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  #11  
Old 08-25-2020, 08:24 PM
Cannon Cannon is offline
 
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This may or may not help, but Formula 1 teams use this all the time to validate their CFD and wind tunnel data. Pretty good video about it:

https://youtu.be/sVU1-zSrqvM
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  #12  
Old 08-26-2020, 01:28 AM
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????????????????
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  #13  
Old 08-26-2020, 05:48 AM
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????????????????
I am really, really, really enjoying the thread and looking forward to more....you know, "This is great!"
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  #14  
Old 08-26-2020, 09:18 AM
PhatRV PhatRV is offline
 
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Default Oil Flow Testing for Sailplane Wings

I found some examples of flow visualization testing on the Standard Cirrus sailplane. These were done using old motor oil. I also remember Dick Johnson used this testing method in many of his sailplane reviews.

http://www.standardcirrus.org/OilFlows.php

An example of flow separation
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  #15  
Old 08-26-2020, 12:23 PM
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Originally Posted by PhatRV View Post
I found some examples of flow visualization testing on the Standard Cirrus sailplane. These were done using old motor oil. I also remember Dick Johnson used this testing method in many of his sailplane reviews.

http://www.standardcirrus.org/OilFlows.php

An example of flow separation
Not really flow separation. This is a laminar separation bubble followed by turbulent reattachment.
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  #16  
Old 08-26-2020, 01:04 PM
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Good info here on mixing powders into engine oil to visualize flow:

http://hdneubert.com/Reno_Presentation.pdf
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  #17  
Old 08-26-2020, 06:09 PM
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Agreed! Very exciting!
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  #18  
Old 08-27-2020, 09:19 AM
Paragon Paragon is offline
 
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Steve,

Thank you for your interesting posts on surface flow visualization techniques.

Many years ago, a co-worker and I were dispatched on short notice by the boss to the Mojave desert to do flow vis testing inside a turbofan aircraft engine on a test stand. It was a short test window availability situation.

He supplied us a kit full of oils of different viscosities and black & white colorants. We were trying to determine if there was flow separation on the inner fan duct of a high bypass turbofan engine.

However, when you are in Mojave heat in the summer, and the surfaces are inside an engine, even the most viscous oil is going to get moving early in a throttle up cycle.

We managed to obtain some interesting results at ground idle power. The oil clearly showed flow separation in the fan duct and in front of the upper bifurcator pylon. However, it was pointless to try to obtain any results at higher power settings because the most sticky, viscous oil available had already flowed and been blown out the nozzle at ground idle power.

We also saw that oil drops moved aft down the fan duct, around the fan outlet guide vane airfoils, radially outward along the entire trailing edge of the outlet guide vanes, then streaked downstream along the outer fan duct. I couldn't believe the droplets stayed together long enough, (in hurricane force winds), to make this journey, but they did.

Sometimes even engineers get to have some fun.

-Paragon
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  #19  
Old 08-27-2020, 11:28 AM
scsmith scsmith is offline
 
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This is a great story, thanks. Illustrates again the special challenges in doing tests like this, even on a test stand. Imagine trying to do that in flight!

I'm glad I'm not the one that had to clean the oil out of the acoustic liner in the inlet or bypass duct!

An alternative to oil flow that can sometimes be very useful is tufts. We have used very fine nylon monofilament glued on with a drop of CA glue in a syringe. Then illuminate the area with UV light and the nylon fluoresces blue.
For an engine inlet duct test, you would have to do it at night, but the micro-tufts are durable enough to withstand that environment. Otherwise, conventional white thread tufts might work for daylight illumination and photography.

Quote:
Originally Posted by Paragon View Post
Steve,

Thank you for your interesting posts on surface flow visualization techniques.

Many years ago, a co-worker and I were dispatched on short notice by the boss to the Mojave desert to do flow vis testing inside a turbofan aircraft engine on a test stand. It was a short test window availability situation.

He supplied us a kit full of oils of different viscosities and black & white colorants. We were trying to determine if there was flow separation on the inner fan duct of a high bypass turbofan engine.

However, when you are in Mojave heat in the summer, and the surfaces are inside an engine, even the most viscous oil is going to get moving early in a throttle up cycle.

We managed to obtain some interesting results at ground idle power. The oil clearly showed flow separation in the fan duct and in front of the upper bifurcator pylon. However, it was pointless to try to obtain any results at higher power settings because the most sticky, viscous oil available had already flowed and been blown out the nozzle at ground idle power.

We also saw that oil drops moved aft down the fan duct, around the fan outlet guide vane airfoils, radially outward along the entire trailing edge of the outlet guide vanes, then streaked downstream along the outer fan duct. I couldn't believe the droplets stayed together long enough, (in hurricane force winds), to make this journey, but they did.

Sometimes even engineers get to have some fun.

-Paragon
Cincinnati, OH
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RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Jan 2020
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  #20  
Old 08-29-2020, 02:26 PM
PhatRV PhatRV is offline
 
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Quote:
Originally Posted by scsmith View Post
Not really flow separation. This is a laminar separation bubble followed by turbulent reattachment.
Thanks for the correction. I re read the article and it says the turbulent flow has less drag because it has lower skin friction drag but higher form drag
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