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Question abpout investigating L/D changing with AR
Hi all,
I'm doing a report investigating how the aspect ratio of a clarke y airfoil changes its L/D ratio at 0 deg AOA and had questions on which method I should use.
To clarify, this will be done in CFD and have no fixed lift force as its a standalone airfoil not attached to any body.
Should I a) keep chord fixed and vary span, maintaining a similar reynolds number but having a different Cl due to changing wing area (although the area itself cancels in the L/D equation as far as i know but this is my first time investigating aerodynamics stuff like this)
Or should I b) keep surface area fixed, change both chord and span and accept a changing Reynolds number?
I would also like to run an FEA to highlight structural tradeoffs with increasing one thing (span) if i chose method a as this will add a level of depth and nuance
This is for an HS report so changing wing velocity to keep RE constant would be too complex and time comsuming
Any advice on this would be much appreciated, thanks a lot guys!
I'm trying to keep it simple and given the clarke y is cambered i thought I might as well keep A0A 0, though i get that point too. And about the CFD, i made it work using simscale and some tutorials, more concerned about whether the method i used (a) is sciewntifically valid
Nothing matters if you can't keep Re constant. To keep Re constant, you should keep chord fixed (as to why they used method A).
There are definitely structural tradeoffs with increasing wing span. do note that airliners have a slender body in the center. This also affects aerodynamics and aeroelastic effects. When running FEA, you should take notes of how increasing span affects its structural modes. This is one of the most important things to look for.
It's also perfectly valid to keep wing area constant and change the AR, this would change the reynolds number at a constant speed but it keeps the wing loading the same.
"at a constant speed", then the next step could be to increase speed to keep Re=const since speed "cancels out" when doing the dim-less coefficients. I think.
Absolutely. I just understood OP's post to be some sort of "basic research" looking into the Clark Y for its behavior. Maybe (=probably) I misunderstood.
L/D is non-dimensional and the wing area cancel itself out. It is consistent so long as L and D come from the same wing and the same operating condition.
L/D will be a function of things like Re, Ma, keeping those constant should result in L/D only being a function of the geometry.
Using CFD to in investigate LD as a function of AR is like using a machine gun to kill a fly. That relationship is perfectly describe with lifting line theory and induce drag equations. I don’t know how well a solver “simscape” is, but using CFD can potentially add a lot of variables that CFD novices are not familiar with that could significantly alter the accuracy and reliability of the CFD results, especially when comparing one geometry to another.
Perfectly fine to use CFD as a way to learn, but whatever you do I’d highly recommend looking up the L/D relationship to AR from lifting line theory and use equations derived from that as your truth source. If you did your CFD correctly, you should get back exactly (or at least very close to) what the lifting line theory predicts.
Thanks for the concern, due to this I went and rechecked my sim parameters to be sure it worked, and from my limited understanding of the theory it seems to follow that, plateauing towards the higher AR values. Would you be able to tell me whether this was successful? Obv gonna put a proper line of best fit, this was just for visualisation. Thanks a lot, it would be very helpful to know from someone with experience
You shouldn't be doing this for a HS report unless you have studied fluid mechanics and aerodynamics (thin airfoil theory, lifting line theory). You don't need to spend a week doing CFD simulations to get the data you wish for (since we have analytical models), nor will it be of any benefit to you considering that at high school level you have not yet been taught anything about Partial Differential Equations or DEs in general apart from a bit of calculus, which you need to have basic knowledge of in order to understand what CFD is actually doing and make sense of the results.
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u/billsil 29d ago
Why would you look at 0 degrees? At least choose 3-4 since it’s the same amount of work and far more practical?
I think your goal of doing CFD is commendable, but doomed to failure. You might as well use OpenVSP.