what is value of D and kinematic viscosity in calculating Reynolds Number?? Whether it should be the default value or actual experiment condition value. Default value of chord length is 1...but the test airfoil is 0.15m... so which value should be taken for calculating Re
I think I'm going to create a video where I run through an example of this so that it is more clear. Stay tuned! Also, I do have a video talking about a major assumption that XFOIL makes when calculating the RE and coefficients that might help clarify this a little. It's called "XFOIL's Cl, Cd, Cm, and RE Equations (Major XFOIL Assumption!!!)" and is located here: ruclips.net/video/SLe2nrysnrU/видео.html .
The command CPWR (stands for Cp Write) outputs to a .txt file the Coefficient of Pressure, Cp, vs the (x,y) coordinate pairs of the surface. You must give this command the filename you want it saved as and it will save the file to the same folder as the xfoil.exe that you used to start the XFOIL software. Example: In this video, after STEP 4 where you prescribed a coefficient of lift (or after you prescribe an angle of attack using the alfa command, which is more common) you would type CPWR filename.txt and hit (it will prompt you asking for the filename if you forget). Then you can open the filename.txt file in notepad/notepad++ or use the import wizards to import it into MS Excel or MATLAB.
@@thescienceofflight1404 Thanks a lot. I am new to the xfoil. Can this CPWR command work, if I use the aseq command and can it save all the cp data for these different Alfa values. If not is there an alternative
Unfortunately, not at this time. The basic way XFOIL currently handles memory is that it holds the last analysis in it's memory and when a new analysis is done it will hold the new data and drop the old data. The exceptions being that it doesn't refresh the Cp vs x pressure plot until a new analysis command is issued and/or if you use the PACC command (stands for "polar accumulation" and is covered in the video on polar plots) to force the memory to hold the lift, drag, moment, and transition data (but not the pressure data) for each angle of attack. This is the reason that the CPWR command will only output the last value of the ASEQ command. It's simply what XFOIL has in its memory at the time. XFOIL is open source software and this is on my list of future improvements I hope to make to the source code someday. The work around for right now, if you could call it a work around, is to simply use the ALFA command and save off the pressure data at each angle of attack. It's a bit of a pain... for now. lol
@@thescienceofflight1404 I am currently saving by using ALFA command. But thanks a lot for the reply. Just a suggestion: If your working on the source code, is there a way to you can make a module in the python. Because that can be really helpful and handy in the future.
Yeah, no problem. And yeah, I'm hoping to make some edits/improvements to the source code that will get incorporated in the next released revision. Depending on when I'm finished, I might look at a temporary solution (like with python) that can be used to accomplish this while we wait for the new revision to be released. If you, or any other viewers, have any other ideas on how to improve the software I'd love to hear them, even if it may take a while to get them incorporated.
Yes, kinda. "" stands for carriage return or cartridge return depending on your preference. Nowadays it's the key labeled "return" or "enter" on your keyboard. So if you type in the text "" and hit enter it will not work but if you have nothing typed into the command prompt and hit the enter key, or the return key, on your keyboard it should work. Let me know if this helps.
@@thescienceofflight1404 Thank you. Unfortunately, when I tried to use mdes menu to design new geometry of airfoil, MIT user guide suggested to return to the top level to save new buffer airfoil. When I did, it got out of the menu, could not get the output
If I had to guess based on the more common missed steps, when in the MDES menu after you have adjusted the surface speed distribution to your liking you have to use the EXEC command to actually execute the inverse design routine and convert the current surface speed distribution into an airfoil shape. The EXEC command will then put the new airfoil shape into the buffer airfoil in the top level menu. You then have to hit the enter key on the keyboard to go to the top level. When in the top level you have to move the airfoil from the buffer airfoil memory to the current airfoil memory by entering the PANE command. After this, you can save off the airfoil to a file, go to the OPER menu and start some off-design point analysis, or perform some other task as needed.
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Thank you enlightening video.
You should make MSES tutorial as well, very informative explanation
Thank you!!
No problem. Thanks for the kind comment.
what is value of D and kinematic viscosity in calculating Reynolds Number?? Whether it should be the default value or actual experiment condition value. Default value of chord length is 1...but the test airfoil is 0.15m... so which value should be taken for calculating Re
I think I'm going to create a video where I run through an example of this so that it is more clear. Stay tuned!
Also, I do have a video talking about a major assumption that XFOIL makes when calculating the RE and coefficients that might help clarify this a little. It's called "XFOIL's Cl, Cd, Cm, and RE Equations (Major XFOIL Assumption!!!)" and is located here: ruclips.net/video/SLe2nrysnrU/видео.html .
Can you tell how to save pressure plots are data files
The command CPWR (stands for Cp Write) outputs to a .txt file the Coefficient of Pressure, Cp, vs the (x,y) coordinate pairs of the surface. You must give this command the filename you want it saved as and it will save the file to the same folder as the xfoil.exe that you used to start the XFOIL software.
Example:
In this video, after STEP 4 where you prescribed a coefficient of lift (or after you prescribe an angle of attack using the alfa command, which is more common) you would type CPWR filename.txt and hit (it will prompt you asking for the filename if you forget). Then you can open the filename.txt file in notepad/notepad++ or use the import wizards to import it into MS Excel or MATLAB.
@@thescienceofflight1404 Thanks a lot. I am new to the xfoil. Can this CPWR command work, if I use the aseq command and can it save all the cp data for these different Alfa values. If not is there an alternative
Unfortunately, not at this time. The basic way XFOIL currently handles memory is that it holds the last analysis in it's memory and when a new analysis is done it will hold the new data and drop the old data. The exceptions being that it doesn't refresh the Cp vs x pressure plot until a new analysis command is issued and/or if you use the PACC command (stands for "polar accumulation" and is covered in the video on polar plots) to force the memory to hold the lift, drag, moment, and transition data (but not the pressure data) for each angle of attack. This is the reason that the CPWR command will only output the last value of the ASEQ command. It's simply what XFOIL has in its memory at the time. XFOIL is open source software and this is on my list of future improvements I hope to make to the source code someday.
The work around for right now, if you could call it a work around, is to simply use the ALFA command and save off the pressure data at each angle of attack. It's a bit of a pain... for now. lol
@@thescienceofflight1404 I am currently saving by using ALFA command. But thanks a lot for the reply.
Just a suggestion: If your working on the source code, is there a way to you can make a module in the python. Because that can be really helpful and handy in the future.
Yeah, no problem. And yeah, I'm hoping to make some edits/improvements to the source code that will get incorporated in the next released revision. Depending on when I'm finished, I might look at a temporary solution (like with python) that can be used to accomplish this while we wait for the new revision to be released.
If you, or any other viewers, have any other ideas on how to improve the software I'd love to hear them, even if it may take a while to get them incorporated.
does the command works in xfoil? for some weird reasons it does not work for me
Yes, kinda. "" stands for carriage return or cartridge return depending on your preference. Nowadays it's the key labeled "return" or "enter" on your keyboard. So if you type in the text "" and hit enter it will not work but if you have nothing typed into the command prompt and hit the enter key, or the return key, on your keyboard it should work. Let me know if this helps.
@@thescienceofflight1404 Thank you. Unfortunately, when I tried to use mdes menu to design new geometry of airfoil, MIT user guide suggested to return to the top level to save new buffer airfoil. When I did, it got out of the menu, could not get the output
Your videos are really helpful. can you make a video on getting airfoil geometry from surface speed distribution.? in future
If I had to guess based on the more common missed steps, when in the MDES menu after you have adjusted the surface speed distribution to your liking you have to use the EXEC command to actually execute the inverse design routine and convert the current surface speed distribution into an airfoil shape. The EXEC command will then put the new airfoil shape into the buffer airfoil in the top level menu. You then have to hit the enter key on the keyboard to go to the top level. When in the top level you have to move the airfoil from the buffer airfoil memory to the current airfoil memory by entering the PANE command. After this, you can save off the airfoil to a file, go to the OPER menu and start some off-design point analysis, or perform some other task as needed.
@@thescienceofflight1404 Thank you. I will let you know if I am facing any trouble
does anyone know how xfoil actually calculates the pressure distribution? like what method does it use to calculate it?
have you discoverd?
can you share with us ?
panel method
Hello. Is it possible to get a velocity profile at some x/c position on xfoil?
VELS can do this