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Dissertations / Theses on the topic 'Moderate reynolds'

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Published: 4 June 2021

Last updated: 1 February 2022

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1

Biswas, Anupam. "Hydrodynamic interaction between cylinders at moderate Reynolds numbers." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44730.

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The hydrodynamic interaction between two cylinders perpendicular to the freestream, in a tandem arrangement was studied for moderate Reynolds numbers (1≤Re≤40). The influence of multiple geometric variables was considered: separation distances between the cylinders, ellipticity of the cylinders, the cylinder aspect ratio, and the angular inclination between the cylinders. In the first part of this study, a numerical investigation of the two-dimensional steady flow past cylinders was carried out. The characteristic length, D, in all simulations was taken to be twice the major axis of the cylinder cross-section, (i.e. equal to the diameter for cylinders of circular cross-section). The two-dimensional flow was studied for separations up to 50D. Four different ellipticities were studied. The drags experienced by front and rear cylinders were compared with that experienced by a single cylinder of the same cross-section. The second part of the study consisted of the steady three-dimensional flow analysis for parallel cylinders in tandem for separations ranging from 2D to 20D and cylinder lengths up to 20D. In the third part of this thesis, a steady flow analysis was done for two circular cylinders in tandem with lengths equal to 5D but with the cylinder axes in different orientations relative to the plane normal to the flow. This angular separation between the cylinders produces a hydrodynamic moment, which is dependent on the geometry and the flow Reynolds number. The fourth and final part of this work is the study of the unsteady three-dimensional flow that would result from the hydrodynamic moment discussed in relation to the third part of the thesis. The thesis closes with some remarks on the implications of these findings to papermaking and recommendations for future work.

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2

Tang, Tongdar Danny. "Periodic flow in a bifurcating tube at moderate reynolds number." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/17066.

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3

Sirisup, Sirod. "Linear stability of plane Couette flow at moderate Reynolds numbers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq64453.pdf.

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4

Van, Hirtum Annemie. "Moderate Reynolds number ﬂow. Application to the human upper airways." Habilitation à diriger des recherches, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00747213.

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The study of ﬂuid ﬂow is an amasingly ordinary as well as fascinating subject. During the past few years I had the opportunity to work as a researcher in the ﬁeld of ﬂuid ﬂow modelling applied to airﬂow through the human upper airways and related phenomena such as speech production, . . . The current document is a brief report on the research to which I participated aiming a small contribution to this rich and stimulating research area.

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5

Giacobello, Matteo. "Wake structure of a transversely rotating sphere at moderate Reynolds numbers." Online version, 2005. http://repository.unimelb.edu.au/10187/2840.

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Over the last century, the problem of a viscous flow past a sphere has received on-going attention due to its many engineering applications. These include combustion processes, sediment transport processes and atmospheric flow problems, where the sphere serves as a good model for more general bluff body particles. In these environments, particles may be subjected to both translational and rotational velocities. The objective of this study was to investigate the effect that sphere rotation, about an axis transverse to the freestream flow, has on the characteristics or the vertical wake structure and the forces exerted on the sphere. That was achieved by solving the time-dependant, incompressible Navier Stokes equations, using a highly accurate Fourier Chebyshev spectral collation method.

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6

Bell, Martin Derek. "Ordering of particulate suspensions in Couette flow at moderate Reynolds numbers." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28901.

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A remarkable ordering phenomenon has been seen to occur when a suspension of particles undergoes shear at particle Reynolds numbers of the order of or greater than one in the annular gap of a Couette type shearing device. This particulate ordering was observed and studied with both suspensions of rigid spheres and suspensions of polystyrene latex aggregates formed in the presence of shear within the gap. Each of these systems was studied under a variety of initial conditions in order to define the particular flow conditions required for particle alignment to occur. It was found that particulate ordering occurred under similar conditions to those used by Segré and Silberberg (35) to observe the "necklace formations" that formed within particulate suspensions flowing inside tubes. The separations between aligned particles was found to be strongly dependent on the particle Reynolds number and the ratio between the particle diameter and the width of the annular gap. An insight into the hydrodynamic interactions occurring was provided by the comparisons made between the ordered aggregates and the ordered rigid spheres under similar flow conditions.
Science, Faculty of
Chemistry, Department of
Graduate

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7

Konozsy, Laszlo. "Multiphysics CFD modelling of incompressible flows at Low and Moderate Reynolds Numbers." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7860.

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In this Ph.D. thesis, a novel high-resolution Godunov-type numerical procedure has been developed for solving the unsteady, incompressible Navier-Stokes equations for constant and variable density flows. The proposed FSAC-PP approach encompasses both artificial compressibility (AC) and fractional step (FS) pressure-projection (PP) methods of Chorin [3, 4] in a unified solution concept. To take advantage of different computational strategies, the FS and AC methods have been coupled (FSAC formulation), and further a PP step has been employed at each pseudo-time step. To provide time-accurate solutions, the dual-time stepping procedure is utilized. Taking the advantage of the hyperbolic nature of the inviscid part of the AC formulation, high-resolution characteristics-based (CB) Godunov-type scheme is employed to discretize the non-linear advective fluxes. Highorder of accuracy is achieved by using from first- up to ninth-order interpolation schemes. Time integration is obtained from a fourth-order Runge-Kutta scheme. A non-linear fullmultigrid, full-approximation storage (FMG-FAS) acceleration technique has been further extended to the FSAC-PP solution method to increase the efficiency and decrease the computational cost of the developed method and simulations. Cont/d.

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8

Beirutty, Mohammad Hussein. "Development of a hot-wire measurement technique for moderate intensity three-dimensional flows /." Thesis, Connect to this title online; UW restricted, 1987. http://hdl.handle.net/1773/7074.

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9

Oshida, Takeshi. "Surface equation of falling film flows with moderate Reynolds number and large but finite Weber number." 京都大学 (Kyoto University), 2000. http://hdl.handle.net/2433/181170.

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10

Patrick, Wilfred Vinod. "Computations of Flow Structures and Heat Transfer in a Dimpled Channel at Low to Moderate Reynolds Number." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33415.

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Time-accurate calculations are used to investigate the three-dimensional flow structure and understand its influence on the heat transfer in a channel with concave indentations on one wall. A dimple depth to channel height ratio of 0.4 and dimple depth to imprint diameter ratio of 0.2 is used in the calculations. The Reynolds number (based on channel height) varies from Re = 25 in the laminar regime to Re = 2000 in the early turbulent regime. Fully developed flow and heat transfer conditions were assumed and a constant heat flux boundary condition was applied to the walls of the channel. In the laminar regime, the flow and heat transfer characteristics are dominated by the recirculation zones in the dimple with resulting augmentation ratios below unity. Flow transition is found to occur between Re = 1020 and 1130 after which both heat transfer and friction augmentation increase to values of 3.22 and 2.75, respectively, at Re = 2000. The presence of large scale vortical structures ejected from the dimple cavity dominate all aspects of the flow and heat transfer, not only on the dimpled surface but also on the smooth wall. In all cases the thermal efficiency using dimples was found to be significantly larger than other heat transfer augmentation techniques currently employed.
Master of Science

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11

Ames, Richard Gene. "On the flowfield and forces generated by a rectangular wing undergoing moderate reduced frequency flapping at low reynolds number." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12468.

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12

Hasanuzzaman, Gazi [Verfasser], and Christoph [Gutachter] Egbers. "Experimental investigation of turbulent boundary layer with uniform blowing at moderate and high Reynolds numbers / Gazi Hasanuzzaman ; Gutachter: Christoph Egbers." Cottbus : BTU Cottbus - Senftenberg, 2021. http://d-nb.info/1238598064/34.

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13

Wu, Chia-Shan, and 吳佳珊. "Numerical computations for moderate Reynolds number flows with a moving body." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/38665551741570060964.

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碩士
國立臺灣大學
土木工程學研究所
97
In this thesis, the numerical model which is the finite-difference model with hybrid Cartesian/immersed boundary method is applied for solving the 2D and 3D Navier-Stokes equations with immersed and moving boundary on a fixed Cartesian grid. There are two studies in 2D which are carried out to verify the robustness of the present model with reference data from uniform flow past a stationary circular cylinder, and in-line oscillating circular cylinder in a fluid at rest. However, the numerical model is applied to simulate a moving boundary problem which is dropping sphere with constant velocity in 3D flow field. Therefore, the flow field is asymmetric at Reynolds numbers above 500 from both experimental and numerical results. Moreover, the flow field after impact at Reynolds number equals to 800, the combined vortex ring rolls upward to contact the primary vortex ring and acts as a 3D motion in all directions. Therefore, the numerical simulations can fill up the lack of the results in experiment within 3D visualization.

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14

Tu, Tsung-chieh, and 塗宗杰. "The Interaction of Two Sphere Wakes at Moderate Reynolds Numbers in a Turbulent Environment." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/95899350807178865063.

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碩士
國立成功大學
系統及船舶機電工程學系碩博士班
97
The purpose is to study the interaction between two sphere wakes at moderate Reynolds numbers in a turbulent environment; and compare with a single sphere. The experiment has two parts, single sphere and side by side. The test range: sphere Reynolds numbers from 149 to 360, inflow turbulent intensity from 1.5% to 4%. The result of this study shows that in the different of inflow turbulent intensity, velocity and turbulent intensity has linear superposition effects. It’s property similar to single sphere.

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15

Meng, Chao-De, and 孟昭德. "Shear Flow around a Cylinder at Low and Moderate Reynolds Numbers：Experimental and Numerical Study." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/97858194639205021029.

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16

Nugroho, Giri, and 謝琦力. "Direct-forcing immersed boundary modeling of vortex-induced vibration of structures at moderate Reynolds numbers." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/24393753525298834595.

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碩士
國立臺灣科技大學
機械工程系
100
Vortex-induced vibration (VIV) of structures is one of the practical interests in various engineering studies such as wind engineering, ocean engineering, aerospace engineering, and so on. When a structure is exposed to a flow field, the resultant hydrodynamic force may cause the vibrations of the structures. Furthermore, this vibration phenomenon may cause the failure of the structure especially for the so-called lock-in situation. In this present study, VIV of a circular cylinder placed in a uniform fluid flow at moderate Reynolds number is simulated using the direct-forcing immersed boundary method. The cylinder is allowed to vibrate in transverse direction and both in the in-line and transverse directions. The effect of reduced velocity on VIV is discussed in this study. Aerodynamic coefficients of a freely vibrating cylinder are analyzed in time and spectral domains. The maximums of the lift coefficient and the mean drag coefficient show hysteresis jumps at low end of the lock-in region. Hysteresis in the response of the cylinder is observed at the low end of the synchronization region. The ratio between the vortex shedding frequency and the natural frequency of the structure experiences the so-called soft lock-in. Moreover, the 2S vortex shedding mode can be found at low amplitudes of vibrations of the cylinder. The C(2S) mode is observed when the oscillation amplitude is large. Good agreements of the results with the previous experimental and numerical data prove the capability of the present method. This established model can be useful for the investigation of VIV of the structures.

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17

Zhou, Yun-Hui, and 周贇輝. "Direct-forcing immersed boundary modeling of vortex-induced vibration of sphere at moderate Reynolds number." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/5by2qd.

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碩士
國立臺灣科技大學
機械工程系
107
A numerical study of the vortex-induced vibration (VIV) of an elastically mounted sphere using the direct-forcing immersed boundary (DFIB) method incorporating the virtual force term is undertaken. The fluctuating hydrodynamic forces may cause damage when a solid structure interacts with fluid flow. Especially in the so-called lock-in situation, the vibration phenomenon results in the failure of the structure. The present study shows that a dynamically mounted sphere is allowed to vibrate transversely only or both in the in-line and the transverse directions in a uniform flow at a moderate Reynolds number of 300. The effect of reduced velocity on VIV is discussed in this study. Aerodynamic coefficients of a freely vibrating sphere are analyzed in time and spectral domains. The maximums of the lift coefficient and the drag coefficient show hysteresis jump at the low end of the lock-in region. The ratio between the vortex shedding frequency and the natural frequency of the structure reveals the so-called soft lock-in. Moreover, two shedding mode hairpin and spiral mode are found in different vibration response regimes. This study proves the capability of the proposed DFIB model can be useful for the investigation of VIV of the structure.

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18

"Drag Reduction in Turbulent Pipe Flow by Transverse Wall Oscillations at Low and Moderate Reynolds Number." Master's thesis, 2019. http://hdl.handle.net/2286/R.I.53884.

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abstract: This work helps to explain the drag reduction mechanisms at low and moderate turbulent Reynolds numbers in pipe flows. Through direct numerical simulation, the effects of wall oscillations are observed on the turbulence in both the near wall and the bulk region. Analysis of the average Reynolds Stresses at various phases of the flow is provided along with probability density functions of the fluctuating components of velocity and vorticity. The flow is also visualized to observe, qualitatively, changes in the total and fluctuating field of velocity and vorticity. Linear Stochastic Estimation is used to create a conditional eddy (associated with stress production) in the flow and visualize the effects of transverse wall oscillations on hairpin growth, auto-generation and structure.
Dissertation/Thesis
Masters Thesis Mechanical Engineering 2019

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19

Finn, Justin Richard. "A numerical study of inertial flow features in moderate Reynolds number flow through packed beds of spheres." Thesis, 2013. http://hdl.handle.net/1957/37715.

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In this work, flow through synthetic arrangements of contacting spheres is studied as a model problem for porous media and packed bed type flows. Direct numerical simulations are performed for moderate pore Reynolds numbers in the range, 10 ≤ Re ≤ 600, where non-linear porescale flow features are known to contribute significantly to macroscale properties of engineering interest. To first choose and validate appropriate computational models for this problem, the relative performance of two numerical approaches involving body conforming and non-conforming grids for simulating porescale flows is examined. In the first approach, an unstructured solver is used with tetrahedral meshes, which conform to the boundaries of the porespace. In the second approach, a fictitious domain formulation (Apte et al., 2009. J Comput. Phys. 228 (8), 2712-2738) is used, which employs non-body conforming Cartesian grids and enforces the no-slip conditions on the pore boundaries implicitly through a rigidity constraint force. Detailed grid convergence studies of both steady and unsteady flow through prototypical arrangements of spheres indicate that for a fixed level of uncertainty, significantly lower grid densities may be used with the fictitious domain approach, which also does not require complex grid generation techniques. Next, flows through both random and structured arrangements of spheres are simulated at pore Reynolds numbers in the steady inertial ( 10 ≲ Re ≲ 200) and unsteady inertial (Re ≈ 600) regimes, and used to analyze the characteristics of porescale vortical structures. Even at similar Reynolds numbers, the vortical structures observed in structured and random packings are remarkably different. The interior of the structured packings are dominated by multi-lobed vortex rings structures that align with the principal axes of the packing, but perpendicular to the mean flow. The random packing is dominated by helical vortices, elongated parallel to the mean flow direction. The unsteady dynamics observed in random and structured arrangements are also distinct, and are linked to the behavior of the porescale vortices. Finally, to investigate the existence and behavior of transport barriers in packed beds, a numerical tool is developed to compute high resolution finite-time Lyapunov exponent (FTLE) fields on-the-fly during DNS of unsteady flows. Ridges in this field are known to correspond to Lagrangian Coherent Structures (LCS), which are invariant barriers to transport and form the skeleton of time dependent Lagrangian fluid motion. The algorithm and its implementation into a parallel DNS solver are described in detail and used to explore several flows, including unsteady inertial flow in a random sphere packing. The resulting FTLE fields unambiguously define the boundaries of dynamically distinct porescale features such as counter rotating helical vortices and jets, and capture time dependent phenomena including vortex shedding at the pore level.
Graduation date: 2013

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20

Lin, Yung-Sheng, and 林詠盛. "A mechanism of thrust enhancement on a heaving plate due to flexibility at moderately low Reynolds numbers from the perspective of the force element theory." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/25t2dt.

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博士
國立臺灣大學
應用力學研究所
106
A numerical study is conducted to investigate the force mechanisms for a 3D heaving flexible plate from the perspective of a diagnostic force element analysis. The problem is relevant to a simplified flapping fish-tail with the leading edge held heaving in the space. The flow is assumed to be laminar with the Reynolds numbers fixed at Re=200, 500 & 800, and the Strouhal number St ranging from 0.1 to 0.6, and the flexure amplitude of the plate a0 from 0.1 to 0.2 (dimensionless). As the finite plate is set into unsteady motion, complicated vortex patterns around the plate are generated. It is shown that in the case of a rigid plate (a0=0.0) under a constant heaving frequency (f), the generation of thrust is increased, while friction drag is reduced. As in the case of a rigid plate heaving upon a fixed amplitude (h0), both the thrust and friction drag are enhanced. When the flexibility (a0) of the plate increases from zero, the thrust generation and frictional drag on the plate both increase significantly under the two distinguished cases of having constant heaving frequency (f) and heaving amplitude (h0). In the literature, the force (thrust) exerted on the tail-mimicking plate is largely credited to the vortices (vorticity) in the wake. However, this study performs a regional force analysis to show that the vorticity in the wake region supplies approximately 20-30% of the total thrust, especially in the cases of strong thrust generation under the constant heaving frequency. Comparable contributions come also from the regions direct above and below the heaving plate (mainly including the attached vortices) as well as from the two side regions (mainly including the tip vortices) next to the flexible plate. In the case of fixed h0, 25% of the thrust is contributed from the wake region, and the secondary thrust contribution is obtained from the two side regions of the plate. In addition, the potential motion associated with the unsteady flapping and the contribution from the surface vorticity are non-negligible constituent force components. The net thrust generated is larger at higher St and a0, but this is of course limited by the maximum flexibility and heaving amplitude allowed. The relative importance of each of the various force contributions was analyzed in detail, and the results may shed light on how a flapping tail generates propulsive efficiency above the critical Strouhal number St=0.2.

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