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[ICEM] Having problems meshing an helicopter body and loading the mesh into Fluent

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Old   March 5, 2016, 12:46
Smile Having problems meshing an helicopter body and loading the mesh into Fluent
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Nader Khattabi
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Welcome everyone
I am a mechanical engineering student and I am working on my graduation project, my task is to run multiple simulations on a preliminary design of a helicopter body and the rotor-blades,to optimize their performances.To do that I am using ICEM CFD 16.2 for meshing,Fluent 16.2 for the simulations and results.
The preliminary design was made using SolidWorks 2015.
At this point I am having troubles meshing the model using ICEM CFD.The geometry isn't simple, and it's causing failure of the mesh,therefore Fluent won't read the mesh.Lately I've been using DesignModeler to mesh my model and it actually worked this time, I was able to obtain my first results.
Now I need to re-mesh the model using ICEM CFD and I don't really know how to start since I am not an expert using this software.

Is there any rules to follow when choosing the domain ? like what are the dimensions of the domain?
how to read results? how to find the lift and drag coefficients ?


If anyone is interested in helping I would really appreciate it.Thank you

here you find the first results,the design,and the step where I am paused in ICEM CFD.
Attached Images
File Type: png design modeler meshing.PNG (145.1 KB, 20 views)
File Type: jpg ICEM meshing.jpg (192.9 KB, 20 views)
File Type: jpg pressure contour.jpg (34.0 KB, 18 views)
File Type: jpg Turbulence Kinetic energy.jpg (33.7 KB, 20 views)
File Type: jpg cd,cd.jpg (47.3 KB, 12 views)

Last edited by bboynido; March 7, 2016 at 05:52. Reason: to explain the problematic
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Old   March 12, 2016, 19:15
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In order for your drag/lift monitors to make sense you need to set appropriate Reference values in FLUENT. I think for helicopters the convention is to use the area described by the rotor blades for the reference area (check this for confirmation). So, use that value in the Area field under Reference values and Cd and Cl are going to make much more sense.

As far as the domain size goes, usual recommendations are 10-20-30 body lengths or chord lengths. You could also do a grid independence study (or in this case a domain size independence study): try to use 5 helicopters lengths as the buffer, then try 10, then try 15 and see at which point the results differ <2%. This is when you can say "the solution is independent of the domain size". Same goes for mesh refinement (both in direction normal to the wall or "y+" and for wakes or similar).

Since vehicle aerodynamics and aerospace are pretty similar, you might want to check the link in my signature for a more step by step guide for novices.
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Old   March 12, 2016, 22:46
Default Having problems meshing an helicopter body and loading the mesh into Fluent
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I'm very thankful for your reply.the link is also very helpful and I was looking for those informations for so long.
Well that makes more sence, at first I thought that I can do two separate simulations for the body and one of the rotor blades .I think that what I understood from your reply that I need to run a simulation for the body and the rotor as one final body in order to set the area described by the rotor blades as a reference value for the simulation.

Can I run two separate simulations for each the body without the rotor and the rotor itself before running a combined simulation?!
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Old   March 13, 2016, 05:13
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Erm, no. I think that usually body is simulated on it's own to optimize the behavior of lift/drag/pitching moment coefficients. Running a simulation of the helicopter body with a rotating blade all in one simulation would require a lot more resources and slightly more advanced techniques. Blades as such are pretty much well-known and the presence of the body (a slightly different body in each case) shouldn't really affect the efficiency of the blade dramatically.

Blades in this case don't have anything to do with the simulation of the body, you still set the reference area of the described blade disk as the reference value. It just serves the purpose of non-dimensionalizing the results (same as how frontal area is used for road vehicles).

As far as running a full simulation goes, first look into using SRF and MRF in FLUENT (single & multiple reference frames, sliding meshes, interfaces etc). But I wouldn't think you need it. You could just run two separate simulations for now. Also, try looking into what are the best practices for helicopter simulations in the industry, there might be some white papers written and/or shared somewhere.
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Old   March 14, 2016, 09:25
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I set the area in the reference values without considering the blade, I projected the area of the body in X-axis direction and it gave reasonable values for a good pixel map of the frontal area.the length of the body is 9800 mm so i set it in the reference values too.

Would it be efficient to use it for my simulation or does it only apply on automotive vehicle that circulates on a road?

yeah I am still searching for documents but there are only few of them, do you recommend any documents that can help me as a beginner in this domain ?

Thanks in advance you've been really helpful to me and I appreciate it.
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Old   March 14, 2016, 12:14
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Don't use projected frontal areas.. this is used in automotive CFD. Used the agreed upon value of "blade disk area" if you want to have a chance in hell of comparing your results to any values that you find online.

Length only matters for Cm calculations so it does nothing if your only goals are Cd and Cl.

As far as documentations goes.. Google scholar, science direct etc.. I can't help you there. Also, some general books on helicopter flight should be helpful.
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Old   March 14, 2016, 14:41
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yeah after considering the document you sent,the rotor blades disk is the reference value for the area when dealing with helicopters.

At first it came up strange as the value was a bit too high (length of one blade^2*Pi=4.7m^2*Pi=69.6m^2) that's what made me confused about it , but now I recognize the difference between the two reference values, the first is only used for a vehicle circulating on a road, the second is used for aerial bodies that are surrounded by fluid, well I screwed since I'm a beginner but now I know why Thanks to you , I am so grateful for your support and help.
I am searching for CD, CL and CM so that's why i set the length in the reference values.

Waiting for the results,I will post them as soon as I get them
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Old   March 14, 2016, 18:50
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As far as Cm and length goes.. I don't know if the overall length of the helicopter is the value that people agreed on. In vehicle aerodynamics the reference length L is actually the wheelbase and not the overall length of the vehicle, for choppers I have no clue what it is. Search more.
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