Theres no better test tank than the surf but for a more visual representation of hydrodynamics Im building a surf flume or more correctly a surfboard fin flume. A flume is a water channel where surfcraft fin shapes can be tested for various values and their interaction with the flow can be seen. Hopefully I can get some great shots of water flow from various angles and while it cant tell you how the fin will ride it will give some values that can be compared against other shapes like comparing board dims and volume.
Theres also scope for different speeds, angles, temperatures, salinity, Reynolds numbers, foil shapes and thickness and of course my favourite multi blade fins.
Any thoughts or ideas for this hydrodynamic flume ?
Any way to add something to the flume to make the flows more visible, like smoke in a wind tunnel?
In a flow-through trough/flume, you could possibly introduce a small steady stream of food coloring or “muddy” (turbid) water to the clear flow-through water at a given distance in front of the fin.
In a clear trough, maybe view currents/turbulence via light refraction (polarized lenses?).
Or maybe some of those polyethylene microbeads that are getting removed from beauty products in the US. If the flume was a closed system they would not be an environmental contaminant.
Microbeads would be interesting. The beads should have neutral buoyancy.
For turbid water (like smoke in air), I was thinking a mixture of flour and water. Shouldn’t have any negative environemental impact.
A closed sytem would conserve water use for sure. If light refraction would work, there wouldn’t be any particles that could affect water movement patterns over a surface (not likely that particles would create any significant drag effect though).
Red_boards, thank you, that’s a great idea ! I’ll work thru the table and add pics so people can see what’s happening. Add more parameters if you think they’re worthy of comparison.
Did not have time to watch the entire video of either. Looks like one flume is mostly viewing the effects of resistance (drag) to water flow – rising water level. I didn’t watch enough of the other to say much. But I believe water flow rates may create some limitations.
The main issue I see is that the flow of water will be laminar as long as the velocity does not exceed 240 feet/min. Above that, turbulence will develop along the bottom and walls of the flume. This velocity is fairly slow relative to surfboard speeds. To go faster without wall and bottom turbulence interfering with your results, I believe you will have to change the size and depth of your flume significantly.
But I think you could collect some interesting information.
I think that’s a good starting point as I haven’t seen anyone else making a flume specifically for surfcraft. It’s a first step and if things go well, I’ll make a bigger one. I’ve got a massive water pump that has the highest water volume output from residential power, so that in itself will be fun to harness.
Simple construction technique of building the flume out of 20mm ply and later add clear windows for videoing.
Testing a fin at low AOA (<20 deg) is where all the lift/drag happens, but in the higher AOA is where it’s lateral resistance comes into play for snaps and any turn where you’re pushing against the side of the fin. So I’ll make the flume 8 " deep x 8 " wide to accomodate the higher AOAs.
Would it be worth testing how the fins work when they’re flexed a little bit? Like tweaking the foil a little to one side to kind of shape the fins flex if you were mid turn? Might be more noticeable on a bigger fin that may not fit in the 8x8 flume.
You’ve probably seen this as well… tiny holes drilled along the leading edge and in linear patterns down each face? Insert strands of thread with super glue and evaluate how the laminar flow is affected by AOA, foil, etc? I watched a video of an air stream on tuburcle fan blades with threads attached that demonstrated their effectiveness beautifully. Tubulent flow was clearly manifested by threads randomly flailing about while laminar flow was demonstrated by the threads laying perfectly flat against the blade surface.
To The Buellster, certainly flex is going to be a factor, especially at higher AOAs, it’s easy to predict that a flexing tip will bend or torsion to allow better flow but at what AOA, what cant and what speed. This Alpha design is definitely just about working out the basic flume design, construction, methods of testing and recording and getting great pics and video. The Beta version could handle any fin size. See what happens…
Hi John, my computer died and I couldn’t log in as SURFFOILS at all so I had to create a new account so SRFDCO it is. You’re right about trying the thin strands and I wonder what results will come from testing those dimpled fins, C-Drive fins, recycled fins and varying degrees of smooth/rough surfaces.
With the intention of being impartial I’d like to also test all the new variations of ingenious, unique and long time fin designs. It’d be amazing to see just how a Greenough fin moves through the water Vs a Brewer Vs a Starfin Vs a Wavegrinder Vs a …
