Global dynamics and aerodynamic flow vectoring of wakes

1997 ◽  
Vol 338 ◽  
pp. 231-248 ◽  
Author(s):  
D. A. HAMMOND ◽  
L. G. REDEKOPP
Keyword(s):  
Bluff Body ◽  
Wake Flow ◽  
Global Dynamics ◽  
Control Input ◽  
Near Wake ◽  
Directional Control ◽  
Fixed Base ◽  
Mechanical Movement ◽  
Streaming Flow

A methodology for vectoring the near-wake flow behind a bluff body without any mechanical movement of the physical boundaries of the generating body is described. The sole control input is suction applied at the fixed base of the forebody. Once the suction volume flux exceeds a critical value needed to suppress the global dynamics associated with vortex shedding, local directional control of the near wake can be achieved. The distribution of suction velocities across the base can be varied to obtain proportional directional control. The role of symmetries in stimulating aerodynamic vectoring of a streaming flow is emphasized and illustrated.

The Interaction of Porous Metal Coating With the Near Wake of Bluff Body

2012 ◽  
Author(s):  
Hanru Liu ◽  
Jinjia Wei ◽  
Zhiguo Qu
Keyword(s):  
Circular Cylinder ◽  
Bluff Body ◽  
Porous Metal ◽  
Metal Coating ◽  
Wake Flow ◽  
Navier Stokes ◽  
Aerodynamic Forces ◽  
Near Wake ◽  
Drag Forces ◽  
Flow Induced Noise

The flow around a circular cylinder with porous metal coating (PMC) is numerically investigated based on an approach of unsteady Reynolds Averaged Navier-Stokes (URANS) at subcritical Reynolds number. The model validation is carried out through comparison with some available experimental results in the literatures. It is found that the simulated results in the present work coincide well with the experimental data. The interaction of PMC with the near wake of circular cylinder such as streamline, vorticity and shear stress are studied in detail. The result reveals that PMC has capability of manipulating the wake flow so that the near wake of PMC cylinder is substantially different from that of smooth one. In addition, the fluctuations of aerodynamic forces are mitigated effectively. Varying the thickness of porous metal coating causes various velocity distributions and aerodynamic performance of bluff body. When the thickness is appropriate, the drag forces can be reduced to a certain extent. It is expected that the modification of flow characteristic and aerodynamic forces also produces the suppression of flow-induced noise generated by bluff body. These studies on wake flow and analysis of its relationship to flow-induced noise will be useful to understand the mechanism of controlling bluff body flow-induced noise by using PMC and to optimize the PMC for controlling flow and flow-induced noise.

Multi-Time-Delay LSE-POD Complementary Approach Applied to Wake Flow Behind a Bluff Body

2007 ◽  
Author(s):  
Vibhav Durgesh ◽  
Jonathan W. Naughton
Keyword(s):  
Time Delay ◽  
Surface Pressure ◽  
Bluff Body ◽  
Wake Flow ◽  
Time Varying ◽  
Pressure Measurements ◽  
Near Wake ◽  
Time Resolved ◽  
Complementary Approach ◽  
The Time Domain

An understanding of the near wake dynamics of a bluff body is desired to better link base drag reduction observed on these bodies with the coherent structures in the wake. This investigation explores different Linear Stochastic Estimation-Proper Orthogonal Decomposition (LSE-POD) methods that can be employed to estimate the dynamics of the energy containing structure. Statistically independent two-dimensional PIV measurements and time-resolved surface pressure measurements are used to determine spatial POD modes and LSE coefficients for estimating the time-varying POD coefficients using measured surface pressures. These results are used with the time-resolved surface pressure measurements to estimate the time-varying POD coefficients that may be used for a low-order, time-resolved reconstruction of the flow field. The multi-time LSE approach formulated in the time domain (multi-time-delay LSE) is found to be successful in capturing the important near wake dynamics.

Global dynamics of symmetric and asymmetric wakes

1997 ◽  
Vol 331 ◽  
pp. 231-260 ◽  
Author(s):  
D. A. HAMMOND ◽  
L. G. REDEKOPP
Keyword(s):  
Vortex Shedding ◽  
Wake Flow ◽  
Global Dynamics ◽  
Flow Modification ◽  
Frequency Selection ◽  
Directional Control ◽  
Developing Flow ◽  
Flow Approximation ◽  
Firm Basis ◽  
Global Modes

The two-dimensional wake–shear layer forming behind a rectangular-based forebody with independent ambient streams on either side of the forebody is examined by direct numerical simulation. Theoretical aspects of global modes and frequency selection criteria based on local and global stability arguments are tested by computing local stability properties using local, time-averaged velocity profiles obtained from the numerical simulations and making the parallel-flow approximation. The theoretical results based on the assumption of a slightly non-parallel, spatially developing flow are shown to provide a firm basis for the frequency selection of vortex shedding and for defining the conditions for its onset. Distributed suction or blowing applied at the base of the forebody is used as a means of wake flow modification. The critical suction velocity to suppress vortex shedding is calculated. It is shown that local directional control (i.e. vectoring) of the near-wake flow is possible, but only when all global modes are suppressed.

A freely yawing axisymmetric bluff body controlled by near-wake flow coupling

2019 ◽  
Vol 863 ◽  
pp. 1123-1156 ◽  
Author(s):  
Thomas J. Lambert ◽  
Bojan Vukasinovic ◽  
Ari Glezer
Keyword(s):  
Shear Layer ◽  
Time Scales ◽  
Attitude Control ◽  
Bluff Body ◽  
Cross Flow ◽  
The Body ◽  
Wake Flow ◽  
Small Scale ◽  
Near Wake ◽  
Yaw Attitude

Flow-induced oscillations of a wire-mounted, freely yawing axisymmetric round bluff body and the induced loads are regulated in wind tunnel experiments (Reynolds number $60\,000<Re_{D}<200\,000$) by altering the reciprocal coupling between the body and its near wake. This coupling is controlled by exploiting the receptivity of the azimuthal separating shear layer at the body’s aft end to controlled pulsed perturbations effected by two diametrically opposed and independently controlled aft-facing rectangular synthetic jets. The model is supported by a thin vertical wire upstream of its centre of pressure, and prescribed modification of the time-dependent flow-induced loads enables active control of its yaw attitude. The dynamics of the interactions and coupling between the actuation and the cross-flow are investigated using simultaneous, time-resolved measurements of the body’s position and phase-locked particle image velocimetry measurements in the yawing plane. It is shown that the interactions between trains of small-scale actuation vortices and the local segment of the aft-separating azimuthal shear layer lead to partial attachment, and the ensuing asymmetric modifications of the near-wake vorticity field occur within 15 actuation cycles (approximately three convective time scales), which is in agreement with measurements of the flow loads in an earlier study. Open- and closed-loop actuation can be coupled to the natural, unstable motion of the body and thereby affect desired attitude control within 100 convective time scales, as is demonstrated by suppression or enhancement of the lateral motion.

SOOT DISTRIBUTION IN TURBULENT BLUFF BODY NEAR WAKE NON PREMIXED FLAMES

2018 ◽  
Author(s):  
Suzane Nascimento ◽  
Juan Jose Cruz Villanueva ◽  
Luís Fernando Figueira da Silva
Keyword(s):  
Bluff Body ◽  
Premixed Flames ◽  
Near Wake ◽  
Soot Distribution

scholarly journals Global dynamics of international migration systems across South–South, North–North, and North–South flows, 1990–2015

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Diego F. Leal ◽  
Nicolas L. Harder
Keyword(s):  
International Migration ◽  
Network Effects ◽  
Global Dynamics ◽  
Core Set ◽  
Migration Dynamics ◽  
Key Drivers ◽  
Migration Flows ◽  
And Migration ◽  
Migration Systems

AbstractEvidence from 184 countries over the span of 25 years is gathered and analyzed to understand North–North, South–South, and North–South international migration flows. Conceptually, the analysis borrows from network theory and Migration Systems Theory (MST) to develop a model to characterize the structure and evolution of international migration flows. Methodologically, the Stochastic Actor-oriented Model of network dynamics is used to jointly model the three types of flows under analysis. Results show that endogenous network effects at the monadic, dyadic, and triadic levels of analysis are relevant to understand the emergence and evolution of migration flows. The findings also show that a core set of non-network covariates, suggested by MST as key drivers of migration flows, does not always explain migration dynamics in the systems under analysis in a consistent fashion; thus, suggesting the existence of important levels of heterogeneity inherent to these three types of flows. Finally, evidence related to the role of political instability and countries’ care deficits is also discussed as part of the analysis. Overall, the results highlight the importance of analyzing flows across the globe beyond typically studied migratory corridors (e.g., North–South flows) or regions (e.g., Europe).

scholarly journals Flow Turbulence Characteristics and Mass Transport in the Near-Wake Region of an Aquaculture Cage Net Panel

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 294
Author(s):  
Dongdong Shao ◽  
Li Huang ◽  
Ruo-Qian Wang ◽  
Carlo Gualtieri ◽  
Alan Cuthbertson
Keyword(s):  
Mass Transport ◽  
Near Field ◽  
Lateral Spreading ◽  
Wake Flow ◽  
Wake Region ◽  
Near Wake ◽  
Turbulence Characteristics ◽  
Macro Scale ◽  
Flow Turbulence ◽  
Fish Cages

Cage-based aquaculture has been growing rapidly in recent years. In some locations, cage-based aquaculture has resulted in the clustering of large quantities of cages in fish farms located in inland lakes or reservoirs and coastal embayments or fjords, significantly affecting flow and mass transport in the surrounding waters. Existing studies have focused primarily on the macro-scale flow blockage effects of fish cages, and the complex wake flow and associated near-field mass transport in the presence of the cages remain largely unclear. As a first step toward resolving this knowledge gap, this study employed the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) flow imaging technique to measure turbulence characteristics and associated mass transport in the near wake of a steady current through an aquaculture cage net panel in parametric flume experiments. In the near-wake region, defined as ~3M (mesh size) downstream of the net, the flow turbulence was observed to be highly inhomogeneous and anisotropic in nature. Further downstream, the turbulent intensity followed a power-law decay after the turbulence production region, albeit with a decay exponent much smaller than reported values for analogous grid-generated turbulence. Overall, the presence of the net panel slightly enhanced the lateral spreading of the scalar plume, but the lateral distribution of the scalar concentration, concentration fluctuation and transverse turbulent scalar flux exhibited self-similarity from the near-wake region where the flow was still strongly inhomogeneous. The apparent turbulent diffusivity estimated from the gross plume parameters was found to be in reasonable agreement with the Taylor diffusivity calculated as the product of the transverse velocity fluctuation and integral length scale, even when the plume development was still transitioning from a turbulent-convective to turbulent-diffusive regime. The findings of this study provide references to the near-field scalar transport of fish cages, which has important implications in the assessment of the environmental impacts and environmental carrying capacity of cage-based aquaculture.

The Calculation of Train Slipstreams on Platform of Underground High-Speed Rail Station

2013 ◽  
Vol 842 ◽  
pp. 445-448
Author(s):  
Wei Chao Yang ◽  
Chuan He ◽  
Li Min Peng
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Horizontal Distribution ◽  
Wake Flow ◽  
Railway Tunnel ◽  
Long Distance ◽  
Near Wake ◽  
High Speed Rail ◽  
Numerical Work ◽  
Rail Station

This paper describes the results of numerical work to determine the flow structures of the slipstream and wake of a high speed train on platforms of underground rail station using three-dimensional compressible Euler equation. The simulations were carried out on a model of a simplified three-coach train and typical cross-section of Chinese high-speed railway tunnel. A number of issues were observed: change process of slipstreams, longitudinal and horizontal distribution characteristics of train wind. Localized velocity peaks were obtained near the nose of the train and in the near wake region. Maximum and minimum velocity values were also noticed near to the nose rear tip. These structures extended for a long distance behind the train in the far wake flow. The slipstream in platform shows the typical three-dimensional characteristics and the velocity is about 4 m/s at 6 m away from the edge of platform.

scholarly journals Observed and modeled near-wake flow behind a solitary tree

2019 ◽  
Vol 265 ◽  
pp. 78-87 ◽  
Author(s):  
E. Dellwik ◽  
M.P. van der Laan ◽  
N. Angelou ◽  
J. Mann ◽  
A. Sogachev
Keyword(s):  
Wake Flow ◽  
Near Wake
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