BrightLampShade posted this in another section and I thought it was very interesting but it was hidden under another thread. So I decided to reproduce it here so we can have a better discussion on it. i am not sure how to get the photos added but you can go to Merceses AMG04 - page 16 to see them. or maybe someone could help me put them over here. I think it is a very interesting topic. It sent me reading and I will post what I found out after reproducing what BrightLampShade posted. Here is what he posted: Revealed: The secret behind Mercedes getting on top of tyre issues Kind of been discussed before but now theres a proper summary. I'm always a fan of seeing some clever yet simple engineering: One of the defining stories of this 2013 F1 season has been the rise of Mercedes and the way they not only grabbed pole position in eight of the first 12 qualifying sessions (by getting the most out of the Pirelli tyres), but also got on top of heavy tyre wear issues in races to allow Rosberg to win twice and Hamilton once. Analysis by former Williams chief engineer and JA on F1 technical adviser Mark Gillan of photos of Mercedes wheels, taken by leading F1 photographer Russell Batchelor of XPB Images, shows the complex internal design which Mercedes has evolved to master thermal management of the tyre. It is F1 innovation in action. Mercedes’ steady improvement in tyre management in races has not happened without controversy, as they took part in a 1,000 Pirelli test in May which landed them in the FIA International Tribunal, where they were found to have breached the Sporting Regulations, but the Tribunal found that the breach had been made in “good faith” based on communications with the FIA. Here is Mark Gillan’s analysis: Background Take a look at what the regulations say about wheels (at the bottom of this post). As the wheels are easy for other teams to look at one is always very careful to ensure that their legality is crystal clear and if there are any ‘grey areas’ then one will run the idea past Charlie Whiting at the FIA to ensure that there are no problems. Whilst wheels are relatively inexpensive to manufacture (per item) the manufacturing lead times are relatively long and one typically needs 30+ sets of wheels (i.e. 120+ wheels) to remain operationally efficient at races so wheel upgrades during a season are not too common. The Mercedes wheels in detail In my experience conjecture about what a team is actually doing with a particular design is often wide of the mark. What one can say is that to modify a wheel a team needs a good reason to do so because of the lead-times and quantities involved. As tyre thermal management has been a major performance differentiator this season all teams have been working on mechanisms/process to get the tyres into their operating temperature window as soon as possible and then keeping them in this window for as long as possible. The thermal window is quoted by Pirelli as typically 20C to 25C, with running temperatures of between 90C to 135C, depending on compound. Mercedes has been evolving what it does inside the wheels. Mercedes now has a new set of front and rear wheels which were captured very clearly in Monza by photographer Russell Batchelor. On the inner surface of the wheel there is a complex dimple pattern, which is actually fully integral to the wheel itself and almost certainly there solely for thermal management purposes in order to get and keep the tyres within their optimal temperature window. This complex dimpled and scalloped pattern (see close up of the front tyre, below) is not straightforward to manufacture and therefore indicates a lot of research and development has gone into developing this component and proving its benefit before committing to its manufacture. This type of pattern is quite common on modern heatsink designs, where dimples have been shown to give up to 25 to 30% thermal transfer improvements over the smooth surface variant. Only Mercedes will know whether the effort was worthwhile and how good the correlation was to their simulation and rig programme, but one has to applaud their ingenuity and effort. What the F1 regulations say Firstly, Article 12 of the 2013 Technical Regs determines what a team can/cannot do with the design of their wheels. The regulations are pretty prescriptive, but the main points can be summarised as: i) Wheel must be made from a magnesium alloy (AZ 70 or 80); ii) The width and diameter of the complete wheel (wheel and tyre) is specified within a range; iii) The wheel minimum thickness is 3mm increasing to 4mm at the bead; iv) The wheel must not be handed i.e. the left and right wheels on a given axle must be identical; v) Surface treatments are only allowed for appearance and protection e.g. painted/clear coated to avoid corrosion and allow for livery schemes. vi) One can then add to the wheel a limited number of items such as spacers, balance weights, tyre pressure and temperature monitoring systems, pegs etc
Ok..I have been reading up and I found this piece at : http://www.not606.com/showthread.php/229370-Tyres-and-rims-new-innovations?p=5350215#post5350215 (again, I don't know how to get the photos posted to this to someone with more experience can go to the site and post them for me thanks. I know it's a bit long but I think if someone can do it with the photos it would be easier for readers to understand..oh and I have to do in two parts in order to fit here.) It seems as though it was tried by Ferrari some time ago but they didnt get it to work, so if mercedes can get it working...power to them! Ok, this is what it says and it makes a lot of sense: PART 1 Can dimpled aerodynamic surfaces reduce drag? By Sam // April 24, 2011 A pub conversation that has probably been had by most engineering students at some point revolves around the application of golf ball-style dimples to the aerodynamic surfaces of an aeroplane or a car. Sometimes it is sparked by a re-run of a badly scripted and badly acted Australian TV movie about a solar car race. The film follows some plucky Aussie youths trying against the odds to race across the country using only the power of the sun. It’s a rubbish film in reality, but one of the youths suggests that they cover the car’s surface with dimples, ‘just like a surfboard or a golf ball.’ The car (which looks alarmingly like the one that British politician John Prescott famously crashed a few years ago) of course goes one to dodge road trains and win the race by miles. But that’s all in the fictional land of TV, where the laws of physics are only employed when it suits the script. In the real world, the use of dimples has seemingly been restricted to the outer surface of golf balls almost exclusively. In golf ball manufacture, dimples have been accepted practice since the 1930s, when research showed how they could increase lift and reduce drag of a spherical object in flight. But what seems to have muddied the waters – at least as far as racecar engineering is concerned – is the fact that golfing is all about a spinning ball rather than simply reducing drag over a non-spinning body. So could the same principle really be applied to racecars? It is rumoured that in recent years a Formula 1 team, thought to be Ferrari, experimented with dimpled surfaces but failed to make them work beyond the wind tunnel. However, a chance encounter at PRI between editor CAW and oval track suppliers Fast Wings resulted in a picture of one of the US firm’s dimpled wings being published in RCE V16N3. ‘The dimples seem to work. The car gripped much better with it on, the rim even turned inside the tyre’, explained a Fast Wings’ spokesman, yet the firm had no non-anecdotal data available on using dimples on an aerodynamic surface. Nevertheless, the picture was noticed in Indianapolis, and Josh Poertner of Zipp Speed Weaponary, one of the world’s market leaders in racing bicycle wheels, contacted Racecar. Poertner’s firm, Zipp, hold the world patent on dimpled disc cycle wheels, and they seem to work, being chosen by a number of top teams including some Tour de France front runners. Zipp had spent time and money developing the dimples in the Texas A&M low-speed wind tunnel The dimpled wheels showed very good Reynolds numbers, especially when compared to similar, non-dimpled versions. For those who do not worship at the altar of aerodynamics, the Reynolds number of interest is the point at which the flow changes from laminar to turbulent flow (or Recr). On Zipp’s smooth discs this was much higher than for the dimpled wheels and, suggesting the Recr is reduced by the presence of the dimples. It also suggests that the dimples make the flow turbulent at an earlier point so the more energetic turbulent flow may stay attached to the surface for longer. In theory, this could make a dimpled wing surface far more effective than a non-dimpled one. Also of interest is the fact that to date all dimples experimented with in racecar terms have been circular or oval in shape, yet Golf research has suggested that hexagons are actually the most effective shape (on balls at least). In fact Zipp has tried a different shape, but has so far encountered difficulties in the production process: ‘We are actually using icosahedral (20-sided) dimples on our disc wheel, however the moulding process ends up blending the corners a bit so they do look more round that multi-sided,’ explained Poertner. ‘We are looking at other shapes and configurations, and it seems to be the corners of the shape that really trip the airflow and create the effect. As with anything though, the costs associated with testing the myriad options are extremely high, and then there is the perpetual battle between ideal engineering design and manufacturability on a production scale.’ The internal shape of a dimple is another area that is not yet fully understood. Zipp use a roughly meniscus-shaped dimple with a flat bottom that sweeps upwards near the edges. Apparently this shape is popular in current golf ball design, particularly with manufacturer Titleist. The way the Zipp wheels, and most cycle wheels, are tested in a tunnel is a little bit different to the way cars are tested. The wheel is spun in the airflow and the amount of energy taken to spin the wheel measured. This is then taken into account, along with the standard measurements of translational drag, lift and side force relative to the wheel axis. So in effect the two measurements have to be balanced, as some gains in drag may show similar or even greater losses in terms of energy to spin. Zipp’s dimpled wheels showed much better figures compared to its non-dimpled designs in these tests, as did one other area Zipp have experimented with which is rim shape. ‘The leading edge of a bicycle wheel is the tyre, which is essentially round in section, so we have to design rim shapes that can re-capture the air separating off of the tyre. The idea behind our design is that these rim shapes can only take advantage of the airflow if the air is sticking to the surface of the rim. With a v-shaped rim or flat-sided rim, the airflow becomes separated from the leeward side of the rim as soon as the rim begins to face airflow more than one or two degrees off axis. Or in other words, as the wheel yaws into the wind,’ explained a Zipp spokesman. The flow that has separated causes the formation of a vacuous area behind the rim and, on a cycle wheel at least, that is the main source of drag on the wheel. ‘Two years ago we tested dimples on one of our rims that had an essentially parabolic shape, and found that they did absolutely nothing. But the reality of that wheel was that the airflow was separating off of the tyre, so the rim was not able to act as an aerodynamic element as it was not directly seeing any airflow.’ It is quite possible similar scenarios have prevented dimples showing a gain when racecar manufacturers have experimented with them without a complete understanding of how they work. ‘With a curved section, we were able to keep the airflow on the rim surface out to seven or eight degrees of yaw, but eventually the flow begins to separate or ‘stall’ on the backside. Using dimples in combination with these rim shapes, we forced the airflow into a higher energy state, forming a turbulent boundary layer near the surface of the rim which allows the air to remain attached to the rim even at higher angles. The trade-off with this is that we are creating a slightly higher skin friction drag on the rim,’ continues the man from Zipp, ‘but since this is some 10 times lower than the pressure drag, we find a bulged rim to be remarkably analogous to a golf ball in that the pressure drag reduction is many times greater than the total skin friction drag. The result is a wheel that is not just faster in one condition, but faster through the range of conditions you will experience the majority of the time.’
PART 2 Whilst not exactly dimples in the Zipp sense the ‘turbulator’ wing used by Oak Racing in LMP1 exploits a similar concept As well as its work with wheels, Zipp has also developed a dimpled hub for racing cycles, which suggests areas such as the driveshafts on a single-seater racecar could perhaps benefit similarly. An area such as this is constantly exposed to the sensitive rear airflow and, whilst shorter and under somewhat different demands, the principles could potentially be transferred. ‘I think that our new dimpled hub is pretty analogous to a racecar driveshaft, and on the hub we are seeing 14-20g of drag reduction at low yaw angles in the wind tunnel (at 30mph) and this is only a very small part,’ explains Poertner. ‘At the higher yaw angles the flanges (the Zipp hub is only 100mm end to end with flanges at each end), start to block the airflow over the centre of the hub so the effect goes away,’ claims Poertner. This is less likely to be a problem with a racecars’ driveshaft. So what other areas could benefit from a dimpled surface? Perhaps a diffuser or even the entire underfloor? Could dimples make a wing more effective? It seems Lexus has dimpled the floor of one of its road cars to ‘reduce noise’, which begs the question, is this reducing noise by reducing drag? One of Zipp’s engineers had previously been involved with the Chevrolet IRL wind-tunnel programme. ‘One of the points he raised was that this is probably a non-existent issue in IRL or similar racing as the wing angles are so shallow and they never really saw separation issues in the tunnel on any of their designs, so they were tuning wing shapes in very much the same way you would an aircraft wing.’ explained Poertner. ‘In F1, at a place like Monaco, the low speed and transient effects on wings that are in a very high downforce set-up could be interesting. At some higher speed, you will likely see an adequate Reynolds number to keep the flow from separating in some areas of the track (such as the tunnel or Massanet) but your Reynolds number through the Loews hairpin or La Rascasse may be reduced by a factor of 10 or more,’ he continued. Though Monaco is an extreme example in F1, the principle could apply to other types of cars on other street circuits like Pau, France or Houston, USA, as well as on some of the twistier road courses like the Hungaroring. ‘I wonder if the dimples may only increase skin friction drag at high speed, but possibly increase downforce and reduce drag at low speed. Or at least just lower the stall speed of the wing by some percentage, sort of like vortex generators on an aircraft wing which serve to either increase stall angle or decrease stall speed,’ Poertner concludes. Of course, numerous other unanswered questions still exist, such as how big do dimples need to be? And how deep? In a control formula like F2 or GP2 could putting a dimpled sticker on the underside of the cars’ wings be an unfair and legal advantage? If every surface of the car were dimpled, would it have an even better effect? After all, sharks have rough skin over their entire body, which is said to allow them to pass through the water more efficiently. There are many misconceptions and unknowns relating to dimples in aerodynamic design, as one aerodynamicist told racecar, ‘It’s something that comes up every now and again, but has never really got anywhere, at least not yet…’
BrightLampShade, thanks for making me go dig up this info online...lol...I think this is very interesting and I hope people here with the technical know how will give us their take on it. Thanks
Remember Braun saying a few weeks ago that mercedes were looking for some big solution to their tyre problem and they decided to take a step back to think about what they missed ? He said that they solution was the problem wasn't the big thing that they were looking for all along...maybe this is what he was asking about.
Hello dhel. Following on from your PM which I read earlier today, I will re-iterate some of the response I gave. Clearly you have found this an interesting subject and I am a little disappointed to see that you have not had a single response in this thread. Perhaps this is because your research already seems pretty thorough?! I have read most of what you've reproduced in this thread, although not yet the links you've provided; but I will tell you what little I know on the matter. Firstly, dimples and scallops increase surface area. When used on surfaces which are subjected to airflow, the effect can be to 'capture' the airflow because each dimple creates localised low pressure, relative to air which is slightly further away. Although the low pressure zones are only a tiny bit lower in pressure, there can be enough difference to suck in the slightly higher pressure air from close by whilst maintaining a low pressure 'bubble' which is doing the work, thus magnifying the effect. This can help the main body of air 'stick' for longer and, oddly enough, more closely than it otherwise would; and it is this 'stickiness' which is an aerodynamicist's nirvana because it reduces overall turbulence – the cause of drag. For most aerodynamic surfaces though , the benefit is likely to be outweighed by manufacturing difficulties, as well as somewhat negated by the fact that F1 evolves at such a rate that such elements are replaced almost every week. For this reason, it may not be worth the effort for parts which will be replaced very quickly, because the time can be better spent on fundamental design. That said, a similar effect can be created by the use of tape applied to a surface – dependant upon the depth of the dimples and the extra weight; but we must bear in mind that this extra weight (including adhesive) would necessarily be spread across large areas and the overall equation might produce a negative answer in the fast evolving world of F1! - - -o0o- - - However, wheels are a different matter altogether. For a start, their design is not subject to fortnightly changes. But there are two considerations which may give a different sort of payback, perhaps enough to make the design effort worthwhile… Rather than 'dimples' as such, a surface which is covered in tiny pyramids* can act as a heat-sink. Furthermore, if this surface is rotating in a localised region (such as inside the recess of a wheel), I would expect it to have the effect of whipping up the air in this confined space more than would occur with a smooth surface. However, the peculiar thing is that the pyramids (or dimples if they could be made deep enough) will trap air very close to their surfaces and only whip up the air further away (towards the centre of rotation). The benefit of this is that it keeps more air in contact with the surface, whilst retaining lower pressures towards the hub, which would make it easier to vector in to the braking system, etc. I ought to have a look at your links but I'll have to save that for another day. Apologies for not responding to your PM sooner. © *Pyramids are far easier to manufacture, since they can be produced by cutting 'V' shaped channels into a raised surface laterally and longitudinally. Very simple.
Thanks Cosicave, for your comprehensive explanation. It seems as though this may have helped correct Mercedes' tyre problem, but maybe now the tyres are taking a bit longer to heat up and costing them a bit in the speed department? Maybe?
by the way Red Bull is using the same rim technology as Mercedes: James Allen Also helping them is the Pirelli move to the harder specification tyres, since Hungary. They have won three of the four races on the new spec tyres. Beyond that, like Mercedes they have done work on the inside of the wheel rims in the field of thermal management and heat rejection. The slots and texturing in the magnesium alloy rims work on flow through the rim. It’s a complex piece of work and quite expensive to do, but it helps with managing the temperature of these tricky Pirelli tyres. This thermal management work has allowed Vettel to run a longer first stint than his rivals and to balance out his stops perfectly in recent races. That's one of Red Bull's wheels.
The article above said Ferarri experimented with it some time ago but they couldnt get it work properly. I am not sure if McLaren did but I will go back into files and see if I find anything.
I just read a forum where someone said McLaren was investigating the dimpled effect in 2009 but they havent heard anything from them since.
I see it as essentially a 'payback for effort' equation. Any physically fixed mechanism or object, including any non-adjustable surface, will have an optimum window within which it operates. A fruitful understanding of aerodynamics relies upon recognising that air behaves as a fluid, and that a fluid is always dynamic, with harmonics which vary with density and temperature. An idealised surface will be one which best accommodates the full range of speeds within which it operates because a net benefit requires very accurate 'tuning' of the technology, and must be something which can be accommodated both below and above an optimum operating window, such that there is a net gain in performance over a full lap. This is far from simple, especially when one factors in other essential parts of the equation such as tyres, suspension and braking efficiency. It is therefore something of a gamble in which to devote and invest time, money and brain power. For this reason, it is very easy to see why some teams may have experimented but subsequently dropped the idea â or at least put it to one side until better understood. Nonetheless, there is no reason to dismiss that some may have found sufficient benefit above and beyond what they had beforeâ¦
That is probably why Mercedes has had an up and down performance especially in qualifying since using this technology..maybe?
Perhaps. The thing is that if it is 'fixed' so that it is exactly the same for different circuits (as outlined above), the differences between circuits adds a further headache: each will have its own, unique 'optimum' – some will be better or less suited to whatever compromise one decides upon at the design stage. IF that's what they've done…
tbh the Mercedes has been one of the most 'erratic' cars for a couple of years, winning races then being totally off pace the following GP, I think the Merc has a small set-up window where it works well, as soon as it's on a track where the set up is out of that window it becomes totally non-competitive at race pace.
Any thoughts on rim management advances? I read somewhere that Alonso's was superlative... But that was a while ago now.
I agree, Miggs. I'm not sure about "rim management" – especially Alonso's(!) – but as far as F1 goes, superlatives should be reserved for Murray Walker!
