scholarly journals Fluid Gauge Theory

2021 ◽  
pp. 113-147
Author(s):  
Tsutomu Kambe
Keyword(s):  
Gauge Theory ◽  
Stress Field ◽  
Fluid Mechanics ◽  
Perfect Fluid ◽  
Turbulent Flows ◽  
Large Scale ◽  
Flow Fields ◽  
Turbulent Shear ◽  
Current Conservation ◽  
Anisotropic Stress

According to the general gauge principle, Fluid Gauge Theory is presented to cover a wider class of flow fields of a perfect fluid without internal energy dissipation under anisotropic stress field. Thus, the theory of fluid mechanics is extended to cover time dependent rotational flows under anisotropic stress field of a compressible perfect fluid, including turbulent flows. Eulerian fluid mechanics is characterized with isotropic pressure stress fields. The study is motivated from three observations. First one is experimental observations reporting large-scale structures coexisting with turbulent flow fields. This encourages a study of how such structures observed experimentally are possible in turbulent shear flows, Second one is a theoretical and mathematical observation: the ”General solution to Euler’s equation of motion” (found by Kambe in 2013) predicts a new set of four background-fields, existing in the linked 4d-spacetime. Third one is a physical query, ”what symmetry implies the current conservation law ?”. The latter two observations encourage a gauge-theoretic formulation by defining a differential one-form representing the interaction between the fluid-current field jμand a background field aμ.

Signature of coalescence during scalar mixing in heterogeneous flow fields

2020 ◽  
Author(s):  
Sabyasachi Sen ◽  
Prajwal Singh ◽  
Joris Heyman ◽  
Tanguy Le Borgne ◽  
Aditya Bandopadhyay
Keyword(s):  
Porous Media ◽  
Fluid Mechanics ◽  
Large Scale ◽  
Scalar Fields ◽  
Flow Fields ◽  
Scalar Mixing ◽  
Heterogeneous Flow ◽  
Strip Method ◽  
Mixing Rates ◽  
Flow Through

<p>Stretching of fluid elements by a heterogeneous flow field, such as the flow through a porous media or geophysical flows such as atmospheric or oceanic vortices, is known to enhance mixing rates of scalar fields[1]. While the mechanisms leading to the elongation of material lines are well understood, predicting mixing rates still remains a challenge particularly when there is a reconnection (or aggregation) between several parts of the mixing interface, leading, at large mixing time, to a so-called coalescence regime[1][2]. In this presentation, we numerically study this coalescence dynamics through scalar transport in two different flow fields, the Rankine vortex and Stokes flow through a periodic bead pack[3]. The former is typical of large-scale turbulent flows [4] whereas the second is generic of small-scale laminar flows in porous media [5]. Both flows show a net elongation of the mixing interfaces, although at very different rates. To solve the transport problem in these flows, we use a Lagrangian method (the diffusive strip method[6]). This method allows us to reconstruct, at high resolution, the scalar concentration fields and to compute the evolution of the distribution of concentrations levels, scalar dissipation rate and scalar power spectrum in time. The signature of coalescence is clearly observed in both flows and we assess the influence of coalescence on the difference in mixing behaviour for the two flows. We finally discuss how coalescence may affect the reaction kinetics of mixing-limited reactive flows. The analysis proposed sheds light on fundamental aspects of transport and mixing in earth surface and subsurface flows.</p><p>[1] Emmanuel Villermaux. Mixing versus stirring. Annual Review of Fluid Mechanics, 51:245–273, 2019.<br>[2] Tanguy Le Borgne, Marco Dentz, and Emmanuel Villermaux. The lamellar description of mixing in porous media. Journal of Fluid Mechanics, 770:458–498, 2015.<br>[3] Régis Turuban, David R Lester, Tanguy Le Borgne, and Yves Méheust. Space-group symmetries generate chaotic fluid advection in crystalline granular media. Physical review letters, 120(2):024501, 2018.<br>[4] RT Pierrehumbert. Large-scale horizontal mixing in planetary atmospheres. Physics of Fluids A: Fluid Dynamics, 3(5):1250–1260, 1991.<br>[5] Brian Berkowitz, Andrea Cortis, Marco Dentz, and Harvey Scher. Modeling non-fickian transport in geological formations as a continuous time random walk. Reviews of Geophysics, 44(2), 2006.<br>[6] Patrice Meunier and Emmanuel Villermaux. The diffusive strip method for scalar mixing in two dimensions. Journal of fluid mechanics, 662:134–172, 2010.</p>

scholarly journals Ridge-type roughness: from turbulent channel flow to internal combustion engine

2021 ◽  
Vol 63 (1) ◽  
Author(s):  
Lars H. von Deyn ◽  
Marius Schmidt ◽  
Ramis Örlü ◽  
Alexander Stroh ◽  
Jochen Kriegseis ◽  
...  
Keyword(s):  
Turbulent Flow ◽  
Turbulent Flows ◽  
Large Scale ◽  
Combustion Engine ◽  
Rough Surfaces ◽  
Turbulent Channel Flow ◽  
Turbulent Shear ◽  
Homogeneous Surface ◽  
Reynolds Number Dependency ◽  
Near Wall

Abstract While existing engineering tools enable us to predict how homogeneous surface roughness alters drag and heat transfer of near-wall turbulent flows to a certain extent, these tools cannot be reliably applied for heterogeneous rough surfaces. Nevertheless, heterogeneous roughness is a key feature of many applications. In the present work we focus on spanwise heterogeneous roughness, which is known to introduce large-scale secondary motions that can strongly alter the near-wall turbulent flow. While these secondary motions are mostly investigated in canonical turbulent shear flows, we show that ridge-type roughness—one of the two widely investigated types of spanwise heterogeneous roughness—also induces secondary motions in the turbulent flow inside a combustion engine. This indicates that large scale secondary motions can also be found in technical flows, which neither represent classical turbulent equilibrium boundary layers nor are in a statistically steady state. In addition, as the first step towards improved drag predictions for heterogeneous rough surfaces, the Reynolds number dependency of the friction factor for ridge-type roughness is presented. Graphic abstract

Coherent Structures in Turbulent Shear Flows: The Confluence of Experimental and Numerical Approaches (Keynote Paper)

2002 ◽  
Author(s):  
Jean-Paul Bonnet ◽  
Joel Delville ◽  
M. N. Glauser
Keyword(s):  
Turbulent Flows ◽  
Coherent Structures ◽  
Large Scale ◽  
Reynolds Numbers ◽  
Turbulent Shear ◽  
Number Range ◽  
Universal Behavior ◽  
Simulation Tools ◽  
Background Turbulence ◽  
Low Dimensional

Physics based low dimensional approaches are playing an increasingly important role in our understanding of turbulent flows. They provide an avenue for us to understand the connection between coherent structures and the overall dynamics of the flow field. As such these approaches are fundamental to the implementation of physics based active control methodologies. In this paper we review applications of various low dimensional approaches (including Proper Orthogonal Decomposition (POD), Linear Stochastic Estimation (LSE), Conditional Averages and Wavelets) to turbulent shear layers and connect the results to simulation tools. The applications of all these methods to the 2D shear layer suggest a kind of universal behavior of both the large scale structure extracted and the background turbulence, irrespective of the technique (filtering method) used. A review of the application of POD and LSE to the axisymmetric jet at Reynolds numbers between 100,000 and 800,000 and Mach numbers ranging from very low to 0.6 suggest a universal behavior where the dynamics can be described with relatively low dimensional information (1 POD mode and 5 or 6 Fourier azimuthal modes) over the Reynolds/Mach number range studied. These results provide physical justification for simulation tools such as VLES, LES and SDM since such computational methods involve different levels of low-dimensional modeling.

The structure of a turbulent shear layer bounding a separation region

1987 ◽  
Vol 179 ◽  
pp. 439-468 ◽  
Author(s):  
I. P. Castro ◽  
A. Haque
Keyword(s):  
Shear Layer ◽  
Turbulent Flows ◽  
Large Scale ◽  
Turbulent Shear ◽  
Turbulence Structure ◽  
Similar Data ◽  
Reynolds Stresses ◽  
Plate Height ◽  
Separated Shear Layer ◽  
Wide Range

Detailed measurements within the separated shear layer behind a flat plate normal to an airflow are reported. A long, central splitter plate in the wake prevented vortex shedding and led to an extensive region of separated flow with mean reattachment some ten plate heights downstream. The Reynolds number based on plate height was in excess of 2 × 1044.Extensive use of pulsed-wire anemometry allowed measurements of all the Reynolds stresses throughout the flow, along with some velocity autocorrelations and integral timescale data. The latter help to substantiate the results of other workers obtained in separated flows of related geometry, particularly in the identification of a very low-frequency motion with a timescale much longer than that associated with the large eddies in the shear layer. Wall-skin-friction measurements are consistent with the few similar data previously published and indicate that the thin boundary layer developing beneath the separated region has some ‘laminar-like’ features.The Reynolds-stress measurements demonstrate that the turbulence structure of the separated shear layer differs from that of a plane mixing layer between two streams in a number of ways. In particular, the normal stresses all rise monotonically as reattachment is approached, are always considerably higher than the plane layer values and develop in quite different ways. Flow similarity is not a useful concept. A major conclusion is that any effects of stabilizing streamline curvature are weak compared with the effects of the re-entrainment at the low-velocity edge of the shear layer of turbulent fluid returned around reattachment. It is argued that the general features of the flow are likely to be similar to those that occur in a wide range of complex turbulent flows dominated by a shear layer bounding a large-scale recirculating region.

scholarly journals Large-eddy simulation of particle-laden turbulent flows

2008 ◽  
Vol 614 ◽  
pp. 207-252 ◽  
Author(s):  
M. BINI ◽  
W. P. JONES
Keyword(s):  
Liquid Phase ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Isotropic Turbulence ◽  
Probabilistic Approach ◽  
Turbulent Shear ◽  
Turbulent Shear Flow ◽  
Eddy Simulation ◽  
Large Eddy

A large-eddy-based methodology for the simulation of turbulent sprays is discussed. The transport equations for the spatially filtered gas phase variables, in which source terms accounting for the droplet effects are added, are solved together with a probabilistic description of the liquid phase. The probabilistic approach for the liquid phase is based on the transport equation for the spatially filtered joint probability density function of the variables required in order to describe the state of the liquid phase. In this equation, unclosed terms representing the filtered Lagrangian rates of change of the variables describing the spray are present. General modelling ideas for subgrid-scale (SGS) effects are proposed. The capabilities of the approach and the validity of the closure models, with particular with respect to the SGS dispersion, are investigated through application to a dilute particle-laden turbulent mixing layer. It is demonstrated that the formulation is able to reproduce very closely the measured properties of both the continuous and dispersed phases. The large-eddy simulation (LES) results are also found to be entirely consistent with the experimentally observed characteristics of droplet–gas turbulence interactions. Consistent with direct numerical simulation (DNS) studies of isotropic turbulence laden with particles where the entire turbulence spectrum is found to be modulated by the presence of particles, the present investigation, which comprises the effects of particle transport upon the large-scale vortical structures of a turbulent shear flow, highlights what appears to be a selective behaviour; few large-scale frequencies gain energy whereas the remaining modes are damped.

scholarly journals Revisiting Taylor's hypothesis

2009 ◽  
Vol 640 ◽  
pp. 1-4 ◽  
Author(s):  
P. MOIN
Keyword(s):  
Turbulent Flows ◽  
Large Scale ◽  
Shear Flows ◽  
Turbulent Shear ◽  
Experimental Measurements ◽  
Turbulent Structures ◽  
Numerical Computations ◽  
Taylor’S Hypothesis ◽  
Spatial Fluctuations ◽  
Cast Doubt

Taylor's hypothesis, relating temporal to spatial fluctuations in turbulent flows is investigated using powerful numerical computations by del Álamo & Jiménez (J. Fluid Mech., 2009, this issue, vol. 640, pp. 5–26). Their results cast doubt on recent interpretations of bimodal spectra in relation to very large-scale turbulent structures in experimental measurements in turbulent shear flows.

Effects of Squish Flow on Tangential Flow and Turbulence in a Diesel Engine

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Yanzhe Sun ◽  
Kai Sun ◽  
Tianyou Wang ◽  
Yufeng Li ◽  
Zhen Lu
Keyword(s):  
Diesel Engine ◽  
Turbulent Flows ◽  
Large Scale ◽  
Radial Flow ◽  
Tangential Component ◽  
Tangential Flow ◽  
Image Velocimetry ◽  
Turbulence Production ◽  
Large Scale Flow ◽  
Main Effects

Emission and fuel consumption in swirl-supported diesel engines strongly depend on the in-cylinder turbulent flows. But the physical effects of squish flow on the tangential flow and turbulence production are still far from well understood. To identify the effects of squish flow, Particle image velocimetry (PIV) experiments are performed in a motored optical diesel engine equipped with different bowls. By comparing and associating the large-scale flow and turbulent kinetic energy (k), the main effects of the squish flow are clarified. The effect of squish flow on the turbulence production in the r−θ plane lies in the axial-asymmetry of the annular distribution of radial flow and the deviation between the ensemble-averaged swirl field and rigid body swirl field. Larger squish flow could promote the swirl center to move to the cylinder axis and reduce the deformation of swirl center, which could decrease the axial-asymmetry of annular distribution of radial flow, further, that results in a lower turbulence production of the shear stress. Moreover, larger squish flow increases the radial fluctuation velocity which makes a similar contribution to k with the tangential component. The understanding of the squish flow and its correlations with tangential flow and turbulence obtained in this study is beneficial to design and optimize the in-cylinder turbulent flow.

scholarly journals Influence of El Niño Wind Stress Anomalies on South Brazil Bight Ocean Volume Transports

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
Luiz Paulo de Freitas Assad ◽  
Carina Stefoni Böck ◽  
Rogerio Neder Candella ◽  
Luiz Landau
Keyword(s):  
Stress Field ◽  
Interannual Variability ◽  
Wind Stress ◽  
Large Scale ◽  
Time Lag ◽  
Surface Wind ◽  
Circulation Model ◽  
Volume Transport ◽  
Wind Stress Field ◽  
Volume Transports

The knowledge of wind stress variability could represent an important contribution to understand the variability over upper layer ocean volume transports. The South Brazilian Bight (SBB) circulation had been studied by numerous researchers who predominantly attempted to estimate its meridional volume transport. The main objective and contribution of this study is to identify and quantify possible interannual variability in the ocean volume transport in the SBB induced by the sea surface wind stress field. A low resolution ocean global circulation model was implemented to investigate the volume transport variability. The results obtained indicate the occurrence of interannual variability in meridional ocean volume transports along three different zonal sections. These results also indicate the influence of a wind driven large-scale atmospheric process that alters locally the SBB and near-offshore region wind stress field and consequently causes interannual variability in the upper layer ocean volume transports. A strengthening of the southward flow in 25°S and 30°S was observed. The deep layer ocean volume transport in the three monitored sections indicates a potential dominance of other remote ocean processes. A small time lag between the integrated meridional volume transports changes in each monitored zonal section was observed.

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