Instabilities and Transition to Chaos in Flows between Concentric Cylinders

2008 ◽  
Vol 6 (1) ◽  
Author(s):  
Aomar Ait Aider
Keyword(s):  
Visual Observation ◽  
Experimental Investigations ◽  
Flow Measurements ◽  
Dean Flow ◽  
Concentric Cylinders ◽  
Computational Fluid Dynamics Analysis ◽  
Long Time ◽  
Taylor Couette ◽  
Geometrical Effects ◽  
Cylinder Rotation

How does turbulence rise? For a long time, a century, the Taylor-Couette system was a paradigm for the researchers who tried to get answers to this question. Fascinating structures and patterns observed in the flow have attracted the interest of many researchers, both experimentalists and theorists. During the last century, many works were done on the closed Taylor-Couette systems. At the end of the seventies, after thousands of contributions, experiments performed in the Taylor-Couette system confirmed a theoretical analysis which concluded that a finite number of instabilities, two or three, are sufficient to lead to chaos or weak turbulence. Our own experiments were conducted at that time on a Taylor-Couette system with a moderate aspect ratio. They were analyzed from visual observation and fine local measurement with an electrochemical method. Scalar time series and data pointed out the frequencies characteristic of the flow. Many geometrical effects are considered by researchers. When the gap is horizontal and not completely filled, the flow obtained is called Taylor-Dean flow. We obtained similar flow in an azimuthally open Taylor-Couette system where a combination of the inner cylinder rotation and external fluid pumping, the Dean flow, produces the so called Taylor-Dean flow. Measurements and analysis were carried out by visualization and Laser Doppler Velocimetry. In addition to the experimental approach, we used Computational Fluid Dynamics analysis to complete the flow study. Numerical and experimental investigations reveal a class of instabilities of the Taylor-Dean flow not previously observed in the Taylor-Couette flow due to the cylinder rotation neither in the Dean flow due to the external pumping fluid.

Numerical Investigation of Flow Around a ROV With Crawler Based Driving System

2012 ◽  
Author(s):  
Tokihiro Katsui ◽  
Satoshi Kajikawa ◽  
Tomoya Inoue
Keyword(s):  
Hydrodynamic Forces ◽  
Point Of View ◽  
Design Parameters ◽  
Experimental Investigations ◽  
Accurate Estimation ◽  
Remotely Operated Vehicle ◽  
Driving System ◽  
Sea Bottom ◽  
Computational Fluid Dynamics Analysis ◽  
Turn Over

The Remotely Operated Vehicle, so called “ROV” which has crawler based moving system is considered as one of the appropriate underwater vehicles for seafloor exploration or seabed resources development [1][2][3][4][5][6][7]. The advantages of crawler driven ROV are to be able to stay on a fixed sea bottom location and to be capable to do heavy works such as digging the seafloor. However, the ROV moving on the sea bottom with crawler based driving system easily turn over due to the buoyancy and hydrodynamic forces [8][9][10][11][12]. Therefore, it is important to know the moving capability of the ROV on the sea bottom for the design point of view. The authors have shown the condition for the normal running of the ROV which moves on horizontal and inclined flat sea bottom by means of a simple dynamic model [11]. Normal running means that the ROV runs without bow-up or stern-up situations and the crawlers touch the ground normally. The normal running condition of ROV indicates the constrained condition of the relation between gravity and buoyancy center locations for any given design parameters such as geometry, weight, displacement and running speed of the ROV. Though this method estimates the ROVs’ moving capability with acceptable accuracy, the hydrodynamic forces on the ROV and its application point are required for accurate estimation. In the previous research, those quantities are roughly estimated from the past experimental investigations. The present study investigated the flow around the crawler driven ROV which runs on seafloor with CFD (Computational Fluid Dynamics) analysis to evaluate the characteristics of hydrodynamic forces acting on the ROV. The open source CFD code, OpenFOAM [13] was applied for flow calculation and the results were validated with model experiments. By using the calculated hydrodynamic forces on ROV, the moving capability of ROV was evaluated with a method the authors had shown. The estimates of the running capability of the ROV by using the CFD calculations are quite different from past estimations in some running conditions.

A flow visualization and superposition rheology study of shear-banding wormlike micelle solutions

Soft Matter ◽  
2016 ◽  
Vol 12 (4) ◽  
pp. 1051-1061 ◽  
Author(s):  
Hadi Mohammadigoushki ◽  
Susan J. Muller
Keyword(s):  
Diffusion Coefficient ◽  
Flow Visualization ◽  
Correlation Length ◽  
Micellar Solution ◽  
Shear Banding ◽  
Shear Bands ◽  
Wormlike Micelle ◽  
Concentric Cylinders ◽  
Stress Diffusion ◽  
Taylor Couette

In this paper, we use rheometry and flow visualization to study the dynamics of the interface between shear bands in a wormlike micellar solution sheared between concentric cylinders, i.e., in a Taylor–Couette (TC) cell, and to evaluate the stress diffusion coefficient and the stress correlation length in the Johnson–Segalman model.

Experimental Pragmatics

2017 ◽  
Author(s):  
Florian Schwarz
Keyword(s):  
Great Depth ◽  
Definite Descriptions ◽  
Experimental Investigations ◽  
Ongoing Research ◽  
Experimental Pragmatics ◽  
Long Time ◽  
History Of ◽  
Actual Interaction ◽  
Referential Expressions ◽  
Linguistic Material

While both pragmatic theory and experimental investigations of language using psycholinguistic methods have been well-established subfields in the language sciences for a long time, the field of Experimental Pragmatics, where such methods are applied to pragmatic phenomena, has only fully taken shape since the early 2000s. By now, however, it has become a major and lively area of ongoing research, with dedicated conferences, workshops, and collaborative grant projects, bringing together researchers with linguistic, psychological, and computational approaches across disciplines. Its scope includes virtually all meaning-related phenomena in natural language comprehension and production, with a particular focus on what inferences utterances give rise to that go beyond what is literally expressed by the linguistic material. One general area that has been explored in great depth consists of investigations of various ‘ingredients’ of meaning. A major aim has been to develop experimental methodologies to help classify various aspects of meaning, such as implicatures and presuppositions as compared to basic truth-conditional meaning, and to capture their properties more thoroughly using more extensive empirical data. The study of scalar implicatures (e.g., the inference that some but not all students left based on the sentence Some students left) has served as a catalyst of sorts in this area, and they constitute one of the most well-studied phenomena in Experimental Pragmatics to date. But much recent work has expanded the general approach to other aspects of meaning, including presuppositions and conventional implicatures, but also other aspects of nonliteral meaning, such as irony, metonymy, and metaphors. The study of reference constitutes another core area of research in Experimental Pragmatics, and has a more extensive history of precursors in psycholinguistics proper. Reference resolution commonly requires drawing inferences beyond what is conventionally conveyed by the linguistic material at issue as well; the key concern is how comprehenders grasp the referential intentions of a speaker based on the referential expressions used in a given context, as well as how the speaker chooses an appropriate expression in the first place. Pronouns, demonstratives, and definite descriptions are crucial expressions of interest, with special attention to their relation to both intra- and extralinguistic context. Furthermore, one key line of research is concerned with speakers’ and listeners’ capacity to keep track of both their own private perspective and the shared perspective of the interlocutors in actual interaction. Given the rapid ongoing growth in the field, there is a large number of additional topical areas that cannot all be mentioned here, but the final section of the article briefly mentions further current and future areas of research.

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry—Part I: Compressor Performance Analysis

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Stefan Ubben ◽  
Reinhard Niehuis
Keyword(s):  
Centrifugal Compressor ◽  
Negative Impact ◽  
Pressure Ratio ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Flow Measurements ◽  
Flow Phenomena ◽  
Compressor Performance ◽  
Compressor Map ◽  
The Impact

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency as long as the diffuser passage is broad enough with respect to the clearance height. The flow phenomena responsible for this detected performance behavior are exposed in Part II, where the results of detailed measurements with pressure probes at diffuser exit and particle image velocimetry (PIV) measurements conducted inside the diffuser channel are discussed. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”

scholarly journals Transient growth in linearly stable Taylor–Couette flows

2014 ◽  
Vol 742 ◽  
pp. 254-290 ◽  
Author(s):  
Simon Maretzke ◽  
Björn Hof ◽  
Marc Avila
Keyword(s):  
Linear Stability ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Transient Growth ◽  
Energy Growth ◽  
Transient Energy ◽  
Taylor Couette ◽  
Semi Empirical ◽  
Essential Prerequisite ◽  
Cylinder Rotation

AbstractNon-normal transient growth of disturbances is considered as an essential prerequisite for subcritical transition in shear flows, i.e. transition to turbulence despite linear stability of the laminar flow. In this work we present numerical and analytical computations of linear transient growth covering all linearly stable regimes of Taylor–Couette flow. Our numerical experiments reveal comparable energy amplifications in the different regimes. For high shear Reynolds numbers$\mathit{Re}$, the optimal transient energy growth always follows a$\mathit{Re}^{2/3}$scaling, which allows for large amplifications even in regimes where the presence of turbulence remains debated. In co-rotating Rayleigh-stable flows, the optimal perturbations become increasingly columnar in their structure, as the optimal axial wavenumber goes to zero. In this limit of axially invariant perturbations, we show that linear stability and transient growth are independent of the cylinder rotation ratio and we derive a universal$\mathit{Re}^{2/3}$scaling of optimal energy growth using Wentzel–Kramers–Brillouin theory. Based on this, a semi-empirical formula for the estimation of linear transient growth valid in all regimes is obtained.

On the Stability of Taylor - Couette Flow With Axial Flow

2012 ◽  
Author(s):  
Emna Berrich ◽  
Fethi Aloui ◽  
Jack Legrand
Keyword(s):  
Flow Direction ◽  
Axial Flow ◽  
Diffusion Method ◽  
Diffusion Limit ◽  
Taylor Flow ◽  
Concentric Cylinders ◽  
Reflected Light ◽  
Helical Vortices ◽  
Taylor Couette ◽  
The Stability

An experimental investigation of Taylor-Couette flows with axial flow is presented. Two techniques are used: Visualization using the Kalliroscope and Electro-diffusion method using electrochemical probes. The fluid is confined between concentric cylinders. It is constituted by an electrochemical solution seeding with 2% of a rheoscopic liquid AQ-1000 (Kalliroscope Corp., U.S.A.). The rheoscopic liquid contains small particles reflecting light in dependence on their orientation imposed by the flow direction. The reflected light intensity of Kalliroscope flakes allows a qualitative study of the flow. While the polarography technique allows the measurement of diffusion limit current intensities delivered by the electrochemical probes. The frequency responses of the probe to the flow allow the determination of the instantaneous and local mass transfer and the instantaneous wall shear rate. Two protocols were adopted to study the effect of an axial flow superposed to Couette-Taylor flows and the history flow effect. The first one consists to impose an azimuthal flow to the inner cylinder. When the regime was established, we superposed the axial flow. This protocol was named “the direct protocol”. While the second protocol consists to impose firstly the axial flow on the gap of the system then the azimuthal flow. We named it “the inverse protocol”. We demonstrated that the Couette-Taylor flow with axial flow is strongly dependent on the flow history (the protocol). For the same Taylor number and axial Reynolds number, the resulting flow is completely different. An axial flow superposed to Couette-Taylor flow can delay the instabilities apparition; generate the displacement of the Taylor vortices in the same direction as the axial flow or in the opposite direction; and modify the instability character of the flow by developing helical vortices or wavy helical vortices.

scholarly journals A new concept to improve microwave heating uniformity through data-driven process modelling

2019 ◽  
Author(s):  
Yingguang Li ◽  
Jing Zhou ◽  
Di Li
Keyword(s):  
Microwave Heating ◽  
Process Model ◽  
Influence Factor ◽  
Data Driven ◽  
Experimental Investigations ◽  
Microwave System ◽  
Long Time ◽  
Heating Uniformity ◽  
Heating Pattern

For a long time, the heating pattern of the workpiece within a multimode microwave oven was considered to be highly sophisticated. As a consequence, the uneven microwave heating problem can only be partly alleviated by a random movement between the electromagnetic field and the workpiece. In this paper, we reported that the heating pattern has a specific correspondence with microwave system settings. The influence factor of the heating pattern and the corresponding mechanism were systematically studied by both theoretical analysis and experimental investigations. On this basis, a data-driven process model was established to learn the material’s dynamic temperature behaviors under different microwave system settings, and a new concept to improve the microwave heating uniformity by temperature monitoring and active compensation was proposed. The effectiveness of the method was demonstrated by a polymer composite microwave processing case study.

Experimental Investigations of the Surface Groove Effect in Taylor-Couette-Poiseuille Flow

2020 ◽  
Author(s):  
Lamia Gaied ◽  
Fethi Aloui ◽  
Marc Lippert ◽  
Emna Berrich
Keyword(s):  
Couette Flow ◽  
Vortex Flow ◽  
Axial Flow ◽  
Vortex Structures ◽  
Base Flow ◽  
Taylor Vortex ◽  
Experimental Investigations ◽  
Surface Groove ◽  
Taylor Couette ◽  
The Impact

Abstract In this paper, we investigate the effects of an imposed axial flow on hydrodynamic instabilities’ Couette-Taylor flow in the case where the wall of the inner cylinder of the system is grouved. Without imposed axial flow, the basic flow of a fluid between two coaxial cylinders known by Couette flow, which is characterized by several temporal and spatial symmetries. The increase in the rotation causes the breaking of these symmetries. In both cases where the surface of the inner cylinder is smooth and grooved, five different flow regimes can be determined: Taylor vortex flow (TVF), wavy vortex flow (WVF), and Modulated Wavy vortex flow (MWVF). Each time the flow passes from one hydrodynamic regime to another until it enters a state of turbulence, which is characterized by the destruction of all the symmetries that existed at the beginning. In addition, when an axial flow is imposed on a Taylor-Couette flow, new helical vortex structures are observed in both cases (with and without surface groove). The influence of surface structures (grooves) on the shear stress of the wall is discussed with and without axial base flow. A spatio-temporal description of several flow models was obtained using firstly, a visualization’s qualitative study using kalliroscope particles. Secondly, a quantitative study by polarography using simple probes have been used to characterize the impact of vortex structures on the Couette-Taylor flows without and with an axial flow on the transfer.

scholarly journals Numerical simulation and in vitro examination of the flow behaviour within coronary stents

2019 ◽  
Vol 5 (1) ◽  
pp. 541-544
Author(s):  
Helena-Sophie Melzer ◽  
Ralf Ahrens ◽  
Andreas E. Guber ◽  
Jakob Dohse
Keyword(s):  
Design Parameters ◽  
Experimental Investigations ◽  
Metallic Stent ◽  
Flow Measurements ◽  
Micro Particle Image Velocimetry ◽  
Micro Piv ◽  
Stent Restenosis ◽  
Image Velocimetry ◽  
Stent Strut

AbstractThis paper discusses the influence of different design parameters of stents by mathematical flow simulations and flow measurements using micro-particle image velocimetry (micro-PIV). A stent strut may cause recirculation areas, which are considered to be the source of thrombosis and the process of in-stent restenosis. The simulations showed that a reduced strut height and a chamfering of the struts reduce these recirculation zones. The numerically determined results were compared with experimental investigations. For this purpose metallic stent structures were transferred into transparent channel systems made of PDMS. The experimental investigations confirm the results of numerical simulations.

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