Stall Angle of a Wing on Solidworks - Flow simulation

Simulation
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1

Hello

I am in the first year of Preparatory Class and I try to reproduce the polars, i.e. the lift and drag coefficients according to the angle of attack of the wing, thanks to Flow simulation .

I have carried out several studies on Solidworks with the same wing profile segment but I get a wing stall much too late    (about 30° instead of 15°-18°).

I have different questions:

1- I have carried out a study without a tunnel (or boxes) around the wing profile pieces and I wonder how it changes the result of putting one in the solidworks simulation? (because with a kind of tunnel I can set up a wind at the entrance over a large area and at the exit the environmental pressure) I tried it and I find the same in drag force but in lift force it's downright infinitesimal...  

2- I have attached a spreadsheet sheet where I have entered the lift and drag forces given by solidworks at different angles of attack, and I have drawn the drag coefficient and lift curves as a function of the angle of attack.                                                                      Problem: The stall of the wing happens much later than expected as you can see on the graph (on the right on the spreadsheet), I checked everything and I don't understand how it's possible. Especially since on the surface visualizations proposed by solidworks (in speed and pressure) I can see perfectly well that around an angle of attack of 22° the turbulent zone behind the wing decreases but not the lift force! 

I tried everything global, surface, volume to try to see a difference but nothing helps!

I hope you can put forward my problem.

Thanks in advance!


feuille_de_calcul.ods
2

Hello

The 404 error file......... but if you have set your objectives well (lift for lift in VO see the link here https://www.youtube.com/watch?v=ErIMxx4tiuE) it must match,  look for an anomaly in your parameters, maybe, if not, submit your model to be studied and make a comparison with the calculation method which you have done  not accessible........

Another complete FLOW simulation

https://www.engineersrule.com/tutorial-performing-flow-simulation-aerofoil/

and the reminder of the formulas from 32 min.

https://www.youtube.com/watch?v=edLnZgF9mUg&ab_channel=MITOpenCourseWare

Have a nice day.

 

 

 

3

For your question about the study box, it is an optimization and allow a reduction in computing power.

The proof from the didactic practical work.

You will notice that the wizard has created a box around the wing. This is our Computational Domain, where all the magic happens. Think of it as the inside of a wind tunnel. Everything inside it is part of the simulation, and everything outside it is irrelevant.

Note that a larger Computational Domain requires more processing.

 

https://www.youtube.com/watch?v=NKw1gPU-JNY

A processed example + a simulation (not Solidworks).

4

Hello

Thank you for the very interesting links. I still haven't been able to find out where the fact that the drop in lift coefficient appears so late comes from . . . I checked, I entered the right lenses etc, I attach the files if you can look at it, thank you.

I have another question, the winged area in the formula to calculate lift and drag coefficients what exactly is it? Because if it is the projection on the horizontal plane, it decreases when the angle of attack increases?

 

Thank you for your help


feuille_de_calcul.ods
5

has


capture_decran_132.png
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cf


capture_decran_131.png
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cf

 


capture_decran_130.png
8

Hello

 

What is your approach to the aerodynamic result?

I don't see in your table the Ra (the aerodynamic resultant).

 

Your file opens well, your lift and drag coefficients are consistent, you can submit your simulation by doing a pack and go to get the results with the wing model (in the Solidworks file menu). The wing area is the surface area of the wing, or lift-generating profile.

Complement to understand the phenomenon of stall and determine Ra.

"The stall is therefore due to a decrease in lift.

The stall is a loss of lift or, more precisely, the stall is the consequence of a more or less abrupt decrease in lift caused by the detachment of the air streams from the upper surface at a large angle of attack and whatever the speed".

                                                                               The factors of the stall:

Among the factors of the stall, the impact is theoretically emphasized, while in practice, the focus is on a stall speed that varies according to the configuration of the aircraft.

However, among the factors, these two elements "incidence and speed" come into play such as the load factor, the aerodynamic choices in the design of the aircraft and the influence of the air density.

Also, the formula that defines the aerodynamic resultant, i.e. the force generated by the pressure differential of the air flowing  above and below the wing, is:

 

Ra =  1/2 ρ S V² Ca

 

 (Ra is the aerodynamic resultant, 1/2 is a constant, ρ denotes the density of the atmosphere "its density", S is the wing area "wing surface",  V² is the velocity squared, Ca is the aerodynamic coefficient, calculated in the wind tunnel, depending among other things on the shape of the wing and the specific gift of each aircraft)

Similarly, the same formula can be produced for lift by simply replacing Ra by Rz  (lift) and Ca by Cz (coefficient of lift), and for drag with Rx (drag) and Cx (coefficient of drag).

Thus, the forces opposing the aerodynamic  resultant Ra, or its components Rz and Rx, are the traction T and the weight P. Note that the V speed depends on the traction but also on the weight uphill and downhill.

 

1 Like
9

Hello 

I didn't calculate the aerodynamic resultant, I just asked to have the force generated on the horizontal axis (column J) and on the vertical axis (column L) which I multiplied by Cos (angle of attack) (column  M).

I have made several profile files at different angles of attack, I put some of them here, please take the time to help me!

 


capture_decran_133.png
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Here is the "pack and go" for the wing at the angle of attack 5°


aile_5deg.zip
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And the wing at 25° for example


aile_25deg.zip
12

Hello @972arthur972,

Is code 972 an indication of your geographical origin in the West Indies? Your personal profile in this forum doesn't say a word about it...

A few preliminary questions about your project:
- Is the profile you are testing a classic profile in the aero field (Clark, Eppler, Gottingen...)?
- What is the origin of the contact information for the profile you use in your model? The sketch curves are not dimensioned and look very "dented".
- What is the source of your comparison reference, which states that the stall must occur around 15° to 18°? Is it trustworthy?
- Are the conditions of your simulation and those of the reference identical? In particular, the flow velocity, which strongly conditions the performance of a wing.
It's difficult to help you identify the gap between your simulation and your baseline without more data.

Good luck, the important deadline is coming up in a year...

m. Blt

13

Hello

Thank you for sharing your simulation, it gives examples for people who want to experience this FLOW module.

I just opened your simulation, you haven't set up equations under Flow it's possible.

In order to avoid errors at this stage, we can program the two equations.

You can set goals by entering your formula, let's start with lift,

you can keep all your assumptions, that of speed to have a comparison with your EXCEL.

It's by clicking directly from the Take tree in your primary objectives, to then perform an automatic calculation with your formula.

This is an example of data entry you have to adapt to your imposed study

Be careful to put without units because it is a coefficient! Don't let it be forced.

Drag  coefficient Cx= (2 * Ft) / (S*rho*v^2 )  (your EXCEL)

with Wing area [m^2]      0.017     angle of attack at 5°   take your density at 20°c is ok 1.204 kg/m^3

 

Enter the second formula as follows:

ok for the density.

Then continue with the notion of dropping out, good work.

 

1 Like
14

Hello m.blt,

- It's a profile I took a picture of in my school's lab. I imported these photos and sketched them on solidworks with splines to have a profile similar to the one you want to try in the wind tunnel in real life. Normally I reproduced the right length of the rope and the thickness.

- I have passed my aeronautical initiation certificate where it is written on my courses that "when you tilt the wing beyond a certain angle of incidence (about 18°) the flow of the wing becomes vortex on the upper surface [...]   This results in a rapid and significant decrease in lift. It's the stall [...] "Can the geometric parameters delay the stall as much as that? 

- I have no reference to carry out this simulation. I tried to take velocity values to get a Reynolds number down. I referred to a wing profile bank on the internet. I have the characteristics of the blower fan but no speed indication.

Thank you for your help 

And yes indeed 972 is the departmental code of Martinique and the competitions are next year but you might as well get started now!

15

Hello spectrum,

I was entering the equations but I stopped with all these profile files at different angles!! I just noted the forces given by solidworks for the calculations in the spreadsheet. Doesn't that change anything?

However, I still don't understand why the abrupt drop in the lift coefficient comes so late.

Thank you for your help

16

Hello

I think maybe the origin of your problem in the simulation, it's the definition of your flow speed which is dependent on the number of reynolds, this one involves the characteristics of the profile see below:

https://www.lavionnaire.fr/AerodynEcoulAir.php       Origin of the document.

Concerning the speed on different simulations, the velocity is dependent on the number of reynolds.

Change turbulence to 0.2%

Let's see if it works with these parameters to adapt to the chord length of your kite of 0.17 m.

Have a nice weekend.

 

1 Like
17

Hello spectrum,

I calculated the speed from the length of the string and the Reynolds number with this formula. It's just the number of Reynolds I had to choose and after looking I don't know what to choose. Is it necessary to have a low number of Re to avoid turbulent air and rather to favor laminar air? What is the limit of using formulas to calculate drag and lift coefficients? 

I tried to change the "percentage of turbulence" parameter but nothing significant changes.

Thank you and have a good day.

Arthur

18

Hello

Let's say that it's not that simple, using experiments we can see that when you arrive at a position on the wing profile and depending on the incidence, the transition between the two regimes will be shifted in time....................

The percentage of turbulence may be a dynamic correction between transient phases.................. I don't know.

Books have been written on Flow simulation but not with a parallel (theoretical formula and analogy by Flow), the influence of the environment and parameters are to be managed on a case-by-case basis............. A very important job I think.

I don't know when Flow simulation will do its management between the two states and when it will decide to switch from one regime to the other according to the Reynolds number, to illustrate the phenomenon, a theoretical reminder and a simulation on a simulator (not Flow simulation):

If you have time to look at the attached doc you will find a processed model, it would have to be simulated to have a basis and a protocol, understand the implementation of flow simulation, I am still looking for me to limit myself to simple work for now.

Have a good day to you.


001.docx
2 Likes