Thorsten Poehler

Bergische Universität Wuppertal, Wuppertal, North Rhine-Westphalia, Germany

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Publications (6)7.18 Total impact

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    ABSTRACT: Three-dimensionally (3D) resolved ion trajectory calculations within the complex viscous flow field of an atmospheric pressure ion source are presented. The model calculations are validated with spatially resolved measurements of the relative sensitivity distribution within the source enclosure, referred to as the distribution of ion acceptance (DIA) of the mass analyzer. In previous work, we have shown that the DIA shapes as well as the maximum signal strengths strongly depend on ion source operational parameters such as gas flows and temperatures, as well as electrical field gradients established by various source electrode potentials (e.g., capillary inlet port potential and spray shield potential). In all cases studied, distinct, reproducible, and, to some extent, surprising DIA patterns were observed. We have thus attempted to model selected experimental operational source modes (called operational points) using a validated computational flow dynamics derived 3D-velocity field as an input parameter set for SIMION/SDS, along with a suite of custom software for data analysis and parameter set processing. Despite the complexity of the system, the modeling results reproduce the experimentally derived DIA unexpectedly well. It is concluded that SIMION/SDS in combination with accurate computational fluid dynamics (CFD) input data and adequate analysis software is capable of successfully modeling operational points of an atmospheric pressure ion (API) source. This approach should be very useful in the computer-aided design of future API sources.
    Journal of the American Society for Mass Spectrometry 06/2013; · 3.59 Impact Factor
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    ABSTRACT: In this study, the validation and analysis of steady state numerical simulations of the gas flows within a multi-purpose ion source (MPIS) are presented. The experimental results were obtained with particle image velocimetry (PIV) measurements in a non-scaled MPIS. Two-dimensional time-averaged velocity and turbulent kinetic energy distributions are presented for two dry gas volume flow rates. The numerical results of the validation simulations are in very good agreement with the experimental data. All significant flow features have been correctly predicted within the accuracy of the experiments. For technical reasons, the experiments were conducted at room temperature. Thus, numerical simulations of ionization conditions at two operating points of the MPIS are also presented. It is clearly shown that the dry gas volume flow rate has the most significant impact on the overall flow pattern within the APLI source; far less critical is the (larger) nebulization gas flow. In addition to the approximate solution of Reynolds-Averaged Navier-Stokes equations, a transport equation for the relative analyte concentration has been solved. The results yield information on the three-dimensional analyte distribution within the source. It becomes evident that for ion transport into the MS ion transfer capillary, electromagnetic forces are at least as important as fluid dynamic forces. However, only the fluid dynamics determines the three-dimensional distribution of analyte gas. Thus, local flow phenomena in close proximity to the spray shield are strongly impacting on the ionization efficiency.
    Journal of the American Society for Mass Spectrometry 08/2011; 22(11):2061-9. · 3.59 Impact Factor
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    ABSTRACT: In this paper the analysis of CFD results of three-dimensional turbine stator vane designs combined with non-axisymmetric endwalls is presented. A Design of Experiments (DoE) method has been used to generate 120 different combinations of the geometrical parameters. By means of a statistical approach the generic correlations and sensitivities of geometrical parameters on the aerodynamic behavior of three-dimensional turbine airfoils are demonstrated. The interpretation of the correlations leads to the finding, that different parameters of the three-dimensional shape fulfill different tasks. The reduction of turbulent kinetic energy and secondary kinetic energy are particularly sensitive to different geometrical parameters. By means of the same statistical approach it is also shown that for three-dimensional designs a distinction should be made between losses that occur within the vane passage and losses expected to arise downstream of the evaluation plane. By consideration of this distinction four modified designs have been chosen for a more detailed analysis. The results indicate that the losses produced by the secondary flow can be diminished by means of a three-dimensional shape of the turbine vane. However, this leads to increasing losses occurring at the laminar-turbulent separation bubble on the suction side of the vane. Therefore, non-axisymmetric endwall contouring should be implemented early in the design process to compensate this behavior by adapting the profile pressure distribution.
    ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition; 01/2011
  • Thorsten Poehler, Jochen Gier, Peter Jeschke
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    ABSTRACT: Numerical and experimental investigations have been performed to determine the effects of non-axisymmetric stator endwall contouring on the efficiency of an axial turbine stage. The influences of the contoured endwalls on the secondary flows in the stator and the rotor have been analyzed by conducting steady and unsteady RANS simulations as well as measurements in the 1.5-stage axial cold air turbine test rig of the Institute of Jet Propulsion and Turbomachinery. Both numerical and experimental results show an aerodynamic improvement of efficiency and secondary kinetic energy through non-axisymmetric endwall contouring. The non-axisymmetric endwall contour induces a vortex, which separates the pressure side leg of the horseshoe vortex from the passage vortex resulting in redistributed and reduced secondary flows. The modified secondary flow pattern increases the torque of the rotor blade in the hub region as a consequence of improved inlet conditions for the rotor as well as a reduction of the time interval the secondary flows are convected through the rotor passage within. Concerning the shroud region the endwall contour had no significant impact on the efficiency as a consequence of a dominating tip clearance vortex system.
    ASME Turbo Expo 2010: Power for Land, Sea, and Air; 10/2010
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    Proceedings of the 58th ASMS Conference on Mass Spectrometry and Allied Topics, Salt Lake City, UT, USA; 01/2010
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Publication Stats

14 Citations
7.18 Total Impact Points

Institutions

  • 2013
    • Bergische Universität Wuppertal
      • Physical and Theoretical Chemistry
      Wuppertal, North Rhine-Westphalia, Germany
  • 2010–2013
    • RWTH Aachen University
      • Chair and Institute of Jet Propulsion and Turbomachinery
      Aachen, North Rhine-Westphalia, Germany
    • Salt Lake City Community College
      Salt Lake City, Utah, United States