Aren’t Turbulators doing similar thing i.e. its keeps the boundary layer for longer before it totally turns into turbulent layer?
A fundamental principle of aeronautical engineering has been overturned
51–60 of 143 posts
Re: A fundamental principle of aeronautical engineering has been overturned
#52Uhh. I was taught that in university in the late 80s. Some surfaces have a lot of friction and if you add surface imperfections the turbulent airflow actually reduces drag.
You learned something different then because this finding is that some kinds of additional roughness delay the transition to turbulent flow which is pretty clear in the article.
https://phys.org/news/2014-01-smooth-rough-surfaces.html
A quick search looks to show the same general topic from more than a decade ago. I too have a recollection of this being discussed in the late 80s or early 90s. Maybe some folk wisdom that's just now getting quantified.
Re: A fundamental principle of aeronautical engineering has been overturned
#53Uhh. I was taught that in university in the late 80s. Some surfaces have a lot of friction and if you add surface imperfections the turbulent airflow actually reduces drag.
You learned something different then because this finding is that some kinds of additional roughness delay the transition to turbulent flow which is pretty clear in the article.
Thanks for clarifying.
Re: A fundamental principle of aeronautical engineering has been overturned
#54Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
Yeah I'm pretty sure I remember reading something in a pop science magazine 20 or 30 years ago when MEMS nano structures were all the rage and how they were gonna use mass arrays of them on airplane wings to somehow increase flow
Re: A fundamental principle of aeronautical engineering has been overturned
#55Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
The core tenant of the paper is that roughness reduces drag IN the transition zone. A very small region of the total flow.
Thats the region between laminar and turbulent flow. Laminar flow is typically 5x less drag than turbulent, and will be encountered about a Reynolds number of 500K-1M (ratio of inertial flow to viscous flow).
Surfboards will have a Reynolds number of 10^7 which is entirely turbulent.
A Cessna aircraft will have a Reynolds number of 1-5x10^6.
Re: A fundamental principle of aeronautical engineering has been overturned
#56Fascinating.
I wonder what the implications for radar-absorbing finishes are. Could they be more aerodynamic already?
Re: A fundamental principle of aeronautical engineering has been overturned
#57Earlier quoted context omitted.
I wonder how quickly airlines will adopt sanded/rough wings. It's also interesting that the efficiency of winglets were known for quite awhile but only somewhat recently have nearly all airliners adopted them.
It’s probably operationally easier to keep surfaces smooth than to keep them a specific amount of roughness.
It’s presumably easier to keep a smooth surface clear of bugs, dust and ice too.
Re: A fundamental principle of aeronautical engineering has been overturned
#58Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
> and airfoils also benefit from micro-roughness for lowest friction.
I thought this was known to some extent that smooth surfaces are not always the best e.g. golf balls have dimples on them? No?
Re: A fundamental principle of aeronautical engineering has been overturned
#59Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
Yeah I'm pretty sure I remember reading something in a pop science magazine 20 or 30 years ago when MEMS nano structures were all the rage and how they were gonna use mass arrays of them on airplane wings to somehow increase flow
Not uncommon to hear bold claims with every new and emerging technology that isn’t well understood by the media or general public. The excitement over nanobots seems to have run its course (for now?).
Blockchain managed to find its way into every market imaginable.
Battery technologies have consistently delivered bold claims on an almost yearly cycle, but we have at least seen incremental improvements.
AI is obviously the worst offender in the current timeline.
Re: A fundamental principle of aeronautical engineering has been overturned
#60Any competitive sailor or foil-racer knows that the underwater surface has the least friction and best laminar flow when sanded with fine-grid sandpaper, around 1000 to 1500 grid. It always surprised me that this was not true in air and airplane wings were supposedly best when glossy. So now it turns out that this is indeed not true, and airfoils also benefit from micro-roughness for lowest friction. Now the surprisi…
> and airfoils also benefit from micro-roughness for lowest friction. I thought this was known to some extent that smooth surfaces are not always the best e.g. golf balls have dimples on them? No?
Never mind. I didn't read the article (paywalled) and someone in the comments below answered this exact point.