Tesla's Valvular Conduit

[Mark]

A few good references.
Mark

[Mark]

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[Narada]

Wow Mark! Good stuff, thank you. One of the things said in the article there brings to mind another question I had/have. Has anyone tested a lockwood or another of the rear facing pulsejets in a situation that simulates what it would experiance in flight, i.e. in a an airstream. What I'm wondering is at what airspeed will the partial vacuum in the chamber be insufficient to overcome the momentum of air moving past it, and reverse it's direction to draw it into the chamber.

[Bruno Ogorelec]

Seems to me that a fair amount of energy must be lost when the flow goes around that 180 degree bend. I wonder if there is a large enough body of experimental knowledge on the forum to compare how a lockwood compares to some of the more linear pulsejets, like the chinese or Larray's PWPJE. That is to say, different geometries, but the same combustion chamber volume. Cause I can say that I think the less changes in the direction of the flow that are made the more efficent the engine will be till the cows come home

Well, I would normally have though so, but it seems not to be the case. The bend apparently doesn’t trouble the pulsejet engines much. This is curious, given that there is solid documentary evidence of fluid flow being bothered seriously by such bends. I have seen several papers describing the problems in detail, including measurements and charts of the terrible turbulence.

This is just another piece of evidence pointing towards the fact that the pulsejet has been invented by an enemy of common sense. It is a device purposely designed to frustrate the thinking man.

My personal theory – for what it’s worth – is that acoustically modulated pulsating flow has fewer problems with the bends than steady flow. Most experiments have been performed with steady flows, so that the scientists involved may simply have failed to appreciate the fact.

Namely, the pressure wave has no difficulty whatever negotiating any kind of a bend – even bending 180 degrees backward around a blade separator. Since the flow in the pulsejet tailpipe is a curious mixture of wave propagation and conventional flow, in which the wave helps push the fluid down the duct, maybe the wave action smoothes out the passage of gas, which would otherwise be quite turbulent.

[Bruno Ogorelec]

Wow Mark! Good stuff, thank you. One of the things said in the article there brings to mind another question I had/have. Has anyone tested a lockwood or another of the rear facing pulsejets in a situation that simulates what it would experiance in flight, i.e. in a an airstream. What I'm wondering is at what airspeed will the partial vacuum in the chamber be insufficient to overcome the momentum of air moving past it, and reverse it's direction to draw it into the chamber.

Narada, that problem arises only at rather great speeds and is easily helped by simple deflectors that aim air towards the intake and exhaust. (Not everyone thinks about it, but airflow at exhaust is just as important for pulsejets as at the intake.)

Up to about Mach 0.6, airflow actually helps pulsejets perform – even those, like Lockwood, that have their ports turned backwards. One of the main reasons for that is the shape of the exhaust plume. Due to the pulsating nature of the flow, the hot gas bursts out of the tailpipe, rather than flowing out in an elongated plume. This scatters the thrust vectors a lot and diminishes effective thrust. At speed, airflow acts to entrain the exhaust flow much better.

This was brought home for me very effectively by a rare old photo of a V-1 in level flight, shot from the side. Unfortunately, I no longer have it on my files. It seems mysteriously to have disappeared. At any rate, the exhaust plume of the flying V-1 engine looks long and elegantly narrow. All the hot gas is visibly streaming backwards. If you look at the plume of a stationary Argus engine, you can see that the plume is shaped like a fat pear, with much of the hot gas spewing in all directions.

This happens to turbojet engines, too, and is helped by the so-called ejector nozzles, which aim the airstream at an angle against the exhaust stream to squeeze it together. But, in pulsejets it is much more of a problem.

[Mark]

Wow Mark! Good stuff, thank you. One of the things said in the article there brings to mind another question I had/have. Has anyone tested a lockwood or another of the rear facing pulsejets in a situation that simulates what it would experiance in flight, i.e. in a an airstream. What I'm wondering is at what airspeed will the partial vacuum in the chamber be insufficient to overcome the momentum of air moving past it, and reverse it's direction to draw it into the chamber.

The Lockwood folks put theirs on a motor vehicle and drove it at a speed or 80 or 90 mph on a runway. They found thrust improved, perhaps because of better evacuation of the exhuast gases they said. Still, I can't help but think that the best way to go would be to streamline a straight duct and do something fancy with the inner workings. There are supersonic aircraft that have been propelled by pulsejets too.
As anyone who has held their hand out the window in a car, flat against the wind, going 80 mph, drag is very apparent. Those folded engines seem troublesome in that respect, even if you installed little air scoops to feed and make up for/rectify the lost backflow at higher speeds.
That's a good question though, at what speed would an Ecrevisse or Lockwood start to give out under high forward air speed. There have been several ideas about making a pulsejet transition into a ramjet mode too.
Mark

[Bruno Ogorelec]

That's a good question though, at what speed would an Ecrevisse or Lockwood start to give out under high forward air speed.

About Mach 0.6 according to Melenric, but it must differ a bit from design to design.

[Mike Everman]

My opinion on the VC is this:
The point perhaps being missed is that the effect of primary importance in the pulsejet duct is getting the partial vacuum as low as it can go. That means that you want the gasses to get out of the CC in as big a hurry as you can.
This is a dead end, and if it actually runs with this type of front end, it will be gasping for air, and nothing left for thrust!

[Mark]

While not the same intention, what Foa said about air rectifiers or aerodynamic valves is that what you gain in one direction you lose in the other. Look at the Tesla valve, how much drag is that going to produce, a lot to be sure. You could also take the opposite view and say that the primary importance is getting as much compression as possible, as opposed to getting the highest vacuum, and that forward air speed with a folded twin exhaust is not going to get it. Foa said something to the effect of "many have tried in vain to ....". If you could gain more in one direction over the other you might try and apply it to perpetual motion. You have to pay for everything.
I say ram in as much air in the front as your engine can gulp, handle as much air as possible. The inverse square law comes into play here too. If you double the speed you have to quadruple the thrust. And I feel sure/certain it applies to drag as well. Twin pipes, the banana-o-dyne, might equal 4 times the drag. You are never going to beat a ramjet or scramjet for speed and low drag at high speeds. And this necessitates a straight duct.
Mark

[Narada]

My opinion on the VC is this:
The point perhaps being missed is that the effect of primary importance in the pulsejet duct is getting the partial vacuum as low as it can go. That means that you want the gasses to get out of the CC in as big a hurry as you can.
This is a dead end, and if it actually runs with this type of front end, it will be gasping for air, and nothing left for thrust!

I'm not sure I follow what you're saying Mike. The VC is for practical purposes a valve. You put it ont he front end of an engine, the flow of the gasses is out the back. How is the VC going to slow down how the gases leave the chamber? And as far as gasping for air, that's just in the sizing. Again, think valve; if you size it appropriately, do the valved pulsejets gasp for air?

Of course, it's a little bit of a moot point, since we have no evidence to go on.

[Narada]

I just burned all my discretionary spending money for the next six months, but as soon as I have a positive cash flow again I'll put together a crude approximation, test it and what not. I was thinking about how to do it with out a CNC lathe, which I do not have. I think I can make a reason able approximation using pipe fittings. To be specific, using wyes, short nipples and 45 degree elbows.

[Mike Everman]

Well it's an interesting diversion but a dead end nonetheless.

Mark, one begets the other, my friend, the lower it goes, the higher it goes. the lower it goes, the better chance you have for a sonic choke in the front, which gets you higher pressure after the pop and so on.

I'm preaching I know, but another misconception we need to dispell is that there is compression that leads to combustion. Combustion begins on or around zero compression in these motors. The heat release needs to begin as the pressure is rising.

[Narada]

Well it's an interesting diversion but a dead end nonetheless.

You seem pretty convinced Mike, have you done some experiments with flow rectifiers? Or is there an old thread on the forum where someone has tried something similar?

[Mike Everman]

Don't get me wrong, I'd never discourage anyone from proving things to themselves! A lot of what we think we know is pure anecdotal horsecrap, though and I've seen a few rules die recently, so have at it.

I am trying to find the reference to experiments with this thing. the conclusion was that it is such a soft valve it damps out the very waves we need to be nice and sharp.

There may be a type of cycle that doesn't care, I'm just saying I don't think so. Nothing so far is better than achieving near sonic inflow at the intake.

[Mike Everman]

there's still work to be done to reach the ideal sonic inflow. I'm still looking for the bit on flow diodes, but here is some about the sonic plugging. Read the top left, really nice stuff.