"Fat Boy" 12/118 thrust engine

[dieselguy86]

Nov 19, 2017 0:17:07 GMT -5 jetjeff said:

Hi John,

Have you ever checked the direction of your exhaust with a metal flag, as Kamps talked about in his book (page 93 - 3rd edition)?

"A minor swirl angle of up to 15 degrees in the direction opposite to turbine rotation is normal. A greater reverse swirl usually indicates too great a reaction level (not sure what that means). Narrowing the cross-section of the turbine nozzle guide vane system whilst enlarging the rotor cross section should remedy the situation."

Regards

Jeff

Jeff, better take good care of that book, they're up to $450 on amazon!

John, ive seen pre-swirlers advertised before for turbos to "decrease spool-up time". Its funny though i thought that IGV were always meant to straighten flow so the compressor got a better "bite" of air. And thank you for sharing that link, i saved it for future reading.

-Joe

[racket]

Hi Jeff

Nope haven't tried the "flag" method , my exducer angle and hence outflow angle has more to do with getting enough flow area rather than "reaction" ,..........reaction simply means expansion within the wheel's "nozzles" , by opening up the outflow "nozzles" theres less expansion , less velocity , less power .............to counteract that its necessary to increase the NGV expansion by tightening its "nozzles" to increase velocity and restore the overall gas deflection , the gas deflection combined with the mean blade speed provides the horsepower to drive the comp , so to maintain the rpm we've shifted some of the deflection from the wheel to the NGV .

Cheers
John

[racket]

Hi Patty

Valid point .

But its the overall "balance" that I'm hoping will be beneficial

The production of inlet swirl also improves compressor efficiency , this then requires less horsepower , another benefit .

I'm not all that concerned where the improvement comes from , as long as it helps get this engine running.

All of the commercial/industrial land based centrif air compressor manufacturers have IGV options , checkout Ingersoll Rand , Seimens ..............interesting reading :-)

In my trusty Cohen and Rogers, circa 1954, they give a nice example of adding IGVs to a large centrif comp aircraft engine to reduce inlet Mach numbers when at "cold" altitude , without IGV the PR was 3.18 , with swirl from the IGV its down to 2.87 , now assuming a T I T of 900 C and a 50/50 split of PR between NGV and turb , so 1.78 and 1.78 for no swirl and 1.69 and 1.69 PR with swirl , so ~140 deg drop through the NGV with no swirl and a velocity of ~1880 ft/sec , with swirl ~129 deg drop and a velocity of ~1800 ft/sec or a 4.4% drop in velocity but theres a 10% drop in PR .

Theres a lot less energy being required than the drop in velocity indicates , maybe the fuel flow would need decreasing ( lower temperatures) which would be fine for me , I keep the same temps and the excess horsepower will accelerate the rotor .

LOL.............R & D for a backyard builder like me means trying different things in the hope one of them works :-)

Cheers
John

[racket]

Hi Joe

Yep , IGVs for axial comps help get the air aligned correctly , but for us guys theres added benefits it seems , it breaks up the the "rotary acceleration" into a couple of stages which would mean less acceleration rate than if only one with a higher rate and more losses ...............theres lots more for me to learn :-)

Cheers
John

[jetjeff]

Hi Joe,

I didn't realize the Kamps book is rare, must be out of print. I'll start taking better care of it, keeping it locked away with my original Spiderman comic books and Hustler magazine from the 80's, the one with the scratch and sniff centerfold model,,,LOL.

Jeff

[racket]

Yep , Traplet Publications went bust

[Johansson]

That was news to me, sorry to hear it since they had lots of interesting stuff to read.

[racket]

Hi Guys

I've started on the IGV at last ...........LOL, I seem to take longer thinking about how to, than actually doing the job

There'll be 9 vanes so as not to get in phase with the 8 comp blades , and so that every third one can be aligned downstream of the 3 starter mount blades .

The central mounting hub is the same dia as the sliding mount for the starter alignment so that theres no "steps" to interfere with airflow .

Pic of cutting the 9 mounting slots in the hub ............gotta love metal cutting discs



I can't seem to find a "nice" solution to providing structural support at the bellmouth end of each vane that won't create turbulence , so might just run a bead of silicone glue along the edge to create a "fillet" rather than have some sort of "interconnecting" metal support .

I'll try to use 1.2 mm sheeting for the vanes so as not to interrupt air flow too much, stainless if its not too hard to work with , or mild steel if it is .

Cheers
John

[racket]

Hi Guys

The 9 vanes have been made , cut from a leftover piece of 6" stainless afterburner pipe I had laying around , 1.2 mm wall thickness , so just right

Just need to TIG tack each into the hub , then silver solder to secure .............a slow job making the vanes as they needed a fair bit of grinding to get all the bellmouth curves right so theres not much gap .







Cheers
John

[enginewhisperer]

looks good!

[Chuks]

neat!
so many things to copy/learn.

[Johansson]

Nice one John!

[Deleted]

Hi John

Very impressive :-)

[turboron]

John, referring to your post of November 18 regarding gas deflection and blade speed I see a need for further discussion. Sheppard says regarding Axial Turbines and Compressors "So applying the Euler equation with the centrifugal component absent (see equation). Thus the energy transfer is by means of changes of kinetic energy and relative velocity diffusion effect." I think this says that gas deflection and blade speed are kinetic energy changes. Also, when you are working with a centrifugal compressor or a radial inflow turbine the centrifugal effect due to the radius change can not be neglected. The calculations I use normally ignore the radius change by using a "pressure coefficient" which is determined experimentally.

Thanks, Ron

[bigkwaka]

That turf is good enough to be in the Gabba outfield! nice work John