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the same question. i didn't get that point

Hi Mohammad, In spiral channels, you have to define a cut plane that is exactly perpendicular to the flow in order to be able to visualize the dean flow, otherwise (by using predefined planes) you can't observe the vortices.

You're welcome. So, have you tried decreasing the timesteps? Like use 0.001 instead of 0.01

Has your problem been solved? I also encountered the same problem.Can you give me some advice?

Glad it was helpful.

Hi... What are your channel dimensions? Dean number? particle radius? It all matters. Maybe both particle sizes are significantly large and they equilibrate near the inner wall.

@@moeinpoi Hi, thanks for replying. I'm replicating the spiral in this video ruclips.net/video/GFV89cOAg9c/видео.html The spiral has five turns with channel dimension of 300 um width and 50 um height. Dimensions of particles are 5 um, 20 um and 40 um. For a flow of 100 ul/min or more, both 5 um and 40 um particles equilibrate near the inner wall while the 20 um particle is the furthest away. For 50 ul/min, 40 um particle equilibrates closer to the inner wall following the 20 um and then the 5 um, as expected. I don't know why the smallest particle equilibrates in the inner wall for velocities higher than 50 ul/min. It doesn't make sense to me, probably a higher velocity might be inducing instabilities in the simulation idk.

@@moeinpoi I think I solved the problem. I changed the dimensions of the particles to 20, 30 and 40 um and added a multyphysics that coupled the laminar flow and particle tracing. Not sure why it worked but at least I'm getting good results now.

Hi Naveen, I'm glad it was helpful! Hope you succeed in your research.

Hi, you're welcome! Are you sure you have correctly defined your boundary conditions?

@@moeinpoi yes i did i am quite sure

@@charifaberkanekrachai1558 Are you sure you're looking at the results in the last time-step? Maybe you're looking at the results for t=0.

Hi, you're welcome! So, to do that, you have to go to Results node > Particle Trajectories(fpt), and then right-click on Particle Trajectories 1 and choose Color Expression. From there, find and select Particle Radius as Expression and it will assign each particle size a different color.

Is that a question or a fact? 😃

No problem! I'm glad it was helpful.

Hi, I know what you are talking about. I had the same problem with spiral channels. Is your geometry also a spiral?

Also do you offer any tutoring services, would be happy to pay for a brief session over zoom. Thanks!

@@moeinpoi Yes it is also a spiral. I'm trying to model a spiral microfluidic device and I want to show the dean vortex in my project.

@@saucebaws9058 Sure, you can contact me on LinkedIn: Moein Naderi

@@saucebaws9058 You have to manually change the position of the cut plane until it shows the correct results.

You're welcome! I'm glad it was helpful.

You're welcome! I'm glad it was helpful.

I actually haven't worked on magnetophoresis myself. All I know is that you can also add it to the lift forces in the particle tracing module.

@@moeinpoi am stack in this problem do you recommend some tips for m

@@aliumara1205 What exactly is your problem?

Moein Naderi i cant make the particles response to external magnetic field

Thanks! I'm glad it was helpful. I have actually recently uploaded a video titled 'Visualizing Dean Flow Vortices Arrow Plot' which might also be helpful to you. Here's the link to it: ruclips.net/video/W_WRiO-MsYE/видео.html I will try to upload on various topics as well. Do let me know if there is a specific topic you'd like me to cover.

Thanks, you can contact me in Linkedin: Moein Naderi

@@moeinpoi your email please

Thanks! I'm glad it was helpful.

You're welcome! Glad to hear that.

Thanks! Glad it was helpful.

Hi! It's great to hear that. I hope you get the results you want.

Hi, you're welcome! Sure, I'll try to make a video on that whenever I get the chance.

Hi! What exactly do you mean by the particle trajectories being 'unstable'?

hi! fast reply! I started again a new simulation and turns out now the particles trajectory is fine. Did you do any post processing on that particle trajectory at the end? My particles size is way bigger than their real size. i adjusted the ratio scale factor to 1 but they disappear. thank you EDIT: when i said the trajectories were unstainble i meant that they didnt have that laminar behavior. the would pass through the wall and make abrupt changes.

@@vitorhugoRH Well, you'd have to play with the 'Radius scale factor' under Point Style until your particles are the size that you want. For this case, something between 0.02 to 0.009 would work. But it might be different case by case. You can change it by trial and error until you get to the value you want.

@@vitorhugoRH Hi Vitor, my particle trajectories are not laminar, pass through the wall. When you said you started a new simulation, what exactly did you do? Did you go for a better mesh?

Hello Praneetha, I think you should decrease your time-steps.

Hi, I'm glad it was helpful. To get the velocity profile along some particular cross-section, you can first right-click on the 'Results' node and add a '3D Plot Group' (choose the 'Dataset' according to the study you are looking for). Then, right-click on the '3D Plot Group' and select 'Slice'. In the settings for your 'Slice' plot, locate 'Plane type' and change it from 'Quick' to 'General'. Here you can define the plane on which you would like to have velocity profile (However, it might be hard to define such a plane if you have a complex geometry). Then you can change the 'Expression' to plot velocity profile or whatever parameter you're looking for.

Thank you very much!

Moein, i wait for the next video. good luck

You're most welcome. To my understanding, Saffman is just a rotation-induced lift force, and is rather negligible in curved geometries, because of its relatively smaller magnitude in comparison with the wall-induced, shear-gradient, and the Dean drag forces. However, what I have recently found out is that the shear-gradient lift force is actually 'embedded' in the wall-Induced lift force. In fact, Comsol has defined the 'net inertial lift force' equation which is the 'superposition' of the wall-induced and the shear-gradient forces - and for some unknown reason to me - have just called it the 'wall-induced' lift force without mentioning that it indeed calculates the net effect of the two mentioned lift forces. On the other hand, I think I might have mentioned that the Dean drag force is embedded in the 'Drag Force' rather than in the velocity field. In fact, we will have lateral components of the velocity field in the direction perpendicular to the wall ( Dean vortex) in curved geometries like spirals, and the Dean drag force is simply calculated and exerted on the particles using the Drag law ( in this case, the Stokes law) that we add in the Particle Tracing physics.

@@moeinpoi Thanks for your explanation. Could you please give a reference to the informtion that says that the wall-induced lift force is actually the superposition of the wall-induced and shear gradient forces ? That would be extremly helpful. Also, is there any way to give each particle type a different colour in the plots ? I see yours appreaing in 3 different colours.

@@3dsquaduk The formula for the net inertial lift force (F wall + F shear gradient) was proposed by Ho and Leal in their 1974 paper: "Inertial migration of rigid spheres in two-dimensional unidirectional flows". This is the formula: FLift=Fw+Fs=ρU2maxa4/D2h(β2G1+βγG2) If you check the formula equation for the wall-induced lift force in COMSOL, you'll see the exact same formula. For the colors of the particles, you can simply go to the "color expression" section in the particle trajectories results, and set it so that it represents the radius of the particles. I think its default mode is set to "particle velocity".

@@moeinpoi Actually, this is not true. Saffman force arises not because the particle rotates but due to the shear rate caused by the relative speed between the fluid and the particle. Depending whether the particle leads the flow or lags behind the flow, a force will move the particle either toward the wall or the center. And this should not be confused with shear gradient lift force which is a consequence of the parabolic velocity profile in Poiseuille flows and always acts toward the wall.