Table of contents

Preface

This Journal of Physics: Conference Series contains the papers presented at XXIII Fluid Mechanics Conference (XXII FMC) held in Zawiercie in Poland during 09^th-12^th September of 2018. The Conference is organised by Czestochowa University of Technology (CzUT) under the auspices of the Ministry of Science and Higher Education and the Polish Academy of Sciences, Committee of Mechanics.

The Fluid Mechanics Conferences have been taking place every two years since 1974. The first Conference was inaugurated by Prof. Włodzimierz Prosnak from Warsaw University of Technology and since then the scientific centers from Lodz University of Technology, Poznan University of Technology, Silesian University of Technology, Bialystok University of Technology, AGH University of Science and Technology, Gdansk University of Technology, Military Technical Academy, Rzeszow University of Technology, Wroclaw University of Technology, Poznan University of Technology, Institute of Fluid-Flow Machinery Polish Academy of Sciences and Institute of Aviation took responsibility for this scientific event. Częstochowa Universiy of Technology is proud to be the organiser of the conference for the third time. Previous editions of Fluid Mechanics Conference organized by CzUT were held in 1978 and 1998.

The aim of the Conference is to bring together academics, scientists and experts in fluid mechanics and to provide a forum for the exposure and exchange of ideas, methods and most recent results in the field of new experimental techniques and computational methods associated with fluid mechanics and related disciplines.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We present a fractal sub-grid scale model for large eddy simulation (LES) of atmospheric flows. The fractal model is based on the fractality assumption of turbulent velocity field with a dynamical hypothesis based on energy dissipation. The fractal model reconstruct sub-grid velocity field from the knowledge of its filtered values on LES grid, by means of fractal interpolation, proposed by Scotti and Meneveau (1999). The characteristics of the reconstructed signal depends on the (free) stretching parameters, which is related to the fractal dimension of the signal. In previous studies, the stretching parameters was assumed to be constant in space and time and are obtained from experimental velocity signals of homogeneous and isotropic turbulence. To improve this method and account for the stretching parameter variability, we calculate the probability distribution function of the stretching parameter from direct numerical simulation (DNS) data of stratocumulus-top boundary layer (STBL) (courtesy of Prof. J.-P. Mellado from the Max Planck Institute of Meteorology) using the geometric method proposed by Mazel and Hayes. We perform 1D a priori test and compare statistics of the constructed velocity increment with DNS velocity increments.

In this paper, the experimental and theoretical analysis of pressure drop in single-phase and two phase-flow were presented for straight and U-bend smooth tube annulus and tube annulus with wire coil insert. Experiments for various boundary conditions were performed. In case of U-tube and straight tube with and without turbulator, tests were made for the water-water and air-water systems. The study covered a wide measuring range, i.e. Vw = 9*10-5-8.87*10-6 m3/s - for water, and Va = 5.55*10-5 m3/s.-for air. The test elements were made from a copper pipe with an external diameter of 10 mm and 18 mm and wall thickness 1 mm. The helicoidal vortex generator was made from brass wire with a diameter of 2.4 mm, coil diameter 13 mm and pitch 11 mm. For these geometries, the values of pressure drop and heat flux were determined. Obtained experimental results were compared with correlations from literature. The best coherence with database were obtain for Lockhart-Martinelli and Sugawar et al. models for two-phase flow regime.

Stability is a key aspect for aircraft as it directly affects its flight balance and manoeuvre capabilities. This numerical research with Ansys Fluent investigates an airflow around a model of the designed gyrocopter – Aduster to examine its static longitudinal stability for the given ranges of horizontal stabilizer angles and angles of attack. Our calculations give certain aerodynamic forces and moments. The paper investigates drag, lift, a pitching moment at the given angles as well as gives the calculated coefficients of those forces and the pitching moment. The research results and the stability criterion enable us to analyse our gyrocopter's static longitudinal stability.

The paper deals with experimental analysis of passive skin friction control method applied for a high Reynolds number turbulent boundary layer close to separation. A proposed new method is based on the mechanism of scale interaction observed in the wall bounded flows known as amplitude modulation of small scales by large-scale motion. The applied control technique introduces artificially amplification of the modulation mechanism using a corrugated surface in the direction of flow at specific ratio of surface waving parameters. Preliminary results show that the method can be use in an efficient way to postpone the turbulent boundary layer separation for high Reynolds number, where methods based on classical turbulizers fail. This method introduces reorganization of turbulence production, which introduces asymmetry between sweep and ejection events. This results in positive skewness of streamwise fluctuations and additionally increases the momentum near the wall. The momentum is increased only in the inner part of boundary layer. The persistent of the developed flow control method is permanent farther downstream the corrugated wall.

This paper presents theoretical considerations and numerical calculations concerning wind influence on the movement of the load during working cycle. During the test, the load is treated as a rigid body. The first part of this work includes the analysis of the aluminium cubical model of the load, which could move only in one plane, striving to increase the stability of motion and prevent vibrations. Numerical analysis was performed in Matlab/Simulink program and compared with experimental results, which were carried out in a low speed wind tunnel equipped with PIV system. The study was carried out for two cases: with and without seeding. The second part of this work includes the application of this research method for analysing the laboratory mobile crane's duty cycle. Numerical simulations were carried out on a modified simulation model. The sample numerical results present the trajectory and positions of the load carried on the non-deformable rope taking into account the wind influence.

This paper presents numerical and experimental testing of a cycloidal rotor fan (CRF). The tested cyclorotor is made of four NACA0012 profile blades. CFD calculations using the Ansys CFX^® tool and the LDA measurement technique are performed to determine the fan performance for different operating parameters, i.e. rotational speed and the rotor blade maximum swing angle values. One initial position of the blades corresponding to one air-flow direction is considered only. The comparison between the numerical results and the experimental LDA measurements is satisfactory and encouraging further investigation.

On the way to present the detailed description of the thermal processing of fossil fuels, one has to face the task of modeling physico-chemical phenomena as complex as thermal dilatation of particles of granular bed in a hot stream of gases. The work presents main assumptions and description of modeling tool for simulate of coal grains thermal dilatations with increasing temperature. For this purpose we use the Lattice Boltzmann method with some schemes needed when the process, of coupled phenomena, in a representative element of granular media is modeled.

The results of experimental investigation of cavitation in flow over Clark Y foil are presented. The cavitation test rig included a chamber with a blade profile fixed to the rotary disc that enabled to set different angles of attack. Working fluid was water at temperature 16°C. For different flow conditions (water velocity, pressure) the pictures of cavitating flow were taken and analyzed. The pressure at the inlet and outlet of the chamber were measured, as well as the value of volumetric flow rate. That enabled to determine the cavitation number for each case. The mechanism of cavitation structures appearance, growth and collapse was observed and described. The numerical simulation of cavitating flow was also performed by means of Open FOAM software with interphase Change Foam solver. Kunz cavitation model was chosen for calculations, with k-ω SST turbulence model. The assumption of isothermal, two–phase flow was made. The vapour areas appearance, their shapes and changes in time were described and compared with experimental results. The main features of cavitating flow were caught, but the further adjustment of cavitation model is recommended.

The objective of this work is to evaluate fluid flow and heat transfer from a standard photovoltaic module by means of comprehensive analysis for the polycrystalline photovoltaic modules by using three-dimension CFD numerical modelling and experimental measurement. The analysis shows that PV module temperature is incident solar radiation G_T and ambient temperature T_a dependent but also depends on the wind speed as well as wind direction. It has been additionally shown that the mounting conditions which are not included in any advanced mathematical model also plays a significant role. Base on presented results the already existing models for PV module temperature evaluation can be tuned in order to determine the PV module temperature accurately. The experimental and numerical results that were obtained enable the development of a model for the module operating temperature evaluation under varying real environmental conditions.

The paper presents experimental studies on influence of two arbitrary chosen additives on wall shear stress in hydromixture, which consists solid particles of averaged diameter 0.05 mm. Experiments were performed for two mass concentration of solids equal to 20% and 43%. Measurements were performed for varied doses of deflocculants in three different proportions in wide range of shear rates. Experiments confirmed influence of chosen additives on decreasing hydromixture viscosity and as a consequence decreasing of shear stresses. The analysed process is complex and strongly depends on doses of deflocculants and solids concentration. However, the rheological property of such mineral suspension is complex and there is no single parameter that can solely explain it. Physical and chemical properties affect on the level of interparticle interaction or aggregation and therefore it is useful to control them in industrial process such as transportation of slurries.

A flow simulation through a four-stage low pressure turbine (LPT) of aero-engine, using eddy-viscosity based RANS (Reynolds-averaged Navier-Stokes) model, is performed. The numerical results are compared with experimental data obtained in Polonia Aero Lab in Zielonka, Poland. Good agreement between measured and predicted global flow features and the pressure coefficient on surface of inlet strut is reported. The development of vortex structures in inlet duct of the low pressure turbine (LPT), named a turbine central frame (TCF), is analysed. An analysis of secondary flow losses by means of entropy generation rate coefficient is provided.

This paper contains experimental and numerical investigation of the leakage flow over the blade tip in turbine stage. Experiments were conducted in non-rotating linear channel. Test rig was intended to model the geometry of the labyrinth seal of the blades of the lower pressure turbine stage. Investigated model contained two different geometries of labyrinth fins. Moreover smooth and honeycomb stator landing were tested. Experimental measurements have been supported by CFD simulation which gives valuable information of flow structure in labyrinth seal and show complex flow physics in the investigated model.

We present an approach to numerical simulation of two-phase flows in the so-called one-fluid formulation, combining the Entropically Damped Artificial Compressibility (EDAC) method for flow solution and a chosen variant of the Phase Field Method (PFM) that belongs to a wider family of the Diffuse Interface (DI) methods of interface capturing. The resulting governing equations express a set of conservation laws and are of the advection–diffusion type, convenient in numerical handling. These equations, rewritten in the semi-discrete form, can be efficiently solved on parallel devices using the method of lines. We applied the conservative finite difference method for the spatial discretisation and a variant of the Runge–Kutta method to advance the solution in time. The results presented in this work contain the analysis of spurious currents in the case of stationary droplet together with the pressure jump across its surface, as well as the deformation of a droplet subjected to the laminar Couette flow. The presented EDAC–DI approach, offering very high computational efficiency, gives results comparable to other well-established methods for the simulations of the interfacial flows.

Numerical computations on 2d model of blood flow along human aorta based on incompressible axisymmetric Navier-Stokes equations for blood and momentum equations for incompressible viscoelastic arterial wall are compared to the blood flow oscillation curves measured in vivo by Doppler ultrasound in the larger systemic arteries of healthy volunteers. The analysis of the wave propagation and reflection along the geometrical 91-tube model of aorta as a tube with side branches is based on Lighthill's theory of waves in arteries. It is shown due to individual geometry positive wave reflections at some aortic branches and aortic bifurcation may lead to increase of the pressure amplitudes, high pressure and wall shear stress oscillations that may lead to wall damage and development of aortic aneurism and stenoses of branched arteries. The numerical results obtained on the linearized 2d and nonlinear 1d models are compared to the in vivo pressure and flow measurements along the aorta and in its branches. A good qualitative correspondence is obtained. The model can be used for determination of the individual parameters for patient-specific cardiovascular models.

This paper covers topics of energy saving device (ESD) with application to marine propulsore. The form of ESD, considered in this paper, consists of fixed lifting foils mounted in front of the screw propeller (the pre-swirl stator/guide vanes). An algorithm for designing propulsion systems, consisting of guide vanes and screw propeller, is presented. The proposed method relies on hybrid lifting line (guide vanes)-lifting surface (screw propeller) vortex model. Additionally, an analysis method for such systems is also presented. It utilises lifting surface model for guide vanes as well as for screw propeller blades. Accuracy of the proposed method is notably lower in comparison with CFD calculations, however, the former is substantially faster and at the same time capable of providing accuracy sufficient for practical application. Further, the entire process of design and analysis is presented on the example of Nawigator XXI ship. The designed propulsion system, consisting of propeller CP753 and pre-swirl stator ST002, was manufactured and tested in model scale. Model tests revealed increased efficiency by 4% in the design point in comparison with the Nawigator's original propeller CP469. Finaly, model scale experimental results, conducted in Ship Hydrodynamics Division of CTO Gdańsk, are compared with numerical predictions.

The predictive qualities of a newly developed algebraic intermittency model are analysed by simulation of the flow through a linear cascade of low pressure turbine (LPT) blades with endwalls. Both steady RANS (Reynolds-averaged Navier-Stokes) and time-accurate RANS (URANS) simulations are performed. The results are compared with reference LES (Large Eddy Simulation) by Cui et al. (2017, Numerical investigation of secondary flows in a high-lift low pressure turbine, Int. J. of Heat and Fluid Flow, vol. 63) for a turbulent endwall boundary layer (TBL) at the entrance to the cascade. Good agreement is obtained between simulations with the algebraic model and the reference LES for the evolution of the mass-averaged total pressure loss coefficient and for profiles of pitchwise-averaged turbulent kinetic energy.

In order to reproduce the near-surge operation of centrifugal compressor a series of numerical simulations in ANSYS CFX have been conducted. Different settings of boundary conditions have been investigated in purpose of providing a combination allowing to model surge without non-physical flow constraints. This, in turn, would be a step towards modelling of antisurge system. As the conclusions, it was observed that there is no possibility of simulating near-surge working regime without mass flow rate definition as a boundary condition. However, it is achievable to determine a throttle characteristic, which can be used as a function defining the outlet pressure and indirectly the mass flow rate. In case of transient simulations, it would allow to analyse both steady and unsteady regimes of the flow in a centrifugal compressor.

Jet impingement still is one of demanding cases regarding computational fluid dynamics, due to its highly turbulent behaviour, with occurrence of turbulent-laminar transition. Even recently developed methods exhibit some drawbacks – RANS based simulations lack accuracy, LES and DNS based ones require too much computational time. Hybrid methods also exist, but their development and validation is in progress. Nevertheless, CFD application can play major role in the investigation of jet impingement phenomena. While the flat surface impingement is widely discussed in the literature, there is lack of data regarding non-flat surfaces – the ones that might exist for example in the heat exchangers. In the following paper, the numerical simulation of both flat and non-flat surfaces single jet impingement is presented, with the aim of precise description of the turbulence models impact on the thermal and hydrodynamic results. Choice of turbulence model is crucial for sufficient calculation outcome. Only the complex analyses, shown in the article, including the turbulence and momentum budgets comparison between particular models, can reveal significant and meaningful differences.

The paper presents a system created for measuring wind speed and its direction in full-scale conditions. The system consists of devices used to measure environmental parameters in one point at a time and a complex weather station. On the basis of the results obtained from the first part of the system, the static effect of wind action on structures or climatic comfort can be approximated, while the second part of the system is used to determine the dynamic wind action on objects. The use of the designed system is illustrated by in-situ studies.

Cavitation is a phenomenon that is difficult to observe, as well as to analyse. Many methods are being applied in order to study cavitation – high-speed photography is one of them. Analysis of images that were obtained in this way gives the possibility of superficial assessment of the phenomenon, but the use of digital image analysis allows obtaining more information on the studied series of images. In the paper, we propose two methods intended for such analysis - they are destined specifically for obtaining variability maps of cavitating flow based on series of high-speed photography. The work is based on the analysis of three different cavitating flows induced in convergent-divergent nozzles. Obtained results show that described methods can be helpful in analysis of cavitation - variability maps can be used for example as reference images for validation of results of numerical simulations of cavitating flow, which is not possible in case of a direct use of high-speed photographs.

The purpose of the work is to investigate two numerical models of gas flow in a random packed bed of Raschig rings – one based on direct numerical simulation of flow at the level of individual particles and the other simplified approach in which the bed is treated as a homogeneous domain with prescribed pressure drop calculated from Darcy law. The latter model is usually preferred when only average flow characteristics are important in a given application and is expected to provide reasonably accurate results at the macroscopic level. The results show that when the flow enters the bed in a highly non-uniform manner (here – as a jet), the simplified model is not able to reproduce velocity field even averaged over regions of a considerable size. However, the axial average pressure profile is predicted with a good accuracy.

The article presents experimental investigations of the pressure drop during two-phase flow. Experiments were performed for both adiabatic and heated flow of R134a. Obtained flow patterns were compared with the literature. Obtained data is used to validate momentum pressure drop predictions, a set of graphs showing comparisons, for a representative set of experimental conditions, of the two-phase frictional pressure gradients for the adiabatic and diabatic flow. The model proposed in the article allows to predict both values and peak pressure drop with very good accuracy. Verification of the momentum pressure drop predictions for two-phase adiabatic flow showed that all correlations have good agreement with experimental data.

Currently, a grooving body of research devoted to the potential use of acoustic waves in suppression of different flame types can be observed. However, all works related to this issue focus on flame quenching in open environment or inside resonator tube. When concerning the use of acoustic waves in a fire/flame extinction, one may expect that the closest environment of a flame would not be free of obstacles. Thus, the present work investigates experimentally how the acoustic screen – being the simplest model of a single obstacle affects the quenching process. To do so, the sound levels required to extinguish a gas burner flame were determined for both different distances between an acoustic screen and a waveguide outlet and different fuel loads. It was found that when decreasing distance between the acoustic screen and the waveguide outlet a higher sound levels are required to suppress the flame – what is quite surprising as the sound level alone also increases when the screen approaches the waveguide outlet. The physical interpretation of this feature formulated based on the present and earlier researches is also included in the present paper.

Smoothed Particle Hydrodynamics (SPH) is a meshless CFD method, remaining a promising alternative for multiphase flow calculations due to straightforward interface treatment. In the present work we particularly focus on the accurate modelling of wetting phenomena and contact angles. For that purpose we modify the surface tension model in the neighbourhood of the triple line. The necessity of proper boundary conditions in SPH is discussed along the preliminary validation of proposed approach. Results show a great potential of the chosen method.

Interaction of a combustor and turbine in aircraft engines generates still a lot of open questions. Investigation of combustor and turbine separately have been done for a years by research institutes and aircraft engine companies, but there is lack of knowledge about the interaction effect. In the paper, numerical simulations results for combustor simulator and nozzle guide vane (NGV) of the first turbine stage are presented. No combustion is modelled, but the hot flow at the swirler inlet is applied. Geometry and flow conditions are defined according to the turbine stage designed for experimental investigations in FACTOR (Full Aerothermal Combustor-Turbine Interactions Research) project within a framework of European Commission 7^th Framework Programme. The main objective of the presented investigations is an analysis of the location of the high temperature zone upstream of the nozzle guide vane and its effect on the wall temperature. Numerical simulations are carried out by means of Fine/Turbo Numeca with two turbulence models: Spalart-Allmaras and Explicit Algebraic Reynolds Stress Model. As a model validation, a comparison of total pressure, total temperature and flow angles downstream of combustor simulator with experimental data from University of Florence is also presented.

The motivation of the presented study is supporting new ideas about principle of flight by Hoffman and Johnson, see [1]. The new hypothesis of physical mechanism of flight relies on existence of streamwise vortical structures on the suction side of the airfoil and within its wake. The vortices origin is supposed to be the instability of the boundary layer subjected to adverse pressure gradient. The vortices are of highly dynamical nature, changing theirs position, size and other parameters in time very rapidly. For this experiment the simplest airfoil possible was chosen represented by a flat plate in uniform flow and moderate angle of attack. In the suggested paper detailed measurement of the zone of interest will be carried out using stereo PIV method. System of measuring planes perpendicular to the flow will be explored. POD analysis is to be utilized.

In this article a fully three dimensional, multiphase, meso-scale Solid Oxide Fuel Cell (SOFC) anode transport phenomena model is described. The Butler-Volmer model is combined with empirical relations for conductivity and diffusivity - notably the Fuller-Shetler-Giddings equation - for transport of gas reagents. Numerical simulation is used to obtain partial pressure and electric potential fields for each phase, accounting for activation and concentration overpotential as well as ohmic losses. Mesh generator and a solver have been developed to provide an in-house code for the computations. The findings are presented alongside a parametric study of a specific YSZ electrolyte-based SOFC anode microstructure. Despite high dependence of SOFC anode performance on the geometry of its anisotropic, three-phase microstructure, meso-scale numerical models simulating transport phenomena within these electrodes are not very common.

Development of existing and innovative aerodynamic models for the Darrieus wind turbine has become very popular in recent years. Since research in the field of aerodynamics of the Darrieus concept is very limited, the development of simplified aerodynamic methods is very difficult. Therefore, the major objective of the present study is to present the concept of a new aerodynamic model for the Darrieus wind turbine – the actuator cell model (ACM). Aerodynamic loads are added to the unsteady incompressible Navier-Stokes equations as momentum source terms. The source terms are computed basing on instantaneous aerodynamic forces taken from the literature. The numerical results of wake structure computed by ACM are compared with the experimental data. Agreement between the numerical results of velocity profiles and the experimental data is reasonably good.

Tesla turbine is a bladeless turbine and its principle of operation is based on shear stress arising from fluid viscosity and turbulence. A prototype of Tesla turbine is an object of numerical and experimental investigations presented in the paper. Experimental investigations were carried out for different inlet pressures and compared to results from numerical investigations. The roughness of the disc surface was measured and taken into account in the numerical analysis. Numerical investigations were performed in CFX 17.1 commercial software for steady state and transient. Comparison of power and efficiency vs rotational velocity characteristics shows relatively good agreement between experiment and CFD.

Flow visualization techniques have progressed from methods based on qualitative description of flow-field into techniques providing both qualitative and quantitative results. In this paper we present implementation of Background Oriented Schlieren (BOS) technique for measurements of density values at transonic speeds. The density values obtained by BOS were then compared with results from CFD analysis of the same flow characteristics. In both qualitative and quantitative terms, the BOS and CFD results agreed, which proves the applicability of BOS for transonic flows.

The paper presents hybrid MPI+OpenMP (message Passing Interface/Open Multi-Processor) used for paralleled programs including high-order compact method. The main tools used to implement parallelism in computations are OpenMP and MPI which differ in terms of memory they are based on. OpenMP works on shared-memory and MPI on distributed-memory whereas hybrid model is based on combination of those methods. Tests performed and described in this paper present significant advantages provided by hybrid MPI/OpenMP. Testing computations needed for verifying possibilities of MPI, Open-MP and Hybrid of both are carried out using an academic high-order SAILOR solver. Obtained results seem to be very promising to accelerate simulations for fluid flows as well as for application using high order methods. The proposed approach was tested up to 96 cores with up to 4 nodes.

This paper presents a Computational Fluid Dynamics (CFD) study of droplet spray dispersal in the wake of a Mi-2 helicopter up to 600 m downstream. The Reynolds-averaged Navier-Stokes (RANS) equation use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described have the potential to improve current models for aerial spraying and help in the development of new spraying procedure. In this study, models are developed for the sprays released from atomizers mounted on a helicopter. A parametric study of the aircraft model examines the effects of crosswinds on the helicopter's vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of our results with those obtained with AGricultural DISPersal (AGDISP) is also presented.

The paper deals with the numerical analysis of a helicopter rotor in hover conditions, including aeroelastic effects. In existing literature the effects of an aircraft structural deformation on airloads distribution and performance are fairly well described but mainly for airplanes. The purpose of the presented work is to indicate the possible influence of blades elasticity on helicopter rotor loads and performance in hover. Additionally, it aims to validate a new computational method based on a set of experimental results for a UH-60A helicopter rotor. The method used combines a high fidelity Navier-Stokes aerodynamic model coupled with a low-order beam structural model. This approach made it possible to take into consideration blade deformations in simulations and revealed the high influence of aeroelastic effects on rotor loads and performance at hover conditions. To authenticate the results, the presented method was validated with experimental data from two different flight test programs, three small-scale wind tunnel tests and one full-scale wind tunnel test. They were conducted for the UH-60A helicopter rotor by different organizations. The comparison of results revealed that the created computational method has high accuracy.

An influence of the aspect ratio on the Savonius rotor performance was investigated. Three-dimensional 3D numerical models of the classical Savonius rotor equipped in two semicircular buckets with an overlap gap and endplates were studied for different aspect ratios. The simulation results were verified against the experimental data and a blockage effect was taken into account. An increase in the power coefficient and the tip speed ratio for the maximal power coefficient with a growth in the rotor aspect ratio was observed. An effect of the wind displacement beyond the rotor was more intensive for lower aspect ratios.

The conducted research, though still at the preliminary stage, is a step toward a better understanding of the flow phenomena accompanying hot-wire probes. For the flow in the vicinity of a wall, a potentially non-optimal case was analyzed – a single normal hot-wire probe oriented normally to the surface. According to the results, undisturbed flow, as measured in the absence of a hot-wire probe, was significantly altered in its presence. Differences in the vertical profiles of the velocity magnitude in the upstream direction of up to 40% were observed 0.43 mm from the probe's longitudinal axis of symmetry, and up to 8% at a distance of 3.73 mm. The lower Reynolds numbers were considered the more complex velocity profile perturbations were present. The highest differences in undisturbed vs. disturbed flow were observed at the level of the wire and below, regardless of the distance from the hot-wire probe.

Computational domain discretization is the pre-processing stage in CFD analysis and it highly contributes to reducing the level of solution error as well as increasing the numerical stability of a model. The discretization of domain representing a packed bed of granular material is a demanding task due to the topology of the model consisting of spherical granules contacting tangentially and narrow regions in the direct vicinity of the contact point. Therefore the aim of the carried out research is to define guidelines to effectively discretize the computational domain representing the packed bed of granular material and validate it using Particle Image Velocimetry (PIV). Two methods of contact point representation between granules (contact point extension, granule radius reduction) and two mesh types (tetrahedral, polyhedral) are examined within the paper. Differences between the analyzed cases are discussed and compared to experimental research results. The obtained results prove that the applied method significantly affects the calculated porosity but does not affect the flow field considerably. Polyhedral mesh turned out to be preferable as the numerical model converges within substantially lower number of iterations and the obtained results are not as affected by the numerical diffusion as in the case of tetrahedral mesh.

The adsorption technology applied to cooling production is one of the possible means of waste heat utilization and it therefore contributes to a reduction of power consumption in air-conditioning and desalination facilities. Increasing the performance of the adsorption chiller can be achieved by the intensification of heat transfer in the sorption bed which in turn is directly influenced by heat exchanger geometry. The carried out research utilized numerical methods to define the correlation between the fin-tube heat exchanger design and the main factors influencing adsorption chiller performance such as gradient of heating water temperature, logarithmic mean temperature difference, effective mass factor of silica gel, silica gel average temperature and spatial temperature distribution in the sorption bed. The obtained correlations can be used by sorption bed designers to balance the thermal effectiveness of the device and its overall dimensions and mass.

In this paper, the numerical modelling of acetone utilization in the thermocatalytic reactor based on the intermetallic phase of Ni₃Al has been presented. The experimental results of mixtures containing air contaminated with acetone in a thermocatalytic reactor were used for the preliminary calibration of the Computational Fluid Dynamics "CFD" calculations. The thermocatalytic combustion reaction of acetone has been modelled by employing experimental data related to the active surface area. For more accurate application of current model into the gas turbine regime simulation was performed on three different geometrical cases. Effects regarding flows in microchannel are visible especially when "small" geometry is concerned. One should notice that a decrease of acetone concentration at inlet into package, mainly, two millimetres before the thermocatalytic area, is connected with the diffusion fluxes of the other components, mainly water and carbon dioxide. The commercial CFD code has been expanded by User Defined Functions "UDF's" to include surface chemical reaction rates on the interphase between fluid and solid. Results obtained through numerical calculations were calibrated and compared with experimental data to receive satisfactory agreement.

In the current work the jet spray combustion reflecting an experimental piloted spray burner is simulated numerically. In the simulations the diluted ethanol spray evaporates in the hot surrounding, the gaseous fuel diffuses from spray fuel-rich core into the oxidizer fuel-lean region and autoignites. An in-house high-order compact difference LES solver is used to carry out the computations. The reaction rates are modelled using Implicit LES approach based on the single-step global reaction. The continuous phase is modelled in the Eulerian reference frame while the droplets in the Lagrangian form. The studies are focused on the influence of the co-flow temperature and spray initial Sauter mean diameter (SMD) on the flame lift-off height, autoignition delay and the reaction zone features. The results are compared with the experimental data and show good agreement in terms of lift-off height. It is almost linearly related to the co-flow temperatures. It is found that for the same fuel mass loading, droplets with smaller SMDs significantly shorten the autoignition delay. Moreover the autoignition delay and the lift-off heights are influenced mostly by the droplets SMD rather than by the co-flow temperature.

Lattice Boltzmann Method is applied to forced and natural convection heat transfer from the tube banks. Hot tubes are cooled by flowing or passive air. Two Reynolds numbers (Re = 80 and Re = 1600) and two Rayleigh numbers (Ra = 10³ and Ra = 10⁵) of the corresponding heat transfer regime are studied. The method itself is based on the recently derived cascaded collision operator not only for the fluid flow but also for the temperature field. Using this method and moderate space resolution of the lattice we were able to obtain stable and bounded simulations for the non-trivial geometry.

The integral formulation of Ffowcs Williams and Hawkings (FW-H) analogy developed by Farassat is implemented to understand the sound generation and propagation of a rotating slender body like the helicopter rotor blade in hover. Using the linear acoustic theory, the thickness and loading noise terms are implemented in a flexible, new, in-house aero-acoustic tool. The pressure distribution on the blade surface is obtained from CFD simulation which sufficiently captures the correct flow characteristics of the rotor blade. Although, there is an improved estimation of the acoustic pressure signal in comparison to existing numerical noise signal results, there is still an under prediction of the peak amplitude compared to experimental values. The code is validated against the experiment for the UH-1H model helicopter rotor equipped with two rectangular blades having NACA0012 section.

The article explains a new concept (called here ATNC – active thickness noise control) of the application of surface transpiration to the reduction of helicopter main rotor harmonic noise. The ATNC method is based on an introduction of four cavities covered by perforated plates (connected to pressure reservoirs) at the leading and trailing edges of the outer 20% of blade span. For an exemplary, two-bladed (NACA 0012 airfoil) model helicopter rotor of Purcell in low-lifting, hover conditions (tip Mach number M_aT = 0.66 and collective θ = 1.5° ) the results of numerical simulations, based on the SPARC code (Spalart-Allmaras turbulence and Bohning-Doerffer transpiration models), prove that the acoustic pressure fluctuations are significantly reduced by ATNC in the near-field of blade tip. The peak amplitude is attenuated by more than 45%, with a reduction of the Overall Sound Pressure Level OASPL by 3.4 dB. It is shown also that the venting has not only a large impact on the acoustic radiation, but also on the aerodynamic performance of the rotor, expressed in terms of the torque penalty of 38%. The ATNC method proves to be a promising candidate as a mean of helicopter rotor thickness noise control, but not in the current arrangement.

The paper is devoted to experimental and CFD (Computational Fluid Dynamics) studies of heat and mass transfer processes in granular material layers. The 3D numerical model is based on a high-order computational code combined with the immersed boundary method (IB) for modelling the flow and temperature distributions in geometrically complex systems. The temperature measurements are performed using thermocouples placed inside the layers closed in a climatic chamber. Besides providing data for validation of the numerical results one of the key tasks of the experiment was to examine an impact of an external temperature changes on the temperature distribution in the interior of the layers depending on their structures and physical properties. The obtained results reveal very complex flow and heat transfer inside the layers. It is shown that the temperature inside the layers can be effectively changed and controlled by the parameters of air flowing through them.

This paper presents results of discrete-continuous optimisation of an axial flow blood pump. Evolution Strategies (ES) are used as a global optimisation method in order to localise the optimal solution in relatively short time. The whole optimisation process is fully automated. This also applies to geometry modelling. Numerical simulations of the flow inside the pump is performed by means of the Reynolds-Average Navier-Stokes approach. All equations are discretised by means of the finite volume method and the corresponding algebraic equation systems are solved by the open source software for CFD, namely OpenFOAM. Finally, optimisations results are presented and discussed. The objective function to be maximised is simply pressure increase. The higher pressure increase the lower angular velocities required. This makes it possible to minimise the effect of haemolysis because it is mainly caused by high shear stress which are related, among others, to angular velocities.

Experimental analysis of combustion in CI engines is difficult due to the very short duration of this process and the unfavourable thermodynamic conditions prevailing in the combustion chamber (high pressure and temperature). An alternative is to perform numerical calculations using the CFD method based on a defined combustion model. Such an approach was used in this paper to investigate the influence of different fuel injection configurations and different swirl ratio on selected parameters of the combustion process in the designed two -stroke opposed piston engine. The combustion chamber of the tested engine was formed of two movable surfaces of pistons. The AVL Fire software was used to perform the simulation. As a result of the calculations, the dependence of rate of heat release, burnt mass fraction, mean pressure in cylinder and heat transfer coefficient on defined calculation cases was obtained. In addition, a spatial distribution of the combustion stream of injected fuel was obtained. On the basis of the results obtained, conclusions regarding the impact of the fuel injection configuration and the swirl ratio on the obtained engine performance were presented.

The equation of continuity describing the two-phase bubble flow was modified to take into account the influence of the viscoelasticity of the pipe walls. The modified equation of continuity together with the equation of motion was solved using the method of characteristics. Simulations carried out using in-house written program in Matlab indicate a high correspondence between simulated and experimental runs. The modified Shu model is characterized by simple construction, thanks to which it is easy to quickly implement this solution in commercial computer programs used to model transient states in pipes. It takes into account three basic phenomena accompanying these flows, namely: frequency-dependent hydraulic resistance, cavitation and viscoelastic effect off the pipe wall. Further work on its extension is underway.

The presented study is focused on experimental investigation of a boundary layer on a flat plate in adverse pressure gradient. The flat plate is placed in regular flow, the pressure gradient is generated by the plate inclination. The study [9] deals with structure of the wake behind the plate, the presented study concentrates on structure of the flow close to the suction surface of the plate. Dynamical behaviour of the flow structures is studied in details with respect to the streamwise topology changes. In spite of the fact that the time-mean flow field is 2D, constant along the span, the instantaneous structures topology is fully 3D.

A fundamentally new idea in grid generated turbulence is the 3D Sparse Grid (3DS) concept [N. A. Malik. Sparse 3D Multi-Scale Grid Turbulence Generator. US Patent No. US 9,599,269 B2 (2017)] which reduces the effective blockage ratio compared to the 2D flat fractal grids, σ_3DS ≪ σ_2DF, and possess a much greater parameter space which could allow further optimization of the turbulence as compared to the 2D fractal (2DF) grids. Here, we report on some theoretical results regarding blockage ratio reduction in a 3-frame 3DS system, and some results from Direct Numerical Simulations comparing the turbulence characteristics generated by 3DS with Regular (RG) and 2DF grids cases.

In this paper, the numerical modelling of hydrogen production by methanol decomposition in the thermocatalytic reactor based on the intermetallic phase of M3A has been presented. The experimental results of flowing mixtures containing helium and methanol in a thermocatalytic reactor incorporating microchannels were used for the preliminary calibration of the Computational Fluid Dynamics "CFD" calculations. The thermocatalytic decomposition reaction of methanol has been modelled by employing experimental data related to the active surface area. It should be understood that a decrease of methanol concentration at inlet into package, mainly, ten millimetres before the thermocatalytic area, is connected with the diffusion fluxes of the other components, mainly hydrogen and carbon monoxide. The commercial CFD code has been expanded by User Defined Functions "UDFs" to include surface chemical reaction rates on the interphase between fluid and solid. The data extrapolated via the implemented numerical model have made it possible to assess the minimal length of the micro-reactor channels which predicts an optimal dimension at the system outlet. Results obtained through numerical calculations were calibrated and compared with experimental data to receive satisfactory agreement.

We apply statistical mechanics and Madelung hydrodynamical presentation for an effective description of strongly-interacting many-body systems, such as Bose liquids or Korteweg-type fluids. The logarithmic nonlinearity is shown to appear in equations describing such fluids. The resulting equations describe the irrotational and isothermal flow of a two-phase barotropic compressible inviscid fluid with internal capillarity and surface tension. We demonstrate spontaneous symmetry breaking in this class of fluids, which leads to a number of wave-mechanical and topological effects. We show the relationship between the "logarithmic" fluids and those described by polynomially nonlinear wave equations, such as the Gross-Pitaevskii one.