Research Outputs

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Now showing 1 - 4 of 4
  • Publication
    Nonlinear eddy viscosity modeling and experimental study of jet spreading rates
    (Wiley, 2014-02) ;
    Inthavong, Kiao 
    ;
    Sanz, Wolfgang 
    ;
    Indoor airflow pattern is strongly influenced by turbulent shear and turbulent normal stresses that are responsible for entrainment effects and turbulence-driven secondary motion. Therefore, an accurate prediction of room airflows requires reliable modeling of these turbulent quantities. The most widely used turbulence models include RANS-based models that provide quick solutions but are known to fail in turbulent free shear and wall-affected flows. In order to cope with this deficiency, this study presents a nonlinear k-ε turbulence model and evaluates it along with linear k-ε models for an indoor isothermal linear diffuser jet flow measured in two model rooms using PIV. The results show that the flow contains a free jet near the inlet region and a wall-affected region downstream where the jet is pushed toward the ceiling by entrainment through the well-known Coanda effect. The CFD results show that an accurate prediction of the entrainment process is very important and that the nonlinear eddy viscosity model is able to predict the turbulence-driven secondary motions. Furthermore, turbulence models that are calibrated for high Reynolds free shear layer flows were not able to reproduce the measured velocity distributions, and it is suggested that the model constants of turbulence models should be adjusted before they are used for room airflow simulations.
      129Scopus© Citations 10
  • Publication
    Micron particle deposition in the nasal cavity using the v2–f model
    (Elsevier, 2011-07-15)
    inthavong, kiao 
    ;
    ;
    Commercial CFD codes are commonly used to simulate models that involve complicated geometries such as the human nasal cavity. This means that the user has to work within the limitations of the available models of the CFD code. One such issue is the turbulent dispersion of particles in the Lagrangian reference, namely the Discrete Random Walk (DRW) model which overpredicts the deposition of smaller inertial particles, due to its inherent isotropic treatment of the normal to the wall fluctuation, v′ , in the near wall region. DNS data for channel flows has been used to create a function that reduces the turbulent kinetic energy (TKE) to match the v′ profile which has delivered improved particle deposition efficiency results. This paper presents an alternative approach to reduce the TKE to match v′ , by directly taking the profile from the v2–f turbulence model. The approach is validated against experimental pipe flow for a 90° bend and then applied to particle dispersion in a human nasal cavity using Ansys-Fluent which showed improved results compared to no modification.
      137Scopus© Citations 34
  • Publication
    Improving predictions of heat transfer in indoor environments with eddy viscosity turbulence models
    (Springer, 2016) ;
    Tao, Yao 
    ;
    Inthavong, Kiao
    ;
    Heat transfer modelling in indoor environments requires an accurate prediction of the convective heat transfer phenomenon. Because of the lower computational cost and numerical stability, eddy viscosity turbulence models are often used. These models allow modification to turbulent Prandtl number, and near wall correction which influences stagnation points, entrainment, and velocity and time scales. A modified v 2–f model was made to correct the entrainment behaviour in the near wall and at the stagnation point. This new model was evaluated on six cases involving free and forced convection and room airflow scenarios and compared with the standard k–ε, and k–ω–SST models. The results showed that the modification to the v 2–f model provided better predictions of the buoyant heat transfer flows while the standard k–ε failed to reproduce and underestimate the convective heat transfer. The k–ω–SST model was able to predict the flow field well only for a 2D square cavity room, and 3D partitioned room case, while it was poor for the other four cases.
      156Scopus© Citations 2
  • Publication
    Evaluation and improvements of RANS turbulence models for linear diffuser flows
    (Elsevier, 2013-01-30) ;
    Inthavong, kiao
    ;
    Sanz, Wolfgang 
    ;
    Flow patterns produced by linear diffusers are highly dependent on the turbulent momentum exchange process. Hence a realistic computation of indoor room airflows that are produced from plane wall and free jets requires an accurate prediction of the anisotropic turbulent stresses. This is particularly the case in regions near the wall and entrainment effects which are caused by the turbulent shear stresses. For this reason a non-linear eddy viscosity assumption is presented which can be adjusted to account for the turbulent mixing process in the free shear flow region, and to reproduce the redistribution of the turbulent normal stresses near the wall. Based on several test cases such as a free and plane wall jet, IEA (International Energy Agency) Annex 20 room airflow, and a 3D room with a partition, the essential characteristics of the linear and non-linear k-epsilon, k-omega and v(2)-f turbulence models are analysed. Thereby it is shown that the proposed non-linear assumption can improve the prediction of linear diffuser airflows.
      138Scopus© Citations 33