100-150 Hp turboshaft thoughts

[monty]

John,

Yep...but what the fan giveth, the nozzle taketh away, because the pressure is there on the expansion side too. The fan only has a 1.08 pressure ratio anyway, doesn't help much. I think I need a larger diameter inducer on the turbine. The performance is acceptable if I can get the core flow up to 140-150 lb/min at a core PR of 2.4-2.6. Turbine pressure ratio only needs to be around 2.25-2.5 to make this viable. Closer to 3 on the core makes it exciting, but that is a turbine pressure ratio around 3-3.25. I know that is possible with a larger diameter smaller trim wheel, but where to get one?? What about one of those 145mm turbine/NGVs from China??

Monty

[monty]

John and anybody else on here,

Has anyone ordered anything from Yili castings? they have some interesting parts.... I'm hesitant to send large sums into the void.

I can envisage a two stage axial turbine on the same shaft using the 145 and 180mm turbines. Unfortunately they appear to be reverse rotation

So finding a compressor wheel could be a problem-maybe a supercharger wheel.

Monty

[racket]

Hi Monty

Something isn't making sense here :-(

Why can't you run a 3.5 PR ??

If you look at the tractor pulling guys they're running massive PRs through turbos , a standard turbo at 70 lbs of boost ( 5.7 PR ) and a comp at say 70% effic ( probably less) will have a temp rise of 268 C degrees requiring ~164 HP/lb of air .

That 268 C rise will need at least 230 C drop through the turbine , which if at 80% and 900C TIT will need a PR of 2.8 just to power the comp , then theres the 5 or 6 psi of dynamic pressure in the exhaust , so a total PR probably close to 3.5:1 than 3:1 .

Cheers
John

[monty]

John,

I hope you are correct. I need to do the numbers on the NGV, and turbine itself. Right now I've just been using the data off the TV91 turbine map. If all I can get is choked flow at 90lbs/min or so....not gonna work. But I don't know if it was the scroll or the turbine that chokes at that flow rate. Right now all I've done is the cycle analysis, and basically I'm adjusting the core PR to get the work balance and exit mach numbers to work with that turbine PR and the Fan power. IF 3-3.2 total turbine PR at 2.4 lb/s is possible with enough left to expand to .3 or .4 M# this is going to be exciting. Otherwise I might as well go back to the two stroke engine...and I'm tired of casting pistons!....

Monty

[monty]

John,

The one thing missing in what you said about the tractor pull guys is the 150 hp to the fan....only leaves whats left for the core compressor, which means less pressure ratio to work with....which compounds against me. This means the turbine must operate at a higher PR to power both. There isn't a nice source of high pressure high temp gas from an IC engine. The turbine has to generate the work for the PR it needs to operate. Work balance is the problem. If I really can get 3-3.2 turbine PR at 2.4 lb/s with a choked NGV....all is well and good!! I may break out the single malt I've been saving.

Monty

[racket]

Hi Monty

Thats 90 lbs/min CORRECTED , not ACTUAL .

Corrected Flow = Actual Flow , sq root gas temp absolute/288
------------------------------
14.7 + gas pressure entering the NGV/14.7

example Corrected Flow = 2.4 X 60, sq root900+273/288
---------------------------------
3.5PR

Corr Flow = 144 X 2.018
--------------
3.5

Corrected Flow = 83 lbs/min ..................Actual Flow = 144 lbs/min

LOL, I'm trying to squeeze 216 lbs/min "Actual Flow " through my TV91 turb wheel .

Cheers
John

[monty]

Thanks John!

I've been doing it wrong!!

All my calculations are in stagnation temp and pressure, with actual mass flow. I can't imagine trying to do thermo/propulsion calcs if I had to constantly figure out mass flow vs a corrected one!! EVERYTHING is mass flow times change in velocity, and keeping track of losses is much easier if you reference stagnation conditions with actual Mdot. I had a mental block. I'll sharpen my pencil.

Monty

[racket]

Hi Monty

Theres no problems getting 2.4 lbs/sec through your turbine wheel , Anders JU-01 engine jetandturbineowners.proboards.com/thread/53/landspeed-bike-diy-gas-turbine and my 10/98 engine jetandturbineowners.proboards.com/thread/19/10-98-engine flowed similar amounts through the smaller F Trim wheel .

Turbochargers need to use "Corrected Flows" for both their compressor and turbine maps due to the number of variable the turbo might be subjected to , you'll need to do the same for altitude calculations of the engine .

Cheers
John

[monty]

John,

Actually all my numbers are "corrected" It's just that I have corrected them using Mach number and stagnation temps and pressures. This takes care of all of that, while accounting using actual mass flow. It would be incredibly confusing and difficult to be correcting mass flow and calculating local temps and pressures inside the engine. I can't know operating points at altitude without maps for the compressor, fan and turbine...too many variables. The core rpm will need to rise to maintain flow, but all that is tied to the fan. So I will need to design the fan SL operating point lower than max RPM.

I'm not trying to go all that high, or fast. The fan is optimized for flight below 18Kft and mach 0.4 ~250kts. That is how I'm getting away without a diffusing inlet. Higher speeds and altitudes would require one. I'm almost there, and the inlet is going to be the limitation on top speed and altitude. But that is a worthwhile trade-off to eliminate boundary layer diversion drag/complexity and wt. You also give up takeoff and climb performance with a diffusing inlet. I'm content at or below 18Kft and 250kts. Over 18K you have to be on an instrument flight plan and the fun quotient decreases. I've also done an altitude chamber ride, and I really have no desire to fly above 18K in an non-pressurized aircraft. Not a lot fun, and useful consciousnesses for the silly, soft-pink-primate at the controls isn't very long if the O2 stops flowing. Below 18Kft is relatively safe.

Monty

[monty]

Does anyone know where to find a compressor map for a 152mm wheel? All I've found is 141mm wheels. I need to do some rough estimates of the operating line at altitude.

Monty

[racket]

Hi Monty

Nope, theres very few maps out there , Garrett is the only one that provides them in quantity.

Try and find a Garrett map for a similar Trim wheel then extrapolate , but with the large variety of wheel configurations available , backswept blading angles , blade number etc etc , its virtually impossible to calculate anything with accuracy , its all guesstimates

Cheers
John

[monty]

John,

If I'm doing this correctly...

At 5000M alt. Top speed conditions after the fan at compressor inlet: T2=272.6K P2=66.32Kpa SL T=288.15 P=101.3 with an actual compressor flow of 2.4 lb/s and 3.5 PR would give a SL corrected flow of 3.57 lb/s

If I did that correctly, my core is going to be almost identical to the one you and Anders are building. Perhaps I should just use the same compressor wheel and copy you guys. I would have the option of flat rating my engine to 150 hp, and lowering the TIT at SL takeoff conditions - or having closer to 180hp at takeoff TIT 1650 and 150 in cruise at lower TIT. I could also lower the TIT and fan PR at altitude, for economy cruise. While operating on a constant rpm line or very close to it.

Monty

[racket]

Hi Monty

Is your fan going to be able to "consume" 150 HP at altitude with air at roughly half sea level density , the colder air will compress easier , but you'll need twice as much volume of air ??

I suppose you can "fiddle" with the fan PR to "adjust" HP requirement.

Cheers
John

[monty]

John,

SL condition for the fan is the largest flow, and then I would trim the nozzle to give the PR in cruise that matches or is close. It's like having a constant speed prop attached to the core. The main problem is not hitting surge on the fan at SL or the core compressor at altitude. It doesn't take much of a change on the fan PR to make a big difference. The fan drives the inlet. Ideally the fan PR is controlled by monitoring the pressure on the inlet lip to keep the stagnation point in the middle. Indicating there is no ram drag, and the inlet is swallowing all the air it can at V0 or a bit more. The real question is can I make this work with a fixed NGV....that I don't know yet.

Monty

[racket]

Hi Monty

You'll also need to "correct" turbo comp rpm for altitude/temperature , the colder conditions will increase the Pressure Ratio for a given rpm which may or may not be a help .

Cheers
John