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The necessity to change systems generating electrical energy is evident. The best solution would be to use installations utilizing renewable energy sources, complemented by efficient electric energy storage. This process requires time and further development, as well as new achievements in this area. Improving the situation can also result from enhancing the efficiency of devices already in operation. For a coal-fired power block, an important aspect is the variability of loads and ensuring the highest efficiency of all devices that make up the technological chain of such a unit, especially in variable working conditions. The article presents a new solution for regulating the working parameters of a radial fan for use in power engineering, which has high efficiency over a wide range of loads. The proposed six-blade solution allows one to obtain 115 Pa higher total pressure compared to four-blade systems, and efficiencies higher by 4.6 percentage points. The process of selecting elements and design parameters of the fan and its control system is discussed. The performance characteristics of the device with the new control system are presented. [ABSTRACT FROM AUTHOR]

Results obtained with computational fluid dynamics (CFD) rely on assumptions made during a pre-processing stage, including a mathematical description of a fluid rheology. Up to this date there is no clear answer to several aspects, mainly related to the question of whether and under what conditions blood can be simplified to a Newtonian fluid during CFD analyses. Different research groups present contradictory results, leaving the question unanswered. Therefore, the objective of this research was to perform steady-state and pulsatile blood flow simulations using eight different rheological models in geometries of varying complexity. A qualitative comparison of shear- and viscosity-related parameters showed no meaningful discrepancies, but a quantitative analysis revealed significant differences, especially in the magnitudes of wall shear stress (WSS) and its gradient (WSSG). We suggest that for the large arteries blood should be modelled as a non-Newtonian fluid, whereas for the cerebral vasculature the assumption of blood as a simple Newtonian fluid can be treated as a valid simplification. [ABSTRACT FROM AUTHOR]

The article presents a development of numerical model for a single propeller simulation and comparison of obtained results with experimental data available from a test campaign in scale 1:1. Described simulation is a steady state computation taking advantage of Multiple Reference Frame model implemented in Ansys CFX. The paper includes an analysis of rotating domain thickness influence on numerical values of thrust and power. The results indicate that this type of simulation may be sensitive to the sizing of rotating domain especially when disc solidity is low, or when the number of blades is 2, a frequent situation in all electric flight vehicles. The analysis shows that performing simulations, using one domain sizing, for a number of flight scenarios requiring analysis of a few rotational speeds can produce unintuitive results. Therefore, it is suggested to calibrate the model, preferably by experimental results. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. Methods: DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. Results: Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis - the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. Conclusions: The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented. [ABSTRACT FROM AUTHOR]

The Ciminio-Brescia arterio-venous fistula is a preferred vascular access for haemodialysis, but it is often associated with the development of vascular complications, due to changes in hemodynamic conditions. Computational fluid dynamics methods were involved to carry out seven simulations of the blood flow through the fistula for the patient specific (geometrical) case and various boundary conditions. The geometrical data, obtained from the angio-computed tomography, were used to create a 3-dimensional CAD model of the fistula. The blood flow patterns, blood velocity and the wall shear stress, thought to play a key role in the development of typical complications (stenoses, thromboses, aneurysms, etc.), have been analyzed in this study. The blood flow is reversed locally downstream the anastomosis (where the artery is connected to the vein) and downstream the stenosis in the cannulated vein. Blood velocity reaches abnormal value in the anastomosis during the systolic phase of the cardiac cycle (2.66 m/s). The wall shear stress changes in this place during a single cycle of the heart operation from 27.9 to 71.3 Pa (average 41.5 Pa). The results are compared with data found in the literature.