Multistage Axial Turbine Aerodynamic Design...design and test performance known. AT1DP AT3DP BLADE3D Demonstrate their validity. Investigate aerodynamic design philosophy behind. 1st

Multistage Axial Turbine Aerodynamic Design

Case Study 1A

March 17, 2019

Dr. Justin Jongsik Oh

TurboAeroDesign.com 1

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)


PRELIMINARY DESIGN – AT1DP

Design Specifications


Root menu of AT1DP program


Inputs for Preliminary Design


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


Single-stage Design


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


Two-stage Design


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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Three-stage Design


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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Three-stage Design (continued)


Good exit Mach level (of 0.43)

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Velocity Triangles for Single-stage Design


Impulse type rotor, due to very high stage loading


Velocity Triangles for Two-stage Design


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


Velocity Triangles for Three-stage Design


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


Velocity Triangles for Two-stage Design with Symmetric Option


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

MEANLINE DESIGN – AT1DP

Better prepared for meanline design with lessons learnt from preliminary



Two approaches of design, but the 2nd one will be a final design.


1. Design procedure shown in “Gas Turbine Theory”2. Justin Oh’s design process


Results


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


Velocity Triangles (Compromised Design)


A constant swirl at rotor inlet from hub to tip

Higher exit swirl on rotor hub to keep reaction


Flow path


NASA Design

Radius14 in

9.56 in

15 in

8.56 in


Velocity Triangles of NASA Design


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.

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.


TURBINE MAP PREDICTION – AT1DP


For 14 speed ratios, in this case

To be continued


Documents

Multistage Axial Turbine Aerodynamic Design...design and test performance known. AT1DP AT3DP BLADE3D Demonstrate their validity. Investigate aerodynamic design philosophy behind. 1st