Race 1 Preparations

The really rearward balance of the car used at the test race prompted a re-think about the season ahead. Rather than working on a whole chassis and chasing downforce and balance I decided to enter the introductory class (KVRC2) for the season ahead, this will give a solid base with minimal areas to work on which keeps things simple and easier to understand.

The base car:

jfp2ve8

In the above image you can see how much of the car is supplied but also how much still needs to be created (floor, front suspension cover, rear fenders front and rear wings).

The first iteration has a full width single element front wing with small elements just below that are less than a quarter of the width of the main element. There is also a collection of dive planes on the side of the front fairings:

uhh36ww

  • Total drag: 1486.65 N
  • Drag area – Cl.A: 1.24m2
  • Total Downforce: -5235.10N
  • Downforce area – Cl.A: -4.37m2
  • Centre of pressure: 1.977m
  • Engine power: 100%

The results showed that changing approach was the right thing to do. The drag has been reduced a good amount but has lost a little downforce however the engine has full power and the centre of pressure is moving towards the front of the car.


The second iteration saw more angle of attack on the main front wing element along with a fourth dive plane at the front corner, all four getting slightly more AoA too. A further four elements were introduced behind the front wheel to try and gain some more downforce around the centre of the car. Finally the rear wing end plates were shrunk and the mounting point for the rear wing was brought inboard.

d2owjzt

  • Total drag: 1474.68N
  • Drag area – Cl.A: 1.23m2
  • Total Downforce: -5068.52N
  • Downforce area – Cl.A: -4.23m2
  • Centre of pressure: 1.940m
  • Engine power: 100%

For the third iteration the front wing and various elements were removed and a new twin element front wing which spans the full width of the car was introduced along with dive planes with the same airfoil as the front wing.

hdit9l7

  • Total drag: 1467.31N
  • Drag area – Cl.A: 1.22m2
  • Total Downforce: -5225.71N
  • Downforce area – Cl.A: -4.36m2
  • Centre of pressure: 1.863m
  • Engine power: 100%

With the centre of pressure heading in the right way the fourth iteration had one change, the rear wing element was changed to have a shorter chord.

wcj9ruw

  • Total drag: 1330.97N
  • Drag area – Cl.A: 1.11m2
  • Total Downforce: -4753.07N
  • Downforce area – Cl.A: -3.96m2
  • Centre of pressure: 1.795m
  • Engine power: 100%

Again the CoP was heading towards the front but in the last run the total downforce came down a bit so for the next iteration I looked at reducing some drag by lowering the rear wing element.

yv4f6hz

  • Total drag: 1309.02N
  • Drag area – Cl.A: 1.09m2
  • Total Downforce: -4594.73N
  • Downforce area – Cl.A: -3.83m2
  • Centre of pressure: 1.764m
  • Engine power: 100%

This latest iteration saw the rear wing profile return to its original shape and position but the front wing and associated airfoils received more AoA.

uulcid4

  • Total drag: 1505.02N
  • Drag area – Cl.A: 1.26m2
  • Total Downforce: -5328.76N
  • Downforce area – Cl.A: -4.44m2
  • Centre of pressure: 1.799m
  • Engine power: 100%

The final iteration which became the race car for Nurburgring saw an addition to the front of the car. The dual element wing used in the last simulation was duplicated and place above the original profiles.

xryfp3f

  • Total drag: 1578.48N
  • Drag area – Cl.A: 1.32m2
  • Total Downforce: -5247.95N
  • Downforce area – Cl.A: -4.38m2
  • Centre of pressure: 1.699m
  • Engine power: 100%

5cqeiwv

dlqloyv

As the two graphs show, the majority of the drag is produced from the front wing but so is the downforce. The front suspension cover is creating some lift which will be stopping the CoP coming forward as quickly as I would of liked with the changes made.

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Pre-Season Testing

For KVRC 2016 I decided to carry on entering into the full class (KVRC1) as I had a good base with the car that I finished the 2015 campaign with.

So this was the car that finished 2015:

race5

Going into the pre-season test I ran a few simulations with minor changes to this car but ended up changing some areas. The floor area was found to be working very well so this stayed and became the literal base to the car. This was accompanied by the KVRC supplied nose, tub and cockpit although the engine cover behind the cockpit was removed. I took the decision to use the sidepods from the supplied car and then design my own front wheel fairings and rear half of the rear fairings (as this is not supplied). To this I added last seasons front suspension cover then introduced a front diffuser and twin element front front wing.

car

Initial testing showed a lack of front downforce that needed to be addressed for test race so the two element front wing was changed to a four element wing:

ricme20motorsport

This modified car finished 9th in the pre-season test at Nurburgring in a field of 15 cars with a lap time of 412.79 seconds.

Unfortunately the car wasn’t optimised very well so had balance issues which saw a centre of pressure of 2.052m (the ideal being ~1.65m). Drag was in an ok range at 1.38 Cd.A but downforce was lacking at only 4.79 Cl.A, normally that wouldn’t be the end of the world but when the front of the car was starving the radiator intake of air the engine was running at only 63.66% of its capacity.

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KVRC 2016

This season will see the team return to the original name of RicME Motorsport.

Chris, Richard and Julien have been hard at work behind the scenes working on the new rulebook which has been released in draft form –¬†http://www.khamsinvirtualracecarchallenge.com/the-challenge-2016/KVRC2016publicdraft1.pdf?attredirects=0&d=1

There are 2 major changes for 2016:

1) The addition of a ‘subclass’ where the bulk of the bodywork is provided, and the entry consists only of the areas around the front wing, rear wing and floor. The rulebook is substantially simpler for these entries – look for the sections highlighted in blue. Anyone choosing to compete in the subclass still earns points towards the main championship, but there is an additional championship for the best-placed entrant in the subclass. Anyone entering the subclass may choose to start modifying the supplied parts at any point during the season, taking themselves out of the running for the subclass championship and competing only for the main championship. The supplied bodywork for the subclass will look something like the images below, with an adjusted “bodywork volume” to match:

2) The geometric requirements for the inlets and outlets have been simplified (the “outer templates” have been removed and the rotation limits are less restrictive), and instead we are specifying some aerodynamic requirements on the inlets and outlets. If the design is found to not meet these requirements when the CFD simulation has been performed, then an engine power penalty is applied in proportion to the under-performance of the cooling system. We are also adding a second option for the cooling inlets and outlets: you may choose to model the entire internal duct running from the inlet to the outlet, with a heat exchanger in the duct. The aerodynamic requirements will apply to the heat exchanger only, the rules on the inlets and outlets are relatively free for this option. We’re still including some restrictions on the area of the inlet and outlet faces, since this is new territory and we want to keep this in place in case we’ve misjudged the numbers.

There have been many other small tweaks to the rulebook. There are a couple of points in particular that we’d like feedback on:
– Should the rules on the visibility of the front suspension templates be relaxed or removed?
– Should the maximum height of the diffuser (320mm in 2015) be lowered?
We’re also undecided whether the mandated subclass bodywork should include the bodywork surrounding the front wheels, or if this should be left to the competitor to model themselves.

CAEdevice will keep supporting the KVRC during the 2016 season, in two (I hope interesting) ways.

1) The winner of the next KVRC edition will receive a 12 months subscription to the magazine Racecar Engineering

2) In the next few weeks a model of CAEdevices MP003D will be available for AssettoCorsa. The MP003D is derived from the car that CAEdevice used during the previous season (MP003B), with some improvements that make it a hybrid between 2015 and 2016 KVRC cars.

 

 

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KVRC 2015 Final Standings

Team Round 1 Round 2 Round 3 Round 4 Round 5 Total
Variante 25 18 15 25 18 101
JJR Racing 18 25 25 15 15 98
CAEdevice 15 12 12 12 12 63
DynaRace 12 0 0 0 0 12
MantiumRAY 10 15 18 18 25 86
TF 8 10 6 8 10 42
DH Racing 6 2 0 0 0 8
Brook Motorsport 4 8 4 2 4 22
Mercury Motorsport 2 1 1 4 2 10
Pure Power Racing 1 6 0 0 0 7
Talno Racing 0 4 8 0 6 18
Kineuton 0 0 10 10 8 28
sjns-Racing 0 0 2 6 0 8
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Round 5 Result

1st – MantiumRAY

2nd – Variante

3rd – JJR Racing

The newly tweaked car came in 8th, might not look like it was worth the effort but the gap was reduced to the cars ahead and gives a good base and amount of knowledge to take forward in to the 2016 season when rules are expected to stay almost the same.

 

 

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Round 5 Car – the final

Latest run has flat underside to front wheel pod and a wider throat to the diffuser.

You can see in the table above that the last change has decreased front end downforce compared to the previous iteration, so the COP movement backwards wasn’t just as a result of the increased rear downforce… in my eyes this suggests that maybe the “front wheel diffuser” isn’t so bad afterall… it is not possible to completely confirm this conclusion from the data provided however, as we don’t know if one change is masking the other (e.g. removing the “front wheel diffuser” may have decreased drag, but the wider Diffuser throat might have increased it… or maybe vice versa?!)… all we know is that together those two changes included in the last test resulted in no change to the drag and a little change in balance… I would hazard a guess that this last iteration would actually result in a slower car (I haven’t confirmed this on Virtual Stopwatch however) than the previous one (“New Diffuser Strakes”)….

However… a change to a single element rear wing, (which produces slightly less overall downforce and hopefully a lot less drag) could redress the balance and make the overall result better than the “New Diffuser Strakes” iteration… !!!!


Actually… this is worth looking at too… I’ve shown the “effective” or “useable” Cl.A-front, Cl.A-Rear, Cl.A overall and L:D.. essentially this “gets rid of the COP problem” by ignoring any excess downforce at whichever end of the car has relatively “too much”:-

You can see that configuration 8 is actually considerably worse than configuration 7 (actually, it is worse than configuration 2!).. but as per my previous post, maybe overall it could be better if the balance can be re-dressed (by changing the rear wing as LVDH suggests, for example)…

But one thing is for certain: don’t submit configuration 8 as it stands!


One more analysis… My post above might come across as suggesting that the final change wasn’t good… however it depends on what your starting position is… if the original car (Run No. 1 in the table below) had had a little more front-end downforce, then the final change (No. 8 ) may have actually brought the car into balance and we would be singing its praises…

For that reason it is worth looking at the coefficient changes that each change brought about, which I present here:

(The conclusion about the entire configuration 8 is still relevant: it is slower than configuration 7, as a result of being less well balanced).

Wider diffuser throat but with the original underside front pod

Machin proposed rear pod – flat front pod, wider diffuser throat

Interesting….

Looks like you were definitely right to keep the flat front pods for run 10, as run 9 shows they were actually creating lift at both ends of the car! I presume they were causing some disturbance to the flow which is why they affected both ends …

Run 10 gained you a nice chunk of efficiency (although downforce was down a bit)…. so that was definitely worth doing. I’m wondering if the fact you lost some downforce with this change indicates that there is still potential in the diffuser… i.e. there is another way of getting the downforce back without messing up the flow where it joins the free-stream…? I don’t know… and its probably a marginal gain now anyway if we compare your downforce profile to Mantium Ray’s… Out of interest it would be nice to see a horizontal flow line slice like you did before; to see the improvement in flow in the diffuser…


Efficiency is just “Lift divided by drag” (L/D or L:D). But you should set the angle of attack (AoA ) so that the downforce is the same (or roughly the same) with each different wing section you try… If you look back at page 2 of this topic you can see the L:D of that NACA element I posted is around 20:1 at very low angles of attack, but falls to around 12:1 at the sort of AoA you probably should be aiming for… So if you don’t test each wing element at the same/similar downforce level then you might be lulled into thinking one element is better when it is actually worse when you put it on your car at the AoA required to balance the car…

Unfortunately it does mean probably multiple runs of the same element to set the AoA to give the same/similar downforce levels… The starting point is your current wing at the current AoA… See how much downforce that gives, and then adjust each element you try until you get the same downforce… Then pick the one with the lowest drag… Sounds simple! :?

So here we have it, the final iteration of the 2015 car thanks to the help and knowledge of Richard Machin.

race5

 

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Round 5 Car – part 3

The two main areas as discussed before I think are the diffuser and the flow in the middle of the car.

The flow in the diffuser area is showing the effects of the entrainment of the rear wheel contact patch wake (I’ve exaggerated the blue area on the velocity plot for clarity, see below). This low velocity “cloud” spreads out and starts to “take over” the diffuser. I’ve found that adding diffuser strakes can help to control the spread of that low velocity “cloud” and increase downforce and decrease drag… so this might be something to have a play with amongst others.

In front of the side-pod side there is still that area of recirculation. Maybe you should try your/Wesley’s idea to extend the front suspension fairing to enclose the side-impact structure to further prevent this air moving vertically and direct it through this area and out of the sides of the car instead, and I think you can improve the leading edge of the floor as well: remember air doesn’t like flowing across a “sharp” object: it just detaches…

Once you’ve had a play with those (and other aspects of the diffuser, such as different expansion ratios, different angles, etc) then you’re down to looking at small areas of the body to look for improvements. As we said before: you’re looking for low pressure areas on top and back of the body which manifest themselves as areas of lift and drag.

On the images below I’ve marked on the direction of the resultant forces due to the surface pressures (These are just perpendicular to the surface): anything pointing vaguely backwards is creating drag and upwards is causing lift. I don’t think there is a huge amount to be gained here, but maybe a few modifications to the tops of the wheel fairings could be tried; remember you’re trying to avoid downward curving surfaces… sometime purposely causing the air to separate from the bodywork can be of benefit (i.e. so the air doesn’t follow the downward curving bodywork and create lift).

You may also want to try changing things like slot gaps and wing element profiles, although yours seem to be working quite well…

Also remember that any gains in Downforce at one end need to be balanced with more downforce at the other end…

And finally: best try one thing at a time so you can be sure how each change has affected the car…

I have run a couple of tests today and thought you might be interested in the results

Test 1
Changed the rear section of the rear wheel pod so that it has a flat top. To do this the rear wing elements have been raised and the slots in the endplates have been removed. (these changes are in the following tests too)

Test 2
Changed the front suspension cover to resemble the rear suspension cover on Variante’s early car.

Test 3
Changed the front suspension cover to resemble the front suspension cover on Variante’s early car.

That is cool.. not a huge improvement then, but a little (note COP has moved backwards slightly though).

Actually I thought I’d do another post(!)… this one is kind of a “If this….then try this…”. The idea being that someone can identify areas of undesirable pressure on the surface of their car, find on the drawing below the applicable/nearest shape and then try out the proposed shapes to try and get rid of the undesirable pressure…

…Then underneath those I’ve put in a few ideas for manipulating flow in the underfloor and diffuser which I found to have a big improvement on drag and downforce… The curved objects in my case were 25mm tall “fences” which generated vortices… The ones at the floor edge behind the front wheels were used to attempt to seal the floor from the high pressure air outside the car. The diffuser strakes seemed to help control the rear wheel wake where it spilled into the diffuser (as mentioned in my last post), and to be honest I’m not entirely sure what the vortex generators under the leading edge of the floor actually did -I put them in to see if they would affect the rear wheel wake in the diffuser, but I do know they increased downforce and reduced drag!

(You probably can’t apply these vortex generator ideas directly because of the flat floor rule, but maybe you can try to generate the vortices either in front of the leading edge of the floor, or down the sides of the car near the floor?)

Looking again… Test 1 came with a significant increase in drag… So some part or all of that change should be taken off the car… I wonder if it is the lack of wing end plate slots that is doing the damage?

Or the inside face of the new wheel fairings? Those dark blue patches under the wing do face backwards slightly…

On the previous picture of the rear there looked to be significantly less dark blue on these panels (and the panels were not as tall because of the drop down behind the wheel): looks like it is better to accept a little lift over the wheel in favour of less drag…

  • Original “good” car with the original wheel fairings, wing end plates and front suspension fairings: 41.7 seconds
  • Modified car with new wheel fairings (“Test 1”): 41.9 seconds (+0.2 seconds compared to previous)
  • Modified car with new wheel fairings and Modified front suspension fairings (“Test 3”): 41.76 seconds (-0.14 seconds compared to previous)

So I think you’ll be better off with the original rear wheel fairings but with the modified front suspension fairings… this potentially might give you a lap time of 41.56 seconds (41.7-0.14 = 41.56)… however, what we don’t know is that maybe the modified front suspension and original lower rear wing may work less well together than the original configuration….!!!

That leads me to think that the safest way to proceed is to do one change, get the result, decide if it is better or not: if it is better then try another modification using the new car as the basis… if it is not better go back and use the previous car as the basis for the new modification… that way you don’t lead yourself down a blind alley…


 

Thought I’d overlay the drag graphs from the original car, and the one with the modified rear wheel fairing (“Test 1”):

You can see the slight reduction in drag (and lift, but not shown on this graph) that came about by removing the curvature on the top of the wheel fairing… but also the big increase in drag right at the rear….

Next I looked at whether to have strakes or not in the diffuser.

Without strakes

With strakes

These slice are taken every .5 in Paraview (50mm?)

Captured a vortex!

Interesting…

Looking at your diffuser I’m wondering whether the outward flare should start early and have a larger radius… So the outward turning of the air is less extreme as the air exits the diffuser .. Look at the transverse direction of the flow at the back of the diffuser! This might help with the flow above the rear deck as well… Also I wouldn’t follow the line of the wheel fairing exactly with the strake.. I’d have it somewhere between straight and slightly curved… and/or maybe cut it short as per Wesley’s idea?

Personally I’d also be inclined to move the outer-most strake in a bit so the gap between the wheel fairing and it is bigger: to see if that captures more of the rear tyre contact patch wake…

New strakes have improved the downforce of the car.

About 4% increase in DF with very little change in drag or COP… Not bad…. But I still feel there’s another “step change” hidden somewhere in that diffuser if you can find it!

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