Automotive Engineer here, this is a meme where the CFD Engineers need empirical testing to help "teach" their model to be more realistic. I'm doing the empirical testing :)
@robertpalin5878
10 ай бұрын
Sadly, having done both, I find neither to be truly reliable with respect to on-road, real environment performance, and that the best pragmatic approach is to use each to their strengths, and to 'fill in' the weaknesses of the other.
@bobguarnieri280
11 ай бұрын
Very good discussion, thank you. I have never run a CFD analysis, but have done many structural analyses over my career, and I have to say that it took years of training, learning the nuances of the software, being able to do hand calculations to verify I was in the ballpark (and to understand what was going on), and comparing the analyses to physical results to get to a position of doing valuable work. An amateur with no training/experience, and no engineering background would have produced laughable, and dangerous results. My favorite aero book is Racing Car Aero by Katz, but I do have yours also and find that it complements the Katz book very well.
@CurboroughSprinter
11 ай бұрын
Back when I was a kid my parents used to say “don’t believe everything you read in the papers”. Sometimes in the modern world it seems we’ve forgotten to critique things and just accept what people say on social media. Luckily there are people like you to set things straight. To be honest all his makes me think I won’t bother with CFD and just jump to ancient tech of wool tufts and magnehelic gauges. 👍
@JulianEdgar
11 ай бұрын
Yes, if you can accurately measure the real thing it's always going to be better than a model of a model.
Currently my 4th year of automotive engineering engineering degree and have to say every small detail you give in these videos gives me that much more help on my finishing it. Thank you very much
@JulianEdgar
11 ай бұрын
Great to hear!
@JanTonovski
11 ай бұрын
Thanks for this video Julian, I was about to invest a whole bunch of time in a CFD programme. I think I am going to buy some wool and duct tape instead 😂
@robhills2613
11 ай бұрын
I purchased a cheap 3D model of a Mazda MX-5 NC (Mk3) and used AirShaper to run some CFDs. While the 3D model was clearly deficient in many areas, I did nonetheless think that the CFD artefacts were interesting, and the CFD-derived Cd was in fact very similar to the value obtained by a German car magazine in a full scale windtunnel. Next step is to buy the car and try using some of the methods that Julian has provided in his many books!
@JulianEdgar
11 ай бұрын
See my book for how different the CFD-derived drag and lift values were on the Mercedes compared to the CFD...
@AirShaper
11 ай бұрын
@@JulianEdgar @robhills2613 There is no simple "yes or no" answer to the question if CFD is accurate / useful or not. Julian rightfully points out that it highly depends on the 3D model, which is true. And that was the major reason those drag values were off on the Mercedes. We've done simulations on a highly accurate scan of the Rivian R1T and got very good results (which were endorsed by Andrew McAllister of Rivian himself). Just to show that when the model is correct (and the selected accuracy at AirShaper is high enough) we can get very close: kzitem.info/news/bejne/ra6OqYOKbnt1ZWU Does that mean CFD is useless for anything else? No, not necessarily. Through automation we can take away some of the errors that are made by many users. Also, if you're looking for overall flow patterns to get insights into for example the angle of attack towards a wing, then 3D models off the internet can still make sense. But I fully agree - you need to look at CFD results with a healthy dose of skepticism.
@JulianEdgar
11 ай бұрын
@AirShaper In fact the angle of attack of a wing is a good example of how CFD should *not* be used to look at aero elements in isolation; the best angle may well depend on the car to which it is fitted!
@AirShaper
11 ай бұрын
@@JulianEdgar Yes, the best scenario is to fit the wing on the car and run a full car analysis - completely agree, and we also saw this working on the Pikes Peak car - wing worked well in isolation and was bad when placed on the car. But if you're for example shopping for after market components and you're on a tight budget, it's still valuable to know what the "base" airflow pattern around your car is like, to know where & how to put a wing (and yes, that wing will influence the base airflow pattern in turn, but you'll still learn a lot).
@JulianEdgar
11 ай бұрын
Yes, and finding the "the 'base' airflow pattern around your car" can be achieved in 30 min and at no cost... no CFD needed!
@HadiKamalzadeh-bo7fq
4 ай бұрын
I realized many new things about aerodynamics and CFD. thanks a lot.
@JulianEdgar
4 ай бұрын
Not a problem!
@kcwolffan6900
11 ай бұрын
When driving on highway,I'd like to watch other cars on raining days.So I can "see" the airflow by observing the flying water mist.😆
@JulianEdgar
11 ай бұрын
It's a good technique, if you know what to look for.
@kcwolffan6900
11 ай бұрын
😄😄@@JulianEdgar
@ivanmelnikovabramov2177
10 ай бұрын
For real, your channel its a gold mine for me, i will try to buy some of your books!
@JulianEdgar
10 ай бұрын
Awesome, thank you!
@matteoricci9129
11 ай бұрын
Another KZitemr Bjorn Nyland tested a car with a roof box, without, and with a trailer itch box ( just a box hanging from the hook not a trailer with wheel). He was measuring the efficiency reported on the same road, quite accurately, not as much as you, but still good . The end result was that the difference between none and trailer itch box whas minimal Maybe you should collaborate To improve
@jasonrivers7518
5 ай бұрын
I once removed the factory rear spoiler from my car and drove it, with the bootlid unlatched, on an empty road at 100, and it was still unlatched when I stopped. I then repeated the process with the spoiler refitted, and the boot latched at not quite 80- I heard it. I thus concluded that my rear spoiler wasn't entirely ornamental... Thinking that this is an effective, if wholly unscientific method of testing.
@JulianEdgar
5 ай бұрын
Very good!
@hoapham7389
11 ай бұрын
your book is not available in Google Play bookstore. I did buy the previous edition, looking forward for current one to also to come into Play Store
@JulianEdgar
11 ай бұрын
It won't ever be available on Google Play Store.
@kewinczarny5985
11 ай бұрын
As the person who works a lot in CFD, i need to add something really important about your first point - CAD model doesnt need to be precise to every mm, because before you open the CFD program you still need to simplify the model to make the simulation in reasonable time (like 8 hours). That does not mean that precise models are not used - they are but in fields that require you to calculate downforce right to 0,001 N. And also good mesh is really important. With bad quality mesh you will never have right results.
@JulianEdgar
11 ай бұрын
Yeah, but we're talking CAD models with no underside detailing (just flat floors), steps in body shape that aren't there, wheels that aren't detailed (and sometimes don't turn) etc.
@OgamiItto70
11 ай бұрын
Good points. Ancient computer technology saying: "Garbage in, garbage out." Computer modeling is only as effectively predictive as the data and programming that drives it. Also, be careful not to misinterpret the result(s). Use critical thinking. It's always good to be skeptical in matters of engineering (and many other facets of life).
@LoganLeGrand
11 ай бұрын
One thing I’ve already disliked was lack of radiator airflow modeling, most just block it off lol a solid or free flow through it like it’s open. Also for track cars they always model them with windows up but in the US tracks require windows down. The window opening is a massive influence on down stream airflow and it’s never modeled!
@JulianEdgar
11 ай бұрын
Yes, both very valid points.
@piedpiper1172
4 ай бұрын
Have you ever experimented with an automatically variable front air dam/grill? My modified little Gen 1 Veloster hatchback runs cool until it doesn’t, and I think it would be quite the fun pursuit to devise a way to have a speed and temperature controlled air dam, but I’m wondering if you’ve ever looked into it, or if you can think of a method that would be remotely cost viable. Once my intercooler and/or oil coolers Heatsoak, it needs all the deep breaths it can get. Just the nature of squeezing fun and horse power out of a 1.6L 4 banger. Don’t worry, I know your book will teach me how to test any implementation of such a harebrained idea, and I’ve already ordered it. More just a question of feasibility.
@JulianEdgar
4 ай бұрын
Pretty easy - just use temp switch and solenoid.
@piedpiper1172
4 ай бұрын
@@JulianEdgar lol. I meant the moving bits, sensors are the easy part. But fair enough, I wasn’t clear in how I asked. To me, the hard part is devising something that can open/close all or part of the grill, fits inside the engine bay, and can survive the heat environment. Once all that is in, sensors to tell it when to move seems the easy bit
@JulianEdgar
4 ай бұрын
Get the grille shutter from another car. I have one from a Ford Focus that looks pretty adaptable.
@piedpiper1172
4 ай бұрын
@@JulianEdgar Ty!
@nigelsmith7366
11 ай бұрын
There is a reason why automotive companies spend millions of dollars on RnD for most vehicles since mid 80's
@JulianEdgar
11 ай бұрын
Yes, but that misses the point. The point is that aero measurement on the road is vastly better in accuracy, cost and ease than amateur level CFD.
@jasonrivers7518
5 ай бұрын
The reason car companies spend all that money is because the government makes them, mate- they would much prefer not to!
@indopleaser
11 ай бұрын
Looks like they scanned your cad model from a dicast car instead of the full scale car. Not sure
@JulianEdgar
11 ай бұрын
I guess that is possible but it was the best free model I could find... just like any other amateur wanting to do CFD.
@neilbreen6998
11 ай бұрын
Beautiful garbage in beautiful garbage out
@jamessever8936
7 ай бұрын
What about measuring scaled models? You can 3d print different iterations that way. The only issue I can see is that the Reynolds number will be different due to the size difference. But I guess you could change the wind speed for that
@JulianEdgar
7 ай бұрын
Reynolds numbers a very large problem. 1/10th scale model - 1000 km/h wind speed needed. No good. How big does your model need to be? Also, surface roughness a real issue.
@jamessever8936
7 ай бұрын
@JulianEdgar I see. My main concern was just seeing if an addition made a positive or negative impact to the Cd, but not trying to see the scale of the impact. I assume that cfd MIGHT be good for that since I am not trying to get perfect results. But even then a scale model might be better. But I think the largest I could print on my machine is only .42 meters...
@JulianEdgar
7 ай бұрын
Making a positive or negative impact on Cd is highly based on Reynolds numbers and surface finish. If you can print at 0.42 metres (1/10th scale?) then you will not be able to test it very well. Also, wouldn't a printed model need a massive amount of work to give the correct surface finish? Maybe you could try testing it in a water tunnel - higher density fluid will allow slower speeds. Personally, I think making a full size mockup will, overall, give better results for less work.
@piedpiper1172
4 ай бұрын
@@JulianEdgar3D printed surfaces have gotten massively better, but, I think you’d still have to at the absolute minimum sand it smooth and put automotive clear coat over it, which to get that well applied-You’d basically need a real car paint booth. Unless painting cars happens to be your hobby, I think you’re right about full scale mock-ups.
@twinforce_fusion6560
11 ай бұрын
That is a big question I'm always asking, does a automobile company ad's a spoiler for look or efficiency (hopefully both)? I'm personally debating on removing my factory spoiler to see if I could gain any MPH/KM's down the track (1/4 and half mile). Next Spring planning to do the full mile, maybe that would be the perfect place to test it! Already got taller tires (%5), drop the car 0.9", now the big decision will be with OEM spoiler or not?
@JulianEdgar
11 ай бұрын
Covered in detail in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country.
@potatosfortots9909
11 ай бұрын
Whenever people bring free cfd up to me when i talk about pressure testing I always have to explain to them the simple fact that theyre relying on a free program to emulate the laws of physics, and be able to interpit it. Its just not reasonable to be able to emulate the laws of physics that we still arent 100% sure of on a dell laptop with a free program and a video game model of your car that has a flat underside
@indopleaser
11 ай бұрын
Do a video of flow viz, put it on a car would make a great video
@JulianEdgar
11 ай бұрын
Never had any success with it - and tufts are less messy.
@hectorae86
4 ай бұрын
Question.... If the wind is coming in from the side at say 60 miles per hour and you're driving forwards at 60 miles an hour..... Isn't the air then flowing over your car diagonally?
@JulianEdgar
4 ай бұрын
Yes, and you don't even need a 60 mph wind to have yaw airflow - and all its effects.
@hectorae86
4 ай бұрын
@@JulianEdgar do you have videos about that effect on KZitem too?
@JulianEdgar
4 ай бұрын
I thought I did but I can't quickly find it. All covered in my book - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country
@hectorae86
4 ай бұрын
@@JulianEdgar knee deep in psychology books right now, but I added them to my wishlist .
@nigelsmith7366
11 ай бұрын
I would be very interested in your thoughts on Aero packages on hill climb and super lap cars
@JulianEdgar
11 ай бұрын
My book covers in detail how to develop (and measure) downforce - www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country. It's all pretty easy.
@eddieelectric4938
10 ай бұрын
Hey i am very curious about ur thoughts on spoilers on fwd, especially for sedan shape (notch back), do u believe a low angle spolier is good for them to give a bit off stablity on the rear during corners to them but not to much because it is fwd ?
@JulianEdgar
10 ай бұрын
Makes no difference whether the car is front, rear or all wheel drive. Spoilers can be effective if well designed. All covered in my book!
@eddieelectric4938
10 ай бұрын
@@JulianEdgar may I know which book it is that would cover it the most, might try to get it than to get a better understanding, thank youuu so much for your content by the way
@JulianEdgar
10 ай бұрын
www.amazon.com/Vehicle-Aerodynamics-Modification-Development-alternative/dp/B0C87VYVL8 or Amazon in your country. Shows how to develop and measure rear spoilers, including on a sedan shape.
@tomast9034
11 ай бұрын
only fool who totally believes in any cad/cae / climate/ finacial market simulation is the head of sales in any company. of course if you have decades expertise doing similar stuff and able to test it in real life it different. you have to know what you do and what the program can do.
@THEANIMALGUY
11 ай бұрын
So a question is eyeballing(like proper eyeballing with attention to detail)better than a for the lack of a better word crappy cfd?
@JulianEdgar
11 ай бұрын
No. Eyeballing can be completely wrong. Testing is best.
@THEANIMALGUY
11 ай бұрын
@@JulianEdgar so even bad cfds are better than eyeballing with detail?
@JulianEdgar
11 ай бұрын
Whaaat? Both approaches are crap - and why would you use either, when you can easily, accurately and cheaply measure the real vehicle?
@THEANIMALGUY
11 ай бұрын
@@JulianEdgar doesn't that count aS eyeballing since you still have to look Yeah my apologies I seem to have abnormal explanationz for words 😅
@JulianEdgar
11 ай бұрын
Measurement is nothing like just standing there looking at a car ("eyeballing").
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