Has anyone tried a diagonal compressor?

[propellanttech]

I'm just wondering.....

Has anyone??

With the advent of 5 axis being quite common now, I don't see why someone couldn't try a diagonal compressor.

I would love too, but I need to find someone with a 5 axis to make the compressor.

I think the design could be quite revolutionary, at least to the small engines.

James

[wolfdragon]

Image or link to see what the idea is?

[turbochris]

I think diagonal compressors were an attempt to get the cross section down and reduce the frontal area of the engine. I don't think it worked that well but it has been used over the years, everyone seems to use radial or axial compressors. A diagonal compressor looks a like a turbocharger compressor but the gas doesn't leave the wheel at 90 degrees to the shaft, it leaves at a shallower angle.

it's like this, a radial compressor is blades on a flat disk and the gas leaves along the edge of the spinning disk 90 degrees to the shaft. Imagine using a 45 degree cone instead of a disk, the gas will leave at 45 degrees off the back edge of the cone, between axial and radial. You can make the diffuser smaller in diameter this way.

[propellanttech]

Sept 7, 2011 7:37:50 GMT -5 turbochris said:

I think diagonal compressors were an attempt to get the cross section down and reduce the frontal area of the engine. I don't think it worked that well but it has been used over the years, everyone seems to use radial or axial compressors. A diagonal compressor looks a like a turbocharger compressor but the gas doesn't leave the wheel at 90 degrees to the shaft, it leaves at a shallower angle.

it's like this, a radial compressor is blades on a flat disk and the gas leaves along the edge of the spinning disk 90 degrees to the shaft. Imagine using a 45 degree cone instead of a disk, the gas will leave at 45 degrees off the back edge of the cone, between axial and radial. You can make the diffuser smaller in diameter this way.

Actually....if you look at a turbocharger wheel it is a cross between a diagonal compressor and a radial compressor, although it is called a radial compressor.

I think a diagonal compressor has merit for small engines. I know Mazda has some turbochargers using more of a diagonal compressor.

James

[propellanttech]

Sept 7, 2011 7:00:57 GMT -5 wolfdragon said:

Image or link to see what the idea is?

I'll draw one in 3D. They are pretty rare, and finding a picture is almost impossible.

That should help......give me a day or two.

James

[propellanttech]

Ok....so I got it done quicker than expected. It is not perfect, but is a good representation of what I think would work very well in a small turbine engine. May need some half height blades, but not sure. I'm not a turbine design engineer.



Tell me what you think.

James

[Johansson]

To get a decent PR out of the compressor is would have to be fairly long, and thin, long blades like the ones you´ve drawn would be very fragile I think.

A good discussion though, the only place I´ve seen one of those mentioned is in the Kamps book. Would be fun to read more about the attempts made with this compressor style.

[propellanttech]

Sept 7, 2011 16:21:42 GMT -5 Johansson said:

To get a decent PR out of the compressor is would have to be fairly long, and thin, long blades like the ones you´ve drawn would be very fragile I think.

A good discussion though, the only place I´ve seen one of those mentioned is in the Kamps book. Would be fun to read more about the attempts made with this compressor style.

Well the blades may be a little thin, but I don't know the thickness of a turbocharger blade. I don't think a regular thickness (like a turbo) would be very fragile. The curvature would make it much stronger than a straight blade.

I don't see why it would need to be long. I think the ratio of blade radius change would determine PR. I believe it could be slightly longer than a turbo compressor, and provide close to the same PR. It will never achieve the same PR due to the radial component a turbocharger wheel uses. I do believe it could have a better mass flow though. I wouldn't even know where to start for a map for a design like this.

James

[propellanttech]

I'm looking at the design in this aspect:

Imagine this a full compressor, but in one single unit. Most compressor sections have multiple blade sets with the hub ever increasing. The same idea is presented here, but all in one unit. It won't be as efficient as a multiple disk compressor, but probably would have advantages over a radial compressor.

I'm going to redraw the unit, but with some changes......one being thicker blades.

James

[propellanttech]

Here is the changed design:

The interior "solid" is modeled after a rocket engine nozzle. It is optimized for expanding gas for thrust, so why wouldn't the reverse be true?

It is not a direct copy, more of a copy from amateur rocketry nozzles.

The blades are thicker, and the whole design is longer.

Front diameter is 50mm, with the rear being close to 66mm.

Blade height in front is 18 mm, with the rear blade height at approximately 10.69 mm. I may modify this to have a rear blade height of 7mm.

[propellanttech]

The latest one. It breaks the internal solid angle some, but makes the rear blade height 7mm.

Looks cool if nothing else.



James

[racket]

Hi James

The diagonal comp , for our use anyway , isn't going to give the benefits of either a radial or axial compressor , its a "compromise" , sorta like a high pressure axial wheel , but low pressure radial wheel .....................OK for small frontal area , but not a lot else .

I have read papers where they've discussed their use for low pressure supercharging as there are "benefits " .

Probably one of those hybrids thats best left on the drawing board :-)

Cheers
John

[enginewhisperer]

yep, the main advantage of a radial compressor is a fairly high pressure ratio in a single stage.

A single axial fan can't give you much pressure, and the diagonal / mixed flow compressor will only be a bit better I think, since it can't make use of the centrifugal force a radial compressor has.

[propellanttech]

Sept 8, 2011 4:05:04 GMT -5 enginewhisperer said:

yep, the main advantage of a radial compressor is a fairly high pressure ratio in a single stage.

A single axial fan can't give you much pressure, and the diagonal / mixed flow compressor will only be a bit better I think, since it can't make use of the centrifugal force a radial compressor has.

I don't think it's quite that grim.

I would believe the diagonal would be better than a run of the mill radial compressor in the area of flow, and be better than an axial in the area of pressure (single stage).

The problem; a turbocharger compressor is not a pure radial compressor. It is a blended design. It is basically already using the diagonal benefits with a radial discharge. Because of this, a true diagonal design will not compete.

I know this because, some of the early Schreckling designs actually used a pure radial compressor.

So if you think about it, the designs we are using now are more of a diagonal compressor than a radial compressor with respect to flow.

I've done some research, and most turbocharger compressors are called radial, but they are actually far from a pure radial design.

This comes down to semantics I guess. It really is a blended design, and has become adopted as the standard for radial compressors. By doing so, the diagonal compressor has been basically discarded.

With this in mind, it is doubtful any pure diagonal design would show benefit.

But as an after thought, it was a nice brain exercise. It also helped with learning some new things for CAD drawing.

James

[turbochris]

James,
if you really like the obscure, try to find the one wheel turbine. It's a turbine with one wheel! The rotor looked just like a turbine wheel but with thick hollow blades. The compressor was the hollow blades! There was a cavity at the root of the wheel where all the intake air went in and was flung outwards into a diffuser through the hollow blades. The air looped around through a combustor and back through the turbine wheel. The hollow blades were cooled by the intake air as a benefit. The problem is the compressor design was horrible.

try to make a drawing of that!