Quantitative classification of vortical flows based on topological features using graph matching

Vortical flow patterns generated by swimming animals or flow separation (e.g. behind bluff objects such as cylinders) provide important insight to global flow behaviour such as fluid dynamic drag or propulsive performance. The present work introduces a new method for quantitatively comparing and classifying flow fields using a novel graph-theoretic concept, called a weighted Gabriel graph, that employs critical points of the velocity vector field, which identify key flow features such as vortices, as graph vertices. The edges (connections between vertices) and edge weights of the weighted Gabriel graph encode local geometric structure. The resulting graph exhibits robustness to minor changes in the flow fields. Dissimilarity between flow fields is quantified by finding the best match (minimum difference) in weights of matched graph edges under relevant constraints on the properties of the edge vertices, and flows are classified using hierarchical clustering based on computed dissimilarity. Application of this approach to a set of artificially generated, periodic vortical flows demonstrates high classification accuracy, even for large perturbations, and insensitivity to scale variations and number of periods in the periodic flow pattern. The generality of the approach allows for comparison of flows generated by very different means (e.g. different animal species).

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Feature Extraction From Time Resolved Reacting Flow Data Sets

Volume 4B: Combustion, Fuels, and Emissions ◽

10.1115/gt2018-77051 ◽

2018 ◽

Cited By ~ 2

Author(s):

H. Ek ◽

I. Chterev ◽

N. Rock ◽

B. Emerson ◽

J. Seitzman ◽

...

Keyword(s):

Swirling Flow ◽

Azimuthal Velocity ◽

Flow Fields ◽

Swirl Flow ◽

Reacting Flow ◽

Data Sets ◽

Time Resolved ◽

Recirculating Flow ◽

Flow Features ◽

Dynamical Flow

This paper presents measurements of the simultaneous fuel distribution, flame position and flow velocity in a high pressure, liquid fueled combustor. Its objective is to develop methods to process, display and compare large quantities of instantaneous data with computations. However, time-averaged flow fields rarely represent the instantaneous, dynamical flow fields in combustion systems. It is therefore important to develop methods that can algorithmically extract dynamical flow features and be directly compared between measurements and computations. While a number of data-driven approaches have been previously presented in the literature, the purpose of this paper is to propose several approaches that are based on understanding of key physical features of the flow — for this reacting swirl flow, these include the annular jet, the swirling flow which may be precessing, the recirculating flow between the annular jets, and the helical flow structures in the shear layers. This paper demonstrates nonlinear averaging of axial and azimuthal velocity profiles, which provide insights into the structure of the recirculation zone and degree of flow precession. It also presents probability fields for the location of vortex cores that enables a convenient method for comparison of their trajectory and phasing with computations. Taken together, these methods illustrate the structure and relative locations of the annular fluid jet, recirculating flow zone, spray location, flame location, and trajectory of the helical vortices.

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Modular Turbulence Modeling Applied to an Engine Intake

Journal of Turbomachinery ◽

10.1115/1.4025232 ◽

2013 ◽

Vol 136 (5) ◽

Cited By ~ 8

Author(s):

Ugochukwu R. Oriji ◽

Paul G. Tucker

Keyword(s):

Surface Roughness ◽

Turbulence Modeling ◽

Fluid Dynamic ◽

Navier Stokes ◽

Test Cases ◽

Laminar Separation ◽

Streamline Curvature ◽

Favorable Pressure Gradient ◽

Flow Features ◽

The One

The one equation Spalart–Allmaras (SA) turbulence model in an extended modular form is presented. It is employed for the prediction of crosswind flow around the lip of a 90 deg sector of an intake with and without surface roughness. The flow features around the lip are complex. There exists a region of high streamline curvature. For this, the Richardson number would suggest complete degeneration to laminar flow. Also, there are regions of high favorable pressure gradient (FPG) sufficient to laminarize a turbulent boundary layer (BL). This is all terminated by a shock and followed by a laminar separation. Under these severe conditions, the SA model is insensitive to capturing the effects of laminarization and the reenergization of eddy viscosity. The latter promotes the momentum transfer and correct reattachment prior to the fan face. Through distinct modules, the SA model has been modified to account for the effect of laminarization and separation induced transition. The modules have been implemented in the Rolls-Royce HYDRA computational fluid dynamic (CFD) solver. They have been validated over a number of experimental test cases involving laminarization and also surface roughness. The validated modules are finally applied in unsteady Reynolds-averaged Navier–Stokes (URANS) mode to flow around an engine intake and comparisons made with measurements. Encouraging agreement is found and hence advances made towards a more reliable intake design framework.

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Finite-Volume Simulation of 3-D Vortical Flow-Fields About Road Vehicles with Various After-Body Configuration

10.4271/931896 ◽

1993 ◽

Cited By ~ 2

Author(s):

Kiyohira Aoki ◽

Ming Zhu ◽

Toshikazu Ohbayashi ◽

Hideaki Miyata

Keyword(s):

Finite Volume ◽

Flow Fields ◽

Vortical Flow ◽

Road Vehicles ◽

Finite Volume Simulation

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Large Eddy Simulation of the Flow Around a Diffuser-Equipped Bluff Body in Ground Effect

Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B ◽

10.1115/imece2011-62673 ◽

2011 ◽

Cited By ~ 2

Author(s):

Lara Schembri Puglisevich ◽

Gary Page

Keyword(s):

Large Eddy Simulation ◽

Bluff Body ◽

Vortex Formation ◽

Ground Effect ◽

Vortical Flow ◽

Navier Stokes ◽

Flow Structures ◽

Eddy Simulation ◽

Large Eddy ◽

Flow Features

Unsteady Large Eddy Simulation (LES) is carried out for the flow around a bluff body equipped with an underbody rear diffuser in close proximity to the ground, representing an automotive diffuser. The goal is to demonstrate the ability of LES to model underbody vortical flow features at experimental Reynolds numbers (1.01 × 106 based on model height and incoming velocity). The scope of the time-dependent simulations is not to improve on Reynolds-Averaged Navier Stokes (RANS), but to give further insight into vortex formation and progression, allowing better understanding of the flow, hence allowing more control. Vortical flow structures in the diffuser region, along the sides and top surface of the bluff body are successfully modelled. Differences between instantaneous and time-averaged flow structures are presented and explained. Comparisons to pressure measurements from wind tunnel experiments on an identical bluff body model shows a good level of agreement.

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Quantum networks: topology and spectral characterization

EPJ Web of Conferences ◽

10.1051/epjconf/201818202014 ◽

2018 ◽

Vol 182 ◽

pp. 02014

Author(s):

Vesna Berec

Keyword(s):

Quantum Information Processing ◽

Theoretic Approach ◽

Quantum State Transfer ◽

Complexity Measures ◽

Quantum Networks ◽

Graph Theoretic ◽

Topological Features ◽

State Transfer ◽

Quantum Complexity ◽

And Control

To utilize a scalable quantum network and perform a quantum state transfer within distant arbitrary nodes, coherence and control of the dynamics of couplings between the information units must be achieved as a prerequisite ingredient for quantum information processing within a hierarchical structure. Graph theoretic approach provides a powerful tool for the characterization of quantum networks with non-trivial clustering properties. By encoding the topological features of the underlying quantum graphs, relations between the quantum complexity measures are presented revealing the intricate links between a quantum and a classical networks dynamics.

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On the vortex dynamics of shear-driven deep cavity flows with asymmetrical walls

Canadian Journal of Physics ◽

10.1139/cjp-2016-0305 ◽

2016 ◽

Vol 94 (12) ◽

pp. 1344-1352 ◽

Cited By ~ 2

Author(s):

D. Cornu ◽

L. Keirsbulck ◽

F. Kerhervé ◽

F. Aloui ◽

M. Lippert

Keyword(s):

Physical Nature ◽

Wall Pressure ◽

Vortical Flow ◽

Flow Structures ◽

Cavity Flows ◽

Convective Structures ◽

Deep Cavity ◽

Image Velocimetry ◽

Flow Features ◽

Deep Cavities

The influence of the length-to-depth aspect ratio and of wall asymmetry on the main vortical flow structures evolving in rectangular two-dimensional deep cavities is studied experimentally using wall-pressure and particle image velocimetry (PIV) measurements. Wall-pressure and cavity flow statistics have been analyzed and shown that the flow features are strongly affected especially by the asymmetry. An emphasis is given concerning the behavior of the shear layer oscillations that are compared to the analytical deep-cavity model prediction proposed by P.J.W. Block (NASA Tech. Note. 1976). The results show good agreement with Block’s model if the value of the convection velocity is properly adjusted. Stochastic estimation of the cavity flows demonstrates that convective structures are involved downstream of the cavity along the wall and highlights the physical nature of the pressure-producing flow structures.

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Schlieren photography on freely flying hawkmoth

Biology Letters ◽

10.1098/rsbl.2018.0198 ◽

2018 ◽

Vol 14 (5) ◽

pp. 20180198 ◽

Cited By ~ 4

Author(s):

Yun Liu ◽

Jesse Roll ◽

Stephen Van Kooten ◽

Xinyan Deng

Keyword(s):

Aerodynamic Force ◽

Leading Edge ◽

Vortical Flow ◽

Natural Setting ◽

Optical Flow Method ◽

Flying Insects ◽

Flow Features ◽

Potential Applications ◽

Edge Vortex ◽

Schlieren Photography

The aerodynamic force on flying insects results from the vortical flow structures that vary both spatially and temporally throughout flight. Due to these complexities and the inherent difficulties in studying flying insects in a natural setting, a complete picture of the vortical flow has been difficult to obtain experimentally. In this paper, Schlieren , a widely used technique for highspeed flow visualization, was adapted to capture the vortex structures around freely flying hawkmoth ( Manduca ). Flow features such as leading-edge vortex, trailing-edge vortex, as well as the full vortex system in the wake were visualized directly. Quantification of the flow from the Schlieren images was then obtained by applying a physics-based optical flow method, extending the potential applications of the method to further studies of flying insects.

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On the Importance of Assumptions for Bulk Flow in Hemodynamic Models of the Carotid Bifurcation

ASME 2011 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2011-53437 ◽

2011 ◽

Author(s):

Umberto Morbiducci ◽

Diana Massai ◽

Diego Gallo ◽

Raffaele Ponzini ◽

Marco A. Deriu ◽

...

Keyword(s):

Vessel Wall ◽

Carotid Bifurcation ◽

Flow Fields ◽

Transport Processes ◽

Bulk Flow ◽

Arterial System ◽

Vortical Flow ◽

Primary Role ◽

4D Flow ◽

The Impact

It is widely accepted that the local hemodynamics in the arterial system affects the atherogenic process. In particular the hemodynamic environment at the carotid artery bifurcation has been widely studied due to its predilection for atherosclerosis. Much effort has been spent in the past on image-based CFD carotid bifurcation models to assess the sensitivity to several assumptions of wall shear stress (WSS)-based parameters as indicators of abnormal flow. This luminal-surface-oriented approach was historically driven by histological observations on samples of the vessel wall. The consequence for this was that the reduction of the complexity of 4D flow fields focused mainly on WSS. However, few studies have provided adequate insights into the influence of these assumptions in order to confidently model the 4D hemodynamics within the bifurcation. Only recently the interest in the role played by the bulk flow in the development of the arterial disease has grown dramatically. This is the consequence of the emerging awareness that arterial hemodynamics, being an intricate process that involves interaction, reconnection and continuous re-organization of structures, could play a primary role in the regulation of mass transfer, and of its athero-protective/susceptible effect. Earlier works [1] pointed out the existence of a relationship between helical/vortical flow patterns and transport processes that could affect blood-vessel wall interaction, and might cause alterations in the residence time of atherogenic particles involved in the initiation of inflammatory response. Recently we introduced robust quantitative descriptors of bulk flow that can “reduce” the inherent complexity associated with 4D flow fields in arteries [1]. Here we present a study on the impact of assumptions on blood rheology and outflow boundary conditions (BCs) on bulk flow features within healthy carotid bifurcations, by using 4D flow descriptors. The final goal is to provide adequate insights not only to complement and to integrate, but also to extend with a quantitative characterization of the bulk flow the description currently adopted to classify altered hemodynamics.

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Effects of Geometry on Brush Seal Pressure and Flow Fields—Part II: Backing Plate Configurations

Journal of Turbomachinery ◽

10.1115/1.2101858 ◽

2005 ◽

Vol 128 (2) ◽

pp. 379-389 ◽

Cited By ~ 10

Author(s):

Yahya Dogu ◽

Mahmut F. Aksit

Keyword(s):

Constant Pressure ◽

Decisive Role ◽

Flow Fields ◽

Control Flow ◽

Blow Down ◽

Backing Plate ◽

Seal Design ◽

Pressure Fields ◽

Brush Seal ◽

Flow Features

Brush seal dynamic behavior is strongly related to pressure and flow fields. Developments in brush seal design have led to geometric modifications to control flow field and consequent brush seal issues including blow-down, hang-up, and pressure stiffening. Some of the geometric enhancements have been found to have common use as backing plate modifications. Over the two decades of brush seal evolution, many backing plate configurations have been suggested in numerous patent disclosures. Even so, literature on the effects of geometric modifications on pressure and flow fields remains limited. This study numerically investigates brush seal pressure and flow fields for such common conceptual backing plate configurations as single and multiple grooves, with and without by-pass passages. The CFD analysis presented employs a bulk porous medium approach for the bristle pack. The effectiveness of various backing plate configurations outlining important flow features is discussed. Results indicate that backing plate configurations have a decisive role in shaping seal pressure fields. In general, it has been found that all cases having bypass configuration leak more. Moreover, the major portion of the seal leakage through fence height is fed from the backing plate cavity. The single backing plate groove forms a constant pressure behind the bristle pack. In contrast, multiple grooves form multiple constant pressure regions.

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