We present the development of an experimentally validated computational fluid dynamics model for liquid micro jets. Such jets are produced by focusing hydrodynamic momentum from a co-flowing sheath of gas on a liquid stream in a nozzle. The numerical model based on laminar two-phase, Newtonian, compressible Navier-Stokes equations is solved with finite volume method, where the phase interface is treated by the volume of fluid approach. A mixture model of the two-phase system is solved in axisymmetry using ~ 300,000 finite volumes, while ensuring mesh independence with the finite volumes of the size 0.25 [micro]m in the vicinity of the jet and drops. The numerical model is evaluated by comparing jet diameters and jet lengths obtained experimentally and from scaling analysis. They are not affected by the strong temperature and viscosity changes in the focusing gas while expanding at nozzle outlet. A range of gas and liquid-operating parameters is investigated numerically to understand their influence on the jet performance. The study is performed for gas and liquid Reynolds numbers in the range 17-1222 and 110-215, and Weber numbers in the range 3-320, respectively. A reasonably good agreement between experimental and scaling results is found for the range of operating parameters never tackled before. This study provides a basis for further computational designs as well as adjustments of the operating conditions for specific liquids and gases. Explanation: the project group has in the paper as first published simulation of micro jet under consideration of compressibility of the focusing gas and demonstrated match with the experimental data. The project group has based on this achievement established a long-term collaboration with DESY, Hamburg and obtained exclusive role for simulation and virtual design of different micro nozzles, which are used in femtoscond crystallography. With this, and many other papers that followed this pioniring work, has been in Slovenia established a new, spcialized research direction in the field of high technologies.
D.04 Initiative to set up a new research area in Slovenia
COBISS.SI-ID: 16174107A two-dimensional two-scale slice model has been developed to predict the temperature and microstructure evolution in the solidifying strand with the circular cross section geometry during continuous casting of steel in Xiwang Special Steel Company Limited. The enthalpy equation is solved at the macro level by using meshless local radial basis function collocation method (LRBFCM) based on multiquadrics for spatial discretization and explicit Euler scheme for temporal discretization. The temperature and the solid fraction in computational nodes are calculated by using JMatPro software. The temperature field is interpolated to the micro level by using LRBFCM. At the micro level, the normal distribution and Kurz-Giovanola-Trivedi model are proposed to determine temperature dependent nucleation rate and grain growth velocity, respectively. Meshless point-automata algorithm is applied to implement nucleation and grain growth equations. The model was validated with the experimental data measured in Xiwang Special Steel Company Limited. Explanation: The outcomes of this basic research project have been implemented in meshless simulation system, used in practice in large Chinese steelwork. With this has been the export and the practical use of Slovenian knowledge in global steel industry widely opened.
D.06 Final report on a foreign/international project
COBISS.SI-ID: 513015921A comprehensive, multiphysics, meshless, numerical model is developed for the simulation of direct chill casting under the influence of a low-frequency electromagnetic field. The model uses mixture-continuum-mass, momentum and energy-conservation equations to simulate the solidification of axisymmetric aluminium-alloy billets. The electromagnetic-induction equation is coupled with the fluid flow and used to calculate the Lorentz force. The involved partial-differential equations are solved with the meshless-diffuse-approximate method by employing second-order polynomial shape functions and a 13-noded local support. An explicit time-stepping scheme is used. The boundary conditions for the heat transfer involve the effects of hot-top, mould chill and direct chill. The use of a meshless method and the automatic node-arrangement generation made it possible to investigate the complicated flow structures in geometrically complex inflow conditions, including sharp and curved edges, in a straightforward way. A time-dependent adaptive mesh is used to decrease the calculation time. The model is demonstrated by casting an Al-5.25wt%Cu aluminium alloy billet with a radius of 120 mm. Results on simplified and realistic inflow geometry are considered and compared. The effect of the low-frequency electromagnetic force on the temperature, liquid fraction and fluid flow are investigated under different current densities and frequencies. Explanation: Results of the present basic reserch project enabled the development of the meshless multiphysics and multiscale numerical model for virtual design of new elecromagnetic direct-chill casting technology in IMPOL Slovenska Bistrica aluminium industry.
F.09 Development of a new technological process or technology
COBISS.SI-ID: 15664923Reason: Prof. Šarler developed a new, conceptually simple, meshless numerical approach for treatment of partial differential equations based on radial basis functions with local support, and use it to accurately and efficiently solve numerous natural and technical problems with many unknowns. They encompass multiphase and multiscale systems influenced by electromagnetic fields coupled with nonlinear solid and turbulent fluid mechanics. His main contribution is an original general numerical method, with qualities such as no need for mesh and local integration, simple numerical implementation, adaptivity and usefulness for complex geometries in multiple dimensions. Together with his co-workers he applied the method to systems design in large foreign research centers and for domestic and foreign metallurgical industry. He published the mentioned research in 30 notable articles in leading world scientific journals in the field of development and application of numerical methods. He also received multiple international awards and served as an invited lecturer at several international conferences, universities, and institutes.
E.01 National awards
This paper describes the development of a computational model for the hot rolling of steel in a continuous rolling mill. The solution procedure consists of slices aligned in the rolling direction. The deformation and heat flow are assumed to be only in the direction perpendicular to the rolling and the assumed behavior of the material is ideal plastic. The strongly coupled thermal and mechanical models are solved by a novel meshless, local radial basis function collocation method, based on subdomains with 5 nodes for the thermal, and 7 nodes for the mechanical model. Multiquadrics radial basis functions with firstorder monomials are used for the shape functions. The rearrangement of the collocation nodes in this large deformation problem is based on elliptical node generation. The non-linear relations are coped with a direct iteration, where the material properties are linearized during each of the iterations. Verification is based on comparison with an analytical solution and results from the finite-element method. A complete rolling simulation with 5 rolling stands is presented. The results encompass the roll speed, the separating force and the torque. The displacement and temperature fields of the rolling from the square to the round profile are displayed. Explanation: Results of the present basic reserch project enabled the development of the meshless large deformation model of rolling for virtual design of hot rolling in Štore Steel company - one of the largest sping steel producers in Europe.
F.09 Development of a new technological process or technology
COBISS.SI-ID: 15624731