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Research Papers

Rotordynamics of a Highly Flexible Hub for Inside-Out Ceramic Turbine Application: Finite Element Modeling and Experimental Validation

[+] Author and Article Information
Céderick Landry

Institut interdisciplinaire d'innovation
technologique,
Université de Sherbrooke,
3000 boul. de l'Université,
Sherbrooke, QC J1K 0A5, Canada
e-mail: Cederick.Landry@USherbrooke.ca

Patrick K. Dubois

Institut interdisciplinaire d'innovation
technologique,
Université de Sherbrooke,
3000 boul. de l'Université,
Sherbrooke, QC J1K 0A5, Canada
e-mail: Patrick.K.Dubois@USherbrooke.ca

Jean-Sébastien Plante

Faculté de génie,
Université de Sherbrooke,
2500 boul. de l'Université,
Sherbrooke, QC J1K 2R1, Canada
e-mail: Jean-Sebastien.Plante@USherbrooke.ca

François Charron

Faculté de génie,
Université de Sherbrooke,
2500 boul. de l'Université,
Sherbrooke, QC J1K 2R1, Canada
e-mail: Francois.R.Charron@USherbrooke.ca

Mathieu Picard

Faculté de génie,
Université de Sherbrooke,
3000 boul. de l'Université,
Sherbrooke, QC J1K 0A5, Canada
e-mail: Mathieu.Picard@USherbrooke.ca

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received October 4, 2016; final manuscript received August 1, 2017; published online September 29, 2017. Assoc. Editor: John Yu.

J. Vib. Acoust 140(1), 011013 (Sep 29, 2017) (10 pages) Paper No: VIB-16-1491; doi: 10.1115/1.4037700 History: Received October 04, 2016; Revised August 01, 2017

The inside-out ceramic turbine (ICT) is a promising concept to increase turbine inlet temperatures in microturbines by integrating individual monolithic ceramic. This architecture uses a carbon–polymer composite rim to support the blades mainly in compression. High tangential velocities lead to elevated radial displacement of the rim, and therefore, the rotor hub needs to have sufficient compliance to follow this radial displacement. However, the rotordynamics of a flexible hub is not widely understood. This paper presents the rotordynamic analysis of a highly flexible hub for an ICT architecture. Finite element modeling (FEM) is used to design a simplified turbine prototype that maximizes the hub flexibility to explore the limits of the concept. The rotordynamics behavior of the highly flexible hub is measured by spinning a 171-mm diameter prototype up to 49 krpm. This paper highlights three principal challenges of this particular rotordynamics. First, critical speeds mode shape becomes highly coupled with bearings displacement, shaft bending, and hub deformation. At high-speed, the hub deforms out of phase with the shaft, which can cause high stresses in the hub. Second, the angular position between unbalance masses of the flexible hub and the composite rim changes the unbalance response significantly. Finally, vibration causes high stresses in the hub, due to the relative displacement between the composite rim and the shaft, which could lead to failure of the hub. Nevertheless, the rotordynamics of an ICT configuration is manageable as long as the vibration-induced stress in the hub is kept under its limit.

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References

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Figures

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Fig. 1

Inside-out ceramic turbine [3]

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Fig. 2

Comparison of the real ICT prototype with the highly flexible prototype: (a) original ICT and (b) simplified ICT

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Fig. 3

A close view of the outer finger glued to the aluminum ring and the inner finger which is free to slide in the outer finger

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Fig. 4

Tested rotor prototype. It should be noted that the outer race drawing comes from the real bearing measurements, and the inner bearing is an approximate drawing.

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Fig. 6

Campbell diagram of the rotor (lateral vibrations only)

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Fig. 7

Modal stresses: (a) first critical speed at 34,300 rpm, (b) second critical speed at 45,500 rpm, and (c) third critical speed at 65,500 rpm

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Fig. 8

Unbalance masses on the rotor

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Fig. 9

Zero–peak amplitude of the unbalance response with unbalance masses angular positions to maximize each mode response at (a) the turbine shaft end, (b) the compressor end, and (c) the composite rim

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Fig. 10

Maximum hub stress for an unbalance response with unbalance masses angular positions to maximize each mode response

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Fig. 11

Tested simplified ICT prototype

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Fig. 12

Test bench used for spin test of the ICT prototype with flexible hub

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Fig. 13

Rotational speed of the prototype as a function of time

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Fig. 14

Waterfall diagram of the measured amplitude of the turbine shaft end

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Fig. 15

FEM unbalance response with comparison to experimental data (zero–peak amplitude) for (a) the composite rim, (b) the turbine shaft, and (c) the compressor end

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Fig. 16

Estimated stress from FEM: stresses from vibration only (left) and stresses from vibration and centrifugation combined (right)

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