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I actually read (ok...skimmed) a few interesting articles after my interest was piqued.

Effect of boundary layer transport on the fixation of carbon by the giant kelp Macrocystis pyrifera
I couldn't find this one in the databases, but I'll try again tomorrow. The abstract contained this interesting statement, though:
"Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec-1, the assimilation of carbon was limiting."
Velocity gradients and turbulence around macrophyte stands in streams
http://www.mediafire.com/?a9dvlukzg7czwbn
Turbulence was maintained in the attenuated flow inside the plant canopies, despite estimates of low Reynolds numbers, demonstrating that reliable evaluation of flow patterns requires direct measurements.
You can't trust your intuition as to if it's laminar or turbulent - you have to measure the flows. This article talked about how the plant beds alter the flow. The flows can become more OR less turbulent depending on plant bed characteristics.

Beyond light: physical, geological, and geochemical parameters as possible submersed aquatic vegetation habitat requirements
http://www.mediafire.com/?bzw1tng221vgjag
This had a TON of awesome information. For example:
Production of turbulence within the vegetation is dominated by the plant wake rather than by the bottom boundary shear, as in open channel flows (Nepf et al. 1997).
meaning that in streams and rivers, the turbulence is caused by the shear forces with the channel bed, whereas it was caused by the plants themselves in lakes (where the flow is due to wind driven waves). Also:
The optimal turbulence levels for SAV is yet unknown but it is interesting to note that most SAV beds tend to occur in areas where flow is characterized by the laminar-turbulent transition (Ackerman 1998)
meaning it might be best for the flow to start out laminar but transition to turbulent as it hits the plants! There's a lot more to dig out in this paper, but I don't have time to read the whole thing. Someone please post any more interesting bits if you have a chance to read more.
 

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Just wondering, how did you determine that it was turbulent? Did you use food dye or just observe particles in the flow?
When I set the tank up I didn't wash the substrate very thoroughly and there was a lot of particles. (some really dirty gravel I bought at Stein's) Also I had quite a few tetras and some dannios so when I fed them I'd stick a decent sized pinch of flake under water right above the nozzle. The food would hit the blast from the nozzle and I could watch it do 3-4 laps around the aquarium before they would eat all of it. So I've spent a lot of time inspecting the water flow of my tanks. In fact I spend a lot of time in general with my nose up to the glass inspecting one thing or another, some might say too much time Haha.

Crap and I just noticed this.. In my post I used the word "turbulence" a lot, only it wasn't always in a technical sense such as the definition of "turbulent flow", and I never differentiated between the two very well. I hope you catch my drift:biggrin:
 

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I'm writing this in an effort to remember it by re-wording. My learning effort maybe useful to someone else. Here it is:

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First off, what is a "Boundary Layer"?

Google:
Boundary layer: The layer of fluid that sticks to a solid surface and through which the speed of the fluid decreases.

RedFishBlueFish's quotes say that:

- I cannot maintain only laminar flow in an aquarium.
- I do not need to maintain laminar-only flow in a planted tank.
- It is best to have a transition - the flow starts as laminar and turns into turbulent.
- There is optimal flow. It is a range (not a specific number). The range is 0 to 4 (some units)
- Within that range the plants can seriously increase their growth. (0 - 300%)
- Flow that is too fast can actually stop a plant's growth.

All of the above statements have to do with this "Boundary Layer" thing. But the only thing I can adjust are the pumps. All I can do is increase, reduce, and direct the flow.

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My smartest approach for now is to find videos of tanks that show healthy growth and no algae. And watch for the flow in these tanks - speed and direction. So far I've noticed that ADA's tanks often (but not always) seem to have many plant leaves gently moving from strong flow. From what I read above it looks like it is pretty hard to say if a flow is laminar of turbulent just by looking. I also think that it is hard to say how strong a flow is by just looking. Especially on videos. But once again - it appears that if I make the leaves of my plants gently move in the current I am doing something in the right direction. And there is more to be done. Hopefully with this and other disussions we can find it.

And I will not be surprised at all if the general conclusion on what is optimal flow speed & direction in a planted tank are not far from what Brilliant said above - "very simple".

--Nikolay
 

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RedFishblueFish,

From the quote below you conclude that is is best to have a transitional flow in a planted tank. A flow that starts as Laminar and turns into Turbulent.

What is "SAV" here?

"The optimal turbulence levels for SAV is yet unknown but it is interesting to note that most SAV beds tend to occur in areas where flow is characterized by the laminar-turbulent transition (Ackerman 199...)"

--Nikolay
 

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Here's a cheap (actually costing nothing) hack to achieve a resemblance of a laminar flow:

1. Install and HOB filter on the tank. Best placement - on the left or right side glass. Run it as normal.
2. Setup a second filter - a canister filter. Place the outflow pipe in the HOB filter box. (Place the pipe in front of whatever filter bag is used by the HOB filter.) Place the intake on the same glass on which the HOB filter is hanging.

That's it.

You get a very pronounced U-shaped flow with the HOB anyway. Adding the canister filter flow to it only helps. And it does not counteract the main U-shaped flow in any way.

A predictable thing that you will notice is that your 80gph HOB filter moves more water than the 160 gph canister filter. The main water movement is from the HOB filter. Good thing to remember when looking at flow rate of canister filters - most of them don't even come close to what is written in the box.
 

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Re: Discussion of laminar vs turbulant flow - Experiment

Hello everyone

I have been reading this old thread with interest. Right now I am trying to establish a slow, unidirectional, laminar flow from one side of my 400L tank to the other using a manifold design, similar to the hillstream approach but with a submersible Eheim pump instead of powerheads. And with a gentler flow rate.

My plan is to use a series of eheim spraybars attached via u-bends into a kind of grid. I have no idea if this will work :) It will not be elegant! It will have many a green pipe and black suction cup! But hopefully I can conceal it with some roots and rockery.

The overall intent is to emulate a coastal stream in Cameroon complete with appropriate fish, inverts, and plants. The streams are neither rapids, nor sluggish. Can it be done? Stay tuned...
 

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Here's a cheap (actually costing nothing) hack to achieve a resemblance of a laminar flow:

1. Install and HOB filter on the tank. Best placement - on the left or right side glass. Run it as normal.
2. Setup a second filter - a canister filter. Place the outflow pipe in the HOB filter box. (Place the pipe in front of whatever filter bag is used by the HOB filter.) Place the intake on the same glass on which the HOB filter is hanging.
I've had about 45 days of observations with that kind of setup. It's a 30 gallon tank at my church. The canister is an Eheim.

The tank has no plants. Just 3 small fish and funky blue color gravel (tank is in the kids area). With a once a week 30% water change there no algae developing on the glass or equipment. One place always develops algae - brown dust looking algae develops on the gravel only (no tuffs or strings). The light is only a 15 watt fluorescent which I will soon replace with a T5HO.
 

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Today I got around to hooking up the second big external Eheim pump to my 2 canister filters in a 180 gallon tank. I have the outflow hoses from the canisters plugged into a larger diameter U-shaped acrylic pipes (normally used for overflow boxes).

The flow coming out of the U-shaped pipes does look as close to laminar as it could be with such a setup. The water coming out of the U-pipe looks like acrylic itself - a completely silent smooth pillar of water. Except that is shoots straight down. I'm headed to Home Depot now to find a metal spring and try to heat and bend the end of the U-shaped pipe to an L-shape. Hopefully this will keep the "laminar" flow.

I attached a 90 degree PVC elbow to the end of one of the U-pipes. The water flow shoots out in a chaotic stream and makes a noise. Certainly far from laminar.

I am not hellbent on this laminar flow. I believe that as long as the water in the entire tank moves well you are good to go. The smoother the movement the better because then the water acts as a single body and could pull debries better - that's hard to deny.
 

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Good discussion on flow patterns.

I have a quick question for those who have looked at the flow patterns extensively. I currently have my lily pipe outflow on the front left corner and the intake on the rear left corner. Would it be worth drilling another hole in the stand to move the intake next to the out flow on the front corner?

Thanks for your thoughts.
 

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Allrighs so I did the DIY acrylic bending and ended up with two U-shaped pipes with each end of each pipe pointing along the surface of the water. Think if it as a lily pipe without the lily.

The flow is very smooth. Not as smooth as coming out of the U-shaped pipe without the additional bent but I guess that is as close as it can get to smooth. Now I have 1000 gph actual flow in a 180 gallon tank. The tank is actually 160 gallons without decoration but Oceanic calls it a 180. So my flow is 6 times the tank volume per hour.

Both acrylic outflows are placed on the left side of the tank and close to the front glass. The tank has been drilled for 2 intakes on the bottom - in the left and right corner. I'm not going to change that for now.

UltraBlue,

The way ADA sets the flow pattern is both by the placement of the ouflow and the inflow. Look here:


The red arrows are the water flow along the front glass only. Someone did an experiment with suspended particles added to an ADA tank and they found that there is a U-shaped flow on the surface of the water too. In the current thread we have very much accepted that this double U-shape of the water flow engages water from the back of the tank too IF the current is smooth AND strong enough. The flow is both smooth and strong in an ADA tank. Placing the outflow and the inflow close has a synergistic effect (it multiplies the result without adding any extra effort) - it creates the strongest possible smooth U-shaped flow along the area that is normally free of plants and decorations - the front glass.

The essense of this thread is how to get the water flow smooth because this is a logical conclusion if you watch how the debries are being moved from all parts of the tank toward the intake. A chaotic flow does not engage the debries in a directional movement. And once again - the flow must be both smooth and strong.

Note also the yellow dots with short arrows on the picture above. These are debries that need to be moved toward the intake. Because the ADA intake is placed a little above the substrate there is a slight upward movement of the water along the bottom. This "pulls" particles out of the surface of the substrate and lets them engage in the flow toward the intake. Except that from what I can say now observing a tank without plants only the tiniest particles can be moved upwards that way. I now believe that Amano shrimp have the role of "shaking up" the larger particles, dislodging them from the susbtrate and make them suspended. Amano shrimp are pretty rough little animals and you can often see that they raise small bursts of dirt around them.

And to answer your question: You don't need to change everything in your tank to match ADA's setup. ADA has taken old knowledge and presented it in a cool and modern way. But that does not mean that you have to do everything exactly as ADA does it. As long as you engage the water from all over your tank in a smooth flowing movement you should be good. And if you are not - see if you flow rate is enough, see if dense plant tuffs keep the water from flowing good. Move the intake a little here and there before you install it like ADA suggests. It is hard to beat what ADA does but if you understand why they do things you can tweak them any way you like.
 

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This isn't a perfect gyre, but moving the spray bar to the side accomplished a nice u-shaped flow in my tank. I made this change long ago after the discussion here.

In this video, I drop some small, sinking pellets into the tanks. You can see then move left->right, bounce off the right side and down and right->left.

It doesn't really show up well in this phone video, but I tried to follow some of the particles along the bottom of the tank back towards the intake side.

Not the double-U that a lily pipe can make, but better than a front-to-back arrangement.

 

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I have a mini-m and a superjet ES-600 (After owning one, I love the superjets!) even though the filter is only about 100 gph, the flow was way too intense with a mini lily pipe. I switched to an off-brand lily pipe to decrease the flow, but it still moves the aquasoil on the opposite end of the tank.


If just ordered a 45-P since I wanted to upgrade anyway. If the flow is still too strong, I am considering being a guinea pig and ordering the new lily pipe spin, which is a circular pipe that releases water on both sides. It looks like a tire.

I was wondering how this would positively or negatively affect the flow. It can't be bad if ADA releases it. OTOH, maybe flow doesn't matter that much on small tanks when you are using superjets?

I could order the new superjet es-300, but I can't justify spending $400 or so bucks when my es-600 holds six liters of media and the es-300 holds three and is only 50 GPH.

I am hesitent to use a tap connector to decrease the flow..would it negatively affect the Iwaki pump?
 

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Hey y'all,

Niko and I had a really stimulating talk the other day about flow regimes in planted aquaria and it got me thinking. His example of laminar flow in the San Marcos in a previous post is awesome and I thought I'd expand on it a little. After keeping planted tanks by rote for so long, having a deeper understanding of the science behind what's going on in my aquaria has helped me immesurably. I thought I'd talk a little bit about what I've learned in the hopes it'll increase your understanding of your aquaria and improve your hobby just as it has mine.

Reynold's number (Re) http://en.wikipedia.org/wiki/Reynolds_number

The initial statement "...such as laminar or turbulent flow: laminar flow occurs at low Reynolds numbers, where viscous forces are dominant, and is characterized by smooth, constant fluid motion, while turbulent flow occurs at high Reynolds numbers and is dominated by inertial forces, which tend to produce chaotic eddies, vortices and other flow instabilities." contains the critical element' smooth, constand fluid motion vs. chaotic and other flow instabilities.

Going back to the San Marcos and other plant-filled streams many of us have seen; the flow in such streams is for the most part laminar. It may not be purely unidirectional and constant throughout the water column; however overall the stream flow isn't chaotic. Considering channel morphology; such streams are characterized by a general broad U shape. This is important! Although discharge may be high, the open nature of the channel allows for high flow with little impediment. Such flow regimes are beneficial to aquatic vegetation for multiple reasons:

1) Low shear forces- Although shear stress is present in all natural fluid flow situations; eddies and other turblent flow instabilities are areas of high localized shear stresses. We see this in our aquariums when using spray bars. The flow nearest the outlet is very fast relative to the area around it. This differential velocity creates eddies and vortexes in which shear forces can cause plants to lift out of the substrate or which can tear leaves off the stem; thereby damaging the plant.

2) Chaotic flow (high Re) likewise creates zones of increased and decreased water movement. We see this characterized by zones of deposition and resuspension of mulm in our tanks. The zones of high flow receive good input of nutrients and CO2; whereas the zones with low flow may be deficient in one or the other. Likewise, the deposition of mulm can create zones of localized water quality instability and become a source of harmful chemicals.

Consider the placement of filter outputs for a moment. The convention of placing the filter outflow on the side of the aquarium rather than the back aids in the creation of laminar flow. Why? The increased length of flow helps to disperse the energy related to filter discharge. The farther the stream travels before hitting an impediment such as the side of the tank, the greater the impact viscosity plays in the flow dynamics. Conversely, if I put a spraybar or other outflow on the rear of the tank facing the front, the short distance between the initial outlet and impediment decreases the contribution of viscosity which causes an increase in energy when the flow hits the impediment. The higher the flow energy at point of impediment, the greater the Reynold's number, and the greater the turbulence of flow at the point of impact.
Using the below equation we see the following:



Given a constant viscosity, discharge velocity, and density of water leaving our filters; L, distance to impediment or width of stream flow is the characteristic which defines flow regime. If L is small, Re will be large. If L is large, Re will be small. Remember, we're multiplying L by two constants and dividing by another constant. The greater the pVL term the lower the overall ratio.

What the hell does this mean for my aquarium? In order to create an environment with the greatest potential for laminar flow we must set up a situation where either L is high or V (discharge velocity) is low. To use my aquarium as an example. I have spraybars placed along the substrate surface and tank sides which face the front of the tank (small L). In order to maximize laminar flow potential I have to decrease V. Assuming my pump is always discharging at a constant rate and the viscosity and density of the water leaving the spray bars is constant, I must either increase the size of the holes in the bar, increase the number of points of discharge, or both in order to reduce the Re.

Why would I care about that? Don't I want the highest velocity possible from my spraybar to suspend mulm so it can be picked up by the filter or transport it to a place where I can syphon it out? No!!!!!!! Remember, high V creates turbulent flow which, in turn, creates flow instabilities as discussed above. I want smooth, laminar flow to uniformly distribute water. This uniform flow distribution may be slower than turbulent distribution, but it is more effective in both nutrient distribution and removal of undesireable materials from the water column over the long term. Why?! Because laminar flow reduces differential zones of suspension and deposition. The greater the proportion of zones of suspension to deposition, the greater the volume of particles removed from the water column OVER TIME. This is the big secret and science behind the Lily Pipe and convention of placing the filter outlet on the side, rather than back, of the aquarium. Since stability is, by definition, a characteristic of change over time, one must consider efficacy over time rather than instantaneous or immediate efficacy. Turbulent flow can improve results in the short term, that's why we stir the water in planted areas at times when cleaning our aquaria. The instantaneous turbulence suspends the particles we want to remove. In general, however, this is not a desireable condition.

Im a commercial photographer that specialises in liquids, far from academic, but find liquids fascinating to film and shoot. new on the site and not totally shaw where to ask this question? I have a fascinating shoot on where I need to create a very even on mass flow of water from the left side of the tank to the right. Im attempting to build a tall and wide laminar flow, so that the water form the pump in from the left is moving about 4 litres a second but is smooth, no vortexing. Reason for this is there are objects that are designed to move in very specific ways in water, so a even flow is essential to monitor the precise movement.

Ill upload the design, build... Its a test. used a simple laminar flow jet before, but this is moving water on mass from the left to the right of a large tank and being sucked out from he right, and around it goes..

Any ideas - suggestions, very welcome. If your curious about my work, its www.davidlund.co.uk

Thanks for your time. I should be filming some Behind The Scenes which I can share.

David
 
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