Not sure about PZ, but I would like to see the wake from the "regular" mirror of the same frontal area. Is it that the slots somehow emulate having a proper tapered tail?
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Team: Mattia Binotto (CTO), Simone Resta (CD), Loic Bigois (HA), David Sanchez (CA), Jock Clear (ED), Corrado Onorato (DCD), Rory Byrne (Tech Advisor), Massimo Rivola (SD), Matteo Togninalli (CRE), Maurizio Arrivabene (TP), Sergio Marchionne (Chairman)
Drivers: Sebastian Vettel (5), Kimi Raikkonen (7), Esteban Gutierrez (reserve)
This is a good example. Channels introduce high-speed jets of air who influence both laminar flow around the mirror and turbulent wake. Injecting high energy air increases total pressure on the mirror surface, reducing pressure difference and thus drag.
I've scrolled trough this paper just now and noticed that mirror design in it is oval, not rectangular in front/rear view. So the effect is even bigger because of full 3D effect and that's why the turbulence behind the mirror on the video above is smaller than on my CFD results.graham.reeds wrote: ↑28 Feb 2018, 03:54This paper tends to agree
Low Drag Automotive Mirror Using Passive Flow Jet Control
Fully agree with the conclusion, but to be certain you can increase the calculated area beyond the body of the mirror, lets say put the boundaries at the actual height of the mirror to the ground and 1m ahead and 1m behind the mirror.Vanja #66 wrote: ↑22 Mar 2018, 21:57Here it is.
https://ibb.co/ktpzZc
I had to simplify it quite a bit, since no quarter of these mirrors is the same since air flow is far from perpendicular in this area of the car. To save computing resources, I decided to abandon my original idea to make the CFD model as close as possible in terms of geometry, which allowed me to test just a single quarter of this mirror.
The big unknown here is, of course, the internal geometry of mirrors and fairing, this is why it wouldn't be useful to make the model externally similar to actual thing.
There were 9 simulations in total, a combination of different slot gaps - 1, 2 and 3mm; and a combination of different air velocities - 30, 60 and 90 m/s, translating to around 100, 200 and 300 km/h. It is very hard to distinguish if there even is a slot around actual mirror, let alone the height of it. At first, I was looking at 1, 3 and 5mm slots, but realized 5mm is way too much.
Meshing, turbulent model and overall CFD set up is the same I used to correlate wind tunnel results with CFD for a much more complex model, so these results weren't dropped out of thin air. Let me show you the mesh, on the right you can see refined mesh made with adaptive meshing, automated by software. Blue cells pure fluid, green are partial cells.
https://ibb.co/dKfyAH
So here are the results, side view in symmetry plane, pressure distribution with streamlines.
https://ibb.co/ceYkqH
Our discussion was about whether or not there is choking inside these channels at different speeds and CFD results of this model show none of that. Pressure distribution is practically the same for the same slot height, while slightly different shapes of turbulent wake shouldn't be taken too much into consideration - it's turbulence after all and these were steady state simulations, not transient.
Numbers, in terms of drag coefficient multiplied by referent surface, tell the same tale. Differences are between 1-3% for the same slot height, which is within a tight margin of numerical error. Also, slots 2 and 3 offer almost 20% drag reduction compared to 1mm slot. Perhaps the optimum slot height is 2.5mm or something like that. Whatever it is, to make sure it is the same height all around the mirror with 2 or 3mm is not an easy thing with carbon fiber.
https://ibb.co/jPr8cx
Other views of pressure distribution offer the same, let me show you a top view of 2mm slot at 60 m/s, hardly different from other 8 results.
https://ibb.co/mXs9jc
The separation on outer surface here should be ignored, since this is just a single model without any optimisation. From this point of view, to achieve even better results the inside cone should be a bit more tapered in top view, as should the side fairing.
Just to add another thing into the mix, I first did a simulation of fairing with extended trailing edge:
https://ibb.co/fD84Hx
Wow, a huge difference, isn't it?It is, but not because of fairing, it's because of a decimal point in a turbulent factor value, which was 10 times bigger than it should be. This is why I always double check my first simulation, mistakes like that creep up all the time.
Having said that, here's hoping this discussion will not be resurrected.Based on these simulations, there is no reason to believe there is much more to these mirrors other than drag and turbulent wake reduction.
Ok i see.Vanja #66 wrote: ↑24 Mar 2018, 18:42Cheers mate!PlatinumZealot wrote: ↑24 Mar 2018, 14:44Great work! You are a true scientist and engineer.
First of all your good work rubbishes the air deflector to side-pod theory. Secondly I would have liked to have seen the model without any slot, and finally I am also interested in your last conclusion, with the turbulent factor value - in layman's terms was it good or bad?
Do you mean a "regular" mirror design or this same design with slot height 0?
The turbulent factor I was talking about is related to energy dissipation, meaning the bigger it is the faster the turbulence dissipates (in layman's terms). So by making it bigger than it should've been, ie bigger than it was for other (more realistic) simulations, the turbulence is "gone" faster. That's why the flow was so much different.
No problem Ringo, will do it gladly.ringo wrote: ↑25 Mar 2018, 01:44Fully agree with the conclusion, but to be certain you can increase the calculated area beyond the body of the mirror, lets say put the boundaries at the actual height of the mirror to the ground and 1m ahead and 1m behind the mirror.
I would like to see the result in that case. The larger volume would make a difference to the results. Also include an ordinary mirror for us to see what the real difference is with the best slotted one that you have designed.
I know it's a lot of work i am giving you but you already did quite a lot of work to get to this point.
It will take a few days, but why not, let's see what we can get.Of course, PZ.PlatinumZealot wrote: ↑25 Mar 2018, 03:41Ok i see.
You know what. Sometimes we tend to overthink things. A poster seemed to ask why Ferrari does not use two fairings (top and bottom) on the mirror - since the sims show that two is aerodynamically superior. I thought about it and I came to this conclusion:
Adding the bottom fairing would block the driver's view of the mirror! The window of view would be so reduced that the driver wouldn't see half of the mirror much less his rear tyres. So yes, a simple answer in the face of complicated engineering questions.
As I said, not everything is super complicated in F1, sometimes it's just elegant engineering.
You say that, but teams were perfectly happy to install the outboard mirrors around 2008 - that were pretty useless as an instrument of seeing behind you - purely for aerodynamic benefit.PlatinumZealot wrote: ↑25 Mar 2018, 03:41Ok i see.Vanja #66 wrote: ↑24 Mar 2018, 18:42Cheers mate!PlatinumZealot wrote: ↑24 Mar 2018, 14:44Great work! You are a true scientist and engineer.
First of all your good work rubbishes the air deflector to side-pod theory. Secondly I would have liked to have seen the model without any slot, and finally I am also interested in your last conclusion, with the turbulent factor value - in layman's terms was it good or bad?
Do you mean a "regular" mirror design or this same design with slot height 0?
The turbulent factor I was talking about is related to energy dissipation, meaning the bigger it is the faster the turbulence dissipates (in layman's terms). So by making it bigger than it should've been, ie bigger than it was for other (more realistic) simulations, the turbulence is "gone" faster. That's why the flow was so much different.
You know what. Sometimes we tend to overthink things. A poster seemed to ask why Ferrari does not use two fairings (top and bottom) on the mirror - since the sims show that two is aerodynamically superior. I thought about it and I came to this conclusion:
Adding the bottom fairing would block the driver's view of the mirror! The window of view would be so reduced that the driver wouldn't see half of the mirror much less his rear tyres. So yes, a simple answer in the face of complicated engineering questions.
Do you have any evidence for this?
Here is the shot - 03:10 - link
I do think they would sacrifice quite a lot of vision for performance but FIA conducts tests in which the driver has to see behind him, so right now this discussion is rather hypothetical.
14.3.1 All cars must have two mirrors mounted so that the driver has visibility to the rear and both sides of the car. 14.3.2 The reflective surface of each mirror must be at least 150mm wide, this being maintained over a height of at least 50mm. Additionally, each corner may have a radius no greater than 10mm. 14.3.3 All parts of the rear view mirrors, including their housings and mountings, must be situated between 200mm and 550mm from the car centre plane and between 550mm and 750mm from the plane C-C.