Vortices

DoctorIt

At 400um at its widest point, I reckon this qualifies as a macro, but who's arguing.

This is an image I made in the lab today. It's not an amazing phenomenon, it won't win me any grants, or get me any publications (at least not on it's own), but it is a very good, or at least smooth and pleasing, example of a streak image.

I sometimes forget that my work can be pretty cool.

tsk1979

What is it anyway. Closeup of that nose booger in the previous profile photo?

Skippy

DoctorIt wrote:

At 400um at its widest point, I reckon this qualifies as a macro, but who's arguing.

This is an image I made in the lab today. It's not an amazing phenomenon, it won't win me any grants, or get me any publications (at least not on it's own), but it is a very good, or at least smooth and pleasing, example of a streak image.

I sometimes forget that my work can be pretty cool.

Well that's different, I love the pattern Doc.
Kinda looks like a mask, interesting how there are 3 different motions going on yet they don't mix together.

Good on Doc .... Skippy
.

DoctorIt

tsk1979 wrote:

What is it anyway.

Exactly "what" is not so important, but I guess that to feel the motion, as I see it, you should understand that its a fluid flowing through an abrupt contraction. It's going from the top of the frame (a channel about 400 micrometers wide) and being forced, at the bottom, into a channel only 26 micrometers across.

To visualize the intriciate flow patterns, we seed the fluid with flourescent particles. Those streaks are the "streamlines" of the flow.

Can you feel it now?

DoctorIt

Skippy wrote:

Well that's different, I love the pattern Doc.

Thanks Skip. MrsIt reckons it looks like an owl.

tsk1979

DoctorIt wrote:

Can you feel it now?

Ok, If I take a long jar and make a pin hole at the bottom and attach a straw to the pinhole this is what I get(except for the scale which will be in centimeters instead of nanometers).
and were the votices rotating clockwise or anticlockwise?

Dizzy

Love the image! Definately see the owl as well, first thing I thought of as I scrolled down the image. Would be interested in seeing a color version since you 'streak' them with a glowy material. I enjoy abstract images alot and this is one of the cooler one I've seen in a while. THX for sharing. dizzy

DoctorIt

tsk1979 wrote:

Ok, If I take a long jar and make a pin hole at the bottom and attach a straw to the pinhole this is what I get(except for the scale which will be in centimeters instead of nanometers).

Yes and no.

The fluid you use would have to be at least weakly viscoelastic (also called non-Newtonian) to see vortices upstream of the pinhole. If you used water (a Newtonian fluid) in the exact same geometry you see here, at the exact same flow rates, you would see nearly the same picture, but as a mirror image, downstream of the contraction. Kinda neat, eh?

And if even you did use a viscoelastic fluid in your jar, well, it could be a very long answer...

One of the reasons we use these micro-geomtries is because we can avoid turbulence, which happens at high Reynolds numbers, which is dependant on length scales. To balance out the length of the jar, you'd have to use a very viscous fluid to avoid going turbulent. Although you see swirls and vortices here, this is a completely stable flow. It's reversible and predictable.

and were the votices rotating clockwise or anticlockwise?

left - clockwise, right - anticlockwise (what you would intuitively expect)

DoctorIt

Dizzy wrote:

Love the image! Definately see the owl as well, first thing I thought of as I scrolled down the image. Would be interested in seeing a color version since you 'streak' them with a glowy material. I enjoy abstract images alot and this is one of the cooler one I've seen in a while. THX for sharing. dizzy

thanks Diz!

As for color, I can make it any color you want... in photoshop!

The flourescent "glowy" particles only emit light in a narrow wavelength and through a certain filter, so by nature it's a monochrome image. If you were to look down my microscope at these particular particles, you would see the same image in shades of red.

Ospi

This is very cool, did a full semester on fluid dynamics at uni last year and this was by far the most interesting unit I have done so far. Great photo and great subject.

will-jum

I don't like people that over-blow there trumpet, therefore this image is dire.

DoctorIt

will-jum wrote:

I don't like people that over-blow there trumpet, therefore this image is dire. <img src="https://us.v-cdn.net/6029383/emoji/thumb.gif&quot; border="0" alt="" >

Glad I could terrify or give you a desperate urge. <img src="https://us.v-cdn.net/6029383/emoji/thumb.gif&quot; border="0" alt="" > <img src="https://us.v-cdn.net/6029383/emoji/headscratch.gif&quot; border="0" alt="" >

Main Entry:dire [URL="javascript:popWin('/cgi-bin/audio.pl?dire0001.wav=dire')"][/URL]Pronunciation: \ˈdī(-ə)r\ Function:adjective Inflected Form(s):dir·er; dir·estEtymology:Latin dirus; akin to Greek deinos terrifying, Sanskrit dveṣṭi he hatesDate:1565 1 a: exciting horror <dire suffering> b: dismal, oppressive <dire days>2: warning of disaster <a dire forecast>3 a: desperately urgent <dire need> b: extreme <dire poverty>

Frog Lady

DoctorIt wrote:

Exactly "what" is not so important, but I guess that to feel the motion, as I see it, you should understand that its a fluid flowing through an abrupt contraction. It's going from the top of the frame (a channel about 400 micrometers wide) and being forced, at the bottom, into a channel only 26 micrometers across.

To visualize the intriciate flow patterns, we seed the fluid with flourescent particles. Those streaks are the "streamlines" of the flow.

Can you feel it now?

fun pic and interesting... I would have thought that the fluid was being forced through the small end and expanding/erupting (maybe it's the orientation - for some reason I tend to think the flow is "up"). How different would the image be if the flow was reversed? I would guess, thinking about it more, that you wouldn't have the nice "neat" vortices near the opening...

C.