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Post by racket on May 7, 2020 19:54:24 GMT -5
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Post by enginewhisperer on May 8, 2020 6:26:13 GMT -5
yep, all their high performance turbos have had 9 blade turbines. This new G Series range seems to be pretty good from what I have seen  |
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Post by finiteparts on May 9, 2020 17:51:26 GMT -5
I noticed that they didn't put a peak efficiency on that map. Fundamental physics suggest that it will be much lower than the GT/GTX55 turbine that shows max efficiency of 74%. Reduced blade count means higher blade loading, which leads to higher cross passage gradients, i.e. higher secondary flows/losses. Then you notice that the trim is 90. Yikes! Shroud curvature is definitely going to hurt the efficiency...but that mass flux is up roughly 4.1% lbm/(s*in^2)...maybe worth the trade. I did a few quick choked flow calculations at the corrected conditions to back out the choked flow effective areas of 4.614 in^2 for the G57 and the GT/GTX55 showed to be around 3.670 in^2. The increase in diameter accounts for 96% of the flow area increase, but looking at the photos, we can see that there is less flow turning. When I estimate the exducer blade turning (estimate throat area via Cosine relation) the G57 has a lower turning angle, which can be verified in the photo. The G57 exit angle is estimated to be around 62.8 degrees as opposed to the GT/GTX55 which is estimated to be around 67.7 degrees (estimated form 1-d calculations not approximation from images). Now of course these angles are for sure incorrect, since I do not have a G57 to measure the blockage due to blade thickness, etc., but they should show the relative difference in turning angle. I am basing most of the calculation unknowns on the assumption that it is geometrically scaled similar to my GT55 , but it does look like the hub to tip ratio may be smaller. Also, the GT55 blade roots are super thick, and from the image, the root thickness of the G57 looks to be a bit thinner...maybe. My thought was that they are both Inco rotors and stresses are likely similar, so the idea that the hub or root thicknesses are smaller seems counter intuitive. Of course it shouldn't miss anyone's attention that this turbocharger is aimed at the drag racing market. The lower flow turning equates to lower turbine torque at a given rpm, which means that this turbine is designed to shift the peak torque/efficiency to higher rpm region, which is great for our applications. I do wonder how much the reduced flow turning helps to reduce the blade loading and if it is possible to reduce the blade loading enough to counter the increased loading caused by reducing blade count..  Humm.... Definitely interesting. Thanks for posting this John. - Chris |
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Post by racket on May 9, 2020 18:32:00 GMT -5
Hi Chris
It certainly looks like "horses for courses" with this turbo .
The turb inducer tip height appears to be very wide at nearly 30 mm .
After doing some rough numbers it still looks like the turb stage is a bit undersized for our use at only 87 lbs Corrected with the 1.41 A/R housing , even when running at nearly 5:1 PR from the comp we'd need to keep the temps down below the wheels potential just to get a reasonably efficiently compressed flow from the comp .
A slightly larger turb scroll A/R might be in order , maybe a 1.60 . ............I've got an old turb flow map for our trusty F Trim TV91 wheels of 129/106 mm size that has a Corrected Flow of 90 lbs/min using a 1.70 A/R housing , 85 lbs with a 1.46 A/R ............and from reading the various auto drag racing Sites it appears that the G Trim wheel's 129/112 mm should flow ~100 lbs Corrected , the GT6041 flowed ~95 lbs with a 1.47 A/R .
A CHRA with our homemade housings/NGV/flametube would be interesting :-)
Cheers
John
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CH3NO2
Senior Member
Joined: March 2017
Posts: 455 
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Post by CH3NO2 on May 21, 2020 9:51:11 GMT -5
I noticed that they didn't put a peak efficiency on that map. Fundamental physics suggest that it will be much lower than the GT/GTX55 turbine that shows max efficiency of 74%. Reduced blade count means higher blade loading, which leads to higher cross passage gradients, i.e. higher secondary flows/losses. Then you notice that the trim is 90. Yikes! Shroud curvature is definitely going to hurt the efficiency...but that mass flux is up roughly 4.1% lbm/(s*in^2)...maybe worth the trade. ....... I am basing most of the calculation unknowns on the assumption that it is geometrically scaled similar to my GT55 , but it does look like the hub to tip ratio may be smaller. Also, the GT55 blade roots are super thick, and from the image, the root thickness of the G57 looks to be a bit thinner...maybe. My thought was that they are both Inco rotors and stresses are likely similar, so the idea that the hub or root thicknesses are smaller seems counter intuitive. ........ Definitely interesting. Thanks for posting this John. - Chris The G57 turbine is close but not quite a up-sized copy of the GT55. Its hub diameter is reduced quite a bit. Otherwise, yes, it probably has an efficiency lower than the GT55. Attached is what I calculated (from the CFD results) of the GT55's efficiency. So it seems likely the G57 turbine efficiency will be lower than this.  The simulated GT55 turbine efficiency measurements were taken using air as the working fluid (which is more similar to a gas turbine condition) but that’s just an assumption. Efficiency will change alot at a 12:1 A/F ratio at the same temperature. Which is what would be expected on an internal combustion engine. With air as the working fluid the turbine efficiency is ranging from 74% to as low as 50% (as simulated in Solidworks and calculated by hand via total to static efficiency calculations). A slight change in the assumptions can swing the efficiency significantly. Total to total Vs total to static. The way Garrett measures efficiency at 74% is unknown.  |
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Humm....
