their out gearbox, no?
Re: Blown Diffuser??
Posted: 10 Jul 2010, 18:04
by xpensive
Indeed, while what do yo know, they bolted the engine to the tub all by themselves, but what's the "code" anyway,
sounds just as engineerish as getting the tyres to "work"?
Re: Blown Diffuser??
Posted: 10 Jul 2010, 20:02
by timbo
xpensive wrote:Indeed, while what do yo know, they bolted the engine to the tub all by themselves, but what's the "code" anyway,
sounds just as engineerish as getting the tyres to "work"?
What, all those
Code: Select all
while e[i].w<mid do inc(i);
while e[j].w>mid do dec(j);
are not engineerish enough for you?
Re: Blown Diffuser??
Posted: 10 Jul 2010, 23:02
by speedsense
autogyro wrote:I am coming round to this retarded ignition idea.
Scarbs article is fairly convincing.
It would have to be applied through mapping only during braking and cornering though IMO. The heat and fuel needed would not be acceptable for any longer use.
Does anyone have video of Vettel or Webber operating a map change under braking on a regular basis during a lap. Specificaly in Q3?
It could be even simpler than that. With assorted timing maps and arguments that can be written into the ECU software, a timing map could be automatically installed by using an argument for a percentage of throttle (>10% for example) and a rpm/speed range,time or even GPS location, as additional parameters. The driver wouldn't need to input anything, just the "conditions" need to met. Quite a standard feature of most racing ECU's. And the conditions can be manually switched on or off (by the driver), as another function of the argument.
I did pay attention to qualifying today, especially the off throttle of the Red Bull in car camera. There is definitely a tonal difference of the engine in off throttle.
Re: Blown Diffuser??
Posted: 10 Jul 2010, 23:43
by mep
I did pay attention to qualifying today, especially the off throttle of the Red Bull in car camera. There is definitely a tonal difference of the engine in off throttle.
hahahahahahaha
You really impress me, you hear a difference between on and of throttle.