Wake Flow of Single and Multiple Yawed Cylinders

2004 ◽  
Vol 126 (5) ◽  
pp. 861-870 ◽  
Author(s):  
A. Thakur ◽  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Wake Flow ◽  
Upstream Region ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Dimensional Approximation ◽  
The Face ◽  
Drag And Lift

An experimental and computational study is performed of the wake flow behind a single yawed cylinder and a pair of parallel yawed cylinders placed in tandem. The experiments are performed for a yawed cylinder and a pair of yawed cylinders towed in a tank. Laser-induced fluorescence is used for flow visualization and particle-image velocimetry is used for quantitative velocity and vorticity measurement. Computations are performed using a second-order accurate block-structured finite-volume method with periodic boundary conditions along the cylinder axis. Results are applied to assess the applicability of a quasi-two-dimensional approximation, which assumes that the flow field is the same for any slice of the flow over the cylinder cross section. For a single cylinder, it is found that the cylinder wake vortices approach a quasi-two-dimensional state away from the cylinder upstream end for all cases examined (in which the cylinder yaw angle covers the range 0⩽ϕ⩽60°). Within the upstream region, the vortex orientation is found to be influenced by the tank side-wall boundary condition relative to the cylinder. For the case of two parallel yawed cylinders, vortices shed from the upstream cylinder are found to remain nearly quasi-two-dimensional as they are advected back and reach within about a cylinder diameter from the face of the downstream cylinder. As the vortices advect closer to the cylinder, the vortex cores become highly deformed and wrap around the downstream cylinder face. Three-dimensional perturbations of the upstream vortices are amplified as the vortices impact upon the downstream cylinder, such that during the final stages of vortex impact the quasi-two-dimensional nature of the flow breaks down and the vorticity field for the impacting vortices acquire significant three-dimensional perturbations. Quasi-two-dimensional and fully three-dimensional computational results are compared to assess the accuracy of the quasi-two-dimensional approximation in prediction of drag and lift coefficients of the cylinders.

Aero-Thermal Investigation of a Rib-Roughened Trailing Edge Channel With Crossing-Jets: Part I—Flow Field Analysis

2008 ◽  
Author(s):  
Alessandro Armellini ◽  
Filippo Coletti ◽  
Tony Arts ◽  
Christophe Scholtes
Keyword(s):  
Flow Field ◽  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Field Analysis ◽  
Trailing Edge ◽  
Present Contribution ◽  
Numerical Predictions ◽  
Flow Features ◽  
Rib Roughened

The present contribution addresses the aero-thermal experimental and computational study of a trapezoidal cross-section model simulating a trailing edge cooling cavity with one rib-roughened wall. The flow is fed through tilted slots on one side wall and exits through straight slots on the opposite side wall. The flow field aerodynamics is investigated in part I of the paper. The reference Reynolds number is defined at the entrance of the test section and set at 67500 for all the experiments. A qualitative flow model is deduced from surface-streamline flow visualizations. Two-dimensional Particle Image Velocimetry measurements are performed in several planes around mid-span of the channel and recombined to visualize and quantify three-dimensional flow features. The jets issued from the tilted slots are characterized and the jet-rib interaction is analyzed. Attention is drawn to the motion of the flow deflected by the rib-roughened wall and impinging on the opposite smooth wall. The experimental results are compared with the numerical predictions obtained from the finite volume, RANS solver CEDRE.

scholarly journals Quasi-two-dimensional approximation for numerical simulation of flows in engine ducts

2019 ◽  
Author(s):  
V. Vlasenko ◽  
A. Shiryaeva
Keyword(s):  
High Speed ◽  
Fuel Injection ◽  
Three Dimensional ◽  
Preliminary Design ◽  
Two Dimensional ◽  
Combustion Chambers ◽  
New Approach ◽  
One Dimensional ◽  
Dimensional Approximation ◽  
3D Flows

New quasi-two-dimensional (2.5D) approach to description of three-dimensional (3D) flows in ducts is proposed. It generalizes quasi-one-dimensional (quasi-1D, 1.5D) theories. Calculations are performed in the (x; y) plane, but variable width of duct in the z direction is taken into account. Derivation of 2.5D approximation equations is given. Tests for verification of 2.5D calculations are proposed. Parametrical 2.5D calculations of flow with hydrogen combustion in an elliptical combustor of a high-speed aircraft, investigated within HEXAFLY-INT international project, are described. Optimal scheme of fuel injection is found and explained. For one regime, 2.5D and 3D calculations are compared. The new approach is recommended for use during preliminary design of combustion chambers.

Corrugated SNOM probe with enhanced energy throughput

2008 ◽  
Vol 16 (4) ◽  
Author(s):  
T. Antosiewicz ◽  
T. Szoplik
Keyword(s):  
Near Field ◽  
Three Dimensional ◽  
Energy Output ◽  
Dipolar Field ◽  
Two Dimensional ◽  
The Core ◽  
Dimensional Approximation ◽  
New Type ◽  
Difference Time ◽  
Main Factor

AbstractIn a previous paper we proposed a modification of metal-coated tapered-fibre aperture probes for scanning near-field optical microscopes (SNOMs). The modification consists in radial corrugations of the metal-dielectric interface oriented inward the core. Their purpose is to facilitate the excitation of surface plasmons, which increase the transport of energy beyond the cut-off diameter and radiate a quasi-dipolar field from the probe output rim. An increase in energy output allows for reduction of the apex diameter, which is the main factor determining the resolution of the microscope. In two-dimensional finite-difference time-domain (FDTD) simulations we analyse the performance of the new type of SNOM probe. We admit, however, that the two-dimensional approximation gives better results than expected from exact three-dimensional ones. Nevertheless, optimisation of enhanced energy throughput in corrugated probes should lead to at least twice better resolution with the same sensitivity of detectors available nowadays.

scholarly journals Computational Study of Zigzag Spacer Design with Elliptical Cross-Section Filaments

2020 ◽  
Vol 307 ◽  
pp. 01047
Author(s):  
Gohar Shoukat ◽  
Farhan Ellahi ◽  
Muhammad Sajid ◽  
Emad Uddin
Keyword(s):  
Mass Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Computational Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Two Dimensional ◽  
Permeate Flux ◽  
Elliptical Cross

The large energy consumption of membrane desalination process has encouraged researchers to explore different spacer designs using Computational Fluid Dynamics (CFD) for maximizing permeate per unit of energy consumed. In previous studies of zigzag spacer designs, the filaments are modeled as circular cross sections in a two-dimensional geometry under the assumption that the flow is oriented normal to the filaments. In this work, we consider the 45° orientation of the flow towards the three-dimensional zigzag spacer unit, which projects the circular cross section of the filament as elliptical in a simplified two-dimensional domain. OpenFOAM was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments. Properties that impact the concentration polarization and hence permeate flux were analyzed in the domain with elliptical filaments as well as a domain with circular filaments to draw suitable comparisons. The range of variation in characteristic parameters across the domain between the two different configurations is determined. It was concluded that ignoring the elliptical projection of circular filaments to the flow direction, can introduce significant margin of error in the estimation of mass transfer coefficient.

Modeling of low-cement extruded curb of concrete-faced rockfill dam

2011 ◽  
Vol 48 (1) ◽  
pp. 89-97 ◽  
Author(s):  
Ga Zhang ◽  
Jian-Min Zhang
Keyword(s):  
Numerical Simulation ◽  
Damage Model ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Direct Simulation ◽  
Construction Technique ◽  
Displacement Analysis ◽  
Rockfill Dam ◽  
The Face ◽  
Cushion Layer

As the key structure of a practical construction technique, the low-cement extruded curb has been widely used in recent concrete-faced rockfill dams (CFRDs). The extruded curb exhibits significant interactions with the neighboring gravels and with the face slab. These interactions were investigated using element tests, and a new model was proposed. This model is composed of three parts: (i) the equivalent slab that is described using an ideal elastoplasticity model, (ii) the equivalent interface between the curb and the gravel cushion layer that is described using an elastoplasticity damage model, and (iii) the interface between the curb and the face slab that is described using a modified ideal elastoplasticity model. This model was verified via a two-dimensional numerical simulation of an ideal CFRD to capture the main behavior of the extruded curb with interactions between the extruded curb and the neighboring soil – face slab, employing a significantly smaller number of elements and a shorter calculation than direct simulation. The model was used to perform a three-dimensional stress–displacement analysis of the Bakun CFRD (205 m in height), and the results showed that the extruded curb causes a change in the stress of the face slab.

scholarly journals Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

2011 ◽  
Vol 278 (1725) ◽  
pp. 3670-3678 ◽  
Author(s):  
Brooke E. Flammang ◽  
George V. Lauder ◽  
Daniel R. Troolin ◽  
Tyson Strand
Keyword(s):  
Three Dimensional ◽  
Flow Patterns ◽  
Wake Flow ◽  
Ring Vortex ◽  
Vortex Wake ◽  
Two Dimensional ◽  
Volumetric Imaging ◽  
Dimensional Flow ◽  
Classic Problem ◽  
Two Dimensional Flow

Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns.

Transient Growth of Three-Dimensional Vortex Perturbations During Near-Parallel Collision With a Circular Cylinder

2006 ◽  
Author(s):  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Circular Cylinder ◽  
Vortex Core ◽  
Computational Study ◽  
Three Dimensional ◽  
The Body ◽  
Transient Growth ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Flow Features

A computational study is reported that examines the transient growth of three-dimensional flow features for nominally parallel vortex-cylinder interaction problems. We consider a helical vortex with small-amplitude perturbations that is advected onto a circular cylinder whose axis is parallel to the nominal vortex axis. The study assesses the applicability of the two-dimensional flow assumption for parallel vortex-body interaction problems in which the body impinges on the vortex core. The computations are performed using an unstructured finite-volume method for an incompressible flow, with periodic boundary conditions along the cylinder axis. Growth of three-dimensional flow features is quantified by use of a proper-orthogonal decomposition of the Fourier-transformed velocity and vorticity fields in the cylinder azimuthal and axial directions. The interaction is examined for different axial wavelengths and amplitudes of the initial helical waves on the vortex core, and the results for cylinder force are compared to the two-dimensional results. The degree of perturbation amplification as the vortex approaches the cylinder is quantified and shown to be mostly dependent on the dominant axial wavenumber of the perturbation. The perturbation amplification is observed to be greatest for perturbations with axial wavelength of about 1.5 times the cylinder diameter.

Three-dimensional secondary instability of a spatially developing von Kármán vortex street in a far wake

2010 ◽  
Vol 467 (2127) ◽  
pp. 675-694 ◽  
Author(s):  
J. T. C. Liu ◽  
X. Yu
Keyword(s):  
Nonlinear Interaction ◽  
Three Dimensional ◽  
Secondary Instability ◽  
Vortex Street ◽  
Wake Flow ◽  
Two Dimensional ◽  
Primary Flow ◽  
Von Karman ◽  
Von Karman Vortex Street ◽  
Far Wake

This paper presents studies of a three-dimensional secondary instability of a spatially developing von Kármán vortex street. It develops owing to the nonlinear interaction between a two-dimensional mean far-wake flow and its most unstable disturbances. This forms a nonlinear primary wake flow. Sections of this flow are selected to perform a temporal secondary stability study under the assumption of parallel flow. The eigenvalue characteristics of the secondary instability are compared with the results from the use of a linear primary flow comprising unmodified mean wake flow coexisting with a linear primary fundamental disturbance with an empirical amplitude as a parameter, resulting in a simpler Floquet analysis. The maximum amplification rates occur at about the same spanwise wavenumber for both the nonlinear and linear primary flows, in qualitative agreement. But the amplification rate versus the spanwise wavenumber spectrum are both qualitatively and quantitatively different, the nonlinear primary flow results in a lower magnitude of the amplification rates. Some interpretations of controlled experiments are made, and it is concluded that the two- and three-dimensional disturbances so obtained appeared to be from the primary instability, where the amplification mechanisms come from the unmodified mean flow. A general discussion of the nonlinear interaction between the primary two-dimensional flow and the three-dimensional secondary instability is given, which may well form the basis for further nonlinear studies.

Sign in / Sign up

Export Citation Format

Share Document