Thursday, December 13, 2012

Inside wind tunnels

In Formula 1 world there are three types of testing validation for new parts: CFD, on the track (free practices or tests) and Wind Tunnel installations.
Lot has been said about the latter, so I'm not going into details about rolling floors or boundary layer suction, but instead I'm going to focus on what and how specifically is being measured in a Wind tunnel and why is that of paramount importance for F1 teams.

One of them has recently been all over the specialized news feeds, namely Ferrari, with their Wind Tunnel struggles, failing to produce correct correlation between tested parts and what's actually being measured on the track as results.
Various sources have been suggesting that Ferrari F1 Team will shut the tunnel down and make re-calibration, system checks, improvements, even calling external consultants, presumably from aerospace industry to check what's wrong. Just how much of all these is true is unknown to the general public, but talks about new wind tunnel construction have also appeared. It is perhaps worth saying that this is large investment and its rough estimated cost is about 40 to 50 million US dollars, besides it takes a lot of time for pure construction and realization.
UPDATE [20.Dec.2012]: Stefano Domenicali confirmed that Ferrari's wind tunnel will be undergoing major overhaul, will remain closed until August and Ferrari's 2013 car will be developed exclusively in TMG facility - see details below.

Apart from the economic outlook, teams are allowed to test with scaled model, up to 60% of the real size, and use speed of up to 50 m/s, which is 180 km/h max or 111.8 mp/h if you prefer imperial units.

Since the model parts do not represent the real world car size, Reynolds number is, for example, used to make coefficient correlation between the 60% model parts and 100% model. However, it is important what the source data shows.

Below you may find a sample spreadsheet with totally bogus and unrelated data, which is there to simply demonstrate the various parameters being measured in a wind tunnel session. Time spent inside the installation is also precious, as teams are having certain time frames allowed.



 Let's break down the data sheet into details:
  1. Cell B holds the value for Lift, in our case there is downforce generated, hence the negative sign. It's usually being measured in Nm, but it may vary in different wind tunnels implementation (Kilograms are often seen, too). 
  2. Next we have Drag, which is pretty obvious.
  3. L:D is lift-to-drag ratio - one of the most used measures for aerodynamic efficiency - sure, you can add more downforce via Angle of attack settings, but this comes at the expense of added drag, too, so balance is important. 
  4. Drag power - this is the consumed horse power, the power required to overcome aerodynamic drag.
    Note: this is a velocity-sensitive parameter, and the formula is simple:
    DRAG HP = ( Drag coefficient (0.9 or 1 for F1 car) * Frontal Area in square meters (assume 1.35) * current velocity (200 km/h = 55 m/s) cubed ) / air density (1225 kg/m3) = ~ 124 HP to overcome aero drag. The same formula gives about 380 HP at 250 km/h, etc.
  5. The next three columns, FY, FX and FZ are moments, measured as distribution of aerodynamic forces around Center of gravity, aligned with the three axes:
    Copyright: F1 Framework
  6. Next, in columns I and J we have vertical loads on the front and the rear, which is very important parameter measured from suspension point of view. While measures here differ, these are usually Newton meters, in this sample sheet the values are in kilograms.
These are some of the most common parameters that teams are measuring in a wind tunnel. Apart from those numbers, more can be crunched as a mathematical representation of the measurements taken, namely calculating coefficients. All of those numbers and their values are carrying certain amount of knowledge in regards to how your car will supposedly behave and that's why it is very important that the output is correct, as this decides what configuration and parts to put on the car.

TOYOTA MOTORSPORT 

The next chunk of details goes directly into the heart of Toyota Motorsport GmbH wind tunnel facility in Cologne. F1 fans have heard a lot about it, especially when it comes to Ferrari, but first, I, with "no wax", like to thank their staff for being gracious enough to release those images and data for the public and being patient enough to explain everything. Below you may find some exclusive images from the tunnel.

Outside look of the tunnel's diffuser section
The instrumentation of this state-of-art facility consists of two wind tunnels : one full size and one 60% scales.
Both wind tunnels use a continuous steel belt rolling road which has a maximum speed of 70 m/s. What can really describe those installations is accuracy and high quality - 512 pressure measurement channels are available. The tunnels are also equipped with Particle Image Velocimetry system (PIV) - an optical method of flow visualization used to obtain local flow velocities. The PIV system is usually used to validate CFD predictions and thus better calibrate the setup.
One of the advantages of such PIV system is that its preparation time is almost zero, due to the seeding technology used. That means that the local air is filled with tracer particles and there's no cleanup needed after that. During the process of measurement, cameras are used to obtain images and samples, which are then processed by computer software.
A laser is used to illuminate the flow field around the car’s front wheel to take particle image velocimetry (PIV) measurements (see below).

One of the main advantages of this method, just as well as the PSP method, is that it's non-intrusive, as opposed to the traditional pressure taps.
"Many of today’s motorsports cars are based on existing, commercially-available cars." Frank Michaux, a researcher at TMG, reveals.
"If researchers can identify a way to reduce drag on a motorsports car, it’s reasonable to assume that this information also may apply to future versions of a normal road car." Frank continues: "We need to deliver data quickly. If you see that you are not capturing the flow correctly, then you need to adjust your CFD methodology until you get it right".

After gathering the raw data from the PIV measurements of the “separation point” on the front tires, engineers post-process the data using Tecplot software, which allowes them to see and measure the exact position of separation. Each of Toyota’s PIV measurements consist of 300 datasets, with each dataset containing two images taken 10–20 microseconds apart.

The Tecplot software package itself is widely recognized and used throughout the industry.

INTEGRATION POINT - PIV & CFD

During the 2009 season, F1 engineers wanted to carefully study the flow wake behind the front wheels. Since this is critical part of overall car performance, the goal was to push this flow as outboard as possible. Engineers have realized that they need precise back-to-back correlation, and here's a direct comparison between CFG and PIV images: 


In order to get to those precise points, the CFD methodology has to be optimized, and here's a real case:




The next thing about Toyota Motorsport GmbH is its Continuous Motion System.

In CMS mode, a user-defined programme of ride height, yaw, roll, steer and individual pre-load changes provides continuous motion on a predefined trajectory while the HSDA system is continuously acquiring data at high frequency.
This allows realistic road or track analysis and increasing the amount of useful data from each individual test compared to standard motion and acquisition systems.
The typical "Wind-On" time is reduced by 70 to 100%  with CMS, which allows more time to be dedicated to, for example, changing parts. This Wind-On time is extremely precious for F1 teams, which we all know run under certain restrictions when it comes to wind tunnel time. 

Below you may find some exclusive images from inside the tunnel (full sizes available upon click): 
Very good representation of scaled model compared to a man

Toyota TS030 early prototype version

The control and monitoring room


Testing preparation - Toyota TF110
Front wing flap angle at 27 degrees
Surveillance and monitoring  
Glad you have reached this point - I assume you were very interested or your scroll button was stuck :)
As usual, comments and questions are welcome.



Tuesday, December 4, 2012

The evolution of pitstops

The following article is originally posted by Marc Priestley (ex-Mclaren mechanic) at his blog and I have his written permission to repost it here, which I'm very grateful for. His, Marc's website is here - F1 Elvis.
Also, you can follow his Twitter account.



Fangio, British GP, 1950
If you look back at footage of pitstops in Formula One from the early days of the championship in the 1950′s, they’re an all together different spectacle than those of 2012. They appeared leisurely, disorganized and, in the case of refueling, downright terrifying.

Drivers got out of cars while tyres were changed using large copper hammers and fuel was poured into, and often over, the back of the vehicle. Well over a minute later he’d hop back into the moving car as it was pushed away by mechanics and rejoin the race. All this took place at the edge of the track, circuits had no such thing as a separate pitlanes and there were certainly no speed limits.
Now I’ve stood with a front jack in pitlane as a modern F1 car brakes from 100kph to a stop at my feet and it raises the heart rate I can assure you. Mechanics of the 50′s and 60′s faced a series of dangers that would put today’s health and safety officers into an uncontrollable frenzy and have the sport shut down for good. Thankfully Formula One’s moved on in every area and pitstops are no exception. Today’s world record breaking stops to change four wheels in under 2.5 seconds are impressive to say the least, but they’re the culmination of years of development, learning, and improvements in technology. Here’s how they have done it.

For many years we’ve had pitstops becoming faster and faster as the sport woke up to the reality that the pitstop or stops can play a real part in a Grand Prix outcome. Teams initially threw more and more people at the process and gradually, over time, made improvements to their equipment used for the job too.
Just as competitors will always find innovative ways to make their cars faster on track, teams from every era and every formula have found ingenious ways to shave time from their pitstops. Some have done it legally, some questionably and some downright illegally, but the fact that it’s an area where time can be gained over rivals means it’s also an area where they’ll use resources and expertise to minimize the time it takes to service their cars.

1983 saw a number of fires as teams tried all means possible to shove as much fuel into their cars as quickly as possible at a pitstop and back then it was often a form of highly volatile rocket fuel, making it perilously dangerous. Refueling was banned the following year and this brought the focus away from pitstops and into the ability to conserve fuel and tyres during a race.
1983, Keke Rosberg is on fire

In an effort to spice up the show after a ten year break, 1994 saw the reintroduction of mid-race refueling and inevitably teams very quickly began to look at ways of speeding up their stops once more.
Perhaps the most infamous example was the Benetton pitstop fire of the same season, which allegedly uncovered that the team had removed a filter in the standard fuel rig, designed to restrict the flow rate of fuel from rig to car. The increased flow rate would mean the required amount of fuel could be pumped into the car faster than their rivals and of course reduce the time spent in pitlane.
During my early years at McLaren we developed a system to shave tenths of a second off the refueler’s reaction time once the fuel rig had delivered it’s required quantity.
Where normally the ‘nozzle man’ would react to a standard set of lights on the rig telling him to pull off the hose when the fuel was in, we used a stethoscope type device to listen for the valve closing inside the nozzle itself.

Just before the required amount of fuel was delivered, the motorized valve would begin to ‘whir’ and close, a process which took a couple of tenths, and once shut, the lights on the nozzle would illuminate to alert the fuel man he could begin detaching from the car. With the operator listening through an earpiece for the ‘whirring’ of the valve starting to close, he could start to react and be pulling the nozzle off the car by the time the lights switched on, therefore saving valuable time.
In those days of course, refueling was almost always the limiting factor in a pitstop. Time was saved or lost in connecting and disconnecting the rig from the car and the reactions of the lollipop man and the driver in getting away from the box. Although everyone had to use the same refueling rig, pumping at the same rate of 12 litres per second, the same hose, nozzle and valve in the side of the car, teams tried simple ways to make the operation smoother, more reliable and ultimately faster. Extra handles were welded onto the nozzle for someone to assist in pulling it off, fluorescent strips stuck on the nozzle end for the lollipop man to spot when it was completely detached from the car and the same hi visibility vinyl stuck onto the car valve to aid the refueler in lining himself up.
The sport’s always pushing the envelope in terms of technology in all areas, but whereas groundbreaking developments of ten years ago in the ‘real world’ may now seem a little dated, Grand Prix racing moves at a considerably faster pace. Technology in Formula One supersedes itself often before new parts even make it onto a car, such is the rate of R & D, but until now pitstop equipment has been something which got attention only when time permitted within the busy schedule.

Today the focus is different. With refueling gone once more, pitstops are all about replacing four wheels and tyres as fast as physically possible. For the first time in years, F1 teams have a relatively blank canvass with which to create equipment and systems to complete the operation in the shortest time. Wheel changing technology was almost an untapped market if you like, there was no desperate need to change them in 3 seconds when refueling would always take at least another 4 or so. With FIA rules being comparatively open when it comes to pit equipment and procedures, it’s been a case of micro-analyzing every element of the stop to see what can be done to save time. In the past that might have meant finding the fastest way to work with the car and equipment they had, but today there’s considerable resource allocated to the project and so the car and any new equipment can be designed from the ground up around the necessity for the ultimate stop.
Many years ago, frustrated at the difficulty of working on one of Adrian Newey’s complexly designed McLarens, I asked him one day how much of the design brief is about making the car practical and easy to work on? His answer was simply “None”. For the first time in modern F1 designers have had to think, not just about making the car light and fast, but about how they can improve the way wheels are changed during the race, with the realisation that it now has a direct impact on the outcome of a Grand Prix.
Stub axles on the car have as little as three threads of engagement for the wheel nut, to minimise the number of revolutions it has to do in tightening or releasing the wheel and the axle tip’s rounded to guide the wheel into place. Wheel nuts themselves are retained within the rims to reduce the opportunity for cross threading and take away the possibility of one falling out of the socket. In days gone by it wasn’t an uncommon occurrence to see wheel nuts spinning off down pitlane during pitstops or pitstop practice as they popped out of the gun as the wheel was removed. Of course it was hardly ever an issue as a spare nut could be picked up and fitted long before the fuel man had finished his part of the job.
Like the stub axles, drive pegs on the car’s uprights and the wheels themselves are designed to guide them seamlessly together and avoid ‘pegging’, where the two butt up against each other and fail to engage.
The jacking points, particularly at the rear of the car, are specifically made to make it easy to slot the jack into place. Whereas it used to be quite easy to ‘miss’ the old, relatively small, lifting hook with the jack when doing at speed, now things are designed differently. Most don’t even use a ‘lifting hook’ as such and a large carbon ‘splash’ on the jack can be thrown in anywhere under the rear crash structure to avoid the need for two bites at positioning it.

When it comes to the equipment and tools used in today’s pitstops, the advances are somewhat staggering.
The days of four ‘standard’ wheel guns, a couple of compressed air bottles, two basic steel jacks and a lollipop seem like a distant memory in 2012. In car terms, that level of technology would equate to the F1 cars of perhaps twenty years ago, but that basic layout of the pitstop area was still in use by almost every team just three or four seasons back. If you walk down pitlane now, it’s all very different.
The gantries carrying air lines overhead to the outside of the box are complex and beautiful. Huge moulded carbon structures house lightweight, super flexible airlines, ‘traffic light’ systems to release the driver, cameras and electronic cabling connecting almost everyone involved in the stop. As each operation’s completed, the ‘system’s’ notified through either mechanics pushing a button, or an automatic switch. Once all four wheels are on tight and the car’s on the ground, the chief mechanic gets a light and once he’s happy, he pushes a button to give the green light to the driver to pull away.



Wheel gun men now use heavily modified guns from the originals. ‘High flow’ gun backs allow greater air flow through the gun itself and effectively spin the socket faster, around 9000 rpm. Until 2012, when it was banned on environmental grounds, teams used compressed helium instead of air to power the guns. It’s extremely low density again allowed guns to spin faster and therefore remove and replace nuts quicker. The guns of today have bespoke sockets to match the team’s own nut designs, lights to indicate to the user when the nut’s done up to the correct torque and buttons to signify to the jack man that the operation’s complete. Before the recent focus on pitstop speed, gun men would signify they were done by raising a hand in the air and when the jack men saw the two hands at their end of the car, it would be dropped back onto the floor. When the chief mechanic saw four hands and both jacks out of the way, he’d release it. Now the action of raising a hand 50 cm in the air is considered to take too long and so the flick of a switch or button on the side of the gun shaves off valuable hundredths, that’s how thoroughly things are analysed.
One of the very latest developments in wheel gun technology is an automatic direction change. Up to now mechanics slide across a ‘shuttle’ on the back of the gun once the nut’s undone to change it’s direction of rotation, before doing the new wheel back up again. But Rhodri Griffiths of Palindrome Sports, the man credited with most advances in F1 wheel gun technology, has devised a new system which switches direction automatically as the gun’s removed from the first wheel. Whilst it may not directly save time in a standard stop, it’s a device which removes the need for a human operation and therefore one less thing to think about during the two and a half seconds or so that the car’s waiting in the box. Teams carefully study human performance in pitstops as well as that of the equipment, so anything which can simplify an action as well as speed it up, is worth looking at.

There’re teams who have lasers mounted in the overhead gantry which direct two beams incredibly accurately towards each wheel position. The beams cross each other at the exact height from the floor and for and aft position of the wheel nut when the car’s stopped on it’s marks. It enables the gun man to hold the gun ready at the exact height, avoiding any vertical adjustment to his position as the car comes in and hopefully the driver stops right on his marks to avoid having to move left or right.
Front and rear jacks have had a lot of thought put into them recently too. Often now made from carbon fibre to make them light and quick to move into position, they all have a quick release mechanism operated by a lever on the handle. It’s quicker than the motion of raising the jack handle to drop the car on the floor. When the lever’s pulled, the lifting arm of the jack simply breaks away, dropping the car instantly and it’s ‘reset’ ready for the next use. As someone who’s sat in a car for pitstop practice before, I can tell you it’s not a comfortable experience being dropped off the jacks with no comfy cushioned chair and very little in the way of suspension, but ultimately its faster and that’s what counts.
The jack men are looking for two lights from each of their respective gun men in order to dump the car on the floor and teams house those lights in various positions on the gantry, on the jack, or in some cases now, in ‘heads up’ displays inside the jack man’s crash helmet visor. Another example of trying to minimise human reaction times and remove opportunity for error wherever possible.
When the jacks drop they trigger another light for the chief mechanic and if pitlane is clear, he can illuminate the final light for the driver to pull away. Some teams now use a separate spotter to keep an eye on the pitlane, so that the chief mechanic can simply watch his own car and only when the system sees the ‘pitstop complete’ light AND the ‘pitlane clear’ light, does it release the driver.

When the whole procedure’s written down it seems a vast operation and although the bottom line is that it’s just a case of changing four wheels, when you look at it more closely, it is indeed complex. Each of the individual elements are studied using video analysis, onboard car data and of course the good old fashioned stop watch, although these days most teams use their own computer based systems for timing and so even the stopwatch has been replaced to a degree.

One interesting development in the pipeline is an automated jack release system. McLaren have been evaluating for some time, but are yet to race, a jack which drops the car upon receiving an electronic signal from both wheel guns, removing yet another human reaction delay and perhaps saving another tenth or two.

Crews practice over and over and over to the point where, whatever your role in the stop, it becomes literally second nature. Drivers don’t get the chance to rehearse so much and we do still see car’s over shooting, coming in too slowly or too far off center  but mechanics practice for those situations too and normally deal with it without most people noticing.



Throughout F1′s pitstop history they have always played a direct role in the outcome of races and as such, the speed with which they’re completed is crucial. For the ultimate stop, whether it’s tyre changes or refueling, each consecutive action has to preempt the smooth completion of the previous one and that’s where things normally come undone. We’ve all seen lollipops lifted as the fuel nozzle begins to detach from the car, only for it to stick slightly and end in disaster. Today, with stops lasting less than two and a half seconds, there is no room for error or glitch. Everything happens so fast that there isn’t often time to react to anything out of the ordinary, and just as through practice everything’s second nature, you’re conditioned for perfect stops and perfect stops only. Add to that, the pressure that I know only too well and that each of those guys feel when the spotlight’s on them and there’s an incredibly fine line between the perfect stop where all four guns operate perfectly in unison, and complete disaster. Talk of automated jacks, guns and lights is fascinating in terms of the technological advance and perhaps even the ‘show’, but it’ll undoubtedly have many squirming with discomfort at the prospect of the pitstop becoming too fast for humans to react to a problem and the potential safety issues that may cause. At the moment FIA regs are fairly open in this area, but just as with the cars, surely it’s only a matter of time before they step in to restrict spending, close up the field and safeguard everyone involved.


Saturday, November 24, 2012

Young drivers test at Yas Marina 2012 and its importance to 2013 season

"Hello, World!"

This is one of the very first strings that young programmers are printing out on the screen when starting with software development. Here, however, we shall talk about young drivers test in Formula 1 which has taken place in Abu Dhabi, on the most expensive track facility anywhere in the world - Yas Marina. Many testing permutations, tire compounds and interesting testing tools have been used, and we have even seen one driver testing two different cars!
Overall, the feedback from the drivers was very positive, let’s take Esteban GutiĆ©rrez for example:

“The morning session was very interesting for me because we tested a lot of different things, and I hope I gave my most precise feedback to the engineers. After being in the car so recently in India, of course, I feel a lot more confident in handling all the system like KERS and DRS. In the morning session I used only hard tyres, but in the afternoon I certainly enjoyed running the medium as well as the soft compound. The last sector of the track I find a bit tricky, especially turn 20. I don’t have the confidence yet to push harder there.”

The combined time results from the three days look like this:



Later down in the article you can find more interesting stats about this event.

And although this is testing for the young drivers, all teams have used the chance to evaluate certain developments or just to gather aerodynamic data.
Let’s get down into details about the interesting stuff we have observed on the track.
Most of the teams and the drivers told us not to look too much into the times, but it was obvious that top 3 drivers were very quick and their scores were almost half a second better than the rest of the field.

A typical example of a daily session program would look like this:
  • Morning Session: Aerodynamic testing and DDRS iterations. 
  • Afternoon Session: Front Drum testing and tyre assessment Programme. 
  • Total number of laps: 86 
  • Best lap time: 1:42:677 
  • Tyres used: Two sets of hard, two sets of medium and two sets of soft compound tyres.

DRAG REDUCTION DEVICE (DRD)

What can really summarize the testing efforts was the extensive usage of pipes protruding from underneath the engine cover or similar places, which were usually ending below the underside of the rear wing’s main plane. (Credit for the name goes mainly to my fellow blogger and tech analyst Matt Somerfield)

This type of the device appears to be initially tried by Lotus, and it looks like this:

While Lotus’ implementation is bit different than the rest, the principle is believed to be the same: passive blowing certain parts of the rear of the car, i.e. no human interaction is required. Note about next year regulations: DDRS implementations such as the one found in Mercedes car will be prohibited, hence the teams are looking for more efficient and legal solutions.

The next team that has tried similar approach was Mercedes, and the rest followed soon - Toro Rosso had interesting implementation as well, Red Bull and Sauber. Details:

Red Bull


It is immediately obvious that Red Bull may be looking for different approach, as the pipe is directly connected to the rear wing with no obvious open slots. Extensive flow visualization has also been added, something that RBR have demonstrated in almost any free practice so far.

Sauber

The solution from the Swiss team is more closer to Mercedes’ initial implementation. Generally, those types of devices are aiming to create low-pressure area at the underside of the main plane of the rear wing, where, essentially, the downforce is “born”.

Sauber did not have the typical inlets that would feed such passive system with air, though additional pipes have been spotted around the nose cone.

Toro Rosso


From the same bull breed, the younger Reds tested a larger version of the so called “monkey seat” - relatively cheap way to add rear downforce via such device which resembles smaller, scaled down rear wing. There are variations across different teams’ implementations, but STR7 features the largest of them, as of yet. The Italian team have also tried something which looks like a DRD attempt, however, with no clear evidence of ducting at this point. Certain analysts have assumed that this is a result of James Key’s introduction to the team as Technical Director, replacing Giorgio Ascanelli.

What stands above the engine air inlet is called Pitot static tube - an instrument measuring fluid flow velocity.

On the next day, the team has tried another variation of the Monkey seat which was lot more taller than the previous installment, and it was somewhat resembling a DRD, though strict evidence of holes were not immediately obvious - perhaps the team wanted to evaluate just the amount of drag coming from such option:
Image credit: AMuS

AERO RAKE

Literally every team had his chance to run various types of test rigs, mostly known as aero rake.
The aero rake itself could be used for measuring air speed, angle flow, pressure (Pitot-Static probe) and even temperature.

What is really a Pitot tube?

It's a thin tube that has two holes - the front hole is located to face the airstream for measuring the stagnation pressure. For incompressible flow (where the material density is constant) it is a sum of the dynamic pressure and static pressure. The side hole measures the static pressure and the difference between these two is dynamic pressure, which can be used to calculate fluid flow and speed, in our case that's the air. Some of the teams are using a variation which is called “Kiel probe”.

Let’s have a look at teams’ applications:

 Red Bull have been using similar rake for some time, notably this one, used in Canada Free Practice as well:

This is what Caterham team calls “Transition Vortex Rake”. The team also had infrared camera to monitor tires.
Copyright: Caterham F1 Team

Next we have the high tech team of Mclaren:

Notice they are running two applications - one behind front right tire and one behind the Monkey seat, which has the ability to move up and down.

On the second day Mclaren ran a completely different front wing, which bears some resemblance to the one Lotus is using. Here’s a direct comparison - the new one is on top:

The new wing now features two vertical flow conditioners, a la Lotus, which effectively removes the upper R cascade elements (yellow arrow below), which tells us that Mclaren are willing to sacrifice some front downforce. Next we see that the new wing has no outer blade near to the endplate, and in general looks simpler than the old one.
The underside of the main plane (old vortex curvatures) features more nicely curved forms as opposed to the old shapes, which were rather triangular.

Curiously, this test has apparently proved successful for the new wing, which was subsequently raced in Austin and Lewis Hamilton won the race!

Mclaren also had the usual sensor bulge on the nose (inset right) plus pale purple flow-viz on the new front wing (left hand side) – this type of color is less visible on the track (to hide details from rival teams), but it is excellent displayed under ultraviolet light.


Lotus revered to their old exhaust style for the final third day:




BOTTOM LINE

  • Most of the teams are definitely looking at 2013 season and usage of passive devices to gain rear downforce. 
  • Teams did not lose time and various ways to collect data, such as flow viz and aero rake, have been used.
  • The test featured quite good reliability except for one minor incident (oil leak for Caterham).
  • Kevin Magnussen set the best time on the first day, before noon.



STATS

Note: The bars are interactive, hover the mouse over any of them to reveal the actual value.






All images are linked from F1 Zoom (unless otherwise noted) and are posted under the Fair Use Doctrine for purely educational and comment purposes. 



Tuesday, September 25, 2012

PSP in F1

Hello and thanks for tuning in on this frequency again.

The following article comes exclusively with the help of the kind people from ISSI - Innovative Scientific Solutions Incorporated. Their commercial site is located here.

We are not going to talk about PlayStation Portable, as the headline hints, but for Pressure Sensitive Paint (henceforth abbreviated PSP) - a method which stands between traditional F1 development paths - wind tunnels and CFD (but not a replacement for any of them). This is something that has been in use for quite some time, especially when it comes to NASA and airplanes.

WHAT IS PRESSURE SENSITIVE PAINT

In short, this paint-like coating fluoresces under a specific illumination wavelength of incident light and the fluorescent response is a function of the external air pressure being applied locally to its surface.
A typical PSP is consists of luminescent molecule and a polymer binder which must be permeable to oxygen.

There has been some use and some interest by certain F1 teams in using PSP in their own tunnel testing. 30m/s is typically the lower limit of PSP due to smaller pressure gradients below that speed. Most use PSP to validate CFD results or vice versa.

Imagine that in the end you could receive the same pressure distribution picture as you normally get from a CFD simulation run:
Image credit:  http://www.psp-tsp.com/

WHY IS PSP ADVANTAGEOUS 

A key advantage to traditional experimental techniques like pressure taps and transducers:
  • cost savings 
  • not limited by model geometry
  • provides much higher spatial resolution than traditional methods
Essentially you'll have a "pressure tap" at every pixel of your camera. So if you are using a 1-megapixel camera, that's like having 1 million pressure taps on the surface. Once the experiment is set up, many runs at various conditions can be made rather quickly by comparison to CFD and data turnaround is much quicker as it can be processed on site with some knowledge of the test conditions and local pressure taps on the model if available.
Paint formulations have also been developed recently which allow for unsteady measurements of pressure using a high speed camera. Measurements can be made upwards of 10 kHz on the surface.

THE PROCESS

The typical process could be described with the following simple steps:
  1. Painting: Whatever the testing object might be, the usual paint gun or airbrush could be used. 
  2. Excitation: The molecules inside the paint have to be excited, so there is a light illumination source applied to the painted surface.
  3. Data gathering: The CCD camera kicks in collecting the fluorescent response from the illuminated surface
  4. Data visualization: Different software packages could be used to visualize what's already being recorded and thus used for analysis of pressure gradients. 
Two immediate questions have arisen, fortunately Steve Palluconi, a research engineer, was available for this short interview: 

Question: Due to its (PSP's) spraying technique - would that be too much disturbance of boundary layer or not at all? Negligible, maybe?
Answer: Generally the layer thickness is 20-30 microns and is very smooth. Negligible for these types of tests. Pressure taps are more invasive as we’ve actually seen flow separation caused by them.

Question: Are there any estimates on cost? For example, would it be too expensive to implement or improper, for example, due to model scales (in F1 - up to 60% of the real car size)
Answer: Costs depend on the scope of the test and size of the model. Large models like the one referenced would usually be imaged with a multi-camera system. Smaller models can be imaged with a single camera. We've done testing on some large aircraft models.

Should you have more in-depth and scientific questions you can always contact Steve through their web site.


Thursday, August 9, 2012

F1 aero glossary

The idea of that article is to be a reference point for the most used aerodynamic terms in Formula 1.
The list doesn't pretend to be exhaustive or fully descriptive on certain topics, such as CFD, but for now I'd prefer the simpler variant, listed alphabetically for easier navigation. Additions and comments are appreciated , but at the same time I will assume that you know the basics, for example the fact that there are four forces that act on a car: lift, weight, thrust, and drag.

The format is simple:
  • TERM
  • Explanation
  • Illustrated picture (almost all have larger sizes)
Shift into gear!

AIRFOIL
[ExplanationIn British English you can also find the term as "Aerofoil", but generally this is a transverse cross-section of a wing. This is how the term is named in all aerospace sources, but in motorsport that's just another word for wing or its shape.

[Picture] To follow below, when explaining Angle of attack

ANGLE OF ATTACK
[Explanation]
This is the angle between airfoil's chord line and the crosswind airflow, regardless of wing's direction.

[Picture]
image credit: http://wikipedia.org


ASPECT RATIO
[Explanation]  The ratio of the length of wings to their width is called aspect ratio. A high aspect ratio indicates long, narrow wings. A low aspect ratio indicates short, wide wings.
In short, a simple formula to present it mathematically: 
Aspect ratio = wing length / wing width

[Picture
Image credit: http://NASA.gov


BARGEBOARD

[Explanation]
Bodywork piece on an open-wheel race car, which is usually situated between the front wheels and the sidepod. They, the bargeboards, are usually created with trapezoid profile, and their main task is to redirect turbulent air (flow conditioners), from the wake of the front wing, tires and suspension.

Another function of bargeboards is to serve as vortex generators, for example, creating and directing a quite fast vortex around the sidepods.

[Picture
Original concept: deus1066, Model remix: F1 Framework


BERNOULLI'S PRINCIPLE
[Explanation
In 1738 the Swiss mathematician Daniel Bernoulli publishes in his book, Hydrodynamica, the principle stating that an increase in a fluid's speed occurs simultaneously with accompanying decrease in pressure or decrease in fluid's potential energy.
Here we see very close relations and roots with the Conservation of Energy principle, as well as Newton's 2nd law. 

BOUNDARY LAYER
[Explanation]
When an object moves through a fluid or gas the molecules of the fluid near the object are disturbed and aerodynamic forces are created, whose magnitude is dependent on fluid's viscosity and its elasticity.
The former is very important, as the molecules right next to the surface of the object are sticking to it. Then, there's a collision between molecules sticking to the surface and those above it - this creates a tiny layer with 0 to very small velocity which is called Boundary layer.
Boundary layers can be Laminar or Turbulent, which are covered below.

[Picture]
Image credit: NASA.gov


CAMBER (ANGLE)
[Explanation]
Misdirection such as "camber is the top surface of a wing" do exists, but in fact if we look previously at Angle of Attack's picture, we will notice that one of the surfaces is just more curved than the other - than it's said that the airfoil has camber, while the camber angle is the difference between the chord line (red) and camber line (blue).

COMPUTATIONAL FLUID DYNAMICS (CFD)
[Explanation]
CFD is a leaf on the large tree of fluid mechanics which uses numerical and computational methods to solve issues arising during fluid flow.
It is important to note that typical CFD simulation offers approximations and assumptions by solving Navier–Stokes equations, which define any single-phase fluid flow. Recently there is a lot of interest in two or multiphase models.
F1 teams would usually use CFD along with wind tunnel testing to correlate the produced data and produce parts with greater confidence, having done simulations prior to actual fabrication and production. Such simulations often require large computing power in order to complete as fast as possible.

Generally, a CFD task usually consists of three main stages:

  • Pre-processing - where geometry is defined, the total occupational volume of the fluid is divided into cells - mesh creation, as well as physical models and boundary conditions;
  • Solving - the actual process of  iteratively solving the conditions of each cell;
  • Post-processing - the stage where the results for each calculations are being analyzed and then presented in a readable form, usually like the picture below.
    In most of the cases the red color zones will mean high pressure, while the blue is the opposite - low pressure regions. 
[Picture]
ANSYS Fluent pressure gradients in polyhedral mesh

[Picture]
Image courtesy: Voxdale
In this particular case, the colors stand for velocity - red is high, blue is low.


DOWNWASH
[Explanation]
The downwash effect is simply an air which is forced down - due to wing trailing edge or due to the shape of the body in general. In case of downforce inducing airfoil, the downwash occurs in front of the wing.

Video with downwash effect on a finite wing can be seen below, at Wake section.

[Picture]
Original concept: deus1066, Model remix: F1 Framework


END PLATE
[Explanation]
In order to overcome the problem of turbulence created between the front wheels and the front wings, end plates have been introduced (blue color on the picture below). During the years they had different shapes, but have been used to redirect air away from the tires, and also as pressure equalizers (at rear wing), having in mind the usual wingtip vortices.

[Picture]
Original concept: deus1066, Model remix: F1 Framework


FLAP
[Explanation]
The front wing of F1 car consists of end plates, center section, cascade elements and main flap, highlighted in blue on the picture below. Generally, there's a slot gap between each of the elements, in order to keep the air as attached as possible, thus prevent stall and flow separation. This flap is the element that determines the angle of attack of the front wing, it is adjustable, and therefore it is very important part.

[Picture]
Original concept: deus1066, Model remix: F1 Framework


GURNEY FLAP (WICKERBILL)
[Explanation]
That term originates back in 1970's where American Dan Gurney was fixing this small device at the trailing edges of the wings on racing cars. This is really an effective way to increase the downforce of a wing at the expense of small drag induced. Different researches are quoting different numbers, but let's throw some average numbers and give a ratio of 8% more downforce vs. 3% increase in drag.
What is actually little known as fact is that Gurney flap increases lift by changing the Kutta condition (related to sharp trailing edges), so the wake behind the flap are two counter-rotating vortices (also very typical to diffuser lateral edges, where Gurney flaps are present, too).

[Picture]
OR
Original concept: deus1066, Model remix: F1 Framework



LAMINAR FLOW
[Explanation]
Laminar flow is sometimes also known as streamline flow, occurs when fluid flows in a parallel uninterrupted layers. The main characteristics of laminar flow are its smoothness, the lack of swirls or vortex formations (as much as possible), steady velocity and hence stable pressure gradients.
Few more lines below we are going to talk about Reynolds number, but generally laminar flow is characterized with low Reynolds number (Re).

[Picture]


LIFT TO DRAG RATIO
[Explanation]
Most commonly you will find this term abbreviated as L/D ratio or simply Ld - is the amount of lift (or downforce) generated by a wing or vehicle, divided by the drag it creates by moving through the air.
That ratio has lots of components that build it, but for now we will skip the math and the formulas, and will conclude that in F1 engineers are always trying to achieve higher downforce at lower drag coefficients, which is usually a result of a balancing act - in either setup or design stage.


PITCH SENSITIVITY
[Explanation]
While in motion, certain aerodynamic forces act on a race car. The magnitude of those forces is commonly known as pitch movements, and the ability of the car to cope with them is know as pitch sensitivity. That ability is directly related to the way the car feels and handles, for example sudden and excessive diving nose when braking. More can be seen below at Yaw paragraph.


REYNOLDS NUMBER
[Explanation]
Reynolds number can be frequently seen when solving fluid dynamic issues, just as well as characterize different flow modes, such as laminar or turbulent flow. It is generally a ratio of inertial to viscous forces.
For example, at high Reynolds number the flow is turbulent, characterized by unstable formations, such as eddies and vortices, while at low Reynolds number the flow is laminar (usually smooth flow).

Reynolds number as a measure is very useful for aerodynamic engineers which are trying to match data produced by wind tunnels testing with real track data. This is also one the very possible reasons for data correlation mismatch (a popular topic in F1 world) - the Reynolds number is different on a wind tunnel scaled-down model and real car, because the boundary layer is different.

The formula is simple: 

where:
  • v = is the mean velocity of the object relative to the fluid (m/s)
  • L = characteristic linear dimension, (travelled length of the fluid) (m)
  • mu = is the dynamic viscosity of the fluid (Pa·s or N·s/m² or kg/(m·s))
  • u =  is the kinematic viscosity (v = mu / p) (m²/s)
  • p = density of the fluid (kg/m³)
Hence:

Laminar flow: Re < 2000
Transitional flow: 2000 < Re < 4000
Turbulent flow: Re > 4000

SLAT
[Explanation]
This is part of multi-element wing which is installed ahead of leading edge of the airfoil, below the main element. Certainly, it's there to create more efficiency and downforce. See picture below - a typical aircraft installment, imagine it reversed for a race car.

[Picture]
STRAKE
[Explanation]
A flat plate body fixed to race car in order to control and direct airflow (falls under the general category of Flow conditioners).

[Picture]
Original concept: deus1066, Model remix: F1 Framework



TURNING VANES
[Explanation]
The turning vanes on the picture below are rather Mclaren style, as opposed to the L-shaped from Red Bull and recent 2012 Ferrari incarnations. Turning vanes serve similar purpose to bargeboards, but are usually smaller in size. They started as very simple elements, like the ones highlighted with blue below, but have turned into increasingly complex in the recent years, given the strong aerodynamic profiles of modern Formula 1 cars.

[Picture]
Original concept: deus1066, Model remix: F1 Framework



VENTURI
[Explanation]
Here we will talk about both the effect and the tube, named after the Italian physicist Giovanni Battista Venturi.
The Venturi effect is a jet effect per se - in a tunnel the velocity of the fluid increases as the cross sectional area decreases, which is accompanied with a decrease of the static pressure.
In Formula 1 Venturi effect is closely related with underbody aerodynamics, which included shaped channels (before flat floors) aimed to accelerate the air and hence create low pressure areas.
See the picture below and imagine how and where can this be applied in a race car.
Again, the blue areas are low pressure ones and red are high.

[Picture]
Image credit:  http://www.symscape.com


VORTEX
[Explanation]
Vortex in aerodynamics is any fluid or gas formation which usually has turbulent flow. What is typical for a vortex is the low pressure at its core, which rises progressively as we go away from the center to the outer edges where the pressure is very high. This is one of the reasons why aero people generally would like to avoid creating vortices - the high pressure would mean lower velocity of the surrounding layers, thus drag.

Other reason why vortices are generally avoidable is because of the possibility of "vortex burst" - this is the moment where the formation literally breaks and creates even more turbulent and uncontrollable flow. This is less likely to happen with weak vortices and respectively, usually seen with strong vortices, where the core sometimes disintegrates into few smaller vortices.

The reason why, however, vortices are sometimes deliberately induced is to wake or re-energize the boundary layer - the small portion of air which is very close to a surface, where due to skin friction and resistance the velocity of the air is very low. We would like, as aero people, to have less drag, so we create a vortex generators - small winglets, which often induce normally rotating, weak vortices. The trade-off is the smaller portion of drag induced due to the shape of the device, but it's more beneficial in terms of L:D coefficient.
In F1 world we often hear the term referred to as "wingtip vortices", as seen on the picture below. The reason for creation of such formations is the natural tendency of the air to move from high to low pressure regions, being a continuous function. Here, since we operate with negative lift (downforce), the direction of the vortices is upwards.
These wingtip vortices, on the other hand, create lift-induced drag and drag is unwanted in any of its forms in motor sports, where speed matters.

[Picture]


VORTEX GENERATORS
[Explanation]
We have already explained what boundary layer is, so down on the alphabet we reached the vortex generators - small, usually vertical wings (or winglets, if you prefer - the synonym for small wing) whose purpose is re-energize the boundary layer, and thus increase the overall velocity of the air stream.
Generally, they are quite an easy way to direct air (flow conditioning) and enforce some turbulence close to the surface. In Formula1 cases we have even seen plastic-like Vortex Generators used on Toro Rosso's car - most probably a quick prototype parts, still, they do the job.

[Picture]
Original concept: deus1066, Model remix: F1 Framework


WAKE
[Explanation]
This is the turbulent disturbed air behind an object where the total pressure is low. Notice the 3D grid generated behind the wing's trailing edge below.

[Video]


YAW (PITCH AND ROLL)
[Explanation]
Yaw, in particular, is the motion of race car around a vertical axis, which occurs for example during steering.
All three directions are shown below.

[Picture]
Original concept: deus1066, Model remix: F1 Framework




Congratulations, you have been very patient :)
Once again, this is just a reference point to some of the aero-related terms and devices in Formula 1. Some that are not included in the list, one reason or another: diffuser,  rake (article coming on that in the future, studying effect of diffuser angles and rake together), high velocity tunnels (ducts), F-duct like devices, NACA ducts (or "submerged inlets", due to their vortex-generating nature) but they will find their place at the F1 Framework in detailed articles.
As usual, I'm open to topic suggestions - next raft of blog posts are likely to be attributed to exotic technologies that can make it into F1.