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June 12, 2018, 11:07 |
A simple cfd and aeroelasticity question
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#1 |
New Member
Iman Sabahi
Join Date: May 2018
Posts: 17
Rep Power: 8 |
Hello dear forum members
I got a simple question regarding my thesis. Imagine a simple 2dof, 2D airfoil (NACA 0012, for example) in a wind-tunnel. The airfoil is considered a Rigid body, it has no elasticity. The 2 degrees of freedom are rotating and pitching movements and the constraints are a torsional spring and a normal spring both attached to an arbitrary point along the chord. 1. If the flow is considered laminar, can any dynamic instabilities occur at any high-enough wind speed(U)? If yes, how about flutter? 2. What if the wind is turbulent? In general, what is the simplest(simplest to model and simulate) setup in which we can see the flutter phenomenon? I searched the forum and the net for the answer first, but didn't find anything useful. My knowledge is more in structural mechanics, so please pardon me for the stupidity or the simplicity of the question. Best regards Iman Last edited by i.sabahi; June 12, 2018 at 11:11. Reason: add more info |
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June 12, 2018, 11:38 |
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#2 | |
Senior Member
Filippo Maria Denaro
Join Date: Jul 2010
Posts: 6,842
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Quote:
In an air-wind tunnel, you should be aware of the role of the Reynolds number. Considering the kinematic viscosity and a small chord lenght of the airfoil (say 10^-1m), a velocity of 10m/s gives you Re=O(10^5) which on an 0012 airfoil can be still assumed laminar. However, the condition depends also on the inflow produced in the wind tunnel, of the level of turbulence intensity is quite small. Consider that the flow should be steady, no alternate shedding from the trailing edge should be present. About the turbulence question, you should consider if the inflow is already turbulent or you want to study a turbulent separation along the airfoil. I think you can find many references in internet |
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June 12, 2018, 13:36 |
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#3 |
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Martin
Join Date: Dec 2011
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You should determine the instability regions of the coupled aeroelastic system. The instabilities occur even in the laminar regime and even for small rotation angles. See for example, the Hodges book.
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June 12, 2018, 18:52 |
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#4 |
Member
Join Date: Jul 2013
Posts: 56
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As far as I'm concerned, the simplest aeroelastic model that can have flutter instability is a rigid 2d airfoil mounted on a rotational spring.
Depending on the mounting position along the chord, flutter will occurs. I see this as a very (very) rudimentary model of a fluttering flag. |
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June 17, 2018, 06:24 |
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#5 | ||||
New Member
Iman Sabahi
Join Date: May 2018
Posts: 17
Rep Power: 8 |
Thank you all for taking the time to answer,
Quote:
But the question was that even if we neglect the turbulent effects that will occur on the trailing edge and downstream and try to run the simulation with non-turbulent methods, will we ever see any flutter in the simulation? Quote:
The example configuration in Hodges' book, is as follows: Quote:
Look at this quote from the hodges' book regarding the same problem: Quote:
1.How do I simulate the same steady-flow problem(I mean which flow models to use), and 2.How do I capture the flutter using this steady-flow, knowing that it'll make the flow very unsteady and "un-laminar"? Thanks in advance |
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Tags |
aeroelasticity, flutter, laminar, rigid body, turbulent |
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