Isn't it just despicable the way some people will prostitute pure science for tawdry profit? Even worse, using confusing and underhanded marketing techniques to sell their brand.
It's a good thing Edison didn't do that.
Oh ... wait.
(Why am I thinking of dead elephants?)
Ooooh, he uses big words and shiny things. Sounds impressive.
OK, let's look at this empirically.
First, the fan. That's what a fan in a vacuum cleaner and a leaf blower looks like. Dyson is clever to apply common technology in new ways that makes you wonder why no one did it sooner. I said that about his ball joint wheelbarrow and the vacuum handle. I don't have an issue with this kind of cleverness. Just as I don't have an issue with marketing a unique fan design,
as a unique design. It's the flimflam claim of "air multiplier" that I have an issue with in this case.
So how about airflow over the wing shape and the "viscous shear"? Remember, this is a static shape with wind being moved over it, not a wing moving through air. In the case of a wing, the air pressure difference between the top of the wing and the bottom of the wing are effecting lift due to air pressure gradient. That's not what Dyson is claiming. But it sounds good in a marketing pitch.
Dyson explains lift but in his device there is no wing moving through air, there is no air flowing underneath a shorter distance, lift is not relevant. He states that blowing air over a curved surface creates negative pressure. It does. But that lower pressure and faster velocity doesn't affect the fan's wind force after it leaves the curved surface nor does it recruit more air into the flow.
Look at the moving diagram of wind flow around an airfoil in this link. The wind speeds up only while over the wing. As soon as the air leaves the wing, it resumes the same air speed as the wind that did not speed up flowing over the flat surface. The airflow only changes while it is over the wing, and you can get lift, but you get zero effect after the wind leaves the wing. There's some drag on the surface of the wing, and no negative pressure drawing air into the ring that I can see. I'm pretty sure the negative pressure is only over the wing's surface, not behind it.
Just as pressure changes in a fluid flowing through a tube when the tube narrows, that change in pressure doesn't suck more fluid through the narrowed area. It goes against the laws of physics. The volume moving into the narrowing and out of the narrowing is the same. Only the pressures and speed change within the narrowing. If it created the suction Dyson claims, that would have to be a siphon effect. He doesn't have a siphon effect in his fan. You can't get a siphon with a gas, only with a liquid.
Air will flow from higher pressure to a lower pressure, but Dyson claims his fan is "amplifying the air in 3 ways".
The air coming out of the fan is higher pressure than the ambient air. That higher pressure is in between the lower pressure of the air flowing over the wing and the ambient air behind the fan. The air leaving the wing resumes the same speed and pressure as the air that emerged from the fan (minus the drag the air molecules were affected by as they moved over the wing). There is drag and no outflow amplification.
And it is highly unlikely Dyson doesn't know that. He has to know he's flimflamming.
So what about 'viscous shear'?
Dyson, "You add more air through something called viscous shearing."
According to this article,
'Viscous shear' wears down sound waves
It works due to the interaction of porous media with the air through which sound propagates. Sound waves are forced into the parallel tubes which make up the honeycomb-like structure where they shear against the sides losing energy through friction and compressive stresses.
(emphasis mine)
I may not have the right concept here beings as physics is not my field, but what this looks like to me is Dyson is claiming the laminar flow of the air is supposed to recruit air molecules due to the different viscosities of the air layers. But that would slow the air down, not speed it up or recruit air molecules moving from more viscous air to faster moving less viscous air.
Again, Dyson has to know he's flimflamming here.
As for eliminating the buffeting, I have a small fan in front of me. Maybe there is a tad bit of buffeting right at the fan's surface. At 1.5 to 2 feet from the fan, the buffeting becomes imperceptible.
We also have the Consumer Reports review that says the fan's output is nothing special. It would be nice to know the efficiency rating and compare two fans of the same power usage. But the bottom line here is there is not a very big difference.
That sales video demonstrates my point about Dyson, not the special physics of his fan. I'll defer to a physics expert if one joins the thread and explains where I've mucked up my understanding here. I'm not an expert in airflow, but I understand the basics of pressure dynamics.
). It merits some reflection on your part, and maybe even a bit of study, but it could be helpful.
