On the formation of the counter-rotating vortex pair in transverse jets

Among the important physical phenomena associated with the jet in crossflow is the formation and evolution of vortical structures in the flow field, in particular the counter-rotating vortex pair (CVP) associated with the jet cross-section. The present computational study focuses on the mechanisms for the dynamical generation and evolution of these vortical structures. Transient numerical simulations of the flow field are performed using three-dimensional vortex elements. Vortex ring rollup, interactions, tilting, and folding are observed in the near field, consistent with the ideas described in the experimental work of Kelso, Lim & Perry (1996), for example. The time-averaged effect of these jet shear layer vortices, even over a single period of their evolution, is seen to result in initiation of the CVP. Further insight into the topology of the flow field, the formation of wake vortices, the entrainment of crossflow, and the effect of upstream boundary layer thickness is also provided in this study.

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Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.59 ◽

2011 ◽

Vol 676 ◽

pp. 461-490 ◽

Cited By ~ 21

Author(s):

FABRICE SCHLEGEL ◽

DAEHYUN WEE ◽

YOUSSEF M. MARZOUK ◽

AHMED F. GHONIEM

Keyword(s):

Boundary Layer ◽

Boundary Condition ◽

Near Field ◽

Vortex Pair ◽

Transverse Jets ◽

Vortical Structures ◽

Wall Boundary Layer ◽

Wall Boundary ◽

Jet Trajectory ◽

Counter Rotating Vortex Pair

Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.

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On steady and pulsed low-blowing-ratio transverse jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.482 ◽

2013 ◽

Vol 714 ◽

pp. 393-433 ◽

Cited By ~ 19

Author(s):

G. Bidan ◽

D. E. Nikitopoulos

Keyword(s):

Numerical Study ◽

Cross Flow ◽

Vortex Pair ◽

Leading Edge ◽

Mie Scattering ◽

Formation Mechanisms ◽

Transverse Jets ◽

Vortical Structures ◽

Blowing Ratio ◽

Counter Rotating Vortex Pair

AbstractThe present experimental and numerical study focuses on the vortical structures encountered in steady and pulsed low-blowing-ratio transverse jets ($0. 150\leq \mathit{BR}\leq 4. 2$), a configuration hardly discussed in the literature. Under unforced conditions at low blowing ratio, a stable leading-edge shear-layer rollup is identified inside the jet pipe. As the blowing ratio is increased, the destabilization and evolution of this structure sheds light on the formation mechanisms of the well-known transverse jet vortical system. A discussion on the nature of the counter-rotating vortex pair in low-blowing-ratio transverse jets is also provided. Under forced conditions, the experimental observations support and extend numerical results of previous fully modulated jet studies. Large-eddy simulation results provide scaling parameters for the classification of starting vortices for partly modulated jets, as well as information on their three-dimensional dynamics. The counter-rotating vortex pair initiation is observed and detailed in both Mie scattering visualizations and simulations. The observations support a mechanism based on stretching of the starting vortical structures because of inviscid induction and partial leapfrogging. Two modes of cross-flow ingestion inside the jet pipe are described as the pulsed jet cycles from high to low values of blowing ratio.

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Coherent vortical structures in numerical simulations of buoyant plumes from wildland fires

International Journal of Wildland Fire ◽

10.1071/wf04044 ◽

2005 ◽

Vol 14 (1) ◽

pp. 61 ◽

Cited By ~ 43

Author(s):

Philip Cunningham ◽

Scott L. Goodrick ◽

M. Yousuff Hussaini ◽

Rodman R. Linn

Keyword(s):

Three Dimensional ◽

Vortex Pair ◽

Moderate Intensity ◽

Heat Sources ◽

Wildland Fires ◽

Buoyant Plumes ◽

Atmospheric Flow ◽

Vortical Structures ◽

Elliptical Ring ◽

Counter Rotating Vortex Pair

The structure and dynamics of buoyant plumes arising from surface-based heat sources in a vertically sheared ambient atmospheric flow are examined via simulations of a three-dimensional, compressible numerical model. Simple circular heat sources and asymmetric elliptical ring heat sources that are representative of wildland fires of moderate intensity are considered. Several different coherent vortical structures that dominate the plume structure and evolution are evident in the simulations, and these structures correspond well with those observed in plumes from wildland fires. For the circular source, these structures include: (i) a counter-rotating vortex pair aligned with the plume trajectory that is associated with a bifurcation of the plume, (ii) transverse shear-layer vortices on the upstream face of the plume, and (iii) vertically oriented wake vortices that form periodically with alternating sign on either side of the downstream edge of the plume base. For the elliptical ring source, a streamwise counter-rotating vortex pair is apparent on each flank, and a transverse horizontal vortex is observed above the head of the source. In all simulations the plume cross section is represented poorly by a self-similar Gaussian distribution.

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Noncanonical Short Hole Jets-in-Crossflow for Turbine Film Cooling

Journal of Applied Mechanics ◽

10.1115/1.2130359 ◽

2005 ◽

Vol 73 (3) ◽

pp. 474-482 ◽

Cited By ~ 8

Author(s):

Michael W. Plesniak

Keyword(s):

Film Cooling ◽

Cross Flow ◽

Vortex Pair ◽

Structural Features ◽

Global Features ◽

Vortical Structures ◽

Jet In Crossflow ◽

Jet Trajectory ◽

Image Velocimetry ◽

Counter Rotating Vortex Pair

This paper presents a review of research done over the past several years at Purdue on non-canonical jets-in-crossflow. It is a retrospective and an integrative compilation of results previously reported as well as some new ones. The emphasis is on jets emanating from “short” holes, with length-diameter ratios of one or less. A canonical jet-in-crossflow configuration is one in which a fully developed jet issues from a long pipe fed by a large plenum, into a semi-infinite cross flow. The configuration presented here is noncanonical in the sense that jet issues from a short hole and thus the flow is unable to “adjust” to the hole, unlike the case of a long hole in which fully developed pipe flow can be attained. This is motivated by gas turbine film cooling applications. Experimental results acquired with particle image velocimetry will primarily be presented, with some complementary information gained from RANS simulations of the flow. Many different aspects of the problem have been investigated, and in this paper the focus will be on structural features within the hole and in the developing jet and crossflow interaction. A significant result is that the in-hole vortical structures, depending on their sense of rotation, tend to augment or weaken the primary counter-rotating vortex pair. This impacts global features such as jet trajectory and spreading.

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Dynamic Analysis of Flow Field at the End of Combustor Simulator

Jurnal Teknologi ◽

10.11113/jt.v58.1540 ◽

2012 ◽

Vol 58 (2) ◽

Cited By ~ 1

Author(s):

E. Kianpour ◽

Nor Azwadi Che Sidik ◽

Mohsen Agha Seyyed Mirza Bozorg

Keyword(s):

Flow Field ◽

Three Dimensional ◽

Vortex Pair ◽

Recirculation Region ◽

Inlet Temperature ◽

Turbine Inlet Temperature ◽

Turbine Inlet ◽

Flow Field Characteristics ◽

Counter Rotating Vortex Pair ◽

Critical Components

This study was carried out in order to extend database knowledge about the flow field characteristics and define the various flow field contours inside a combustor simulator. The modern gas turbine industries try to get higher engine efficiencies. Brayton cycle is a key to achieve this purpose. According to this cycle industries should increase the turbine inlet temperature to get more engine efficiency and power. However the turbine inlet temperature increasing creates an extremely harsh environment for the downstream critical components such as turbine vanes. In this research a three-dimensional representation of a true Pratt and Whitney aero-engine which studied before in Virginia University was simulated and analyzed to collect essential data. This combustor simulator combined the interaction of two rows of dilution jets, which were staggered in the stream wise direction and aligned in the span wise direction, with that of filmcooling along the combustor liner walls. The overall findings of the study indicate that three-component velocity measurements showed the dilution jet-mainstream interaction produced shear forces and as a result a counter-rotating vortex pair was created. The highest turbulent kinetic energy was found at the top of recirculating region due to the interaction of the second row of dilution jets and mainstream flow. Furthermore, the centers of the counter-rotating vortex pair were spread relatively far apart due to the opposing dilution jets. Along the dilution jet centerline, negative stream wise velocities were measured indicating the recirculation region just downstream of the jet. Into the combustor exit, the acceleration of the flow increased and thereby the uniformity of the velocity profile enhancement was found as well.

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

Volume 4: Heat Transfer, Parts A and B ◽

10.1115/gt2008-50694 ◽

2008 ◽

Cited By ~ 2

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.

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Formation of a Counter-Rotating Vortex Pair in a Plume in a Cross-Flow

2010 14th International Heat Transfer Conference, Volume 7 ◽

10.1115/ihtc14-23283 ◽

2010 ◽

Cited By ~ 1

Author(s):

Masahiko Shinohara

Keyword(s):

Vortex Ring ◽

Three Dimensional ◽

Cross Flow ◽

Vortex Pair ◽

Boussinesq Approximation ◽

Streamwise Vorticity ◽

Three Dimensional Flow ◽

Flow Feature ◽

Heated Area ◽

Counter Rotating Vortex Pair

Numerical simulations are performed to study the formation of a counter-rotating vortex pair (CVP), a dominant flow feature in plumes inclined in a cross-flow. The unsteady three-dimensional flow fields are calculated by a finite difference method using the Boussinesq approximation. A plume rises from an isothermally heated square surface facing upward in air. Calculations show that the CVP originates not from horizontal spanwise vorticity in the velocity boundary layer on the bottom wall around the heated area, but from horizontal streamwise vorticity just above each side of the heated area. When the cross-flow begins after a plume forms a vortex ring in the cap above the heated area in a still environment, the vortex ring does not form a CVP. However, as the cap and the stem of the plume move downwind, a rotation about the streamwise axis appears just above each side edge of the heated area and grows into the CVP. We discuss the effect of entrainment into the stem and cap on the formation of the streamwise rotation that causes the CVP.

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Flow/Acoustic Mechanisms in Three-Dimensional Vortices Undergoing Sinusoidal-Wave Instabilities

Volume 1: Advances in Aerospace Technology ◽

10.1115/imece2007-43163 ◽

2007 ◽

Cited By ~ 1

Author(s):

Wenhua Li ◽

Z. C. Zheng ◽

Ying Xu

Keyword(s):

Flow Field ◽

Three Dimensional ◽

Vortex Pair ◽

Particle Method ◽

Acoustic Signals ◽

Short Wave ◽

Vortical Flow ◽

Vortex Particle Method ◽

Structure Changes ◽

Wave Instabilities

It has been identified that vorticity in a vortex core directly relates to the frequency of a significant sound peak from an aircraft wake vortex pair where each of the vortices is modeled as an elliptic core Kirchhoff vortex. In three-dimensional vortices, sinusoidal instabilities at various length scales result in significant flow structure changes in these vortices, and thus influence their radiated acoustic signals. In this study, a three-dimensional vortex particle method is used to simulate the incompressible vortical flow. The flow field, in the form of vorticity, is employed as the source in the far-field acoustic calculation using a vortex sound formula that enables computation of acoustic signals radiated from an approximated incompressible flow field. Cases of vortex rings and a pair of counter-rotating vortices are studied when they are undergoing both long- and short-wave instabilities. Both inviscid and viscous interactions are considered and effects of turbulence are simulated using sub-grid-scale models.

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IDDES Evaluation of Oscillating Hydraulic Jumps

E3S Web of Conferences ◽

10.1051/e3sconf/20184005067 ◽

2018 ◽

Vol 40 ◽

pp. 05067 ◽

Cited By ~ 1

Author(s):

Vimaldoss Jesudhas ◽

Frédéric Murzyn ◽

Ram Balachandar

Keyword(s):

Flow Field ◽

Hydraulic Jump ◽

Three Dimensional ◽

Wall Jet ◽

Hydraulic Jumps ◽

Vortical Structures ◽

Instantaneous Flow Field ◽

Type Flow ◽

Different Types ◽

Flow Features

This paper presents the results of three-dimensional, unsteady, Improved Delayed Detached Eddy Simulations of an oscillating and a stable hydraulic jump at Froude numbers of 3.8 and 8.5, respectively. The different types of oscillations characterised in a hydraulic jump are analysed by evaluating the instantaneous flow field. The instability caused by the flapping wall-jet type flow in an oscillating jump is distinct compared to the jump-toe fluctuations caused by the spanwise vortices in the shear layer of a stable jump. These flow features are accurately captured by the simulations and are presented with pertinent discussions. The near-bed vortical structures in an oscillating jump is extracted and analysed using the λ2 criterion.

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