multistage axial turbine aerodynamic design...design and test performance known. at1dp at3dp blade3d...
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Multistage Axial Turbine Aerodynamic Design
Case Study 1A
March 17, 2019
Dr. Justin Jongsik Oh
TurboAeroDesign.com 1
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OBJECTIVES
Apply aerodynamic design programs to multistage axial turbine cases with design and test performance known. AT1DP
AT3DP
BLADE3D
Demonstrate their validity.
Investigate aerodynamic design philosophy behind.
1st Case NASA 2-stage axial turbines for aviation gas turbines for Mach 2.5 flight
(NASA TM X-148, 1959)
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PRELIMINARY DESIGN – AT1DP
Design Specifications
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Root menu of AT1DP program
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PRELIMINARY DESIGN – AT1DP
Inputs for Preliminary Design
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Same mean radius chosen in the case design (11.78 inch) Same hub-to-tip radius ratio at the last stage (0.5703) Rotor inlet swirl (of 65° here) input is just an initial guess. Case design has a two-stage design, but a feasibility design was tried
from a single-stage design to a 3-stage design. Two representative options for velocity triangles across rotor are
provided in the program. Both option results will be compared. Symmetrical velocity triangles at rotor inlet and outlet No swirl at rotor outlet
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PRELIMINARY DESIGN – AT1DP
Single-stage Design
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Due to very high stage loading (of 4.0), a normal reaction turbine cannot achieve the required work.
Impulse turbine design was proposed, but a lower efficiency.
Quite high exit Mach of 0.76, expecting further performance drop in the exhaust diffuser
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PRELIMINARY DESIGN – AT1DP
Two-stage Design
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Each stage loading is 1.983, staying still high side, but a reaction design is feasible, leading to a higher efficiency.
A simple assumption of Cm = const. A large variation of spanwise swirl at rotor inlet A high level of flow diffusion on rotor hub A weak reaction on rotor hub
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PRELIMINARY DESIGN – AT1DP
Three-stage Design
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Each stage loading is 1.322, staying around the standard level, leading to even higher efficiencies, but the weight will increase.
Reduced variations of spanwise swirl Mitigated risks on rotor hub
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PRELIMINARY DESIGN – AT1DP
Three-stage Design (continued)
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Good exit Mach level (of 0.43)
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PRELIMINARY DESIGN – AT1DP
Velocity Triangles for Single-stage Design
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Impulse type rotor, due to very high stage loading
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PRELIMINARY DESIGN – AT1DP
Velocity Triangles for Two-stage Design
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Both stages show a high level of diffusion on the hub, from the zero exit-swirl requirement. A compromised design is needed among,
Reaction on the hub * Rotor inlet swirl Stage number * Rotor outlet swirl Overall efficiency
Stage 1 Stage 2
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PRELIMINARY DESIGN – AT1DP
Velocity Triangles for Three-stage Design
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All stages show a good level of diffusion on rotor hub. Smaller flow turning on the tip. Best aero performance, but other factors will come in.
Stage 1 Stage 2 Stage 3
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PRELIMINARY DESIGN – AT1DP
Velocity Triangles for Two-stage Design with Symmetric Option
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Both stages show good diffusion levels on the hub, thanks to rotor exit swirl Higher aero efficiency than Slide 10, but the exhaust diffuser has to embrace higher swirl.
Stage 1 Stage 2
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MEANLINE DESIGN – AT1DP
Better prepared for meanline design with lessons learnt from preliminary
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MEANLINE DESIGN – AT1DP
Two approaches of design, but the 2nd one will be a final design.
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1. Design procedure shown in “Gas Turbine Theory”2. Justin Oh’s design process
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MEANLINE DESIGN – AT1DP
Results
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Reaction on rotor hub = 0.207 (stage 1), 0.234 (stage 2) A constant swirl at rotor inlet from hub to tip
65.2° (stage 1), 59.5° (stage 2) Non-zero swirl to the exhaust diffuser
43.8° (hub), 16.4° (tip) Flow turning on rotor hub
117° in stage 1
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MEANLINE DESIGN – AT1DP
Velocity Triangles (Compromised Design)
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A constant swirl at rotor inlet from hub to tip
Higher exit swirl on rotor hub to keep reaction
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MEANLINE DESIGN – AT1DP
Flow path
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NASA Design
Radius14 in
9.56 in
15 in
8.56 in
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MEANLINE DESIGN – AT1DP
Velocity Triangles of NASA Design
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Stage 1
Stage 2
Tip Hub
Zero diffusion on rotor hub Smaller swirl to the exhaust diffuser
13.3° (hub), 8° (tip) Higher swirl at rotor inlet
70.5° (hub), 62.5° (tip) : stage 1 62.0° (hub), 49° (tip) : stage 1
Higher flow turning on rotor hub 119° in stage 1
Compared to Slide 15 -16, there are some different design concepts between my program and NASA design. Next design steps will show which one would be better.
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TURBINE MAP PREDICTION – AT1DP
Approximate turbine map prediction Based on design characteristics of non-dimensional performance parameters
In general, a good agreement with test, unlike compressors
More refined map will be later predicted by Meanline Analysis.
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TURBINE MAP PREDICTION – AT1DP
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For 14 speed ratios, in this case
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To be continued
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