Hi @dtriano!
While Darren will be able to give you a full description of how to go about doing this analysis, I can try start you off with the basics!
So generally speaking there are several parts to achieving your end results, all of which have their different quirks and potential problems. To simplify everything here are the general steps I take:
- Meshing of geometry
- Simulation of geometry
- Convergence of results
- Post-processing and data extraction
- Validation of results
On top of this, I usually go for a general simulation first to get my base results out then work from there to further increase accuracy rather than trying to get everything right from the get-go.
You must first also know what environment you are simulating in, is it compressible or incompressible flow? Do you have all your values for flow velocity? Ambient pressure? Density? All these will affect your simulation.
Meshing of geometry
This step is probably one of the most difficult to get right as you have to contend with numerous settings. For a wing like yours I’d recommend a few things:
- A large enough bounding box to contain your wing and allow flow to develop before reaching your wing
- Boundary layer inflation
- Surface refinement for the wing
- Region refinement encompassing the wing and another even finer region refinement for the area near at tip where your area of interest is
The meshing part is where things like the Y+ value for determining near wall functions to ensure accuracy all come in. Darren can better give input on this part. The meshing stage is where you usually determine accuracy of the simulation, if the simulation isn’t accurate enough, its usually the quality of the mesh that isn’t good enough. At least that’s what I’ve encountered.
Simulation of geometry
Simulation is slightly simpler if you are doing incompressible flow (which I will assume as such for the rest of this post), there are less considerations and convergence is usually easier since your geometry is also not extremely complex. You would probably want to start off with a steady-state simulation to get a general result out for validation later. Regarding the turbulence model, k-omega SST is a good choice for now. If you want to read more about turbulence models, you can do so here and here.
After deciding our simulation type we can move on to the initial conditions which is based off of what environment you want to simulate in and any other required initial conditions. Then we go on to the boundary conditions.
Boundary conditions are in essence the “rules of the simulation”. We need to define these conditions carefully to ensure our simulation is behaving as intended. So for your case, we need to define several things:
- Inlet velocity and direction
Defined as the “speed” of your flow and whether it is a positive or negative value depends on where the wing is “heading” to, which from your project is the negative x-direction hence your velocity should be input in the x value but negative in value.
- Outlet condition
We want your flow to progress “naturally” through the computational domain so you can set the outlet to pressure outlet with value of 0
- Bounding box condition
Generally to represent “free air” I set the the condition for the bounding box to a wall with slip condition.
- Geometry condition
This is the simplest, your geometry has to be solid so its just a no-slip wall.
Next we need to set your simulation control. The only things we need to change is the End Time Value, Write Control, Write interval, Number of computing cores and Maximum run time.
- End Time Value
This is hard to define at first, so I generally set an arbitrary number about 500s to see if the results converge well.
- Write control
Adjustable timestep is the one I usually use
- Write interval
Since this is a steady-state simulation you don’t really need that many in-between values, so saving just the start, middle and end with a value of 250s for 500s end time is alright
- Number of computing cores
32 cores
- Maximum run time
This is a preventive measure to stop “run away” simulations from eating up your core hours. Just set yours to about 80,000 and it should let your simulation run with no issues
Then we can define result control. Result control is a mixed bag as you have to know what you’re looking for. For my input, setting the result control will allow you to see if the values are converged. This I don’t have much of an input so I’ll let Darren help you out with this. In the meantime if you really want to run the simulation you don’t absolutely have to set this up.
Then from there you can start your simulation under Simulation Runs and leave it till it (hopefully) completes.
Convergence of results
Convergence is basically a way to see if your simulation is “unrealistic” or not. While it is hard and rather complicated to get “good” convergence, the criteria for it is based on either your given task’s acceptable convergence criteria or some general value that is acceptable to you. You can read more about it here. In general, 1E-4 is what most area deem convergence as “acceptable”.
Post-processing and data extraction
This is probably the most difficult part for me to help you on. I do my post-processing in ParaView and for my projects and what I’ve experienced my parts are not that complicated. But for yours, determining what values to obtain, where to obtain and compare them, how to obtain them in ParaView can quite difficult to do. Darren may be able to provide your some insight on this part.
Validation of results
There are a number of ways to validate a simulation/result. For your case, I would do a simple CL vs AOA validation and compare the results that you have simulated against a calculated or experimentally plotted result. If you trend is there and your values are relatively close to the referral case then you can deem that whatever results you have obtained from the solver is usable and a valid data point. If that is not the case then we have to look back to each of our individual steps and to see where this can be improved.
Hopefully I didn’t miss anything out and if anyone has any input regarding what I mentioned feel free to correct me! This should get you started somewhat and optimistically you’ll be able to at least get out a result even if it isn’t exactly accurate.
Cheers and feel free to ask anyone here for more help!
Regards,
Barry
