Numerische Untersuchung der Wechselwirkung zwischen turbulenten Freistrahlen und Biomassepartikeln
Zusammenfassung der Projektergebnisse
In this project, the interaction of non-spherical particles with the carrier fluid was investigated. The non-spherical particles represent an approximation of biomass particles. The present numerical investigation aimed at obtaining highly accurate results to extend the understanding of the dynamics of non-spherical particles in turbulent free jet flow. For this purpose, a finite volume method with a cut-cell method was used on a locally refined Cartesian mesh structure. The particles were fully resolved such that the interaction between the two phases could be studied and quantified in detail. The method guarantees the conservation of mass, momentum, and energy at the fluid–particle interfaces. The dynamics of spherical and ellipsoidal particles in turbulent free jet flow at Reynolds number ReD = 15 546 was studied by direct particle-fluid simulation. The jet was laden with spherical and ellipsoidal particles with aspect ratios in the range 1 ≤ β ≤ 8 with a volume loading of 6.67 × 10−4 . To ensure physically correct particle distributions and flow field characteristics, a slicing technique was developed to determine the instantaneous solution of a simultaneously computed particle-laden fully-developed turbulent pipe flow that defined the inflow boundary distribution of the jet. The proper transfer of the particles through the grid boundaries was achieved by an adaptive mesh generation algorithm which ensured that the particle surfaces were properly resolved and that energy conservation was guaranteed. A single-phase turbulent free jet was simulated first. The setup was used for validation of the slicing technique and for comparison with the particle-laden free jet. The physical parameters were equal to the particle-laden flow. Subsequently, a particle-laden pipe was computed. The data was used as inflow condition for the free jet flow. The slicing technique is one-directional, i.e., the pipe is independent from the jet and constitutes a fully-developed periodic particle-laden pipe flow. The dynamics of the particles in the pipe flow was analyzed. Preferential distributions and orientations in regard to the streamwise direction were discovered. Spherical and non-spherical particles preferred to align close to the pipe wall. However, with increasing aspect ratios the ellipsoidal particle distributions became more random and homogeneous, larger concentrations towards the pipe center were observed. On average, the ellipsoidal particles aligned at 90◦ ±35◦ to the streamwise direction due to the pressure distribution along the elongated particles and the relative velocity differences. The particle-laden free jet flow was investigated next. The focus was on the impact of the particles on the carrier fluid in the near field area. The particle dynamics was shown to be dependent on the particle aspect ratios. With increasing aspect ratios the particle showed larger movement in the radial direction. Due to the increased elongated axis, the elongated surface area of the particles was subject to larger differences in the inhomogeneous turbulent flow field. The rotational dynamics was enhanced such that wider spreading for larger particle aspect ratios was observed. The kinetic energy dynamics of the flow field was further modulated. The temporal development of the fluid kinetic energy showed to be modulated by approx. 9% in the near field whereas the turbulence intensity was reduced by approx. 20% at the end of the near field x/D = 10. The investigation will be extended to include the impact of a non-isothermal environment, i.e., the impact of varying temperatures between the carrier flow and the particles will be investigated. As was shown, the impact of the thermal dynamics varies strongly within the different aspect ratios investigated in this project. A novel model for fully-resolved particles with coupled conjugate heat transfer has been developed. Furthermore, the impact of shape transformations and mass changes as observed in combustion processes will be incorporated. The numerical method is already available, however, an empirical model is still to be derived. To conclude, the numerical approach will finally be used to perform direct particle-fluid simulations for biomass or other particle combustion processes.
Projektbezogene Publikationen (Auswahl)
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Determination of aerodynamic and thermal correlations for ellipsoidal particles via direct numerical simulation. In APS Division of Fluid Dynamics Meeting Abstracts (pp. M18-009).
Schröder, W., Fröhlich, K., Kiwitt, T. & Meinke, M.
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Particle Reynolds number effects on settling ellipsoids in isotropic turbulence. International Journal of Multiphase Flow, 139, 103566.
Fröhlich, Konstantin; Farmand, Pooria; Pitsch, Heinz; Meinke, Matthias & Schröder, Wolfgang
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Nusselt correlation for ellipsoidal particles. International Journal of Multiphase Flow, 149, 103941.
Kiwitt, Thede; Fröhlich, Konstantin; Meinke, Matthias & Schröder, Wolfgang
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An efficient method to determine conjugate heat transfer in moving bodies on parallel computing systems. Physics of Fluids, 37(6).
Kiwitt, Thede; Meinke, Matthias & Schröder, Wolfgang
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Direct particle–fluid simulation of spherical and ellipsoidal particles in turbulent pipe-free-jet flow. International Journal of Multiphase Flow, 194, 105443.
Kiwitt, Thede; Meinke, Matthias; Krug, Dominik & Schröder, Wolfgang
