Technické zařízení budov AdMaS

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    Circular Free Jets: CFD Simulations with Various Turbulence Models and Their Comparison with Theoretical Solutions
    (IOP Publishing Ltd, 2019-02-25) Kmecová, Miroslava; Šikula, Ondřej; Krajčík, Michal
    The theory of turbulent free jet is fundamental for the design of comfort ventilation, as free jets frequently occur in mixing and personalized ventilation systems and their characteristics strongly influence the air quality in the breathing zone of an occupant. The aim of this research is to provide recommendations that help researchers and practitioners improve the accuracy and reliability of their computational models of ventilation systems involving circular free jets. To accomplish this, a review of existing theoretical calculation models is performed, and these models are subsequently investigated by computational fluid dynamics. The theoretical solutions of free jets are compared with CFD simulations using various turbulent models such as the standard k-epsilon model, the k-epsilon realizable model, the standard k-omega model, the shear stress transport (SST) k-omega model, and the Reynolds stress model (RSM). The simulated models are represented by profiles of the centreline velocity for a free jet emanating from a round nozzle, because such presentation of the data proved to be particularly helpful for the comparison of the turbulence models. The k-omega SST turbulence closure scheme with standard coefficients produced results of the centreline velocity closest to the average of theoretical solutions investigated, whereas the discrepancy between the simulations and the theoretical models was about 60 % with the k-epsilon standard turbulence model.
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    Experimental performance analysis of biplane VAWT configurations
    (Institute for Research and Development in Industry, 2017-12-15) Oulhaci, Z. S.; Imine, Omar; Ladjedel, Omar; Yahiaoui, Tayeb; Adjlout, Lahouari; Šikula, Ondřej
    This paper aim to develop a new Darrieus wind turbine configurations based on the concept of biplane blades in order to improve the performances of the machine. The performances of the new design were investigated numerically and experimentally. Firstly a 2-D steady numerical simulation of an isolated two blades is carried out to exhibit the aerodynamic performance behavior. Secondly experiences are made on different Darrieus wind turbine by considering the biplane blade models. The experiments are carried out in wind tunnel by testing firstly: two, three and four blades Darrieus wind turbine as well as the biplane new configurations. The results of static torque and rotational speeds versus a wind velocity are presented. The obtained results corresponding to the new machines present a great improvement in the performances.
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    Insulation panels for active control of heat transfer in walls operated as space heating or as a thermal barrier: Numerical simulations and experiments
    (Elsevier, 2018-01-01) Šimko, Martin; Krajčík, Michal; Šikula, Ondřej; peter, šimko; Kalús, Daniel
    Numerical simulations and experiments were performed for a thermally active wall with pipes arranged in milled channels in the thermal insulation. The advantage of this system is its suitability for installation in both new and existing buildings in the form of precast heat insulation panels attached to their facades. The study shows that by active control of the supply water temperature, it is possible to alternate the walĺs function between space heating and a thermal barrier. The wall system has the potential to significantly reduce heat loss when used as a thermal barrier. When operated as space heating, embedding the pipes in thermal insulation reduced the heating capacity by 50% as compared to systems with pipes arranged in a concrete core and by 63% for pipes arranged in a layer underneath the surface. It is crucial that pipes arranged in channels are embedded in a thermally conductive material. Failing to do so can substantially diminish the heating capacity due to the imperfect contact between the pipes and radiant surface and also due to the air gap that may form around the pipes. The thickness of the thermal insulation, spacing of the pipes, and supply water temperature also have a substantial effect on the heating capacity, whereas the thickness of the concrete core does not.