Transition from ballistic to thermalized transport of the metal sputtered species in DC magnetron

Tunable Diode Laser Induced Fluorescence (TD-LIF) technique has been optimized to accurately measure the titanium (Ti) sputtered Atoms Velocity Distribution Functions (AVDF) in a magnetron discharge operating in Direct Current (DC) mode. The high spatial and spectral resolution achieved unveils some features of the transport of the metal sputtered atoms and their thermalization. The two groups of thermalized and energetic atoms have been very well separated compared to previous works. Hence, the fitting of the energetic atoms group shows dumping from modified Thompson to Gauss distribution when the product pressure-distance from the target increases. In parallel, sputtered metal transport from the target has been simulated using the Monte Carlo collision (MCC) approach. The direct comparison between numerical and experimental results led to an improved cross section for Titanium - Argon momentum transfer, based on the \textit{ab initio} formulae of the interaction potential derived from noble gases interaction. The numerical parametric study of the angular distribution and cut-off energy for the initial distribution of sputtered atoms steered to a precise characterization of the initial conditions, allowed by the accuracy of experimental data. A very good overall agreement is obtained for measured and calculated AVDFs. The confrontation between measured and modeling results emphasized the major role played by the argon ions not only in the sputtering process but also in the neutral metal transport, by the gas rarefaction near the target. The microscopic description provided by the MCC model clearly reveals different transport regimes: ballistic, diffusive, and back-scattering and brings new insights on the thermalization of sputtered species in the intermediate pressure range.

CFD Numerical Investigation of a New Solar Flat Air-Collector Having Different Obstacles with Various Configurations and Arrangements

This work deals with a numerical parametric optimization study of a new Solar Flat Air Collector (SFAC) configuration. The CFD numerical parametric study investigates various SFAC structures inside the air cavity without obstacles and with spherical, cubic, cylindrical, and pyramidal obstacles. The study optimizes the most convenient configuration and arrangement that allow for the increase of the heat-transfer surface and to make the flow homogeneous in order to generate turbulence zones inside the SFAC air cavity. The result shows that the thermal performances of the cubic form are close to those of the spherical obstacles. Another set of simulations was performed to evaluate the performances of the cubic shape baffles for three orientation angles equal to 0°, 22.5°, and 45°, respectively. Each configuration has three forms of arrangement with a relative roughness pitch (b/a) varying between 2, 4, and 6. The results of the simulation study showed that the relative roughness pitch, the Reynolds number, as well as the angle of orientation influence the performance and the operation of the SFAC. The results of the simulations showed that the combination of an orientation of 45° with a roughness pitch of b/a = 2 increases the SFAC thermal performances, which can reach 85%.

Equivalent Geometric Imperfections for Local Buckling of Slender Box-section Columns

Determining the plate or the local buckling resistance is highly important in designing steel buildings and bridges. The EN 1993-1-5Annex C provides a FEM-based design approach to calculate the buckling resistance based on numerical design calculations (geometrical and material nonlinear analysis - GMNIA). Within the GMNIA analysis-based stability design, the application of the imperfections has a special role. Thus, the applicability of the EN 1993-1-5 based buckling curve (Winter curve) has been questioned for pure compression, and previous investigations showed the buckling curve of EN 1993-1-5 Annex B is more appropriate for the design of slender box-section columns subjected to pure compression, the magnitude of the equivalent geometric imperfection to be applied in numerical models for local buckling is also questioned and investigated by the authors within the current paper. The aim of the current research program is to investigate the necessary equivalent geometric imperfections to be applied in FEM-based design calculations using GMNIA calculations. A numerical parametric study is executed to investigate the imperfection sensitivity of box-section columns having different local slenderness. The necessary imperfection magnitudes are determined to each analyzed geometry leading to the buckling resistance predicted by the standardized buckling curves. Based on the numerical parametric study, a proposal for the applicable equivalent geometric imperfection magnitude is developed, which conforms to the plate buckling curves of the EN 1993-1-5 and giving an improvement proposal to the local buckling imperfection magnitudes of the prEN 1993-1-14, which is currently under development.

Design Optimization of Diffuser Augmented Wind Turbine

The wind turbine power decreases at low wind speed. A flanged diffuser plays a role of a device for collecting and accelerating the approaching wind, and thus the optimization of the diffuser shape presents an important way to enhance the wind turbine power. In this work, a numerical parametric study was conducted on the diffuser to obtain the initial optimum form of flanged diffuser. Then, the Simplex algorithm is used to obtain the optimal diffuser shape starting from the obtained initial shape. Finally, the obtained optimum diffuser shape is used with conventional wind turbine blade. The diffuser shape is defined by four variables: open angle, flange height, centerbody length, and flange angle. The numerical simulation of flanged diffuser is carried out using the “CFDRC package. The results indicated that, the optimum diffuser shape can be obtained using simplex algorithm which maximizes the entrance average velocity to reach 1.77 times wind speed. The power augmented by a factor about 2.76:5.26 of a selected small wind turbine using the obtained diffuser shape compared to that without diffuser.

Dimensionless Numbers Relationships for Outer Air Seal of Low Pressure Turbine

The dimensional analysis and the numerical parametric study of the typical outer air seal from a low-pressure turbine were performed in the framework of the presented paper. The most crucial variables for the flow through the outer air seal were identified and further dimensionless numbers were derived. The dependent quantities resulting from the analysis were: the axial Reynolds number (formulated with the bulk velocity, corresponding to the mass flow through the seal), the outlet swirl ratio (incorporating the exit flow angle, important for mixing) and the windage heating (related to the internal losses). Additionally, the discharge coefficient was cross-checked enabling further comparison with the available literature. The comprehensive numerical parametric study included all important contributors for the flow through the seal with a parameter operating range appropriate for engine outer air seals.

Numerical and Experimental Investigation on Concrete Splitting Failure of Anchor Channels

Concrete splitting failure due to tension load can occur when fastening systems are located close to an edge or corner of a concrete member, especially in thin members. This failure mode has not been extensively investigated for anchor channels. Given the current trend in the construction industry towards more slender concrete members, this failure mode will become more and more relevant. In addition, significantly different design rules in the United States and Europe indicate the need for harmonization between codes. Therefore, an extensive numerical parametric study was carried out to evaluate the influence of member thickness, edge distance, and anchor spacing on the capacity of anchor channels in uncracked and unreinforced concrete members. One of the main findings was that the characteristic edge distance depends on the member thickness and can be larger than 3hef (hef = embedment depth) for thin members. Based on the numerical and experimental test results, modifications of the design recommendations for the splitting failure mode are proposed. Overall, the authors recommend performing the splitting verification separately from the concrete breakout to design anchor channels in thin members more accurately.

COMBUSTION OF ALUMINUM POWDER-AIR SUSPENSION IN A SWIRL FLOW

The article is devoted to the numerical solution of the problem of the combustion of powder metal fuel in a combustion chamber with swirling flow. A physico-mathematical model of the flow of an air suspension of aluminum powder in a swirling flow in a cylindrical combustion chamber with a sudden expansion is presented. The physical and mathematical formulation of the problem is based on the approaches of the mechanics of two-phase reacting media. The solution was carried out using the arbitrary discontinuity decay method. The results of a numerical parametric study of the features of the combustion of an air suspension of aluminum powder depending on its composition, the axial flow rate of the mixture at the entrance to the combustion chamber, and the value of the swirl speed are shown.

The numerical parametric study of the stress-strain state of I-beams having versatile corrugated webs

Introduction. The numerical parametric study of the stress-strain state of I-beams, having versatile corrugated walls, was carried out in the ANSYS Mechanical APDL software package. Numerical results are obtained for displacements, equivalent stresses and stability coefficients depending on the change in the inclination angle of web corrugations for trapezoidal, wavy and triangular profiles. The obtained results can help to design and substantiate the design solutions applicable to bending elements. Materials and methods. The parametric study involved a series of numerical experiments conducted using the finite element method in the ANSYS Mechanical APDL software package. APDL parametric language was used to develop the software that was built into the software package. It allowed to perform a parametric reconstruction of the numerical model depending on varied parameters of the corrugated wall, and the reconstruction was followed by the numerical solution and post-processing of the calculation results. The calculations were made with the help of the model whose overall dimensions and material were identical to those of a standard I-beam having a solid wall exposed to a uniformly distributed transverse load. Results. The parametric study enabled the co-authors to identify the main features of the stress-strain state of the beams that had different types of corrugated walls. A parametric numerical model was compiled to determine maximum displacements, equivalent stresses and stability coefficients for various types of corrugated walls and various parameters of the corrugation angle. Isofields of equivalent stresses and buckling modes are provided for characteristic parameters and types of corrugations. The reliability of the obtained results was confirmed by the verification of the numerical model using the method of the strength of materials and corrugation inclination angle α = 0, which was the initial point of simulation for all types of corrugations. Conclusions. The results, obtained in the course of parametric studies, have identified the main features of the stress-strain state of beams having corrugated walls; they allow to substantiate their effectiveness as design solutions applied to bending elements.