Correct, pressures are always positive, except for some strange cases (attractive forces, Casimir effect, etc), which do not apply here, I'll have to re-word it, thanks for that.Ogami musashi wrote: The diffuser area has higher pressure than the undertray area..in addition, "negative pressure" is not a correct term, the static pressure is always positive. It can be lower than a pressure above or below it but it is positive.
I would have thought gauge pressure would be a useful concept when discussing diffusers in that it would be indicative of downforce.Kiril Varbanov wrote:Correct, pressures are always positive, except for some strange cases (attractive forces, Casimir effect, etc), which do not apply here, I'll have to re-word it, thanks for that.Ogami musashi wrote: The diffuser area has higher pressure than the undertray area..in addition, "negative pressure" is not a correct term, the static pressure is always positive. It can be lower than a pressure above or below it but it is positive.
I don't really like the "diffuser" and "downforce" together. Imo, the diffuser doesn't create downforce in the same sense as a wing produces downforce, it just allows the air to expand. This diffuser has got a certain pressure recovery value from the base pressure (which can be found behind the car). This gives you a lowest pressure peak (located exactly where the diffuser starts) which is lower than the atmospheric pressure, therefore creating suction. If this suction is located between the ground and the car, it will suck the car down (obviously). The diffuser angle, shape and as you said its distance to the ground are important parameters that will define the pressure recovery.shamyakovic wrote:the diffusor cannot produce downforce by itself, it needs to be nearer to the ground to produce downforce, isnt it?
I would disagree. The "diffuser" section should have a lower dynamic pressure than the underbody section ahead of it. If this were not the case, then the natural airflow would be in the reverse direction. A fluid usually tends to flow from a region of higher pressure to a region of lower pressure, right?. Diffuser is probably not the best term to describe the divergent aft section of an F1 undertray. A better term might be "extractor".Kiril Varbanov wrote:Correct, pressures are always positive, except for some strange cases (attractive forces, Casimir effect, etc), which do not apply here, I'll have to re-word it, thanks for that.Ogami musashi wrote: The diffuser area has higher pressure than the undertray area..in addition, "negative pressure" is not a correct term, the static pressure is always positive. It can be lower than a pressure above or below it but it is positive.
In an incompressible fluid at the same altitude (geodetic pressure) the static pressure will decrease when dynamic pressure increases. (Bernoulli's principle). Static pressure + dynamic pressure (+geodetic pressue) = constant.riff_raff wrote: I would disagree. The "diffuser" section should have a lower dynamic pressure than the underbody section ahead of it.
Wouldn be better to put wing low pressure side on the end of floor,so low pressure from wing will "suck/accelarate air under floor,so in this case we dont have adverse pressure gradient-situation?Ogami musashi wrote: ↑07 Jun 2013, 02:06There two conservation principle involved there:
Conservation of mass
Conservation of energy
The complete assembly of undertray+diffuser form a tube of section S1 and S2 respectively.
The quantity of air that enters S1 per second must be the same that exits S2 per sec.
Since we're dealing with particle moving we can also say that the speed at which the quantity flows through S1 must be proportional to the speed that flows through S2 i.e S1V1=S2V2.
Since S2 is larger that S1, V1 is greater than V2 so the speed in the undertray is the greater than in the diffuser.
Now why does the diffuser accelerates the flows in the undertray? This is because the air is slowed down in S2...but the density stays the same (at the speed a car travels); the word "expand" is misleading, the air is not stretching is actually just slows down...and thus a "vacuum" is created and since nature doesn't like it it will be filled...by air coming from the undertray...in other words the diffuser will pump air from the undertray to fill the whole S2 section and the S1V1=S2V2 principle will be verified, only that V1 will be even greater than if the diffuser wasn't there and S2 will be slower.
The peak acceleration at the location where the gradient of section is the greatest, since the difference of section will dictate the speed, the quickest and most abrupt change of section will lead the to steepest change in speed and this is where the diffuser starts.
Now, speed are defined, and they're changing, but energy's not. So basically the three (negating the internal energy of the system) forms of energies (derived from static pressure, height and speed) will varying to conserve the total energy of the system.
If speed increase, either potential energy (from height) or static pressure derived energy will need to compensate.
If we take one particle (in fluids dynamics a particle is not one molecule but a bunch of molecules, that is a small volume of air), its potential energy will not change (the particle will stay at the same height) so only the static pressure will decrease.
The static pressure will decrease and thus hopefully the pressure above the car will be higher thus creating a pressure differential and thus downforce.
Hope this helps.
Yes but i find this forum very inactive.Ogami musashi wrote: ↑23 Jul 2020, 14:49Hello IQ 240
I think there are much more knowledgeable people on this forum to answer your questions
