[CFD] Turbulence Intensity for RANS

Рет қаралды 8,617

Күн бұрын

This talk discusses the different reference velocities that can be used in the definition of Turbulence Intensity, and the effect that this choice has on the computed values in RANS CFD.
Time stamps
0:00 Introduction
0:51 Background
2:49 Typical Values
4:20 How to calculate Turbulence Intensity
8:01 Turbulence Intensity for RANS
14:18 Reference Velocity
15:33 Example Problem
19:51 Summary of reference velocity choice
20:59 Contour labels
22:04 Check your CFD code!
23:11 Velocity-inlets
26:53 Summary
27:57 Outro
References
CFD Online, 'Turbulence Intensity', Accessed October 2022
www.cfd-online.com/Wiki/Turbu...
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Disclaimer
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The methods, algorithms, equations, formulae, diagrams and explanations in this talk are for educational and demonstrative purposes only. They should never be used to analyse, design, accredit or validate real scientific / engineering / mathematical structures and flow systems. For such applications, appropriate trained, qualified and accredited (SQEP) engineers / scientists should be consulted along with the appropriate documentation, procedures and engineering standards. Furthermore, the information contained within this talk has not been verified, peer reviewed or checked in any way and is likely to contain several errors. It is therefore not appropriate to use this talk itself (or any of the algorithms, equations, formulae, diagrams and explanations contained within this talk) as an academic or technical reference. The reader should consult the original references and follow the verification and validation processes adopted by your company / institution when carrying out engineering calculations and analyses. Fluid Mechanics 101 and Dr. Aidan Wimshurst are not accountable or liable in any form for the use or misuse of the information contained in this talk beyond the specific educational and demonstrative purposes for which it was intended.

Пікірлер: 45

@ethanjohnson5950 6 ай бұрын

Babe wake up, there’s a new Fluid Mechanics 101 video.

@fluidmechanics101 6 ай бұрын

😂

@jessbuildstech 6 ай бұрын

Really excited to listen to this! Finally some helpful information on KZfaq for CFD!

@opencast1819 6 ай бұрын

Great wrap-up! Even to me a CFD engineer with 25 years in the field it gave great tips for the results visualization! Thank you Aidan, will apply that.

@nerfthis8435 6 ай бұрын

After finishing many of your previous videos, I got an A in my CFD course. I will definitely donate to you if my life gets richer in the future!

@yavuzaks1348 6 ай бұрын

It was a requirement since little information was available on the internet and was not clear enough. I think you will complete uncovering every piece of important concepts in CFD in the future. Thanks.

@botonb4eg1 6 ай бұрын

That's just a masterpiece. Thank you!

@nrc9275 6 ай бұрын

Excellent and simple breakdown of the term with its physical meaning , to the point! Thanks Dr. Aidan

@PeterJang 6 ай бұрын

As always, great lecture!

@whatnonsense2447 6 ай бұрын

You are doing awesome work, your channel helped me alot understanding concepts

@hungnguyenthanh8833 6 ай бұрын

Thanks very much doctor Aidan. Thank to you, I am capable of improving and enhancing my knowlegdes about CFD. I can apply these informations in my researchs and workings much more. You are really genius 😀😀😀

@user-ic7gn3lz4k 6 ай бұрын

Thank you so much for very useful content!

@TheHumanNexus 3 ай бұрын

Thank you for the video…❤

@charlfmare 6 ай бұрын

Great talk! Was really insightful!

6 ай бұрын

Well done, thanks!

@darshangohel6873 6 ай бұрын

Amazing work 👏

@ahmed12op 6 ай бұрын

Great talk

@sabinsapkota3515 5 ай бұрын

what a great person

@TerragonCFD 6 ай бұрын

Great! Thank you 🙂

@mohammadjadidi233 6 ай бұрын

Perfect!

@sergniko 4 ай бұрын

I find this talk very useful :)

@sneakyninja2000 6 ай бұрын

Great video as always, could you do a video on Hybrid models say differences between DES DDES and IDDES?

@alisadeghi4698 6 ай бұрын

nice thanks!

@VinodKumarGuleria 6 ай бұрын

Really good

@dongdongdong2732 6 ай бұрын

Very good presentation. Can you also talk about turbulence viscosity.

@user-cq5jg7iz2e 4 ай бұрын

If I make a contour of turbulence intensity in Fluent, the contour typically use the reference velocity which is defined in the Reference Data Settings Page. But if I want the turbulence intensity based on the local velocity, the typical turbulence intensity in Fluent should be treated as a constant. And after that, multiply it with the velocity magnitude.

@fluidmechanics101 4 ай бұрын

Yep. You can always define a 'custom field function' with your own definition and then you can plot exactly what you want 👍

@TurboAcki 6 ай бұрын

Nice Video. Is it smart to use thisto adapt the mesh size? Or what di I miss?

@digguscience 6 ай бұрын

It seems that for the RANS model you have to use CFD software

@ramongalvich5024 6 ай бұрын

I literally googled this topic, when you released this video. Thanks!

@mariarosales3535 5 ай бұрын

Good day dr. Aidan, from silide 4:25, the step 5 would be a recall to also solve (u'_y ^2) and (u'_z' ^2) as steps 1 to 4 solved (u'_x ^2), right? or is this step 5 an extra mean value to be computed over (u'_x^2) solved in step 4?

@SO-dl2pv 6 ай бұрын

Excellent as usual! In 5:10 the 6th item in the list: "Sum and take the square root". Isn't 'sum' redundant since in step 5 the mean of x,y, and z components is calculated?

@mariarosales3535 5 ай бұрын

Hi. I might have the same doubt of yours, step 5 should be better a recall to also perform steps 1 to 4 for the other velocity components (y and z), and then finally go to step 6 for a unique urms value that involves all the fluctuating velocities

@scugglebottom 6 ай бұрын

Great content as always. I've never understood the pro/con of this same intuition when applied to Pressure&Temperature boundary conditions where the options exist to use TKE & ESP or Length Scale & Viscosity Ratio. Is there a reason you should employ one strategy over another when applied to a URANS sim for example?

@fluidmechanics101 6 ай бұрын

Ultimately the value will be the same, so it doesn't really matter. If you are going to have to change the boundary condition (for example to investigate the effect of a range of different ambient turbulence conditions) then I would choose the option that makes it easiest for you to change, so that you don't have to re-do the calculation yourself (you might make an error).

@vreijs 6 ай бұрын

If I look at an ABL flow (6.44m/sec @10m and z0=1m) I see at 12.5m height;, a speed |U| of 7.2m/sec and a KTE of around 1.6m2/sec2. And this gives an I =sqrt(2KTE)/|U|=sqrt(21.6)/7.2=25% So your boundaries (1 and 5%) do not really work for an ABL environment. Do I misunderstand? Thanks for the feedback.

@fluidmechanics101 5 ай бұрын

You are correct. For an ABL there are profiles of k and epsilon which are recommended (see the original paper by Hargreaves)

@mariarosales3535 5 ай бұрын

That's correct, the BC for turbulents fields (TKE, epsilon or omega) follows variable with height formulas according to the approach you want to use for the ABL: shear stress driven flow (Richard & Hoxey 1993) or pressure driven flow (Deaves and Richard & Norris 2018), taking aside if you want to model neutral or non-neutral ABL. So the standard theory we find in CFD courses to set a fixed value of TI or for the turbulent fields won't match with accurate inlet profiles, and so downwind results may differ a lot from your experimental data.

@ashimchhetri10 6 ай бұрын

I am confused with the definition of urms, isn't it the average of one fluctuating velocity component over time, eg: u' is instantaneous fluctuation along x-direction, urms is square root of u'^2 only? So that T.I is different along 3 different axis, Tx Ty and Tz

@fluidmechanics101 6 ай бұрын

You could define it that way if you wanted. I think the important thing is to check the manual of the CFD code you are using, so that you know what is being reported. If you are doing the post-processing yourself, you can define Tx, Ty and Tz yourself, or any other quantity that you wanted! This is the art of good engineering, knowing what quantity is best to report and in what way, so that you can use it to make good decisions

@felipeescalona4694 6 ай бұрын

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