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EN
Stochastic airfoil flutter in an unsteady flow is discussed using the stochastic P-bifurcation method, taking into account potential effects of the longitudinal and vertical turbulent flow. The critical conditions of stochastic P-bifurcation are deduced by stochastic singularity analysis in order to discuss stochastic P-bifurcation phenomena. The results of parameter analysis show that as the turbulent intensity increases, the critical flutter velocity for sharp stochastic airfoil flutter decreases. And the large amplitude vibration comes earlier; an increase in the turbulent scale causes an earlier appearance of the critical velocity for large amplitude stochastic flutter.
EN
This paper presents the results of experimental testing of parameters of the flow of an agitated liquid in a stirred tank with an eccentrically positioned shaft and with a Rushton turbine. The investigations were focused on the impact of the stirrer shaft shift in relation to the stirred tank vertical axis on the agitated liquid mean velocities and the liquid turbulent velocity fluctuations, as well as on the turbulence intensity in the tank. All the experiments were carried out in a stirred tank with the inner diameter of 286 mm and a flat bottom. The adopted values of the shaft eccentricity were zero (central position) and half the tank radius. The liquid flow instantaneous velocities were measured using laser Doppler anemometry.
EN
This paper presents a numerical analysis on turbulent flow and forced-convection characteristics of rectangular solar air heater tube fitted with staggered, transverse, V-shape, modern obstacles on the heated walls. Air, whose Prandtl number is 0.71, is the working fluid used, and the Reynolds number considered equal to 6×10 3. The governing flow equations are solved using a finite volume approach and the semi-implicit pressure linked equation (SIMPLE) algorithm. With regard to the flow characteristics, the quadratic upstream interpolation for convective kinetics differencing scheme (QUICK) was applied, and a second-order upwind scheme (SOU) was used for the pressure terms. The dynamic thermo-energy behavior of the V-shaped baffles with various flow attack angles, i.e., 50°, 60°, 70°, and 80° are simulated, analyzed, and compared with those of the conventional flat rectangular baffles with attack value of 90°. In all situations, the thermal transfer rate was found to be much larger than unity; its maximum value was around 3.143 for the flow attack angle of 90° and y = H/2.
EN
This work aims to find the influence of the liquid viscosity on the shape of an air Taylor bubble, rising up in a pipe column which contains the liquid under conditions that the liquid is stagnant and the Froude number is approximately equal to 0.35. Five liquid viscosities (from 0.001 to 0.01 Pa · s) were selected for being computationally investigated. An appropriate shape of a Taylor bubble, corresponding to each selected viscosity, was obtained by considering a pressure distribution of the air inside the bubble. Simulation results showed that the Taylor bubble shape would be thicker if the liquid viscosity was decreased. This could be explained by using the theory of the log-law velocity profile.
EN
One of the mathematical tools to measure the generation rate of new patterns along a sequence of symbols is the Lempel-Ziv complexity (LZ). Under additional assumptions, LZ is an estimator of entropy in the Shannon sense. Since entropy is considered as a measure of randomness, this means that LZ can be treated also as a randomness indicator. In this paper, we used LZ concept to the analysis of different flow regimes in cold flow combustor models. Experimental data for two combustor’s configurations motivated by efficient mixing need were considered. Extensive computer analysis was applied to develop a complexity approach to the analysis of velocity fluctuations recorded with hot-wire anemometry and PIV technique. A natural encoding method to address these velocity fluctuations was proposed. It turned out, that with this encoding the complexity values of the sequences are well correlated with the values obtained by means of RMS method (larger/smaller complexity larger/smaller RMS). However, our calculations pointed out the interesting result that most complex, this means most random, behavior does not overlap with the “most turbulent” point determined by the RMS method, but it is located in the point with maximal average velocity. It seems that complexity method can be particularly useful to analyze turbulent and unsteady flow regimes. Moreover, the complexity can also be used to establish other flow characteristics like its ergodicity or mixing.
EN
The present study investigates flow turbulence and dispersion processes in the presence of flexible and dense vegetation on the bed. The turbulent dispersion coefficients and the terms of the turbulent kinetic energy equation are determined by using data collected in a straight laboratory channel with living vegetation on the bed. Results show that the turbulent integral lengths assume an order of magnitude comparable to the stems’ characteristic dimension independently by the direction and the turbulence assumes an isotropic behavior. The coefficients of dispersion have a trend similar to that of the turbulent lengths and assume low values in the longitudinal, transversal and vertical directions. Results also show that, in the mixing layer, the shear and wake turbulence production terms balance the dissipation; the turbulent diffusion term also assumes low values and its sign varies along the vertical indicating a transport of turbulent energy both from the vegetation to the free surface and from the free surface to vegetation.
EN
Velocity profiles upstream and downstream of two aquatic plant species that are similar in morphology but differ in patch structures were measured in a natural river. Turbulence statistics were analyzed after thorough data filtering. In the wake of the M. alterniflorum, which was a slender, 0.3 m wide and 1.2 m long patch of aspect ratio 1:4, there were distinctive peaks in both, turbulence intensity and turbulent kinetic energy, which indicated increased lateral mixing. In contrast to the M. alterniflorum, turbulence statistics in the wake of the M. spicatum, which was the larger, 2 m wide and 2.4 m long patch of aspect ratio 1:1.5, indicated increased lateral shear of a greater magnitude. The turbulent kinetic energy was diminished in the closest layer to the bed downstream the both plants, although, in the case of M. alterniflorum, the observed values were similar to those upstream. The occurrence of the mixing layer below the height of M. spicatum was visible in the power spectral density plot. In both cases, ejections in the wake diminished in favor of other coherent structures. The shape and configuration of a patch are decisive factors governing the occurrence of flow instabilities downstream of the patch.
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.
EN
The aim of this work is to propose an empirical model for predicting shapes of a Taylor bubble, which is a part of slug flows, under different values of the surface tension in stagnant liquids by employing numerical simulations. The k - turbulence model was used in the framework of finite volume method for simulating flow fields in a unit of slug flow and also the pressure distribution on a Taylor bubble surface. Assuming that an air pressure distribution inside the Taylor bubble must be uniform, a grid search method was exploited to find an appropriate shape of a Taylor bubble for six values of surface tension. It was found that the shape of a Taylor bubble would be blunter if the surface tension was increased. This was because the surface tension affected the Froude number, controlling the flow around a Taylor bubble. The simulation results were also compared with the Taylor bubble shape, created by the Dumitrescu-and-Taylor model and former studies in order to ensure that they were consistent. Finally, the empirical model was presented from the simulation results.
EN
Transport of fine sediments depends mainly on the efficiency of flocculation. Flocculation, understood as the result of simultaneous processes of aggregation of particles and floc break-up, is a common phenomenon in marine environments. It is typical of fine sediments. This study presents a mathematical model of fine sediment transport. A model of flocculation is an important part of this model. Its main assumption is that flocculation is governed by turbulence. The model was qualitatively tested in a simplified theoretical waterbody. Such factors as the wind direction, wind speed, river discharge and concentration of suspension in the river were investigated. The results show that the proposed model describes reasonably well the lithodynamic processes characteristic of fine flocculating sediments. Thus it seems possible to apply it for description of fine sediment transport under real wave–current conditions that occur in many marine waterbodies near river mouths.
11
EN
An assessment of operating conditions in a baffled fish passage with pool dimensions of 2:2 3:0 m, and 180 horizontally turning pools, was carried out using numerical computations and a site survey of water flow velocity distribution. Velocity was measured with a PMS electromagnetic flowmeter and a hydrometric current meter in representative cross-sections of the fish passage in the pool centres and in the baffle barrier cross-section area. Numerical computations were also performed for two alternative baffle locations in the fishway. One reflected the actual conditions, and the other was an alternative arrangement designed to improve hydraulic conditions for fish migration. The numerical model used the Large Eddy Simulation (LES) method, which makes it possible to detect large vortexes. The study pays close attention to the velocity field analysis as well as the distribution and sizes of vortexes in the turning pool of the culvert. The results of numerical computations and the site survey show high consistency, and the proposed baffle placement modification significantly improves flow conditions, especially in the entry section of the passage.
PL
Celem artykułu jest zaprezentowanie dynamiki otoczenia współczesnych przedsiębiorstw oraz wyboru strategii ich rozwoju w odniesieniu do zmian w tym otoczeniu. W części teoretycznej omówiono zagadnienia związane z istotą otoczenia, jego rodzajami i tempem zmian. Zasadniczą część prowadzonych rozważań stanowi prezentacja i analiza wyników badań ankietowych przeprowadzona na próbie 63 przedsiębiorstw notowanych na rynkach GPW i NC w Warszawie. Przeprowadzone badania dotyczyły relacji między rodzajem otoczenia, jego monitorowaniem a stosowaną strategią rozwoju przedsiębiorstwa.
EN
The aim of the article is to present the dynamics of the environment of modern companies and to choose their business strategies with respect to changes in this environment. In the theoretical part issues related to the nature of the environment, its types and rate of change have been discussed. The main part of the deliberations is the presentation and analysis of survey results conducted on a sample of 63 companies listed on the Warsaw Stock Exchange and NewConnect. The research concerned the relationship between the type of environment, its monitoring and the company's business strategy.
EN
The control of homing surface-to-air short-range anti-aircraft missile takes place in the atmosphere, in which there are different types of atmospheric disturbances such as: turbulence, gust and wind shear. The atmospheric disturbances is generated with the Dryden power spectral density model. This paper presents a method for control of flying objects such as anti-aircraft missile moving in a disturbed environment. The method of proportional navigation will be applied for the guidance of missile on the ground target. The research will include the analysis of influence of atmospherics on the hitting the target accuracy, the shape of the flight path and the values of generated control forces. Numerical research will be carried out with use of Matlab/Simulink software. Obtained results will be presented in the graphical form.
PL
Sterowanie samonaprowadzającym obiektem latającym, jakim jest przeciwlotniczy pocisk rakietowy (PPR), odbywa się w atmosferze ziemskiej, w której zachodzą różnego typu zjawiska atmosferyczne, jak turbulencje, uskoki i podmuchy wiatru. Zakłócenia atmosferyczne przyjęto jako proces stochastyczny w postaci gęstości widmowej mocy (model Drydena). W artykule zaprezentowano metodę sterowania PPR poruszającym się w atmosferze zaburzonej. Do naprowadzania pocisku rakietowego na cel powietrzny wykorzystana została metoda proporcjonalnej nawigacji. Badania objęły analizę wpływu zakłóceń atmosferycznych na dokładność trafienia w cel, kształt toru lotu oraz wartości generowanych sił sterujących. Symulacje komputerowe przeprowadzone zostały w środowisku Matlab/Simulink, a niektóre wyniki badań przedstawione w postaci graficznej.
14
Content available Beyond one-point turbulence closures
EN
The paper concerns statistical description of turbulence in terms of multipoint velocity moments. A literature survey on possible multipoint turbulence closures and their future perspective is provided. We first consider the transport equations for two-point velocity statistics and their one-point limit. Another form of turbulence description, in terms of multipoint probability density functions is also introduced.
15
Content available remote The results of a mud and rock flow controlling new facility design study
EN
The analysis of the mud-rock flow controlling facility operation enables to reveal regularities and, consequently, mechanisms providing passage of the given values of solid and liquid flow for different slopes of a channel and parameters of its cross section. To solve such problems it is assumed that if the mud-rock moving along a given slope of a prismatic bed with the maximum concentration, then its flow can be controlled and direct along small slopes of the channel, providing at that the constancy of the first value of sediment carrying capacity. At the same time, the sections of the channel where steepness of the bed is relatively gentle require corresponding design innovations of the mud-and-rock flow controlling facilities. The received design solutions for mudflow controlling structures enable reliable control of mudflows where downward grade is small.
PL
Analiza działania układu kontrolującego zapewniającego spływ gruzowy (mieszaniny błota i skał) pozwala na wykrycie prawidłowości, a w konsekwencji mechanizmów zapewniających przepływ o określonych wartościach składników stałych i wody w przypadku różnego nachylenia kanału i parametrów jego przekroju. Aby rozwiązywać ten problem założono, że mieszanina błota i kamieni o maksymalnej gęstości porusza się w kierunku spadku pryzmatycznego złoża, wówczas jego przepływ może być kontrolowany i kierowany w strefę małych spadków kanału, zapewniając tym sposobem zdolność do przenoszenia osadów. Jednocześnie sekcje kanału, w których spadek koryta jest stosunkowo łagodny, wymagają wprowadzenia innowacji konstrukcyjnych urządzeń do regulowania spływu gruzowego. Otrzymane rozwiązania konstrukcyjne dla struktur regulujących spływ gruzowy umożliwiają niezawodną kontrolę przepływu błota i skał w kanałach o niewielkim nachyleniu.
EN
Some of the most recent technologies that improves the performance in continuous casting process has installed infrastructure outside the mold to modify the natural fluid flow pattern to obtain a quasi-steady condition and promote a uniform solidified shell of steel. The submerged entry nozzle distributes the liquid steel in the mold and can be used to obtain the flow symmetry condition with external geometry improvements. The fluid flow conditioners were located near the outlet ports of the nozzle. The aim of the modifiers is to impose a pseudo symmetric pattern in the upper zone of the mold by inhibiting the fluid exchange between the zones created by conditioners. This work evaluates the effect of the thickness and length of the fluid-flow modifiers on the overall performance of the submerged nozzle. These properties of the fluid-flow modifiers were normalized based on two of the geometric dimensions of the standard equipment. Numerical and physical simulations suggest that the flow modifier should be as thin as possible.
EN
A numerical model of propagation of internal gravity waves in a stratified medium is applied to the problem of tsunami wave run-up onto a shore. In the model, the ocean and the atmosphere are considered as a united continuum in which the density varies with height with a saltus at the water-air interface. The problem solution is sought as a generalized (weak) solution; such a mathematical approach automatically ensures correct conditions of matching of the solutions used on a water-air interlayer. The density stratification in the ocean and in the atmosphere is supposed to be described with an exponential function, but in the ocean a scale of the density stratification takes a large value and the density changes slightly. The initial wave running to a shore is taken in the form of a long solitary wave. The wave evolution is simulated with consideration of the time-varying vertical wave structure. Near the shore, the wave breaks down, and intensive turbulent mixing develops in the water thickness. The wave breakdown effect depends on the bottom shape. In the case when the bottom slope is small and the inshore depth grows slowly with the distance from the shore, mixing happens only in the upper stratum of the fluid due to the formation of a quiet region near the bottom. When the bottom slope takes a sufficiently large value, the depth where fluid mixing takes place goes down up to 50 meters. The developed model shows that the depth of the mixing effects strongly depends on the bottom shape, and the model may be useful for investigation of the impact strong gales and hurricanes on the coastline and beaches.
PL
W pracy przedstawiono wyniki termoanemometrycznych pomiarów poziomu turbulencji w funkcji prędkości It(v) w przestrzeni pomiarowej w zakupionym w 2013 roku tunelu aerodynamicznym z obiegiem zamkniętym. Pomiary wykonano z wykorzystaniem standardowej, jednowłóknowej sondy termoanemometrycznej. Wyniki pomiarów w centralnym punkcie przestrzeni pomiarowej wykazały, że wartości współczynnika intensywności turbulencji It.max w tym miejscu utrzymują się poniżej poziomu 0,5%. Stwierdzono, że niewielki wzrost It.max obserwowany dla najniższych prędkości może być wynikiem niestabilnej pracy silnika wentylatora lub podatności układu pomiarowego na zakłócenia elektromagnetyczne generowane przez zespół napędowy wraz z falownikiem.
EN
Investigation of the turbulence intensity conducted with use of hot-wire measurements in the new closed circuit wind tunnel was presented. Measurements were done by means of standard, single-wire hot-wire head. Results in the center point of the measurement area revealed that values of the turbulence intensity parameter It.max keep below level of 0.5%. Small but noticeable increase of this parameter for the lowest velocities may be the result of instabilities of the fan engine work or electromagnetic disturbances.
EN
Characteristics of the turbulent boundary and passive layers of an isothermal dry granular avalanche with incompressible grains are studied by the proposed zero-order turbulence closure model. The first and second laws of thermodynamics are applied to derive the equilibrium closure relations satisfying turbulence realizability conditions, with the dynamic responses postulated within a quasi-static theory. The established closure model is applied to analyses of a gravity-driven stationary avalanche down an incline to illustrate the distributions of the mean solid content, mean velocity, turbulent kinetic energy and dissipation across the flow layer, and to show the influence of turbulent fluctuation on the mean flow features compared with laminar flow solutions. In this paper, detailed thermodynamic analysis and equilibrium closure relations are summarized, with the dynamic responses, the complete closure model and numerical simulations reported in the second part.
PL
Celem przedstawionej pracy jestanaliza wielkości turbulencji w podstawowych jednostkach hydromorfologicznych rzeki górskiej na przykładzie odcinka Skawy. Pomiary składowych prędkości chwilowej sondą MicroADV w ośmiu losowych lokalizacjach na poziomie 20% i 40% głębokości lokalnej wykonano w czterech jednostkach hydromorfologicznych - ploso, nurt, bystrze i rwący nurt. Na podstawie uzyskanych wartości obliczono lokalne wartości prędkości wypadkowej oraz parametry ruchu turbulentnego: intensywność turbulencji i turbulentną energię kinetyczną. Wyniki badań wskazują na duże zróżnicowanie lokalnych wartości parametrów turbulencji w obrębie jednostki. Wielkość turbulencji wzrasta wraz z prędkością układając jednostki w kolejności ploso, nurt, rwący nurt, bystrze. Zauważono wzrost wielkości turbulencji w kierunku dna w jednostkach o niskiej prędkości przepływu – ploso i nurt, natomiast w jednostkach o wyższej prędkości (bystrze i rwący nurt) nie wykazały jednoznacznie podobnej tendencji.
EN
The aim of this study is to analyze the turbulence value in the basic hydromorphologicalunits of mountain river in the example of the Skawa river section. In four hydromorphological units - pool, run, riffle, rapid in eight random locations the instantaneous velocity components were measured usingMicroADV at 20% and 40% of the local depth. On the basis of the measurement the value of the local velocity and turbulent motion parameters: turbulence intensity and turbulent kinetic energy were calculated. The results show a large variation in local turbulence parameters within the one unit. The value of turbulence parameters increases with velocity values andordering unit as follows pool, run, rapid, riffle. It was noticed that turbulence increased towards to river bed in units of low flow velocity values-pool and run. While units with higher flow velocity (riffle and rapid) did not show similar trend.
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