DNS Re=400000 NACA4412

Submission to APS DFD Gallery of Fluid Motion 2015.
A three dimensional direct numerical simulation using high-order methods has been performed to study the flow around the asymmetric NACA-4412 wing at a moderate chord Reynolds number (Rec = 400, 000), with an angle of attack of 5 degrees. This flow regime corresponds approximately to the flow around a small glider. In addition to providing highly accurate data, high-order methods produce massive amount of data enabling proper flow visualization. For instance, in this study vortical structures emerging from tripping the flow to turbulence are visualized using the \(\lambda_2\)criterion. It is interesting to see how interaction of such vortical structures from the turbulent boundary layer and the turbulent wake creates a natural art of its own.
More information: www.flow.kth.se

[@erockromulan9329]

Absolutely stunning. Great job all! I'm excited to have just started a career in this field.

[@nikan4now]

Amazing work. A couple of questions: so an iso surface of velocity travelling downstream is not the same as a fluid parcel is it? Why aren't pathlines used in these simulations? Don't the pathlines tell you more about where the particles go?

[@torstenschenkel2110]

A fluid parcel is the (imaginery) volume of fluid, as it is travelling (convected) and deformed in the flow. Pathlines can be used (if real pathlines are used) to follow particles. However, in continuum mechanics, we are rarely interested in where the particles go, but in where integral properties go - those could be mass, momentum, or, in this case turbulent energy. The lambda2 method used here is, in a way, following "particles", in that it follows turbulent structures as they are transported in the flow. Lambda2 visualises eddy (vortex) structures, which are what makes up turbulence.

[@jjmj9877]

Amazing work!

[@keyvanhp5841]

Good video . Please send any tutorial about this

[@fadoobaba]

what time step you used please?

[@realkanavdhawan]

Mesmerizing ❤❤

[@gabrielmotta4757]

Insane

[@chrisdrake4692]

That's not 5 degrees by any stretch of the imagination - it's not even a positive AoA at all - see @2:08 - at 5-degrees angle-of-attack, the tip of the trailing edge is below the tip of the nose by about half the thickness of the naca4412 shape itself, and there would be no flow separation at all on the undersurface, because it's oblique to the flow (by approximately 3.1 degrees) at all times.

[@vg23air]

lol man, you have a lot to learn, when the airfoil is placed in computer simulation the video output does NOT angle the airfoil to fit your human perspective, I suggest you place a slice of pizza under the left side of your monitor to allow your mind to grasp the simulation rendered within the narrow scope of your reasoning.

[@chrisdrake4692]

@@vg23air explain the *under surface* flow separation then.

[@vg23air]

@@chrisdrake4692 here is my explanation, keep studying until you see the error of your summation.

[@vg23air]

@@chrisdrake4692 The Linné FLOW Centre at KTH started in January 2007 and is one of 20 original centers of excellence set up by the Swedish Research Council, ... but we will listen to you lol

[@chrisdrake4692]

@@vg23air Tip for understanding when you're wrong: if you defer to "reputation" because you can't explain the mistake, you've lost the argument already. Without even *starting* on the fact that almost all "Research centers" are universities (that is to say - mostly inexperienced children just out of school) you only have to look at what else they put out to understand the quality and reliability of their work: kzbin.info/www/bejne/amO0pouCqsh7abM and if anyone is modelling flow that's not parallel to their mesh boundaries (this is what a correct one looks like kzbin.info/www/bejne/a4ran4xmrLWjnqM ) or they're mad enough to represent something purportedly on an angle by showing it as an image that's horizontal, there's already so many rookie screw-ups in evidence that there's no possible way anyone could take their work seriously. In all seriousness - it is NEVER OK to attack someone (me) who is pointing out mistakes in science. The entire POINT of science is to question things. If you can't deal with facts, go find something else to do. Idiots like you are a huge and growing problem: kzbin.info/www/bejne/m4SqqXaPg9x5m5Y

[@Barsik1956]

Hmm... DNS without budget turbulence energy k and the Reynolds stress UiUj - the same thing that a wedding without the bride )))

[@wengchenyang]

I think the bride can be found in their paper. The role of this video is like an amusement at the wedding, where the bride is unnecessary;)

[@umust2651]

agreed!

[@ВоваИванов-г5с]

Я летаю на 80 тыс Рейнольдсах

[@MotivateMomentum224]

Кто от Минакова

[@MathIsInnocent]

impressive but what important physics can be concluded from the simulation, otherwise it was just burning money. 35 million core hours, estimated no less than 250k usd.

[@torstenschenkel2110]

Getting the turbulence model right is the most important part in classical computational fluid mechanics, where simplified models (Reynolds Averaged Navier Stokes Models) are used. These models will be used to simulate the full scale aircraft and will typically run in around 1/100 of the time used here. The parameters that are used in these simpler models have to come from somewhere. That data usually comes from experiments or high-resolution Direct Numerical Simulations like this one. In the past we could only do these DNS simulations for sections of flat plate, leading to parameter sets that were good for that application only (well, I', simplifying here, but strictly speaking it's true). One of the most important problem (and one where most turbulence - RANS - models struggle is the free separation against an adverse pressure gradient, which leads to stall. As a broad generalisation many models will predict separation too late (k-epsilon), while others will be tuned to be conservative and predict it too early (k-omega-SST). Data from simulations like these will help us in developing models that are better at predicting these things and by doing that allow us to build better aircraft and prevent them from falling out of the sky. Note that this DNS is only covering a small portion of the wing (10% relative width) so the actual plane can only be simulated using a turbulence model.

[@fifinoirdefer9458]

@@torstenschenkel2110 Thank you for your explanation, I didn't know most of what you said

[@nikovbn839]

@@torstenschenkel2110 Thank you for the comment, and good luck.

[@MathIsInnocent]

@@torstenschenkel2110 I get your point, very convincing. Thank you

[@YTRusViewer]

@@torstenschenkel2110 you mean this simulation was done only to obtain turbulence statistics and to improve rans models?