Design and Testing of Small Turbomachinery Components at NTUA

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Design and Testing of Small Turbomachinery
Components at NTUA

• G. Sieros, M. Kefalakis and K. D. Papailiou

National Technical University of Athens, LTT
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Work on Small Gas Turbines

• Cycle analysis Optimization
• High-efficiency rotating components development

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Other Possible Applications

• Supercharging
• Fuel cells
• Air conditioning systems

DESIGNS ACTUALLY PERFORMED

• Gas turbines ? Compressor and Turbine Parts
• CHP ? Compressor and Turbine parts
• Air Conditioning ? Compressor, Turbine

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Computational Tools

• 1-D design
• Meridional flow calculation methods
• Meridional ?-O solver
• Meridional primitive variables solver
• Meridional viscous methods
• Blade-to-blade flow calculation methods
• Explicit time-marching
• Pressure correction

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Computational Tools

• Methods for design
• Integral boundary layer optimisation
• Allows derivation of optimum velocity
  distributions
• Inverse potential solver
• Allows geometry derivation without accuracy
  deficiencies of geometrical methods
• Geometry generation
• Optimisation algorithms
• Final checks
• 3-D aerothermal
• Structural

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Radial Compressor Design

• Initial one-dimensional optimization, based on
  semi-empirical correlations
• Specify RPM
• Specify main dimension (exit diameter, backsweep
  etc)
• Quasi-3D design
• Specify blade shape
• Impose manufacturing/structural restrictions
  (often ruled surfaces)
• Specify channel shape
• Design diffuser for optimum deceleration
• Full 3-D calculations
• Aerodynamic behaviour
• Structural analysis

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Radial Compressor Design

• Target eliminate/reduce jet-and-wake structure
  in impeller
• Design approach achieve accelerating flow in the
  impeller radial part

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Radial Compressor Design
Geometry generation
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Radial Compressor Design
Impeller blade loading calculation for a 1.41
compressor
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Coriolis Force Effect
Velocity field inside a compressor blading
computed with the Coriolis effect influence on
turbulence and without
Skin friction coefficient distribution with and
without Coriolis force effects .
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Radial Compressor Design
Leading edge modifications for optimum incidence
(left) and splitter positioning tests
(right) (Impeller for 41 compressor, 86,000RPM,
0.5kg/s)
Splitter at mid-pitch
Splitter near suction-side
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Radial Compressor Design
Hub Mid Tip
Compressor impeller blade loading calculation
(41, as before)
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Radial Compressor Design
Peripherally averaged exit flow angle, and
expected incidence variations for the diffuser
(same wheel as before)
Diffuser blade loading
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Radial Compressor Design
3D calculations (above) and off-design
performance (right) of a vaned diffuser for a
2.5 incidence range
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Radial Compressor Design
1.41 Compressor
41 Compressor
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Radial Compressor Testing
Compressor and turbine test-rig with compressor
mounted (400kW, 80,000RPM)
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Radial Turbine Design

• Initial one-dimensional optimization, based on
  semi-empirical correlations
• Specify RPM
• Specify main dimension (inlet diameter, exit
  area, blade sweep etc)
• Quasi-3D design
• Specify blade shape
• Impose manufacturing/structural restrictions
  (often radial elements)
• Specify channel shape
• Design NGV for minimum losses
• Full 3-D calculations
• Aerodynamic behaviour
• Structural analysis

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Radial Turbine Design
Meridional plane calculations for a mixed-flow
turbine (5.51, 40,000RPM, 1.3kg/s)
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Radial Turbine Design
Meridional plane calculations for a mixed-flow
turbine (30,000RPM, 1.7kg/s, 3.41)
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Radial Turbine Design

3-D calculations for wheel tip and NGV of a
mixed-flow turbine (5.51, 40,000RPM, 1.3kg/s)
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Radial Turbine Design
3-D calculation results for a mixed-flow turbine
for cold operation (3.41, 1.7kg/s) Hub and
tip sections
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Radial Turbine Design
Use of optimised velocity distributions for NGV
design (blade-to-blade) (3.41 cold turbine)
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Radial Turbine Testing
Test set-up for mixed-flow turbine. measured
performance at design point in relation to
existing designs
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Radial Turbine Testing
Experimental results from a mixed-flow turbine
tested at the NTUA rig (intended for use in
air-conditioning applications).
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Axial Turbine Design

• Initial one-dimensional optimization, based on
  semi-empirical correlations
• Specify RPM
• Specify work split-up between stages
• Specify main dimension (hub/tip ratio, mean line
  angles etc)
• Quasi-3D design
• Choose radial equilibrium
• Specify blade shape using inverse optimization
• Impose manufacturing/structural restrictions (e.g
  for cast blades)
• Full 3-D calculations
• Aerodynamic behaviour
• Structural analysis

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Axial Turbine Design
Calculation results on the meridional plane for a
two-stage axial-flow turbine
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Axial Turbine Design
Blade geometry generation
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Axial Turbine Design
Blade design for 1st stage rotor. Blade loading
at rotor hub
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Axial Turbine Design
Final Section Geometry
Final Velocity Distribution (Pressure Side
Modified for Closure)
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Axial Turbine Design

• Exit flow angle ß2-59.9, very close to
  prescribed 60

• Slight Velocity Distribution Difference due to
  Viscous Effects

1st stage rotor geometry and 3-D calculation
results
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Axial Turbine Testing
Experimental results from tests on the axial flow
turbines with blading designed geometrically
(left) or through an inverse procedure (right).
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Conclusions

• Significant efficiency improvements can be
  expected for small turbomachinery components
  through the use of appropriate computational
  methods
• Easy way to improve microturbine overall
  efficiency
• Test results confirm improvements
• Even with strict manufacturing restrictions,
  improvements are noticeable