Wyniki wyszukiwania - BazTech

1

Biomagnetic flow over a flat plate embedded by a magnetic dipole in a porous media

Ferdows Mohammad, Jumana Sadia Anjum

International Journal of Applied Mechanics and Engineering

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2023

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Vol. 28, no. 4

69--78

EN

The present study used a simplified axisymmetric biomagnetic fluid dynamics and porous mediamodel which includes FHD (Ferrohydrodynamics), porosity and inertia effects saturated by magnetic dipole to study the influences of the leading parameters on various flow variables along a flat plate.The governing equations are simplified and solved by finite difference approach. We clarify how the ferromagnetic interaction parameter, B and porosity,ε assumptions contribute in the bio-background of the problem of interest. Moreover, from the results of the flow profiles, accelerating and decelerating phenomena are noticed for B, and ε interaction.

2

The contribution of A.K. Oppenheim to explaning the nature of the initiation of gaseous detonation in tubes

Kuhl Allen L., Hayashi Antoni Koichi, Wolański Piotr

Transactions on Aerospace Research

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2022

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Nr 2 (267)

1--12

EN

This paper analyzes A.K. Oppenheim’s original works on the transition of deflagration to detonation and reviews them from the perspective of new numerical and experimental results recently obtained on such phenomena. Particular attention is focused on processes happening in the boundary layer of the tube walls ahead of the accelerating flame. The results of the theoretical analyses of temperature variations inside developing boundary layer are presented and compared to the temperature variation in a free stream away from the boundary layer. Analyses of temperature increase in such layers clearly indicate that the self-ignition of the mixture happens in the boundary layer ahead of the propagating flame front. New experimental results obtained recently by a research group from the A. V. Luikov Heat and Mass Transfer Institute in Minsk, Belarus, combined with previously conducted theoretical analyses and numerical simulations, show clearly and unambiguously that the origin of the “explosion in the explosion”, postulated by A. K. Oppenheim in 1966, is always responsible for the Deflagration-Detonation Transition (DDT) in gases and is located in the boundary layer ahead of the accelerating flame front.

3

Experimental study on Ahmed’s body drag coefficient

Wysocki Dominik, Szymanek Arkadiusz

Technical Sciences / University of Warmia and Mazury in Olsztyn

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2022

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nr 25(1)

87--105

EN

The work presents an experimental designation of the aerodynamic drag coefficient for two configurations of the Ahmed body model, with slant angle of 25° and with the inactive synthetic jet generator. When analyzing the aerodynamic drag of vehicles, most authors focus on higher Reynolds numbers, describing lower values only by designated trend lines. Which is why the main contribution of this experimental work was to designate the Ahmed’s body drag coefficient for low Reynolds numbers and to verify the obtained results with other authors experiments especially with the trend lines for Reynolds number in the range 0,35x105 – 1,8x105. For data taken from the literature, it can be seen that the value of the drag coefficient for the Ahmed body model decreases when the Reynolds number increases. The results obtained during the experiment show the opposite tendency.

4

Influence of slip parameter, viscous dissipation and Joule heating effect on boundary layer flow and heat transfer over a power-law stretching wedge-shaped surface with the correlation coefficient and multiple regressions

Ali Mohammad, Alim Md. Abdul

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 2

1--21

EN

The influence of slip parameter, viscous dissipation, and Joule heating parameter on MHD boundary layer nanofluid flow over a permeable wedge-shaped surface was analysed. The PDEs and the associated boundary conditions were transformed to a set of non-similar ODEs and the obtained system of equations was solved numerically with the help of the spectral quasi-linearization method (SQLM) by applying suitable software. This method helps to identify the accuracy and convergence of the present problem. The current numerical results were compared with previously published work and are found to be similar. The fluid velocity, fluid temperature, and nanoparticle concentration within the boundary layer region for various values of the parameters such as the slip effect, magnetic strength, Prandtl number, Lewis number, stretching ratio, viscous dissipation, suction, Brownian motion, Joule heating, heat generation, and thermophoresis are studied. It is observed that the Brownian motion, Joule heating, viscous dissipation, and thermophoresis lead to decreases in the heat and mass transfer rate. The skin friction coefficient enhances with slip, magnetic, permeability, and suction parameters, but reduces with the Brownian motion, wedge angle, and stretching ratio parameters whereas there is no effect of mixed convection, thermophoresis, heat generation parameters, the Prandtl and Eckert number.

5

Difference scheme for differential-difference problems with small shifts arising in computational model of neuronal variability

Kodipaka Mamatha, Emineni Siva Prasad, Kolloju Phaneendra

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 1

91--106

EN

The solution of differential-difference equations with small shifts having layer behaviour is the subject of this study. A difference scheme is proposed to solve this equation using a non-uniform grid. With the non-uniform grid, finite - difference estimates are derived for the first and second-order derivatives. Using these approximations, the given equation is discretized. The discretized equation is solved using the tridiagonal system algorithm. Convergence of the scheme is examined. Various numerical simulations are presented to demonstrate the validity of the scheme. In contrast to other techniques, maximum errors in the solution are organized to support the method. The layer behaviour in the solutions of the examples is depicted in graphs.

6

An extended finite difference method for singular perturbation problems on a non-uniform mesh

Swarnakar D., Kumar V. Ganesh, Soujanya G. B. S. L.

International Journal of Applied Mechanics and Engineering

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2022

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Vol. 27, no. 1

203--214

EN

An extended second order finite difference method on a variable mesh is proposed for the solution of a singularly perturbed boundary value problem. A discrete equation is achieved on the non uniform mesh by extending the first and second order derivatives to the higher order finite differences. This equation is solved efficiently using a tridiagonal solver. The proposed method is analysed for convergence, and second order convergence is derived. Model examples are solved by the proposed scheme and compared with available methods in the literature to uphold the method.

7

Pressure distribution on rectangular tall buildings in boundary layer flows

Lipecki Tomasz

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 2

art. no. e83, 1--17

EN

The paper discusses wind tunnel measurements performed on vertically placed rectangular prisms representing medium and high-rise buildings. The results concern mean wind velocity pressure coefficient. The influences of the angle of wind attack, boundary layer and dimensions of models are considered. Two rectangular models of side ratio D/B = 2 (0.5) and two models of side ratio D/B = 4 (0.25) and different aspect ratios are investigated. Four cases of boundary layer flows are simulated. The prisms are examined at a full range of wind angles that change every 15°. Spatial distributions of the mean wind velocity pressure are similar between models and boundary layers at all angles of wind attack but differ significantly in values, especially on windward and side walls. The boundary layer characteristics have slightly stronger influence on the mean pressure coefficient on windward walls than the change in side ratio and dimensions of models. From the other hand, the change in model geometry influences suction a little stronger on leeward and side walls than the change of boundary layer. The wind action on windward wide wall causes greater differences of pressure on this wall and smaller differences of suction on side and leeward walls than the wind action on windward narrow wall. The oblique angles of wind attack cause greater suction at top parts of the models near the roof due to forming conical vortices.

8

Wavelet-based numerical solution for MHD boundary-layer flow due to stretching sheet

Karkera Harinakshi, Katagi Nagaraj N.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 3

84--103

EN

In this paper, a two-dimensional steady flow of a viscous fluid due to a stretching sheet in the presence of a magnetic field is considered. We proposed two new numerical schemes based on the Haar wavelet coupled with a collocation approach and quasi-linearization process for solving the Falkner-Skan equation representing the governing problem. The important derived quantities representing the fluid velocity and wall shear stress for various values of flow parameters Mand βare calculated. The proposed methods enable us to obtain the solutions even for negative β, nonlinear stretching parameter, and smaller values of the magnetic parameter ()M1< which was missing in the earlier findings. Numerical and graphical results obtained show an excellent agreement with the available findings and demonstrate the efficiency and accuracy of the developed schemes. Another significant advantage of the present method is that it does not depends on small parameters and initial presumptions unlike in traditional semi-analytical and numerical methods.

9

Effects of the control parameters on the stability of a laminar boundary layer on a porous flat plate

Lihonou T. F., Monwanou A. V., Miwadinou C. H., Chabi Orou J. B.

International Journal of Applied Mechanics and Engineering

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2021

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Vol. 26, no. 4

113--127

EN

This work is devoted to the analysis of the linear temporal stability of a laminar dynamic boundary layer on a horizontal porous plane plate. The basic flow is assumed to be laminar and two-dimensional. The basic flow velocity profiles are obtained by numerically solving the Blasius equation using the Runge-Kutta method. The perturbations of these basic solutions are expressed in the form of three-dimensional Tollmien-Schlichting waves. The formulation of the stability problem leads to the Orr-Sommerfeld equation modified by the permeability parameter (Darcy number) and the small Reynolds number. This equation is given in a general form which can be applied to the Chebyshev domain and the boundary layer domain and solved numerically using the Chebyshev spectral collocation method. The marginal stability diagrams, the critical Reynolds numbers and the eigenvalue spectra are obtained for different values of the parameters which have modified the stability equation. Numerical solutions indicate the importance of the effect of these parameters on the flow stability characteristics.

10

Potential for Expanding the Range of Fluid Friction while Minimising Friction Resistances and Improving an Oil Film’s Load Bearing Capacity

Krawczyk Krzysztof, Nowiński Emil, Wronka Grzegorz, Żurowski Wojciech, Edwardowna-Burłakowa Wiktoria

Tribologia

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2020

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nr 3

33--38

EN

Traces of mechanical wear appear on co-working surfaces in the operation of precision fluid bearings. This should not be the case, since fluid friction and uninterrupted oil film should be present in a friction pair, which is a concept that this paper attempts to outline. The way friction forces, resistance, and oil film vary as unit pressure rises linearly is discussed. Three stages of the variations are distinguished. At the first stage, the oil film thickness and force of friction remain steady while the resistance declines. Stage two is temporary: Triboelectrical phenomena already escalate considerably and begin to decide effects of the friction process while a lubricant loses rheological properties of the Newtonian fluid. Hydrodynamic friction continues at the third stage, yet the triboelectrical effects are decided by stabilised triboelectrical phenomena. The third range can be identified as boundary friction where the layer separating surfaces is thicker than in the area of Newtonian rheology. This is very good in respect to wear, but higher-energy (not electrically neutral) particles cause increases in friction resistances. This range seems to exhibit a very high potential for being controlled with an adequate selection of oil based additions.

PL

W trakcie eksploatacji precyzyjnych łożysk ślizgowych na współpracujących powierzchniach pojawiają się ślady zużycia mechanicznego. Zjawisko takie nie powinno mieć miejsca, gdyż w węźle ciernym powinno występować tarcie płynne z nieprzerwanym filmem olejowym. W publikacji przedstawiono, w jaki sposób zmieniają się wartości siły tarcia, rezystancji oraz filmu olejowego wraz z liniowym wzrostem nacisku jednostkowego. Wyodrębniono trzy etapy zachodzących zmian. W pierwszym etapie zaobserwowano utrzymywanie się na zbliżonym poziomie grubości filmu olejowego i siły tarcia, przy jednoczesnym zmniejszaniu się wartości rezystancji. Etap II jest etapem przejściowym, w którym znacząco narastają już zjawiska triboelektryczne i one zaczynają decydować o efektach procesu tarcia, a środek smarowy traci właściwości reologiczne cieczy newtonowskiej. W etapie III nadal występuje tarcie hydrodynamiczne, ale o efektach tarcia decydują ustabilizowane zjawiska triboelektryczne. Wobec powyższego zakres trzeci możemy identyfikować jako tarcie graniczne, w którym warstewka rozdzielająca powierzchnie jest grubsza niż w obszarze reologii newtonowskiej. Jest to bardzo korzystne z punktu widzenia zużycia, ale cząsteczki o wyższej energii (nieobojętne elektrycznie) powodują zwiększenie oporów tarcia. Wydaje się, że ten zakres posiada bardzo duże potencjalne możliwości sterowania nim poprzez odpowiedni dobór dodatków do bazy olejowej.

11

Characterizing urban pollution variability in Central Poland using radon-222

Chambers Scott D., Podstawczyńska Agnieszka

Nukleonika

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2020

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Vol. 65, No. 2

59--65

EN

Four years of observations of radon, meteorology and atmospheric pollution was used to demonstrate the efficacy of combined diurnal and synoptic timescale radon-based stability classification schemes in relating atmospheric mixing state to urban air quality in Zgierz, Central Poland. Nocturnal radon measurements were used to identify and remove periods of non-stationary synoptic behaviour (13–18% of each season) and classify the remaining data into five mixing states, including persistent temperature inversion (PTI) conditions, and non-PTI conditions with nocturnal conditions ranging from well mixed to stable. Mixing state classifications were performed completely independently of site meteorological measurements. World Health Organization guideline values for daily PM2.5/PM10 were exceeded only under strong PTI conditions (3–15% of non-summer months) or often under non-PTI stable nocturnal conditions (14–20% of all months), when minimum nocturnal mean wind speeds were also recorded. In non-summer months, diurnal amplitudes of NO (CO) increased by the factors of 2–12 (3–7) from well-mixed nocturnal conditions to PTI conditions, with peak concentrations occurring in the morning/evening commuting periods. Analysis of observations within radon-derived atmospheric mixing ‘class types’ was carried out to substantially clarify relationships between meteorological and air quality parameters (e.g. wind speed vs. PM2.5 concentration, and atmospheric mixing depth vs. PM10 concentration).

12

The Effect of the Type of Wall Material and Grease Composition Pairing on Shear Stresses in Boundary Layer

Czarny Ryszard

Tribologia

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2019

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nr 2

27--36

EN

The paper presents the results of research on the influence of fillers introduced into plastic greases on the rheological properties of the boundary layer of the resultant lubricant compositions. The fillers were PTFE and MoS2 powders. They are added to lubricants to improve their tribological properties; however, these fillers also affect the rheological properties of the composition. This affects the change of the shear stress value in the lubricant during its flow in the lubrication system. Knowledge of this value, especially during the flow of the lubricant composition in the boundary layer, has a significant impact on the operation of automated central lubrication systems in which these compositions can be used. Measurements were carried out by means of a rotary rheometer (Rheotest 2.1). Tests were performed on lithium and bentonite greases (without additives) as well as compositions of these greases containing various percentage of the fillers mentioned above. Test results showed that both the type of grease and the type of filler introduced into this grease affect the rheological properties in the boundary layer of the produced lubricating compositions.

PL

W pracy przedstawiono wyniki badań nad wpływem wypełniaczy, wprowadzanych do smarów plastycznych, na właściwości reologiczne warstwy przyściennej powstałych kompozycji smarowych. Wypełniaczami tymi były proszki PTFE i MoS2. Dodawane są one do smarów w celu poprawy ich właściwości tribologicznych, ale wypełniacze te wpływają też na właściwości reologiczne kompozycji. Wpływa to na zmianę wartości naprężenia stycznego w smarze podczas jego przepływu w układzie smarowniczym. Znajomość tej wartości, a szczególnie podczas przepływu kompozycji smarowej w warstwie przyściennej ma istotny wpływ na działanie zautomatyzowanych układów centralnego smarowania, w których mogą być wykorzystane te kompozycje. Pomiary przeprowadzono na reometrze rotacyjnym Rheotest 2.1. Badaniom poddano smary litowy i bentonitowy (bez dodatków) oraz kompozycje tych smarów z udziałami wymienionych powyżej wypełniaczy. Wyniki badań wykazały, że zarówno rodzaj smaru, jak też rodzaj wypełniacza wprowadzonego do tego smaru mają wpływ na własności reologiczne w warstwie przyściennej wytworzonych kompozycji smarowych.

13

The effect of graphene additive on the tribological properties of bionic lubricant compositions tested by thE SRV method

Molenda Jarosław, Michalczewski Remigiusz

Tribologia

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2019

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nr 6

47--56

EN

The aim of the study was to investigate the effect of the addition of graphene dispersion on anti-wear properties of bionic lubricant compositions based on aqueous sodium hyaluronate solutions. Tribological tests were carried out using a SRV tester, enabling the tests to be carried out in conditions of linear oscillating movement of the bullet-shield type association in which the ball was made of aluminium oxide and the disc was made of bearing steel 100Cr6. For research, a 0.5% solution of sodium hyaluronate in water (composition BSS2) was chosen, which was the base to which the graphene additive was introduced. During the main stage of work, three lubricant compositions were tested, i.e., as well as BSS2 solution, into which 0.05% m/m or 0.1% m/m graphene oxide was introduced, respectively. The study allowed the observation of a clear anti-wear effect associated with the introduction of graphene preparations into the hyaluronan base, manifested in a change in the trend of the graph of the coefficient of friction over time. In addition, a reduction in the volume wear of friction node components was found. Based on the analysis of tribological research results, it was found that the anti-wear effect of the lubricant on the friction elements of the steel-ceramic material combination increases with increasing the content of the graphene preparation in the lubricant composition.

PL

Celem pracy było zbadanie wpływu dodatku dyspersji grafenowej na właściwości przeciwzużyciowe bionicznych kompozycji smarowych na bazie wodnych roztworów hialuronianu sodu. Badania tribologiczne przeprowadzono, stosując tester SRV, umożliwiający realizację testów w warunkach liniowego ruchu oscylacyjnego skojarzenia typu kula–tarcza, w którym kula wykonana była z tlenku aluminium, a tarcza ze stali łożyskowej 100Cr6. Do badań wybrano 0,5-procentowy roztwór hialuronianu sodu w wodzie (kompozycja BSS2), stanowiący bazę, do której wprowadzano dodatek grafenowy. Podczas zasadniczego etapu prac testowano trzy kompozycje smarowe, tj., kompozycję BSS2, a także roztwór BSS2, do którego wprowadzono odpowiednio 0,05% m/m lub 0,1% m/m tlenku grafenu. Przeprowadzone badania pozwoliły na zaobserwowanie wyraźnego efektu przeciwzużyciowego związanego z wprowadzeniem preparatów grafenu do bazy wodno-hialuronianowej, przejawiającego się zmianą trendu wykresu zależności współczynnika tarcia w czasie. Ponadto stwierdzono redukcję zużycia objętościowego elementów węzła tarcia. Na podstawie analizy wyników badań tribologicznych stwierdzono, iż efekt przeciwzużyciowego oddziaływania substancji smarowej na elementy trące skojarzenia materiałowego stal–ceramika wzrasta wraz z podwyższaniem zawartości preparatu grafenowego w kompozycji smarowej.

14

Chemically reacting ionized radiative fluid flow through an impulsively started vertical plate with induced magnetic field

Ahmed T., Alam M. M., Ferdows M., Tzirtzilakis E. E.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 1

5--36

EN

Numerical studies have been performed to examine the chemically reacting ionized fluid flow through a vertical plate with induced magnetic field. This study is performed for the cooling problem. To obtain the nondimensional non-similar momentum, the induced magnetic field, energy and concentration equations, usual nondimensional variables have been used. The numerical solutions for the velocity fields, induced magnetic fields, temperature distribution as well as concentration distribution are obtained for associated parameters using the explicit finite difference method. The local and average shear stresses, current densities, Nusselt number as well as the Sherwood number are also investigated. The obtained results are discussed with the help of graphs to observe effects of various parameters entering into the problem. Also the stability conditions of the explicit finite difference method are analyzed. Finally, a qualitative comparison of the present results with previously published results has been made.

15

Wentylacja autobusu i jej wpływ na warstwę przyścienną opływającego powietrza zewnętrznego

Voznyak Orest, Adamski Mariusz, Kapalo Peter, Dovbush Oleksander

Ciepłownictwo, Ogrzewnictwo, Wentylacja

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2019

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T. 50, nr 4

159--161

PL

W artykule przedstawiono wyniki badań wpływu naturalnej wentylacji części pasażerskiej oraz w przestrzeni kierowcy autobusu na przepływ powietrza wokół pojazdu. Badania eksperymentalne przeprowadzono w tunelu aerodynamicznym. Na podstawie pomiarów określono rozkład prędkości powietrza w warstwie przyściennej na zewnątrz autobusu. Wykonano również analizę wpływu naturalnej wentylacji autobusu na grubość warstwy granicznej powietrza.

EN

The results of research on the impact of natural ventilation in the bus, in the part for passengers and in the driver’s space on the air flow around the bus are presented. Experimental research was carried out in the wind tunnel. Based on the measurements, the distribution of air velocity in the boundary layer outside the bus was determined. The effect of natural ventilation of the internal space on the thickness of the air boundary layer were also analyzed.

16

The lubricity and low friction additives for transmission oil

Sójka M.

Tribologia

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2018

|

nr 1

95--100

EN

The subject of this paper is the extension of the durability of multi-stage gear units working in moments or constant overloads. Gear oils in sugar conveyor systems of the DC tray extractor were tested. Lubrication parameters and modifications of this parameter have been studied by adding additional materials to the oil. Additionally, the noise levels emitted by practical transmissions before and the addition of modifiers were measured. The lubrication tests were carried out on a semi-Timken apparatus, for example, friction roller friction – roller, in oils extracted from the gear unit. Sound level tests were performed using the SoundMeter application with a MIC001 microphone adapter. The results confirmed the effectiveness of the modified equipment, which was raised to a higher value, and also the noise level of the working gear was reduced. It has been shown that, in the current operating systems, a method of increasing the lubricant parameters of the gear oils is required, which translates into the durability of the gear pairs during operation.

PL

Przedmiotem niniejszych badań jest problem wydłużenia trwałości wielostopniowych przekładni zębatych pracujących w chwilowymi lub stałymi przeciążeniami. Badaniom podlegały oleje przekładniowe stosowane w systemach transmisji mocy cukrowniczego ekstraktora korytowego typu DC. Badano parametr smarności olejów i możliwości modyfikacji tego parametru poprzez wprowadzenie dodatków niskotarciowych do oleju. Dodatkowo pomierzono poziom hałasu emitowanych przez pracujące przekładnie przed i po dodaniu modyfikatorów. Badania smarności przeprowadzono na aparacie semi-Timken, na którym zacierano pary cierne rolka–wałek w obecności olejów pobranych z przekładni. Do badań poziomu emisji hałasu wykorzystano aplikację SoundMeter z przystawką mikrofonową MIC001. Wyniki badań potwierdziły skuteczność modyfikatorów – uzyskano wyższe wartości obciążeń zacierających, a także obniżono poziom emisji hałasu pracujących przekładni. Wykazano, że w rzeczywistych systemach eksploatacyjnych istnieje możliwość podniesienia wartości parametrów smarności olejów przekładniowych, co ma bezpośrednie przełożenie na trwałość par ciernych przekładni w trakcie eksploatacji.

17

Experimental analysis of the freestream length scale and turbulence intensity impact on bypass transition in boundary layer on a ﬂat plate

Grzelak J., Wierciński Z.

Transactions of the Institute of Fluid-Flow Machinery

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2018

|

nr 139

23--44

EN

An experimental investigation of the turbulent ﬂow over a ﬂat plate in a subsonic wind tunnel was carried out. The enhanced level of turbulence was generated by ﬁve wicker grids with square meshes, and diﬀerent parameters (diameter of the grid rod 0.3–3 mm and the grid mesh size 1–30 mm). The velocity of the ﬂow was measured by means of a 1D hot-wire probe, suitable for measurements in a boundary layer. The aim of the investigation was to explore the turbulence length scale in the ﬂow behind grids and to study its inﬂuence on the onset of laminar-turbulent bypass transition in a boundary layer on a ﬂat plate. To assess the isotropy of turbulence, the skewness and kurtosis factors of the ﬂow velocity distribution were determined. Several longitudinal scales of turbulence were determined and compared (integral, dissipation, Taylor microscale, and Kolmogorov scale) for diﬀerent grids and diﬀerent velocities of the mean ﬂow 4, 6, 10, 15, and 20 m/s.

18

On streamwise structures in boundary layer under adverse pressure gradient on inclined plate

Uruba V., Prochazka P., Skala V.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2018

|

Vol. 22, No 3

255--267

EN

The presented study is focused on experimental investigation of a boundary layer on a flat plate in an adverse pressure gradient. The flat plate is placed in a regular flow, the pressure gradient is generated by the plate inclination. The preceding studies deal with the structure of the wake behind the plate, the presented study concentrates on the flow structureclose to the suction surface of the plate. The dynamical behavior of the flow structures is studied in details with respect to the topology in the streamwise direction. In spite of the fact that thetime-mean flow field is close to 2D, more or less constant along the span, the instantaneous structures topology is fully 3D. Rather oblique structures are detected instead of those oriented in the streamwise direction. The patterns are travelling in the streamwise direction along the plate.

19

To the question of a logarithmic velocity profile correspondence with the experimental data

Zaryankin A. E.

Mechanics and Mechanical Engineering

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2018

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Vol. 22, nr 2

637--647

EN

The methodology of obtaining a logarithmic velocity profile describing the velocity distribution in the cross section of the boundary layer, which is based on the well-known equation of L. Prandtl, based on its semi-empirical turbulence theory, is considered. It is shown that the logarithmic velocity profile obtained in this way does not satisfy any boundary condition arising from the classical definition of such concept as the boundary layer. The perfect coincidence of this velocity profile with the experimental data of Nikuradze demonstrated in the world scientific literature is a consequence of making these profiles not in a fixed, but in a floating coordinate system. When rebuilding the velocity profiles obtained at different Reynolds numbers, all the profiles lose their versatility and do not coincide with the actual velocity profiles in cylindrical pipes.

20

The possibility of modifying the lubricity of transmission oils in industrial gears

Landowski B., Sójka M., Muślewski Ł.

Journal of KONES

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2018

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Vol. 25, No. 4

231--237

EN

The study deals with the issue of durability extension of multi-phase gears working under temporary or constant loading. The tests were performed for transmission oils used in power transmission systems of beet washers of DC type used in sugar plants. The lubricity parameters of oils and the possibilities of their modification through introduction of low-friction additives to the oil were studied. Additionally, the noise level emitted by working gears was measured before and after addition of the modifier. Lubricity tests were performed on semi-Timken apparatus, on which friction pairs friction roller- roller were tested with the use of oils extracted from the gear. SoundMeter application with MIC002 microphone adaptor was used for measurement of the noise level emission. Tests results have confirmed efficiency of the modifiers as higher values of friction loading were obtained and the noise emission level was reduced. It has been proven that in real operation systems, there is a possibility to increase the value of transmission oil lubricity parameters, which has a direct impact on durability of friction pairs of a gear during its operation.