Table of contents

This volume of the Journal of Physics: Conference Series contains proceedings of the jubilee XXV Fluid Mechanics Conference (FMC2022) https://www.fmc2022.prz.edu.pl/, which was organized by the Rzeszow University of Technology (Poland) under the auspices of the Polish Academy of Sciences, Committee of Mechanics. All submitted papers in this volume have been reviewed and approved by anonymous reviewers, eminent specialists in fluid mechanics, whose names are listed later in the Preface.

This Conference, hold in Rzeszow, was the twenty-fifth in the series started forty-eight years ago (1974) in Jaszowiec, Poland. Meetings, the idea of which is to create a forum for discussing the latest results and experiences in the field of fluid mechanics, are held in Poland and are organized every two years by a Polish university under the auspices of the Polish Academy of Sciences, Committee of Mechanics.

List of Acknowledgments, FMC 2022 International Scientific Committee are available in this pdf.

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

• Type of peer review: Double Anonymous

• Conference submission management system: Morressier

• Number of submissions received: 52

• Number of submissions sent for review: 48

• Number of submissions accepted: 32

• Acceptance Rate (Submissions Accepted / Submissions Received × 100): 61.5

• Average number of reviews per paper: 2.03

• Total number of reviewers involved: 28

• Contact person for queries:

Name: Prof. Anna Kucaba-Pietal

Email: anpietal@prz.edu.pl

Affiliation: Rzeszow University of Technology, Poland

The paper presents the results of wind tunnel tests aimed at determining the model bottom drag in the case of rocket model tests. The balance measurement technique of the rocket model fixed in the wind tunnel test section by the rear sting was discussed. The model was equipped with the two parallel boosters. Based on the wind tunnel test of the rocket twin model the values of the bottom pressure was determined for tested Mach numbers. An algorithm of wind tunnel corrections was shown, which allowed the total drag determination in a case of the rocket active or passive rocket flight. The test results showed the necessity of the bottom drag measurements in wind tunnel tests.

The paper explains further developments of a new concept called TNC (Thickness Noise Control) of the application of surface ventilation to the reduction of helicopter rotor low-frequency in-plane harmonic (LF-IPH) noise. The TNC method is based on introduction of four cavities covered by perforated plates (connected to low and high pressure reservoirs) and positioned symmetrically at the front and rear extremities of the blade tip. Two operational modes are analyzed: constant (steady) and periodically varying (unsteady) transpiration mass-fluxes. For exemplary two-bladed model helicopter rotor of Boxwell et al. (Bell UH-1H Iroquois helicopter) in hover conditions, the results of numerical simulations, based on the CFD code SPARC (Spalart-Allmaras turbulence and Bohning-Doerffer transpiration models), suggest that the acoustic pressure fluctuations are significantly reduced in the near-field of the blade tip. Moreover, the unsteady approach (designed for forward located observers) is almost equally efficient to the basic (steady) operation mode, while substantially lowering penalties in terms of the aerodynamic performance and required transpiration flow intensity. Finally, it is proven that when TNC is activated, the twisted blade (operating in low-thrust conditions) exhibits lower deterioration of the aerodynamic performance compared to its straight (untwisted) counterpart.

Improving machines efficiency and searching for their new applications are the main topics in the development of the renewable energy industry. In the case of Savonius type wind turbines, the works aim at the improvement of aerodynamic performance. The CFD simulations of a turbine equipped with deformable blades showed a significant positive impact of this enhancement on the machine aerodynamic efficiency. Previously, the investigation was carried out for a TSR (Tip Speed Ratio) equal to 0.8, typically recognized as the point of maximal efficiency for conventional Savonius wind turbines with rigid blades. However, the continuously altering shape of blades during their rotation can influence the optimal TSR. Therefore, the efficiency of the deformable blade turbine was investigated in a wide range of TSR. In this paper, the previously developed quasi-2D model with a two-way Fluid-Structure Interaction method was employed to obtain turbine efficiency characteristics as a function of TSR. The maximum power coefficient Cp was achieved at TSR = 0.9. Obtained characteristic was compared with data for a conventional rigid blades turbine, gathered with a comparable sliding mesh model.

This paper aims to present a numerical investigation of the two-phase flow in unbaffled uncovered stirred tanks equipped with a Rushton turbine. The shaft is positioned eccentrically. As simulation software, the Simcenter Star CCM+ 2021.2 is used to carry out multiphase unsteady simulations. Next, the numerical results are compared with results obtained on a test bench.

Despite the wide possibilities of using a cycloidal rotor in the form of propulsion systems for unmanned aerial vehicles (UAV), cycloidal propellers for sea-going ships, rotors of wind turbines or sea or river cycloidal energy converters, there is practically no research on the use of this solution in the form of a cycloidal rotor fan (CRF) for HVAC (heat, ventilation & air conditioning) applications. The main features of such a machine, compared to conventional solutions, is a possibility of changing the flow direction only by changing pitch angles of the rotor blades. This study analysed two variants of the fan, first equipped with an asymmetrical CLARK Y profile, and other with a symmetrical NACA0012. Numerical simulation of cycloidal rotor fan developed in Ansys CFX was presented, that enables the simulation of fan operation. The results obtained from CFD for both variants were compared with those obtained during experimental measurements made with the use of Laser Doppler Anemometry (LDA). The comparison showed good agreement between the numerical analysis and the performed experiment. Despite the operation based on the same cycloidal regulation settings and rotation speed, the fan equipped with symmetrical blades slightly more curved the flow angle than the asymmetrical one.

Immersed boundary method is used for simulation of fluid flow through random packed beds of various particles (cylinders and rings) obtained in a separate numerical simulation of the packing process. Due to complexities of the random packing structure the flow velocity is also highly complex despite the laminar regime. The statistical characteristics of the flow field are examined in detail and compared between various packings - not only probability distribution of flow velocity but also novel statistical measures that provide useful information about the flow applicable to simplified models of flow in similar structures. The measures are based on the statistics of the flow deflection angle i.e. the angle between the local flow velocity vector and the inlet velocity direction. The proposed two-dimensional map allows for assessment of the probability distribution of the flow deflection angle for different values of the velocity magnitude.

This paper presents the high-order Penalized Vortex in Cell method applied to flow past an airfoil with a cavity and a T-106A turbine cascade. The first part of the paper treats about the parallel environment and algorithm performance where times for each operation are measured. Then further validation on the flow past cylinder at Re=9500 was shown, and flow past an airfoil simulation results were extended. For unbounded flow with stream-function correction based on Biot-Savart law, velocity profiles at the boundary were shown. A volumetric imbalance was determined. In the second part, formulation of pVIC method for periodic flows was discussed, and an example of calculation with a turbine cascade with a moving bar wake generator was demonstrated.

The Smoothed Particle Hydrodynamics (SPH) method in the so-called weakly compressible variant (which mimics the incompressibility conditions) is studied in the context of its resolving power of vortical flows. It is well known that the conservative formulations of SPH have serious problems to provide reasonably accurate solutions even in simple flow cases. This deficiency is additionally emphasized by the fact that conservative SPH formulations are not numerically convergent. We investigate and discuss chosen techniques to improve the results; yet, the convergence issue remains. Maintaining the conservative properties (often presented in the literature as the SPH biggest advantage) requires procedures which are in contradiction with the accuracy improvements. Some myths about SPH are discussed and denied.

The purpose of this paper is to discuss the loss of voltage in a Solid Oxide Fuel Cell (SOFC) as a result of the irreversible diffusive transport of gases through the microscopic pores of its fuel electrode. The voltage loss is estimated by solving the diffusive-convective equations, and current conduction equations in a computational domain based on data from Focused Ion Beam Scanning Electron Microscopy. The simulation includes both the binary diffusion and the free-molecular diffusion phenomena by employing Cylindrical Pore Interpolation Model. Butler-Volmer model is used to compute the reaction rate. Ion and electron current conduction is based on empirical relationships reported in the literature. The total losses are decomposed to identify the contribution of the mass transport irreversibilities. The parametric study results form a concave surface, showing non-linear relationship between electrode thickness, and diffusion-related voltage losses. The optimal active layer thickness is estimated.

The aim of the work was to create a CFD model of the flow generated around the drone to estimate the impact of field parameters on the results of actual measurements from PM sensors that are positioned differently in relation to the propellers. The model created with the use of the ANSYS Fluent software allowed one to determine the criterion of their sufficient distance. The robots with four, six and eight rotors were analyzed. For these, the turbulence intensity, velocity and pressure distributions were determined. The paper also presents the results of PM measurements carried out under field conditions using two sensors mounted on the hexacopter robot.

Passive control of turbulent boundary layer (TBL) separation in a channel with adverse pressure gradient (APG) condition towards the outlet is investigated using Reynolds-averaged Navier-Stokes (RANS) methods and Large Eddy simulations (LES) with the help of commercial ANSYS software. Isothermal and incompressible flow in the near-wall area of the flat plate as well as various configurations of wavy wall is studied. It is shown that the amplitude and period of the waviness significantly influence the near wall region and point of separation.

Many issues related to mass and heat transfer through beds of granular materials are still not fully understood. In this work, non-isothermal turbulent flow is analysed within granular layers of spherical and non-spherical elements. We apply a volume penalization (VP) approach formulated in the framework of an immersed boundary technique (IB) on Cartesian computational meshes. It allows modelling flows around solid objects with almost arbitrarily complex shapes and in any form of contact. The validation of the solution accuracy is performed against ANSYS Fluent simulations using body-fitted meshes and experimental literature data. It shows the capability of the IB-VP approach for the simulations of flows in complex geometries. The main research focuses on the comparison of the influence of various types of particles and their temperature on vorticity, turbulence level and pressure drop inside and behind the granular bed. In particular, we analyse how the shape of the solid particles affects the efficiency of heat transfer in different flow conditions. The obtained results reveal the occurrence of very complex flow structures (recirculation and stagnation regions) inside beds. Comparison of results also point out preferred configurations of the beds.

The major goal of this study is comparing the results of heterogeneous and homogeneous condensation through a CD nozzle. The experimental technique for liquid phase assessment in wet steam transonic flow is tested under real conditions in an in-house steam tunnel test rig. The flow was modelled numerically using an in-house CFD code for performing the heterogeneous and homogeneous condensation models. For the comparison between CFD results and experimental data, the static pressure distribution throughout the nozzle bottom wall were chosen. One may observe a good agreement of the CFD results with experimental data. The presented approach can be used in the future for searching the reasons for the lack of accuracy between experimental and numerical static pressure distribution in the condensing steam flows.

The paper focuses on the development of an approximate deconvolution method (ADM) for large eddy simulation (LES) of turbulent reactive flow. We derive the effective filter as a product of the LES filter and the filter induced by spatial discretization performed using high-order compact difference schemes. We analyze the accuracy of the ADM depending on the effective filter definition in the case of modelling unsteady combustion phenomena (ignition and flame extinction) in a forced homogeneous isotropic turbulent field

This work presents an overview of issues for the modeling of laminar flows in monolith catalysts. Both 0-D and 3-D models are evaluated for a parallel channel structured honeycomb catalyst (PC-HC), and a gyroid 3-D printed structured catalyst (G-3D). At the 0-D homogeneous reactor modeling level, the analysis is focused on the effect of the bulk porosity, as well as the model choice to represent Nusselt number effects. Results show the better suitability of a long tube Nusselt number model for the representation of the maximum temperature achievable in the 0-D homogeneous reactor, as well as a modest effect of the porosity on the catalyst CO₂ conversion. A more detailed insight on heat transfer and the core reaction zone inside the monolith can be obtained at the 3-D homogeneous reactor modeling level.

In this paper, various bluff-body shapes (cylindrical, square, star) and two different surface topologies (smooth, wavy) are applied as passive tools for controlling a non-premixed hydrogen flame in a combustion chamber. We focus on the dynamics of the flame and its time-averaged characteristics in the close vicinity of an injection system within formed recirculation zones and also in a far-field. The research is performed with the help of large-eddy simulations (LES) method using the ANSYS Fluent software and a high-order academic code SAILOR. Flame behaviour is found to be strongly dependent on the geometry of the bluff-body whereas its wall topology affects the flame characteristics only slightly. In the cases with the square and star bluff-body, small vortical structures originating at the corners deform large vortical structures created by the Kelvin-Helmholtz instability mechanism. This intensifies the mixing and combustion process and, in the configuration with the square shape bluff-body, translates to the shortening of the recirculation zone by 15% of the equivalent bluff-body diameter and the flame, which in the axis develops closer to the bluff-body. The star shape leads to the most uniform flame at the radial border or the recirculation zone.

The wake past a smooth cylinder perpendicular to the flow is studied 15D (cylinder diameters) downstream by using particle image velocimetry (PIV). Spatial shedding period is used to estimate the spatial Strouhal number (Sh) and to compare with time-resolved hot-wire anemometer (HWA). The vortices are detected within the spatial fluctuation field. The statistical vortex properties do not change within the explored range of Reynolds numbers (from 5 000 to 60 000), similarly the spectra and Sh.

Experimental results on laminar-to-turbulent transition in a separated laminar boundary layer formed over a flat plate in an adverse pressure gradient are provided. Experiments have been performed for a range of Reynolds numbers (1.4 − 2.4 · 10⁵) and for two freestream turbulence levels (Tu =3.6 and 5.3%). The measurements of mean and fluctuating velocity profiles have been carried out at inlet to the test section using Constant Temperature Anemometry (CTA). The data might be useful for validation and development of transition models. In order to characterize the dynamics leading to the transition process in the separated boundary layer on the plate surface, the Particle Image Velocimetry (PIV) measurements have been performed. The results show that the transition process in the separated boundary layer is influenced by breakdown of the Klebanoff streaks.

Presented work is focused on analysis of the flow over the 2D model of Airbus A320 airfoil wing in cruise phase of the flight. For this purpose the measurement channel with an airfoil model was designed and assembled in a transonic wind tunnel to obtain a similar flow pattern as in the reference two-dimensional freestream flow. Experimental investigations were conducted in the IMP PAN transonic wind tunnel with a relative narrow test section which is a novel approach in terms of these type of research. The test section was designed using CFD simulations based on 2D freestream flow for the tested wing profile and in the next step the research were continued experimentally in transonic wind tunnel with a measurement chamber width of 100 mm. This paper presents the results of reference investigations on the A320 wing profile which combines experimental tests and CFD calculations. The obtained results show that the approach presented in the paper is appropriate and the obtained flow features in the tunnel do not differ much from the freestream conditions.

The size distributions of raindrops and precipitation particles were measured in a series of in situ experiments during various weather events in Warsaw, Poland. To perform the measurements, a shadowgraph instrument, "VisiSize D30", was set up on the roof of the Institute of Geophysics, University of Warsaw, together with an "OTT Parsivel²" laser disdrometer. The VisiSize D30, recently introduced to atmospheric research, is capable of accurately determining a wide range of particle sizes, from micrometre-scale cloud droplets to millimetre-scale precipitation particles, while directly measuring droplets by capturing shadow images of them. A comparison of the data collected by the two instruments during simultaneous measurements shows that combining the shadowgraph technique with the optical disdrometer can prevent droplet size distribution truncation and provide more accurate results.

The paper examines the effect of acoustic excitation at broadband frequency range (100 - 650 Hz) on separated boundary layer developing on a flat plate subjected to an adverse pressure gradient. The experiment was conducted with a low inlet turbulence intensity level (Tu < 1%) in order to provide a cleaner environment that magnifies the effects of the excitation frequency. It was shown that acoustic excitation at sound pressure levels: SPL=125 and 135 dB, can lead to a more rapid increase in flow instability followed by an earlier laminar-turbulent (l-t) transition. The boundary layer reattachment point was shifted upstream and the size of the separation bubble was reduced in the flow with the acoustic excitation active.

The paper presents an experimental investigation of air flow around bluff bodies in tandem configurations. The first one concerns two square cylinders and in the second one a triangular cylinder was used as an upstream object. Experiment was performed for two different Reynolds number for the fixed distance between bluff bodies. To have an insight into the fluid flow, particle image velocimetry method was used. Particular attention was paid to examine the effect of the upstream cylinder shape on the flow around the downstream body.

The air flow inside a single-stage test turbine is studied experimentally using the Particle Image Velocimetry technique. The measurements were performed at the axial-tangential plane just behind the rotor at the middle blade radius. The large vortical structures are identified in the shear layers between the blade wakes and channel jet. The phase-locked structures topology of random dynamical structures in the flow behind the stage are to be analysed using the Proper Orthogonal Decomposition method.

Deep learning has been widely utilized to accurately estimate the flow state from the sparse sensor measurements. Yet there is still a lack of understanding of the actual dimension of this type of regression problem. In this study, we propose an Autoencoder (AE) based estimation method to tackle the control-oriented, sensor-based flow estimation problem. This method encodes the input information into a few-nodes bottleneck, then decodes the compressed information to the estimated the flow state. This network stands for the least order representation of the input-output relationship. We choose the fluidic pinball as the benchmark problem which contains multiple-input and multiple-output. The rotations of three cylinders in the flow generates rich flow physics. Consequently, strong non-linearity arises between input measurements and output flow state. For fair comparison the Deep Neural Network (DNN) is also employed to highlight the influence of the encoding-decoding process in AE. The results show that when the flow is periodic, the input vector can be effectively encoded into a five-dimensional subspace without a significant loss of estimation accuracy. However, the five-dimensional encoding will eliminate partial information from the input vector when the forced flow becomes chaotic, resulting in a lower estimation accuracy than DNN.

In the current study we assess an impact of passive and active flow control methods applied to the flames emanating from rectangular nozzles. The passive control is realised by varying a jet aspect ratio using differently shaped nozzles, while the active control relies on applying a forcing to the axial component of velocity. The analysis is performed through a series of high fidelity Large Eddy Simulations (LES) using a high order in-house solver. Combustion process is modelled using the detailed chemistry model of a hydrogen oxidation with a corresponding set of species transport equations. It is shown that the passive flow control affects the jet flames significantly only up to a moderate forcing frequency. For a high frequency excitation the effect of the aspect ratio is weak. A combination of both control methods is found as very efficient in altering important practical flame features like a lift-off height and flame shape.

The use of the Laplace transform gives the solution of water hammer equations in the frequency domain. The inverse transform of this solution over the years seemed impossible to derive, due to the significant complexity and the fact that the square root of the Bessel function was embedded in the argument of the resulting hyperbolic functions. In this work, we consider some generalizations that enable the determination of the modified Calogero-Ahmed infinite series. These generalizations will allow us in the near future (using the machine learning and artificial intelligence algorithms) a return to the time domain in a very wide range of the dynamic viscosity function, which plays the most important role in this complex fluid dynamic problem.

In the realm of compressible viscous flow modelling, we briefly revisit the debate on a possible inconsistency of the Navier-Stokes (NS) equations. Then, we recall a recent proposal from the literature, put forward by M. Svärd. One of its features is the mass diffusive term in the continuity equation. The presence of density diffusion in the Svärd model reduces dispersive numerical errors when simple centred 2nd order, numerical diffusion free, spatial schemes are used, as confirmed in the simulations of a doubly-periodic shear layer at Ma = 0.05 and Re = 10⁴. Further reduction of the dispersive errors at the spatial discretisation level is possible by more sophisticated approximation techniques.

This paper presents selected numerical simulations performed using Johnson–Segalman model with specific setting of the convected derivative resulting in shear-thinning behavior of the model. The results are compared with the generalized Oldroyd-B model, which is typically used to simulate shear-thinning viscoelastic flows. Both models are solved using an in-house finite-volume solver on structured grid simulating steady flow in three-dimensional axisymmetric channel with smooth contraction. The results presented here focus on the flow recirculation behind the contraction and the structure of the forces emanating from the viscoelastic stress tensor.

In this work we investigated the impact of filtering and subgrid-scale modeling on particle settling velocity and collision-related statistics in a turbulent flow. To reduce the complexity of this task we first studied the motion of inertial particles in the low-pass filtered homogeneous and isotropic turbulence, which was subsequently enriched with the subgrid-scale velocity components obtained from a frozen high-pass filtered velocity field. Particular emphasis has been put on the radial distribution function and the radial relative velocity of nearly touching particles both in the presence or absence of the gravitational settling. These statistics are the key input parameters to the kinematic collision kernel which is of crucial importance in determining the collision rate of inertial particles in a turbulent flow. Furthermore, kinematic simulations were selected as a means of enhancing the fluid velocity at particle locations. We analyzed a wide range of Stokes numbers, i.e. a measure of particle inertia, and, in contrast to scientific premises found in the literature, we observed no improvement of particle statistics when the low-pass filtered fluid velocity was enriched with both a synthetic or spectrally-filtered small-scale structures. We discuss the shortages of any frozen-velocity-based subgrid-scale model in predicting both single- and two-point particle statistics. We also indicate that in some cases, particularly concerning the collision rate of particles suspended in homogeneous and isotropic turbulence, subgrid-scale contribution in the particle equation of motion can be neglected.

In maritime heavy industry, the moon pool is an opening through the hull of some vessels. We replicate a generic design of the pool with the Lagrangian approach Smoothed Particle Hydrodynamics (SPH) whose mathematical model efficiently simulates the interphasial surface. In this study we present the capability of our in-house SPH code to handle the sloshing in the moon pool. We validate the SPH approach to flows for the sloshing tank benchmark and show the stability of this approach for the non-trivial case of the moon pool.

Condensation has a negative impact on turbomachinery efficiency in many energy processes. This paper compares the expansion of moist air in symmetric and asymmetric nozzles with a low expansion rate. The presented numerical study is supported by analytical and experimental research. The experimental tWesting was carried out using an in-house experimental test rig where two nozzles were examined for moist air with relative humidity of about 25%. The nozzles were tested for a supersonic outlet, as well as for the outlet condition with elevated pressure, which resulted in the occurrence of a normal shock in the test section. The asymmetric nozzle profile is congruent with the symmetric nozzle. However, the nozzle walls are shifted linearly in the flow direction. The Schlieren photography technique and static pressure measurements on the nozzle wall were used for qualitative identification of both condensation and shock waves. The presented numerical modelling was conducted using commercial computational fluid dynamics software extended with an in-house condensation model. The code was validated against in-house experiment as well as against the data available in the literature. The analysis of the flow in the considered two types of nozzles with a very low expansion rate revealed very interesting structures of pressure waves. The impact of the linear shift of the nozzle walls on the condensation process and the interaction of the condensation wave with aerodynamic oblique as well as normal shock waves were investigated.

This work is devoted to the detection of non-equilibrium turbulence states in atmospheric turbulence. The non-equilibrium scaling contradicts the classical Richardson-Kolmogorov cascade picture and many turbulence models do not account for it. The existence of such scaling has been discovered in various laboratory experiments. We show here that non-equilibrium states are also present in the stratocumulus-topped boundary layers, which indicates the presence rapidly changing external conditions.