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Research Papers: Flows in Complex Systems

Aerodynamic Optimization of a Microturbine Inserted in a Magic-Angle Spinning System

[+] Author and Article Information
Nicoleta Herzog

School of Engineering,
Institute of Energy Systems
and Fluid Engineering,
Zurich University of Applied Sciences,
Winterthur 8401, Switzerland
e-mail: Nicoleta.Herzog@zhaw.ch

Dirk Wilhelm

School of Engineering,
Institute of Applied Mathematics and Physics,
Zurich University of Applied Sciences,
Winterthur 8401, Switzerland
e-mail: Dirk.Wilhelm@zhaw.ch

Stefan Koch

School of Engineering,
Institute of Energy Systems
and Fluid Engineering,
Zurich University of Applied Sciences,
Winterthur 8401, Switzerland
e-mail: Stefan.Koch@zhaw.ch

Armin Purea

Bruker BioSpin GmbH,
Rheinstetten 76287, Germany
e-mail: Armin.Purea@bruker.com

David Osen

Bruker BioSpin GmbH,
Rheinstetten 76287, Germany
e-mail: David.Osen@bruker.com

Benno Knott

Bruker BioSpin GmbH,
Rheinstetten 76287, Germany
e-mail: Benno.Knott@bruker.com

Frank Engelke

Bruker BioSpin GmbH,
Rheinstetten 76287, Germany
e-mail: Frank.Engelke@bruker.com

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 27, 2015; final manuscript received July 5, 2016; published online September 12, 2016. Assoc. Editor: Moran Wang.

J. Fluids Eng 138(12), 121106 (Sep 12, 2016) (16 pages) Paper No: FE-15-1594; doi: 10.1115/1.4034188 History: Received August 27, 2015; Revised July 05, 2016

Abstract

The fluid dynamics of a microturbine system that is applied in a device for chemical and biological analysis—a so-called magic-angle spinning (MAS) probe—is investigated. The drive fluid is pressurized air at ambient temperature provided by nozzles aligned on an intake spiral, driving a Pelton-type microturbine. Computational fluid dynamics (CFD) simulations have been performed and compared with fluid dynamics measurements of the MAS system with 1.3 mm rotor diameter for spinning rates between $23 kHz$ and $67 kHz$. The main optimization criteria of the MAS system are rotor speed and turbine stability and not primarily efficiency, which is standard for turbomachinery applications. In the frame of fabrication tolerances, a sensitivity study has been carried out by varying the nozzles diameter and the nozzle position relative to the rotor. The presented fluid dynamics study of the microturbine system includes the analysis of local fluid flow values such as velocity, temperature, pressure, and Mach number, as well as global quantities like forces and driven torque acting on the turbine. Comparison with the experimental results shows good agreement of the microturbine efficiency. Furthermore, the parameter study of the nozzle diameter reveals optimization potential for this high-speed microturbine system employing a smaller nozzle diameter.

Figures

Fig. 1

Sketch of MAS rotor system with turbine and radial bearing. Rotor is rotating around the z-axis with an angular rotation frequency ω=2πf.

Fig. 2

Top view of the rotor and stator flow region. The drive gas is supplied from the inlet and afterward distributed into the drive nozzles, then driving the turbine and leaving through the various outlet planes.

Fig. 3

Flow geometry with rotor (white), turbine (brown), cap (green), and planes (yellow) for a 1.3 mm MAS system. The inflow comes through planes 1 and 2 and is accelerated in the nozzle in plane 3. After driving the rotor turbine, the gas flow is either directed to the top (through planes 4, 5, and 7) or to the bottom (planes 6 and 8). (Reprinted with permission from Wilhelm et al. [29]. Copyright 2015 by Elsevier, Inc.)

Fig. 4

Computational domain tetrahedral mesh M1 (a); the structured meshed M2 (b), the green surfaces are the outlets; axial section showing the refined blocking mesh near the injection duct walls (c), the region of concentrated cells is the interface separating the rotating domain from the stator; axial section of the structured mesh M2 (f); and hexahedral mesh around the turbine ((d), (e), and (g))

Fig. 5

Relative angular positions of the four-blade turbine with respect to the seven injection ducts: initial position at 0 deg (a), 30 deg position (b), and 60 deg position (c)

Fig. 6

Velocity magnitude in the rotor middle radial section and in the system axial section at the three considered rotation frequencies. Steady-state MRF simulations without turbulence model for the initial relative turbine position ϕ=0deg.

Fig. 7

Absolute static pressure in the rotor middle radial section and in the system axial section at the three considered rotation frequencies. Steady-state MRF simulations without turbulence model for the initial relative turbine position ϕ=0deg.

Fig. 8

Absolute temperature field in the rotor middle radial section and in the system axial section at the three considered rotation frequencies. Steady-state MRF simulations without turbulence model for the initial relative turbine position ϕ=0deg.

Fig. 9

Velocity magnitude, absolute static pressure, and absolute temperature fields in the rotor middle radial section at the highest rotation frequencies f=67 kHz. Steady-state MRF simulations without turbulence model for three relative angular positions, according to Fig. 5.

Fig. 10

Stream tracer lines in the rotor middle radial section at the highest rotation frequencies f=67 kHz for three relative angular positions, according to Fig. 5

Fig. 11

Pressure distribution on the turbine blades at initial relative turbine position ϕ=0deg and rotation frequencies f=67 kHz following the numeration of Fig. 10

Fig. 12

Stream tracer jetting out from a nozzle and impinging a blade. The colors correspond to the velocity magnitude.

Fig. 13

Geometrical setup of the fixed part (red) and the translated part (yellow) in axial direction (a) and axial view of the fixed and translated regions (b)

Fig. 14

Total vertical force as function of the normalized offset position Δz̃ for the three rotation frequencies

Fig. 15

Driving torque as function of the normalized offset position Δz̃ for three rotation frequencies

Fig. 16

Efficiency factor as function of the normalized offset position Δz̃. Comparison between simulation and measurement data.

Fig. 17

Geometrical setup of the fixed part (red) and the variable part (yellow) (a); horizontal view of the MAS setup for two variations of the nozzle dimension (b)

Fig. 18

Driving torque as function of the normalized nozzle size d̃ for the maximal rotation frequency

Fig. 19

Velocity magnitude and absolute pressure in the rotor middle radial section by varying the nozzle normalized diameter. MRF simulations for the initial relative turbine position ϕ=0deg.

Fig. 20

Mach number in the rotor middle radial section by varying the nozzle normalized diameter. MRF simulations for the initial relative turbine position ϕ=0deg.

Fig. 21

Inflow velocity magnitude by varying the nozzle diameter

Fig. 22

Efficiency factor as function of the normalized nozzle size at maximal rotation frequency. Comparison between simulation and measurement data.

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