A phenomenological model for particle dispersion and clustering

• Main Author: Resvanis, Kyriakoulis
• Other Authors: Taylor, Alex ; Hardalupas, Yannis ; Cumspty, Nick
• Published: Imperial College London 2015
• Subjects: 621
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.749094

The objective of this thesis is to propose a new model for particle dispersion and clustering for use within an (unsteady)-Reynolds Averaged Navier-Stokes ((u)RANS) computational framework. The need for an improved model stems from industrial requirements to address certain limitations of the currently used models. Namely, low predicted particle entrance into recirculation zones for particles with large Stokes numbers and unrealistically spatial and temporal uniform predicted particle concentrations. Abstract The literature review presented within this thesis examines the various computational tools available for modeling the Lagrangian phase and identifies Kinematic Simulations (KS) as potentially capable of reproducing accurate Lagrangian statistics and particle clustering across a range of physical scales while at the same time requiring a modest increase of computational resources relative to the presently used methods. Abstract The thesis proposes a combination of (u)RANS and KS in a coupled Eulerian-Lagrangian framework. The (u)RANS calculations will be responsible for modeling the large coherent motions while the KS will be employed to model the effects of all the other scales, that are represented statistically in the (u)RANS context, on particle motion. In other words, the representation of the velocity field within the 'eddies' will be simulated by tracking a particle through an isotropic turbulent field constructed with the aid of KS. The extent of scales and the energy content of the isotropic field modeled by KS at every instance is determined by the local properties of the under-resolved 'eddy' as determined by the Eulerian framework. Abstract The proposed model is evaluated on an axisymmetric sudden expansion test case through comparisons with experimental results, LES calculations as well as RANS simulations employing the current industry standard dispersion model. Improved overall performance was observed with significant differences between the particle trajectories computed with the proposed model and those with a model widely used in industry. This last point is of particular significance as one of the limitations of the currently used models was the high degree of spatial uniformity in the predicted particle distribution.