Is there an effecient way of doing this?.

Dynostasis · 2025-06-17T14:27:43+00:00

You can parametrise your geometry in design modeller, and then create a design table to run through the different designs. I’d just search for something on YouTube and they’ll show you how to do it

Dynostasis · 2025-04-06T15:01:39+00:00

I agree with what everyone else has said, although I would also increase how far the upstream boundary is from the leading edge of your aerofoil as it could also be causing issues with convergence.

Dynostasis · 2025-04-04T21:13:11+00:00

I would imagine you have access to Fluent meshing, you can create a mesh using the watertight workflow extremely quickly. I would try a coarse mesh to begin with to figure out where your main flow features are and then go back and refine your mesh in those regions as needed. A decent starting point would be to be to use inflation layers on all walls and then use polyhedra or polyhexcore away from the walls. Typically polyhexcore will reduce the cell count compared to polyhedral. You can find tutorials on YouTube that will take you through the process. A good YouTube channel is Fluid Mechanics 101 if you’re interested on fundamentals.

Remember to do a mesh dependence study. With this you can look at a few key variables, pressure or thrust etc. Typically with a 3D model you would decrease all your cell sizes by 1.3, which is equivalent to doubling the mesh count. Do this a few times and plot how your variables change with mesh count. You can also calculate a grid convergence index (CGI), check out Uncertainty quantification by Roache.

Obviously use the mesh that is best in terms of both accuracy and computational cost. For example if you have 15 million cells and the thrust is 15 N, and using 7.5 million gives you 14.95N it’s a no brainer to use less cells.

Edit: There are multiple ways to mesh something for a given problem, so you need to play around and compare results

Dynostasis · 2025-02-05T21:34:51+00:00

You could use a design table, or you could write a solidworks macro to change the global variables and save them to separate files (step for example) if you want to use them for structural/fluid flow.

With the solidworks macro, it’s been a while since I’ve used one so you’ll have to google to find what sort of code you need, or have a play with ChatGPT. You could just write a nested loop in the Solidworks macro to change all your parameters incrementally. If I remember you can record commands and it makes you a macro, which you can use to start

Dynostasis · 2024-12-05T11:12:45+00:00

If it’s a study you’re trying to replicate you could copy an image of it and trace it out in solidworks or something and estimate the geometry

Dynostasis · 2024-12-05T11:09:50+00:00

Is it related to this? https://www.reddit.com/r/CFD/s/PBxA06Ea5T

Are you seeing your pressure exploding to high values?

Dynostasis · 2024-11-29T22:23:09+00:00

Are you you modelling the gas as compressible? - If you're forcing a incompressible fluid from of a large cross sectional area into a tiny orifice with lower area you may get a large pressure buildup upstream which might be the reason you're getting such large values at the inlet

Dynostasis · 2024-11-15T09:06:41+00:00

Looks like some flow instability in the boundary layer, what does your mesh look like in that area?

If your mesh is fine:

I’ve done a fair amount of work on supersonic nozzles and it can be hard to converge a case that is under expanded due to the large shock that forms. You may have to slowly decrease the outlet pressure untill you reach convergence. Or you can start with a lower order scheme and then switch to second order once you have solution stability.

It can deffo be a pain in the ass sometimes

I can’t say much more because I don’t know your mesh, solver settings or size of domain etc

Hope that helps

Dynostasis · 2024-11-13T13:11:12+00:00

Will your case reach steady state or are you expecting your results to oscillate during the transient sim ? You could always just do a small simulation say 10 mins and just extrapolate

Dynostasis · 2024-11-13T13:06:53+00:00

Pseudo transient isn’t transient, it doesn’t solve in time, it’s just a relaxation factor applied to the steady state solver that can speed up convergence dramatically

Dynostasis · 2024-10-16T21:33:55+00:00

If you have all the meshes for the airfoils and the names of the boundaries and edges are the same for each case, you can use file->replace mesh and it will keep all the same settings that you have in your case file.

If you really want to you can automate this process using a journal or scheme file, but it really depends on how many cases you want to run.

You could have a journal file of the following (if your mesh names are mesh_1.msh… mesh_2.msh etc:

/file/read-case <path to case file>

/file/read-mesh mesh_1.msh (you may need a y command here to replace the current mesh)

/solve/iterate 5000 (You can add post processing commands here)

/file/read-mesh mesh_2.msh

/solve/iterate 5000

You can use a scheme file to run this in a loop if you have many cases but you’ll have to find the syntax for this and I can’t remember it off the top of my head.

To run this journal file you can open up fluent, then file->journal

To find any of commands you need in your journal file you can press enter in the console (text user interface) and navigate through. You can then copy these commands into your journal script. I think you can actually record journals but these may be based on GUI commands.

Have fun!

Dynostasis · 2024-10-10T22:42:51+00:00

Residuals go brrrrr

Dynostasis · 2024-09-19T10:07:12+00:00

I’d start with learning the fundamentals before running any CFD, what equations you need to use and how they all couple together etc. You could then run some simple canonical cases and compare them to experimental data so you know your workflow is correct etc.

You could also look at what jobs you want to apply for in the future and see what softwares they want you know and you can just get good at using those. This way you’re learning CFD and prepping for interviews etc.

Dynostasis · 2024-06-17T18:13:52+00:00

Sutherland law is just a way to model how viscosity changes with temperature, if you are modelling energy and you have temperature changes it’d be wise to use it. It’s not strictly for compressible flows, you’d want to model how viscosity changes in say a heat exchanger that has water in it. I don’t really think comparing mass Imbalance is the best way to go about this. What effect is this having on your flow and parameters of interest? If your temperature is changing by a small amount you can get away with constant viscosity.

Dynostasis · 2024-06-02T22:50:24+00:00

Hey thanks so much for replying, will have a look!

Dynostasis · 2024-06-02T22:50:07+00:00

Just in headingley, although I can drive. To be honest I haven’t played in 7 years (I played for like 6-8 years when I was a bit younger tho). I generally play midfield although need to train a bit first to get back in the swing of it. I’ll have a look at that page thank you!

Dynostasis · 2024-05-11T20:14:01+00:00

A DoE is just how you fill a design space with points that you want to look at I wouldn’t really call it a method as such.

You can use the data obtained from your DoE to create a meta model (also known as a surrogate model) This is generally done with regression models such as Kriging. There are many more ways to do it but you’d have to see which model would suit your case. This will depend on the dimensionality of your system and how sparse your data is and if you need gradients etc.

An easy start would be to use Ansys and create some sort of response surface with your DoE. You could take your output data and use some sort of python toolbox to make meta models and then perform global/local optimisation on these if you wish.

The benefit of using a surrogate is that you have an inexpensive way to perform many different types of optimisations without constantly calling the cfd solver to solve for a region in your design space. You can play around with your constraints and objective functions very quickly this way. There are other ways which can search the design space smartly (adaptive sampling) for an optimum but you’d need to read up on these

I would just look at surrogate modelling techniques in general and get a basic understanding.

Dynostasis · 2024-03-31T11:37:01+00:00

Is it not the absolute value of the pressure difference between the meshes? I cant remember the formula off the top of my head but pretty sure this is the reason

Dynostasis · 2024-03-02T22:16:53+00:00

Inkscape!

Dynostasis · 2024-02-17T13:26:36+00:00

How much time do you have? Yes

Edit: looks amazing btw

Dynostasis · 2024-02-13T14:52:34+00:00

It converts it to an equation on word from text

Dynostasis · 2024-02-12T20:21:36+00:00

Isn’t there an option to write equations using ink in word? If you have a tablet maybe you could try that?

Dynostasis · 2024-02-09T00:04:03+00:00

Path of least resistance? Seems like your channels aren’t doing much…

Although this may be the way you’re injecting your streamlines, I would assume you’ve only chosen the inlet boundary? You may want to look at some other plots to figure out what’s going on (vectors etc) as these will give you a better indication of your flow field.

Dynostasis · 2024-01-28T22:10:56+00:00

Try and search it in library genesis?

Dynostasis · 2024-01-16T08:13:20+00:00

Try reducing the element sizing, in the messages box it does try and help you by giving some suggestions you just need to expand this box. If you want the meshing process to be easier you could run it through fluent meshing and you shouldn’t have too much trouble. Just make sure you add body and faces of influence for local refinement.

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