SIMULATION STUDY OF HYDRODYNAMIC CAVITATION IN THE ORIFICE FLOW

Hydrodynamic cavitation is a phenomenon that can be used in the water treatment process. For this purpose, venturis or orifices varying in geometry are used. Studying this phenomenon under experimental conditions is challenging due to its high dynamics and difficulties in measuring and observing the phase transition of the liquid. For this reason, the CFD method was used to study the phenomenon of hydrodynamic cavitation occurring in water flow through the orifice and then analyze flow parameters for different boundary conditions. The research was performed for four different orifice geometries and two defined fluid pressure values at the inlet, based on a computational 2D model of the research object created in Ansys Fluent software. As a result of the numerical simulation, the distribution of fluid velocity and pressure and volume fraction of the gas phase were obtained. A qualitative and quantitative analysis of the phenomenon of hydrodynamic cavitation under the considered flow conditions was conducted for the defined orifice geometries. The largest cavitation zone and thus the largest volume fraction of the gas phase was obtained for the orifice diameter of 2 mm with a sharp increase in diameter. However, the geometry with a linear change in diameter provided the largest volume fraction of the gas phase per power unit

THE INFLUENCE OF THE INJECTION TIMING ON THE PERFORMANCE OF TWO-STROKE OPPOSED-PISTON DIESEL ENGINE

The performance of the engine strongly depends on the parameters of the combustion process. In compression ignition engines, the fuel injection timing has a significant influence on this process. The moment of its occurrence and its duration should be chosen so that the maximum pressure value occurs several degrees after TDC. In order to analyze the effect of the fuel injection timing on the performance of the tested two-stroke opposed-piston diesel engine, a zero-dimensional model was developed in the AVL BOOST program. Next, a series of simulations were performed based on the defined calculation points for maximum continuous power, which resulted in power, specific fuel consumption and mean in-cylinder pressure. Finally, the engine map was made as a function of the start of combustion angle

Diffusion of bedload particles in open-channel flows : distribution of travel times and second-order statistics of particle trajectories

Acknowledgments The authors are grateful to the reviewers for thorough reviews, constructive comments and useful suggestions that have been gratefully incorporated in the final manuscript. Funding for this research was provided in part by the Institute of Geophysics of the Polish Academy of Sciences through the Project for Young Scientists No. 16/IGF PAN/2011/Mł ‘‘Dynamics and topography of riverbed forms: an analysis of experimental data and modelling of sediment transport in the light of Einstein’s theory’’, by Ministry of Sciences and Higher Education within statutory activities No. 3841/E-41/S/2015, and by EPSRC, UK (EP/G056404/1) within the project ‘‘High-resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transport.’’ Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Peer reviewedPublisher PD

NUMERICAL CALCULATIONS OF WATER DROP USING A FIREFIGHTING AIRCRAFT

The study involved a numerical analysis of the water dropping process by fixed-wing aircraft. This method, also known as air attack, is used for aerial firefighting, primarily in green areas such as forests and meadows. The conducted calculations allowed for the analysis of the process over time. The calculations were performed based on a SolidWorks model of the M18B Dromader aircraft. After defining the computational domain and setting the boundary conditions, the simulations were carried out using the ANSYS Fluent software. The resulting water dropping area was used to analyze the intensity of water distribution. The volumetric distribution and airflow velocity distribution were analyzed for specified time steps. The boundary layer where air no longer mixes with water during the final phase of water dropping was also determined. The obtained results provide an important contribution to further analyses aimed at optimizing the water dropping process by fixed-wing aircraft

Numerical analysis of the impact of sideslip angle on load of the gyrocopter stabilizers

The paper presents some of the works related to the project of modern gyrocopter construction with the possibility of a short start, known as "jump-start". It also presents a methodology related to numerical calculations using Computational Fluid Dynamics based on ANSYS Fluent three-dimensional solver. The purpose of the work was to calculate the forces and aerodynamic moments acting on the gyrocopter stabilizers. The calculations were carried out for a range of angle of attack α from –20° to +25° and for a sideslip angle β from 0° to 20°. Based on the calculations carried out, analysis of the impact of the slip angle on the load on the stabilizers has been made. First published online 17 February 202

Simulation of an aircraft radial engine misfire detection

The misfire phenomenon is particularly unfavourable in aircraft engines because it affects the stability and reliability of work. This paper presents the algorithm for detecting ignition failure in a radial aircraft engine. The Crankshaft Velocity Fluctuation method was applied, which consists in analysing changes in the crankshaft speed signal as a function of time. A zero-dimensional model of the aircraft engine was developed in order to perform the research. The validation of the model was performed using the results from the test bench. The model was subjected to simulation tests in fixed operating conditions. Based on the engine speed signal obtained as a result of the simulation, the normalized second derivative of the signal was determined based on the adopted algorithm. On the basis of this derivative, a criterion was defined to assess the occurrence of the misfire phenomenon. The results of the calculations can be compared in future with the results of the real engine tests

NUMERICAL ANALYSIS OF THE DRAG COEFFICIENT OF A MOTORCYCLE HELMET

The paper discusses a numerical investigation, using a CFD tool, ANSYS FLUENT, of drag acting on a motorcycle helmet. The simulations were performed on a model of a helmet downloaded from a free CAD model library. A solid model enabled us to generate a mesh, to define boundary conditions and to specify a model of turbulence. Accordingly, the values of forces acting on individual sections of the helmet were obtained and the coefficients of aerodynamic drag were calculated. The test results can be used to optimize the shape of the existing motorcycle helmet construction and to study the impact of generated drag forces on reaction forces affecting a motorcyclist’s body

Thermocapillary marangoni flows in Azopolymers

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings