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Статті в журналах з теми "Interface turbulent/non-Turbulent"
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Teixeira, M. A. C., and C. B. da Silva. "Turbulence dynamics near a turbulent/non-turbulent interface." Journal of Fluid Mechanics 695 (February 13, 2012): 257–87. http://dx.doi.org/10.1017/jfm.2012.17.
Повний текст джерелаАнотація:
AbstractThe characteristics of the boundary layer separating a turbulence region from an irrotational (or non-turbulent) flow region are investigated using rapid distortion theory (RDT). The turbulence region is approximated as homogeneous and isotropic far away from the bounding turbulent/non-turbulent (T/NT) interface, which is assumed to remain approximately flat. Inviscid effects resulting from the continuity of the normal velocity and pressure at the interface, in addition to viscous effects resulting from the continuity of the tangential velocity and shear stress, are taken into account by considering a sudden insertion of the T/NT interface, in the absence of mean shear. Profiles of the velocity variances, turbulent kinetic energy (TKE), viscous dissipation rate ($\varepsilon $), turbulence length scales, and pressure statistics are derived, showing an excellent agreement with results from direct numerical simulations (DNS). Interestingly, the normalized inviscid flow statistics at the T/NT interface do not depend on the form of the assumed TKE spectrum. Outside the turbulent region, where the flow is irrotational (except inside a thin viscous boundary layer),$\varepsilon $decays as${z}^{\ensuremath{-} 6} $, where$z$is the distance from the T/NT interface. The mean pressure distribution is calculated using RDT, and exhibits a decrease towards the turbulence region due to the associated velocity fluctuations, consistent with the generation of a mean entrainment velocity. The vorticity variance and$\varepsilon $display large maxima at the T/NT interface due to the inviscid discontinuities of the tangential velocity variances existing there, and these maxima are quantitatively related to the thickness$\delta $of the viscous boundary layer (VBL). For an equilibrium VBL, the RDT analysis suggests that$\delta \ensuremath{\sim} \eta $(where$\eta $is the Kolmogorov microscale), which is consistent with the scaling law identified in a very recent DNS study for shear-free T/NT interfaces.
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Elsinga, G. E., and C. B. da Silva. "How the turbulent/non-turbulent interface is different from internal turbulence." Journal of Fluid Mechanics 866 (March 5, 2019): 216–38. http://dx.doi.org/10.1017/jfm.2019.85.
Повний текст джерелаАнотація:
The average patterns of the velocity and scalar fields near turbulent/non-turbulent interfaces (TNTI), obtained from direct numerical simulations (DNS) of planar turbulent jets and shear free turbulence, are assessed in the strain eigenframe. These flow patterns help to clarify many aspects of the flow dynamics, including a passive scalar, near a TNTI layer, that are otherwise not easily and clearly assessed. The averaged flow field near the TNTI layer exhibits a saddle-node flow topology associated with a vortex in one half of the interface, while the other half of the interface consists of a shear layer. This observed flow pattern is thus very different from the shear-layer structure consisting of two aligned vortical motions bounded by two large-scale regions of uniform flow, that typically characterizes the average strain field in the fully developed turbulent regions. Moreover, strain dominates over vorticity near the TNTI layer, in contrast to internal turbulence. Consequently, the most compressive principal straining direction is perpendicular to the TNTI layer, and the characteristic 45-degree angle displayed in internal shear layers is not observed at the TNTI layer. The particular flow pattern observed near the TNTI layer has important consequences for the dynamics of a passive scalar field, and explains why regions of particularly high scalar gradient (magnitude) are typically found at TNTIs separating fluid with different levels of scalar concentration. Finally, it is demonstrated that, within the fully developed internal turbulent region, the scalar gradient exhibits an angle with the most compressive straining direction with a peak probability at around 20$^{\text{o}}$. The scalar gradient and the most compressive strain are not preferentially aligned, as has been considered for many years. The misconception originated from an ambiguous definition of the positive directions of the strain eigenvectors.
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Borrell, Guillem, and Javier Jiménez. "Properties of the turbulent/non-turbulent interface in boundary layers." Journal of Fluid Mechanics 801 (July 26, 2016): 554–96. http://dx.doi.org/10.1017/jfm.2016.430.
Повний текст джерелаАнотація:
The turbulent/non-turbulent interface is analysed in a direct numerical simulation of a boundary layer in the Reynolds number range$Re_{{\it\theta}}=2800{-}6600$, with emphasis on the behaviour of the relatively large-scale fractal intermittent region. This requires the introduction of a new definition of the distance between a point and a general surface, which is compared with the more usual vertical distance to the top of the layer. Interfaces are obtained by thresholding the enstrophy field and the magnitude of the rate-of-strain tensor, and it is concluded that, while the former are physically relevant features, the latter are not. By varying the threshold, a topological transition is identified as the interface moves from the free stream into the turbulent core. A vorticity scale is defined which collapses that transition for different Reynolds numbers, roughly equivalent to the root-mean-squared vorticity at the edge of the boundary layer. Conditionally averaged flow variables are analysed as functions of the new distance, both within and outside the interface. It is found that the interface contains a non-equilibrium layer whose thickness scales well with the Taylor microscale, enveloping a self-similar layer spanning a fixed fraction of the boundary-layer thickness. Interestingly, the straining structure of the flow is similar in both regions. Irrotational pockets within the turbulent core are also studied. They form a self-similar set whose size decreases with increasing depth, presumably due to breakup by the turbulence, but the rate of viscous diffusion is independent of the pocket size. The raw data used in the analysis are freely available from our web page (http://torroja.dmt.upm.es).
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Ferrey, P., and B. Aupoix. "Behaviour of turbulence models near a turbulent/non-turbulent interface revisited." International Journal of Heat and Fluid Flow 27, no. 5 (October 2006): 831–37. http://dx.doi.org/10.1016/j.ijheatfluidflow.2006.03.022.
Повний текст джерела
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BISSET, DAVID K., JULIAN C. R. HUNT, and MICHAEL M. ROGERS. "The turbulent/non-turbulent interface bounding a far wake." Journal of Fluid Mechanics 451 (January 25, 2002): 383–410. http://dx.doi.org/10.1017/s0022112001006759.
Повний текст джерелаАнотація:
The velocity fields of a turbulent wake behind a flat plate obtained from the direct numerical simulations of Moser et al. (1998) are used to study the structure of the flow in the intermittent zone where there are, alternately, regions of fully turbulent flow and non-turbulent velocity fluctuations on either side of a thin randomly moving interface. Comparisons are made with a wake that is ‘forced’ by amplifying initial velocity fluctuations. A temperature field T, with constant values of 1.0 and 0 above and below the wake, is transported across the wake as a passive scalar. The value of the Reynolds number based on the centreplane mean velocity defect and half-width b of the wake is Re ≈ 2000.The thickness of the continuous interface is about 0.07b, whereas the amplitude of fluctuations of the instantaneous interface displacement yI(t) is an order of magnitude larger, being about 0.5b. This explains why the mean statistics of vorticity in the intermittent zone can be calculated in terms of the probability distribution of yI and the instantaneous discontinuity in vorticity across the interface. When plotted as functions of y−yI the conditional mean velocity 〈U〉 and temperature 〈T〉 profiles show sharp jumps at the interface adjacent to a thick zone where 〈U〉 and 〈T〉 vary much more slowly.Statistics for the conditional vorticity and velocity variances, available in such detail only from DNS data, show how streamwise and spanwise components of vorticity are generated by vortex stretching in the bulges of the interface. While mean Reynolds stresses (in the fixed reference frame) decrease gradually in the intermittent zone, conditional stresses are roughly constant and then decrease sharply towards zero at the interface. Flow fields around the interface, analysed in terms of the local streamline pattern, confirm and explain previous results that the advancement of the vortical interface into the irrotational flow is driven by large-scale eddy motion.Terms used in one-point turbulence models are evaluated both conventionally and conditionally in the interface region, and the current practice in statistical models of approximating entrainment by a diffusion process is assessed.
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Li, Sicheng, Yanguang Long, and Jinjun Wang. "Turbulent/non-turbulent interface for laminar boundary flow over a wall-mounted fence." Physics of Fluids 34, no. 12 (December 2022): 125113. http://dx.doi.org/10.1063/5.0128609.
Повний текст джерелаАнотація:
The turbulent/non-turbulent interface plays an important role in the exchange of mass, momentum, and energy between turbulent and nonturbulent flows. However, the role played by the interface in the separation and reattachment flow remains poorly understood. This study, thus, investigates the geometrical and dynamic properties of the interface in the separation and reattachment flow induced by a wall-mounted fence by using particle image velocimetry in a water tunnel. The flow undergoes laminar separation, reattachment, and the recovery of the boundary layer. Finally, the fully developed turbulent boundary layer is established. The geometrical and dynamic properties of the interface vary consistently with the vortex structure. The geometrical properties change most quickly above the reattachment point, where the dynamic properties are maximal. Before the reattachment point, the shear motion of the fluid contributes significantly to the interface properties. As a result, the interface thickness does not scale with the size of the nearby vortex until reattachment. Additionally, quasiperiodic shedding vortices significantly affect the interface properties. Remarkable bulges and troughs of the interface form corresponding to the spatial arrangement of the shedding vortices. In addition, the conditional averaged dynamic quantities peak along the interface coordinate as the turbulence intensity is enhanced by the shedding vortex. This study provides a new perspective of the turbulent/non-turbulent interface, improves our understanding of turbulent diffusion in the separation and reattachment flow, and clarifies how the separated flow and shedding vortices affect the interface properties.
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Lee, Jin, Hyung Jin Sung, and Tamer A. Zaki. "Signature of large-scale motions on turbulent/non-turbulent interface in boundary layers." Journal of Fluid Mechanics 819 (April 18, 2017): 165–87. http://dx.doi.org/10.1017/jfm.2017.170.
Повний текст джерелаАнотація:
The effect of large-scale motions (LSMs) on the turbulent/non-turbulent (T/NT) interface is examined in a turbulent boundary layer. Using flow fields from direct numerical simulation, the shape of the interface and near-interface statistics are evaluated conditional on the position of the LSM. The T/NT interface is identified using the vorticity magnitude and a streak detection algorithm is adopted to identify and track the LSMs. Two-point correlation and spectral analysis of variations in the interface height show that the spatial undulation of the interface is longer in streamwise wavelength than the boundary-layer thickness, and grows with the Reynolds number in a similar manner to the LSMs. The average variation in the interface height was evaluated conditional on the position of the LSMs. The result provides statistical evidence that the interface is locally modulated by the LSMs in both the streamwise and spanwise directions. The modulation is different when the coherent structure is high- versus low-speed motion: high-speed structures lead to a wedge-shaped deformation of the T/NT interface, which causes an anti-correlation between the angles of the interface and the internal shear layer. On the other hand, low-speed structures are correlated with crests in the interface. Finally, the sudden changes in turbulence statistics across the interface are in line with the changes in the population of low-speed structures, which consist of slower mean streamwise velocity and stronger turbulence than the high-speed counterparts.
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Yu, Jia-Long, and Xi-Yun Lu. "Topological evolution near the turbulent/non-turbulent interface in turbulent mixing layer." Journal of Turbulence 20, no. 5 (May 4, 2019): 300–321. http://dx.doi.org/10.1080/14685248.2019.1640368.
Повний текст джерела
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Steiner, Helfried, and Christian Walchshofer. "Small-scale mixing at the turbulent/non-turbulent interface in turbulent jets." PAMM 11, no. 1 (December 2011): 601–2. http://dx.doi.org/10.1002/pamm.201110290.
Повний текст джерела
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Neuhaus, Lars, Matthias Wächter, and Joachim Peinke. "The fractal turbulent–non-turbulent interface in the atmosphere." Wind Energy Science 9, no. 2 (February 22, 2024): 439–52. http://dx.doi.org/10.5194/wes-9-439-2024.
Повний текст джерелаАнотація:
Abstract. With their constant increase in size, wind turbines are reaching unprecedented heights. Therefore, at these heights, they are influenced by wind conditions that have not yet been studied in detail. With increasing height, a transition to laminar conditions becomes more and more likely. In this paper, the presence of the turbulent–non-turbulent interface (TNTI) in the atmosphere is investigated. Three different on- and offshore locations are investigated. Our fractal scaling analysis leads to typical values known from ideal laboratory and numerical studies. The height distribution of the probability of the TNTI is determined and shows a frequent occurrence at the height of the rotor of future multi-megawatt turbines. The indicated universality of the fractality of the TNTI allows the use of simplified models in laboratory and numerical investigations.
Дисертації з теми "Interface turbulent/non-Turbulent"
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Cocconi, Giacomo. "Numerical investigation of turbulent/non-turbulent interface." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5237/.
Повний текст джерелаАнотація:
The subject of this work is the diffusion of turbulence in a non-turbulent flow. Such phenomenon can be found in almost every practical case of turbulent flow: all types of shear flows (wakes, jet, boundary layers) present some boundary between turbulence and the non-turbulent surround; all transients from a laminar flow to turbulence must account for turbulent diffusion; mixing of flows often involve the injection of a turbulent solution in a non-turbulent fluid. The mechanism of what Phillips defined as “the erosion by turbulence of the underlying non-turbulent flow”, is called entrainment. It is usually considered to operate on two scales with different mechanics. The small scale nibbling, which is the entrainment of fluid by viscous diffusion of turbulence, and the large scale engulfment, which entraps large volume of flow to be “digested” subsequently by viscous diffusion. The exact role of each of them in the overall entrainment rate is still not well understood, as it is the interplay between these two mechanics of diffusion. It is anyway accepted that the entrainment rate scales with large properties of the flow, while is not understood how the large scale inertial behavior can affect an intrinsically viscous phenomenon as diffusion of vorticity. In the present work we will address then the problem of turbulent diffusion through pseudo-spectral DNS simulations of the interface between a volume of decaying turbulence and quiescent flow. Such simulations will give us first hand measures of velocity, vorticity and strains fields at the interface; moreover the framework of unforced decaying turbulence will permit to study both spatial and temporal evolution of such fields. The analysis will evidence that for this kind of flows the overall production of enstrophy , i.e. the square of vorticity omega^2 , is dominated near the interface by the local inertial transport of “fresh vorticity” coming from the turbulent flow. Viscous diffusion instead plays a major role in enstrophy production in the outbound of the interface, where the nibbling process is dominant. The data from our simulation seems to confirm the theory of an inertially stirred viscous phenomenon proposed by others authors before and provides new data about the inertial diffusion of turbulence across the interface.
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Er, Sarp. "Structure interne, transfert turbulent et propriétés de cascade de l'interface turbulent/non-turbulent d'un jet turbulent." Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILN048.
Повний текст джерелаАнотація:
L'interface turbulent/non-turbulent (TNTI) est une couche très fine entre les régions turbulentes et non turbulentes de l'écoulement. Cette étude vise à mieux comprendre le bilan d'énergie cinétique au voisinage de l'interface turbulent/non-turbulent. L'équation de Kármán-Howarth-Monin-Hill (KHMH) est utilisée pour caractériser le bilan énergétique cinétique local, y compris les transferts d'énergie dans l'espace et entre les échelles. L'analyse est effectuée à l'aide de données obtenues par simulation numérique directe (DNS) finement résolue d'un jet plan turbulent se développant avec le temps. Les lois d'échelles de vitesse et de longueur du jet plan turbulent en evolution temporelle sont différentes de celles de son homologue en développement spatial, dans le sens où ces lois sont indépendantes de l'échelle de dissipation turbulente, qu'elle soit à l'équilibre ou hors équilibre. Il est montré que la variation de la vitesse moyenne de propagation à travers l'épaisseur de la TNTI est fonction de la dimension fractale de la surface à chaque position. Une méthodologie basée sur une opération de moyennage le long de la TNTI est utilisée pour l'analyse de l'écoulement local à proximité de la TNTI. L'analyse du vecteur normal associé à l'orientation locale de la TNTI fournit des informations précieuces sur les caractéristiques géométriques prédominantes de l'interface. Les statistiques moyennes de l'interface sont ensuite conditionnées par sa courbure moyenne et sa vitesse de propagation locale afin de caractériser la variation locale de l'écoulement et le bilan de l'équation KHMH dans les différentes couche de l'interface. Il est démontré que l'épaisseur de la TNTI et de ses sous-couches diminuent de manière significative dans les régions de fort entraînement. Les transferts entre échelles et en espace sont décomposés en une partie solénoïdale et une partie irrotationnelle, ce qui montre l'importance, au niveau de la TNTI, des transferts irrotationnels d'énergie cinétique entre échelles et en espace, associés à la corrélation pression-vitesse. Des phénomènes de compression et d'étirement sont observés en moyenne à proximité de la TNTI, dans les directions respectivement normale et tangentielle à l'interface. L'étude du terme de transfert inter-échelles montre la présence d'une cascade directe dans la direction normale et d'une cascade inverse dans la direction tangentielle. Dans les régions d'entraînement inverse, les statistiques locales montrent un étirement dans la direction normale et de la compression dans la direction tangentielle, ce qui contraste avec les statistiques observées pour l'ensemble de la TNTI et les régions d'entraînement locales. Près de la TNTI, du côté turbulent, un équilibre inattendu ressemblant à celui de Kolmogorov est observé entre le transfert inter-échelle et le taux de dissipation pour une large gamme d'échelles. Pour ces échelles, contrairement à l'équilibre de Kolmogorov habituel pour la turbulence homogène, le transfert inter-échelle est constitué uniquement de la partie irrotationnelle qui est directement associée aux corrélations pression-vitesseThe turbulent/non-turbulent interface (TNTI) is a very sharp interface layer between turbulent and non-turbulent regions of the flow. This study aims to gain insight into the kinetic energy balance in the vicinity of the TNTI. The K'arm'an-Howarth-Monin-Hill equation (KHMH) is used to characterize the local kinetic energy balance including interscale/interspace energy transfers. The analysis is conducted by using a data set obtained by highly resolved direct numerical simulation (DNS) of a temporally developing turbulent planar jet. The scalings for the velocity and length scales of the temporally developing turbulent planar jet are shown to be different from its spatially developing counterpart in the sense that these scalings are independent of the turbulent dissipation scaling, whether equilibrium or non-equilibrium. The variation of the mean propagation velocity across the thickness of the TNTI is shown as a function of the fractal dimension of the surface at each location. Furthermore, a methodology based on a TNTI-averaging operation is used for the analysis of the local flow field in the vicinity of the TNTI. The analysis of the normal vector associated with the local facing direction of the TNTI provides valuable insights into the predominant geometric characteristics of the interface. The TNTI-averaged statistics are further conditioned on the mean curvature and the local propagation velocity of the interface, in order to characterize the variation of the local flow field and KHMH balance in various regions of the interface. The thickness of the TNTI and its sublayers are shown to reduce significantly in regions of fast entrainment. The interscale/interspace transfer terms are decomposed into solenoidal/irrotational parts showing the central importance at the TNTI of the irrotational interscale/interspace transfers of kinetic energy associated with pressure-velocity correlation. Compression and stretching are observed on average at the TNTI location, in the normal and tangential directions of the interface respectively. Investigation of the interscale transfer term shows the presence of a forward cascade in the normal direction and an inverse cascade in the tangential direction. In regions of detrainment, the local statistics display stretching in the normal direction and compression in the tangential direction, which is in contrast with the statistics observed for the entire TNTI and the local entrainment regions. Close to the location of TNTI, on the turbulent side, an unexpected Kolmogorov-like balance is observed between the interscale transfer and the dissipation rate for a wide range of scales. For these scales, unlike the usual Kolmogorov balance for homogeneous turbulence, the interscale transfer consists solely of the irrotational part which is directly associated with the pressure-velocity correlations
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Padovani, Lorenzo. "Enstrophy Analysis of a Turbulent Temporal Plume." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Знайти повний текст джерелаАнотація:
The aim of the present thesis work is to analyse the enstrophy behaviour of a temporal turbulent plume. Several previous works have focused their attention on the role of vorticity or enstrophy in free shear flows, but they mainly concentrate on jets, wakes or mixing layers.
The analysis is performed on a temporal turbulent plume at time t = 40 which shows a Reλ= 89. The analyses performed start from a flow general features assessment. It is retrieved that the coherent vorticity structures inside a plume can be divided in Large Vorticity Structures (LVSs) and Intense Vorticity Structures (IVSs) and that the LVSs are responsible for the Turbulent/Non-Turbulent (T/NT) interface geometrical shape. In addition, the sensitivity to the enstrophy detection threshold is tested and verified retrieving a good interface robustness. The characteristics of the T/NT interface are analysed exploiting the traditional mean enstrophy budget equation and the conditional mean enstrophy budget equation.
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Hernandez, Medina Santiago. "Turbulent interface phenomena in a temporally developing boundary layer." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/14721/.
Повний текст джерелаАнотація:
The purpose of the current study was to examine the characteristics and behavior of the turbulent/non-turbulent interface on a temporally developing boundary layer.
Flow topology, turbulent statistics, enstrophy budgets and spectral statistics were computed with the purpose of acquiring meaningful results.
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Xayasenh, Arunvady. "Étude numérique du dépôt turbulent de particules non-browniennes en suspension dans un liquide : application aux inclusions dans l'acier liquide." Phd thesis, Ecole Centrale Paris, 2013. http://tel.archives-ouvertes.fr/tel-00978528.
Повний текст джерелаАнотація:
Nous étudions par simulation numérique le transport et le dépôt turbulent d'inclusions d'oxydes métalliques (de l'ordre de 10 µm de diamètre) en suspension dans l'acier liquide. Deux surfaces de dépôt sont envisagées : l'interface acier liquide/paroi solide et l'interface métal liquide/laitier. Dans les deux cas, nous nous focalisons sur la couche limite adjacente à l'interface. Le comportement des inclusions en suspension est examiné à l'aide d'un suivi lagrangien où le poids, la poussée d'Archimède, la force d'accélération en volume, la force de masse ajoutée et la force de traînée sont prises en compte dans l'équation de la dynamique. Dans le cas de la paroi solide, nous nous appuyons sur une représentation schématique de l'écoulement du métal liquide dans la sous-couche visqueuse et dans la zone tampon, où les structures turbulentes qui apportent le liquide à la paroi (sweeps) ou l'éjectent (bursts) sont décrites analytiquement (modèle d'Ahmadi). Les simulations numériques montrent que les mécanismes principaux de dépôt des inclusions sont la sédimentation et dans une moindre mesure l'interception directe. Notons cependant que la contribution de l'interception directe croît avec l'intensité turbulente de l'écoulement et peut devenir prépondérante pour les vitesses de frottement les plus élevées (au-delà de 0,1 m.s-1). Les effets inertiels ont, quant à eux, une contribution négligeable sur le dépôt des inclusions (contrairement au cas des aérosols). Enfin, la prise en compte des interactions hydrodynamiques entre les inclusions et la paroi solide conduit à une diminution significative de la vitesse de dépôt des inclusions. Dans le cas de l'interface acier liquide/laitier, l'écoulement du métal liquide est calculé par simulation numérique directe (DNS) à l'échelle de la couche de surface. La turbulence, générée à distance de l'interface par un forçage aléatoire, diffuse vers l'interface métal liquide/laitier modélisée comme une surface libre indéformable. L'évolution des inclusions en suspension est obtenue par un suivi lagrangien à l'aide d'un couplage one-way. Le nombre de Reynolds de surface des simulations varie de 68 à 235. Le diamètre des inclusions varie de 10-5m à 5.10-5m et le rapport entre la densité des inclusions et la densité du métal varie de 0,5 (inclusions d'alumine) à 1 (inclusions fictives). Il apparaît que le dépôt des inclusions d'alumine est contrôlé par la sédimentation. En l'absence d'effet gravitaire, le dépôt d'inclusions est contrôlé par l'interception directe et dépend fortement du nombre de Reynolds de surface. Dans ce dernier cas, nous montrons que la vitesse de dépôt adimensionnée par la vitesse de Kolmogorov de surface est proportionnelle au diamètre des inclusions adimensionné par la longueur de Kolmogorov de surface. La prise en compte des interactions hydrodynamiques entre les inclusions et la surface libre conduit à une diminution de moitié de la contribution de l'interception directe mais affecte peu la contribution gravitationnelle. En outre, en l'absence d'effet gravitaire, la linéarité entre la vitesse de dépôt adimensionnée et le diamètre des inclusions adimensionné est conservée.
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Xayasenh, Arunvady. "Étude numérique du dépôt turbulent de particules non-browniennes en suspension dans un liquide : application aux inclusions dans l’acier liquide." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://www.theses.fr/2013ECAP0078/document.
Повний текст джерелаАнотація:
Nous étudions par simulation numérique le transport et le dépôt turbulent d’inclusions d’oxydes métalliques (de l’ordre de 10 µm de diamètre) en suspension dans l’acier liquide. Deux surfaces de dépôt sont envisagées : l’interface acier liquide/paroi solide et l’interface métal liquide/laitier. Dans les deux cas, nous nous focalisons sur la couche limite adjacente à l’interface. Le comportement des inclusions en suspension est examiné à l’aide d’un suivi lagrangien où le poids, la poussée d’Archimède, la force d’accélération en volume, la force de masse ajoutée et la force de traînée sont prises en compte dans l’équation de la dynamique. Dans le cas de la paroi solide, nous nous appuyons sur une représentation schématique de l’écoulement du métal liquide dans la sous-couche visqueuse et dans la zone tampon, où les structures turbulentes qui apportent le liquide à la paroi (sweeps) ou l’éjectent (bursts) sont décrites analytiquement (modèle d’Ahmadi). Les simulations numériques montrent que les mécanismes principaux de dépôt des inclusions sont la sédimentation et dans une moindre mesure l’interception directe. Notons cependant que la contribution de l’interception directe croît avec l’intensité turbulente de l’écoulement et peut devenir prépondérante pour les vitesses de frottement les plus élevées (au-delà de 0,1 m.s-1). Les effets inertiels ont, quant à eux, une contribution négligeable sur le dépôt des inclusions (contrairement au cas des aérosols). Enfin, la prise en compte des interactions hydrodynamiques entre les inclusions et la paroi solide conduit à une diminution significative de la vitesse de dépôt des inclusions. Dans le cas de l’interface acier liquide/laitier, l’écoulement du métal liquide est calculé par simulation numérique directe (DNS) à l’échelle de la couche de surface. La turbulence, générée à distance de l’interface par un forçage aléatoire, diffuse vers l’interface métal liquide/laitier modélisée comme une surface libre indéformable. L’évolution des inclusions en suspension est obtenue par un suivi lagrangien à l’aide d’un couplage one-way. Le nombre de Reynolds de surface des simulations varie de 68 à 235. Le diamètre des inclusions varie de 10-5m à 5.10-5m et le rapport entre la densité des inclusions et la densité du métal varie de 0,5 (inclusions d’alumine) à 1 (inclusions fictives). Il apparaît que le dépôt des inclusions d’alumine est contrôlé par la sédimentation. En l’absence d’effet gravitaire, le dépôt d’inclusions est contrôlé par l’interception directe et dépend fortement du nombre de Reynolds de surface. Dans ce dernier cas, nous montrons que la vitesse de dépôt adimensionnée par la vitesse de Kolmogorov de surface est proportionnelle au diamètre des inclusions adimensionné par la longueur de Kolmogorov de surface. La prise en compte des interactions hydrodynamiques entre les inclusions et la surface libre conduit à une diminution de moitié de la contribution de l’interception directe mais affecte peu la contribution gravitationnelle. En outre, en l’absence d’effet gravitaire, la linéarité entre la vitesse de dépôt adimensionnée et le diamètre des inclusions adimensionné est conservéeThe deposition of metallic oxide inclusions (of about 10 µm in diameter) suspended in liquid steel is studied by numerical simulation. Two types of deposition surface are investigated, i.e., the liquid steel/solid wall interface and the liquid steel/liquid slag interface. In both cases, we focus on the boundary layer adjacent to the interface. The inclusion behavior is examined thanks to Lagrangian particle tracking: Newton’s second law governing inclusion motion includes the buoyancy force, the pressure gradient force, the added mass force and the steady drag force.For the liquid steel/solid wall interface, the inclusion behavior is analyzed in the buffer layer and in the viscous layer. These layers are described according to Ahmadi’s model, which provides a kinematic representation of the turbulent structures responsible for deposition, i.e., the sweeps and the bursts of liquid. The numerical simulations show that the deposition is mainly controlled by sedimentation. However, since the direct interception contribution increases with the turbulence intensity, direct interception becomes dominant for the highest values of the friction velocity (greater than 0.1 m.s-1). When the hydrodynamic interactions between the inclusions and the solid surface are taken into account, the deposition velocity is significantly reduced. Finally, it should be noted that the inertial forces have a negligible effect on the inclusion deposition velocity. For the liquid steel/liquid slag interface, the inclusion turbulent deposition is investigated using direct numerical simulation of the liquid flow combined with Lagrangian particle tracking under conditions of one-way coupling. The interface is modeled as a non-deformable free-slip surface. Unsheared turbulence is generated by random forcing in a finite-height region parallel to the free-slip surface. In between, the turbulence diffuses toward the free surface. The Reynolds number at the interface varies from 68 to 235. The inclusion diameter varies from 10-5m to 5.10-5m and the particle to liquid density ratio from 0.5 (alumina inclusions) to 1 (fictitious inclusions). It appears that the deposition of alumina inclusions is controlled by sedimentation whereas direct interception is the only deposition mechanism for non-buoyant inclusions. In the latter case, the deposition velocity strongly depends on the surface Reynolds number. It is shown that the deposition velocity made dimensionless by the free surface characteristic velocity scales as the inclusion diameter made dimensionless by the Kolmogorov length scale calculated at the free surface. When the hydrodynamic interactions between the inclusions and the free surface are taken into account, the direct interception contribution of the deposition velocity is significantly reduced (about half of the value without hydrodynamic retardation) but the scaling law is conserved
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Alhamdi, Sabah Falih Habeeb. "INTERMITTENCY EFFECTS ON THE UNIVERSALITY OF LOCAL DISSIPATION SCALES IN TURBULENT BOUNDARY LAYER FLOWS WITH AND WITHOUT FREE-STREAM TURBULENCE." UKnowledge, 2018. https://uknowledge.uky.edu/me_etds/116.
Повний текст джерелаАнотація:
Measurements of the small-scale dissipation statistics of turbulent boundary layer flows with and without free-stream turbulence are reported for Reτ ≈ 1000 (Reθ ≈ 2000). The scaling of the dissipation scale distribution is examined in these two boundary conditions of external wall-bounded flow.
Results demonstrated that the local large-scale Reynolds number based on the measured longitudinal integral length-scale fails to properly normalize the dissipation scale distribution near the wall in these two free-stream conditions, due to the imperfect characterization of the upper bound of the inertial cascade by the integral length-scale. When a length-scale based on Townsend's attached-eddy hypothesis is utilized to describe the local large-scale Reynolds number near the wall, the description of the Reynolds number scaling was determined to be significantly improved and agreed with that found in homogeneous, isotropic turbulence. However, the scaling based on Townsend's attached-eddy hypothesis agreed best for the lowest 40% of the boundary layer thickness and then it degraded due to the loss of the validity of the attached eddy-hypothesis and the onset of external intermittency.
A surrogate large-scale found from turbulent kinetic energy and mean dissipation rate improved the scaling of the dissipation scales, relative to the measured integral length-scale. The probability density functions of the local dissipation scales were calculated. When the three local large-scale Reynolds numbers are used for normalization, the one based on the longitudinal integral length-scale and the one based on the length-scale of attached-eddy hypothesis provide support for the existence of a universal distribution of the local dissipation scales up to the edge of the outer region of the turbulent boundary layer, which scales differently for inner and outer regions. However, the probability density functions of the local dissipation scales normalized by these two large-scale Reynolds numbers are deviated in interface locations for the flow without free-stream turbulence due to external intermittency.
The surrogate large-scale provided the best agreement throughout the entire depth of the boundary layer. However, in the outer part of the boundary layer, a significantly reduced collapse in the scaled probability density functions was shown due to bias in the calculation introduced by the intermittent presence of laminar flow in the time series. To support that intermittency argument, injection of the free-stream turbulence was determined to improve the distribution of these normalized probability density functions in the intermittency locations for the flow regime without free-stream turbulence.
In addition, unlike in channel flow, in the outer part of the turbulent boundary layer, the normalized distributions of the local dissipation scales were observed to be dependent on wall-normal position. This was found to be attributable to the presence of external intermittency in this outer part as the presence of free-stream turbulence was found to restore the scaling behavior by replacing the intermittent laminar flow with turbulent flow.
Thus, the influence of external intermittency on the scaling of the dissipation scale distribution was examined in greater detail for the laminar free-stream condition. Probability density functions of the dissipative scales were compared with, and without, accounting for the external intermittency using an intermittency detection function. Results showed that accounting for the external intermittency produces restores universality in the shapes of the probability density functions at the same wall-normal location at different instances in time. In addition, properly scaling the dissipation-scale-distribution collapses the probability density functions calculated at different wall-normal locations. This improvement in the scaling of the dissipation-scale-distribution supports prior observations of universality of the small-scale description of the turbulence for wall-bounded flow.
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Lacassagne, Tom. "Oscillating grid turbulence and its influence on gas liquid mass transfer and mixing in non-Newtonian media." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI103/document.
Повний текст джерелаАнотація:
L’étude du transfert de masse turbulent aux interfaces gaz-liquide est d’un grand intérêt dans de nombreuses applications environnementales et industrielles. Bien que ce problème soit étudié depuis de nombreuses années, sa compréhension n’est pas encore suffisante pour la création de modèles de transfert de masse réalistes (de type RANS ou LES sous maille), en particulier en présence d’une phase liquide à rhéologie complexe. Ce travail expérimental a pour but l’étude des aspects fondamentaux du transfert de masse turbulent à une interface plane horizontale entre du dioxyde de carbone gazeux et une phase liquide newtonienne ou non, agitée par une turbulence homogène quasi isotrope. Les milieux liquides non newtoniens étudiés sont des solutions aqueuses d’un polymère dilué à des concentrations variables et aux propriétés viscoélastiques et rhéofluidifiantes. Deux méthodes de mesure optiques permettant l’obtention du champ de vitesse de la phase liquide (SPIV) et de concentration du gaz dissout (I-PLIF) sont couplées tout en maintenant une haute résolution spatiale, afin de déduire les statistiques de vitesse et de concentration couplées dans les premiers millimètres sous la surface. Une nouvelle version de I-PLIF est développée pour les mesures en proche surface. Elle peut également s’appliquer dans différentes études de transfert de masse. La turbulence de fond est générée par un dispositif de grille oscillante. Les mécanismes de production et les caractéristiques de la turbulence sont étudiés. L’importance de la composante oscillante de la turbulence est discutée, et un phénomène d’amplification de l’écoulement moyen est mis en évidence. Les mécanismes du transfert de masse turbulent à l’interface sont finalement observés pour l’eau et une solution de polymère dilué à faible concentration. L’analyse conditionnelle des flux de masse turbulent permet de mettre en évidence les évènements contribuant au transfert de masse et de discuter de leur impact relatif sur le transfert totalThe study of turbulence induced mass transfer at the interface between a gas and a liquid is of great interest in many environmental phenomena and industrial processes. Even though this issue has already been studied for several decades, its understanding is still not good enough to create realistic models (RANS or sub-grid LES), especially when considering a liquid phase with a complex rheology. This experimental work aims at studying fundamental aspects of turbulent mass transfer at a flat interface between carbon dioxide and a Newtonian or non-Newtonian liquid, stirred by homogeneous and quasi isotropic turbulence. Non-Newtonian fluids studied are aqueous solutions of a model polymer, Xanthan gum (XG), at various concentrations, showing viscoelastic and shear-thinning properties. Optical techniques for the acquisition of the liquid phase velocity field (Stereoscopic Particle Image Velocimetry, SPIV) and dissolved gas concentration field (Inhibited Planar Laser Induced Fluorescence, I-PLIF) are for the first time coupled, keeping a high spatial resolution, to access velocity and concentration statistics in the first few millimetres under the interface. A new version of I-PLIF is developed. It is designed to be more efficient for near surface measurements, but its use can be generalized to other single or multiphase mass transfer situations. Bottom shear turbulence in the liquid phase is generated by an oscillating grid apparatus. The mechanisms of turbulence production and the characteristics of oscillating grid turbulence (OGT) are studied. The importance of the oscillatory component of turbulence is discussed. A mean flow enhancement effect upon polymer addition is evidenced. The mechanisms of turbulent mass transfer at a flat interface are finally observed in water and low concentration polymer solutions. A conditional analysis of turbulent mass fluxes allows to distinguish the type of events contributing to mass transfer and discuss their respective impact in water and polymer solutions
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Cristancho, Juan. "Statistics of the turbulent/non-turbulent interface in a spatially evolving mixing layer." Thesis, 2012. http://hdl.handle.net/10754/277454.
Повний текст джерелаАнотація:
The thin interface separating the inner turbulent region from the outer irrotational
fluid is analyzed in a direct numerical simulation of a spatially developing turbulent
mixing layer. A vorticity threshold is defined to detect the interface separating the
turbulent from the non-turbulent regions of the
flow, and to calculate statistics conditioned
on the distance from this interface. Velocity and passive scalar statistics are
computed and compared to the results of studies addressing other shear
flows, such
as turbulent jets and wakes. The conditional statistics for velocity are in remarkable
agreement with the results for other types of free shear
flow available in the literature.
In addition, a detailed analysis of the passive scalar field (with Sc 1) in the vicinity
of the interface is presented. The scalar has a jump at the interface, even stronger
than that observed for velocity. The strong jump for the scalar has been observed
before in the case of high Schmidt number, but it is a new result for Schmidt number
of order one. Finally, the dissipation for the kinetic energy and the scalar are presented.
While the kinetic energy dissipation has its maximum far from the interface,
the scalar dissipation is characterized by a strong peak very close to the interface.
Книги з теми "Interface turbulent/non-Turbulent"
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National Aeronautics and Space Administration (NASA) Staff. Aspects of Turbulent / Non-Turbulent Interfaces. Independently Published, 2018.
Знайти повний текст джерелаЧастини книг з теми "Interface turbulent/non-Turbulent"
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Rao, Samrat, G. R. Vybhav, P. Prasanth, S. M. Deshpande, and R. Narasimha. "Turbulent/Non-turbulent Interface of a Transient Diabatic Plume." In Lecture Notes in Mechanical Engineering, 355–61. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-5183-3_38.
Повний текст джерела
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Zhang, Xinxian. "Direct Numerical Simulation on Turbulent/Non-turbulent Interface in Compressible Turbulent Boundary Layers." In Frontiers of Digital Transformation, 155–68. Singapore: Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-1358-9_10.
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Cocconi, G., A. Cimarelli, B. Frohnapfel, and E. De Angelis. "A Numerical Study of the Shear-Less Turbulent/Non-turbulent Interface." In Springer Proceedings in Physics, 37–40. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-29130-7_6.
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Jahanbakhshi, Reza, and Cyrus K. Madnia. "Scalar Transport Near the Turbulent/Non-Turbulent Interface in Reacting Compressible Mixing Layers." In Modeling and Simulation of Turbulent Mixing and Reaction, 25–46. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-2643-5_2.
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Ferrey, P., and B. Aupoix. "Behaviour of Turbulence Models near a Turbulent/Non-Turbulent Interface Revisited." In Engineering Turbulence Modelling and Experiments 6, 137–46. Elsevier, 2005. http://dx.doi.org/10.1016/b978-008044544-1/50012-1.
Повний текст джерела
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Launder, Brian E. "Turbulence Modelling Near Interfaces: The Case for TCL Closures." In Wind-over-Wave Couplings, 313–26. Oxford University PressOxford, 1999. http://dx.doi.org/10.1093/oso/9780198501923.003.0030.
Повний текст джерелаАнотація:
Abstract The problem of predicting turbulent stresses and fluxes in the vicinity of an abrupt interface is considered, a class of flow phenomena that arises widely in stratified flows both in engineering and the environment. Second moment closures have in the past been applied to fairly simple problems of this type with “wall-reflection” terms being used to mimic the non viscous damping of turbulent transport that arises at the interface. It is argued, however, that a more generally valid approach needs to build on a modelling strategy that fully respects the two-component limit (TCL) to which turbulence must reduce at these interfaces. A summary of the closure developed by Craft et al. [5] and a number of applications of the model to flows involving interfaces is shown.
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Thrush, Simon F., Judi E. Hewitt, Conrad A. Pilditch, and Alf Norkko. "The sedimentary environment." In Ecology of Coastal Marine Sediments, 3–18. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198804765.003.0001.
Повний текст джерелаАнотація:
This chapter introduces the roles of sediment properties and hydrodynamic conditions in influencing soft-sediment communities. It identifies environmental factors that are commonly used to characterise soft-sediment habitats and used to tease out the role of habitat variation from other factors that influence populations and communities. The differences between cohesive and non-cohesive sediments that profoundly influence ecosystem functions are described. Hydrodynamics particularly at the sediment–water interface are introduced as a critical factor affecting many ecosystem processes. The chapter introduces the differences in laminar and turbulent flows. Coastal soft sediments in particular are places of high organic matter remineralisation and thus critical for the recycling of primary nutrients and primary production, particularly by microphytobenthos. These factors underpin the important role of marine sediments in biogeochemistry and earth system processes.
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Watanabe, Tomoaki, Koji Nagata, and Carlos B. da Silva. "Vorticity Evolution near the Turbulent/Non-Turbulent Interfaces in Free-Shear Flows." In Vortex Structures in Fluid Dynamic Problems. InTech, 2017. http://dx.doi.org/10.5772/64669.
Повний текст джерелаТези доповідей конференцій з теми "Interface turbulent/non-Turbulent"
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Taveira, Rodrigo M. R., and Carlos B. da Silva. "SCALAR MIXING AT TURBULENT/NON-TURBULENT INTERFACE OF A TURBULENT PLANE JET." In Eighth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2013. http://dx.doi.org/10.1615/tsfp8.520.
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Westerweel, Jerry, A. Petracci, Rene Delfos, and Julian C. R. Hunt. "THE TURBULENT/NON-TURBULENT INTERFACE OF A COOLED JET." In Fifth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2007. http://dx.doi.org/10.1615/tsfp5.1640.
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Kohan, Khashayar F., and Susan Gaskin. "The Turbulent/Non-Turbulent Interface Characteristics in an Axisymmetric Jet." In 7th International Conference on Fluid Flow, Heat and Mass Transfer (FFHMT'20). Avestia Publishing, 2020. http://dx.doi.org/10.11159/ffhmt20.162.
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da Silva, Carlos B., and Rodrigo M. R. Taveira. "CHARACTERISTICS OF THE TURBULENT/NON-TURBULENT INTERFACE AND VISCOUS SUPERLAYER IN TURBULENT PLANAR JETS." In Eighth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2013. http://dx.doi.org/10.1615/tsfp8.2170.
Повний текст джерела
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Ghasemi, Abbas, Vesselina Roussinova, Ronald Barron, and Ram Balachandar. "Analysis of Entrainment at the Turbulent/Non-Turbulent Interface of a Square Jet." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-65355.
Повний текст джерелаАнотація:
Particle image velocimetry measurements are carried out to study the entrainment at the interface between the non-turbulent and turbulent regions in a square jet. Jet Reynolds number based on the hydraulic diameter of the jet is 50,000. Measurements cover up to 25 diameters downstream of the nozzle exit using five horizontal field-of-views in the central plane of the jet. The turbulent/non-turbulent interface is identified using a velocity criterion and a suitable thresholding method. Using vorticity and swirling strength it is shown that the turbulent/non-turbulent interface separates the rotational and irrotational regions of the flow. Instantaneous velocity vector field superimposed with the turbulent/non-turbulent interface are presented. The relation between the vortex cores in the vicinity of the turbulent/non-turbulent interface and the contractions and expansions noticed in the jet velocity field are explained. Entrainment into the jet is evaluated at each axial distance by identifying the points falling inside the turbulent region of the jet. Compared to a round jet, the square jet entrains more ambient fluid. In addition, normal volume fluxes going through the turbulent/non-turbulent interface of the square jet are found to be larger compared to that of a round jet.
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Gampert, Markus, Philip Schaefer, Jonas Boschung, and Norbert Peters. "GRADIENT TRAJECTORY ANALYSIS OF THE TURBULENT/NON-TURBULENT INTERFACE IN A JET FLOW." In Eighth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2013. http://dx.doi.org/10.1615/tsfp8.2180.
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Attili, Antonio, Juan C. Cristancho, and Fabrizio Bisetti. "STATISTICS OF THE TURBULENT/NON-TURBULENT INTERFACE IN A SPATIALLY EVOLVING MIXING LAYER." In Eighth International Symposium on Turbulence and Shear Flow Phenomena. Connecticut: Begellhouse, 2013. http://dx.doi.org/10.1615/tsfp8.480.
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Tichenor, Nathan R. "Turbulent / Non-Turbulent Interface and Uniform Momentum Zones of High-Speed Turbulent Boundary Layers Subjected to Streamline Pressure Gradient." In AIAA Aviation 2019 Forum. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2019. http://dx.doi.org/10.2514/6.2019-3341.
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Terashima, Osamu, Yasuhiko Sakai, and Kouji Nagata. "Study on the Interfacial Layers Between the Turbulent/Non Turbulent Regions in Two Dimensional Turbulent Jet." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-21003.
Повний текст джерелаАнотація:
The interface between the turbulent and non turbulent regions in a two dimensional turbulent jet is investigated by the simultaneous measurement of the velocity and pressure. The measurement is performed by using a combined probe comprising an X-type hot-wire and a static pressure tube. The measurement data are analyzed by the conditional sampling technique and an ensemble averaged technique on the basis of the intermittency function for the turbulent/non turbulent decision. The experimental data at the cross-streamwise edge of the turbulent region show that there is a thin interfacial layer with a sharp jump of physical quantities (such as mean streamwise velocity) at the cross-streamwise edge of the turbulent region, and the thickness of the interfacial layer is 0.08 times the half-width of the cross-streamwise profile of the mean streamwise velocity. The turbulent diffusion term in the turbulent energy transport equation near the interfacial layer is examined. It is also found that the turbulent energy is transported from the inside of the interfacial layer to both the inner side (the side of the turbulent fluid) and the outer side (the side of the non turbulent fluid) by the diffusion term. Furthermore, the components of the diffusion term are separately estimated. It is found that the turbulent diffusion term shows the gain of the turbulent energy at the inner side of the interfacial layer, and the pressure diffusion term transports the turbulent energy to the non turbulent fluid. Moreover, small scale vortices are found in the interfacial layer. From these results, there is a possibility that the existence of the interfacial layer (existence of the vortices) contributes to the transport of the turbulent energy to the non turbulent fluid since the velocity and the pressure field that determine the pressure diffusion is greatly influenced by the existence of the interfacial layer. This hypothesis indicates that the outward propagation from a turbulent fluid can be attributed to the presence of vortices in the interfacial layer.
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Derksen, Jos. "Turbulent Mixing With Density Differences." In ASME-JSME-KSME 2011 Joint Fluids Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajk2011-21002.
Повний текст джерелаАнотація:
Homogenization of initially segregated and stably stratified systems consisting of two miscible liquids with different density and the same kinematic viscosity in an agitated tank was studied computationally. Reynolds numbers were in the range of 3,000 to 12,000 so that it was possible to solve the flow equations without explicitly modeling turbulence. The Richardson number that characterizes buoyancy was varied between 0 and 1. The stratification clearly lengthens the homogenization process. Two flow regimes could be identified. At low Richardson numbers large, three-dimensional flow structures dominate mixing, as is the case in non-buoyant systems. At high Richardson numbers the interface between the two liquids largely stays intact. It rises due to turbulent erosion, gradually drawing down and mixing up the lighter liquid.