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1
Zhao, Fei, Rong Zhu, and Wenrui Wang. "Characteristics of the Supersonic Combustion Coherent Jet for Electric Arc Furnace Steelmaking." Materials 12, no. 21 (October 25, 2019): 3504. http://dx.doi.org/10.3390/ma12213504.
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Herein, a supersonic combustion coherent jet is proposed based on current coherent jet technology to improve the impact capacity of a coherent jet and increase the stirring intensity of the electric arc furnace (EAF) bath. Further, numerical simulations and an experimental analysis are combined to study the supersonic combustion coherent jet characteristics, including the Mach number, dynamic pressure, static temperature, vorticity, and turbulence intensity, in the EAF steelmaking environment. The results show that the supersonic combustion coherent jet exhibits stable combustion in a high-temperature EAF steelmaking environment. The supersonic combustion flame generated by the supersonic shrouding fuel gas can envelop the main oxygen jet more effectively than current coherent jets. Furthermore, the velocity attenuation, vorticity, and turbulence intensity performances of the supersonic combustion coherent jet are better when compared with those of the current coherent jet. The velocity core length of the main oxygen jet for the supersonic combustion coherent jet is 30% longer than that of the current coherent jet, resulting in an improved impact capacity and stirring intensity of the molten bath.
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STEFFEN, JOACHIM, ROBERT BAUER, ANDREW WARKENTIN, and ED BECZE. "PERFORMANCE OF A COHERENT JET COOLANT SYSTEM IN NON-CONTINUOUS DRESS CREEP-FEED GRINDING OF INCONEL 718." Journal of Advanced Manufacturing Systems 04, no. 02 (December 2005): 117–30. http://dx.doi.org/10.1142/s021968670500062x.
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In this work, the effect of the degree of jet coherency on the occurrence of workpiece burn when creep-feed grinding Inconel 718 under non-continuous dress conditions is studied. Different degrees of jet coherency are compared on the basis of the maximum material removal rate achievable before workpiece burn occurs. The comparison is performed at different coolant flow rates as well as at different distances between nozzle and grinding zone. It is found that a more coherent jet results in considerably higher possible material removal rates before workpiece burn occurs. Furthermore, it is determined that nozzle distance from the grinding zone and nozzle orientation and position with respect to the grinding zone, using a coherent jet, does not affect cooling performance. It is also shown that an increase in flow rate will increase cooling performance but only up to a point.
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Lv, Ming, and Rong Zhu. "Research on coherent jet oxygen lance in BOF steelmaking process." Metallurgical Research & Technology 116, no. 5 (2019): 502. http://dx.doi.org/10.1051/metal/2019020.
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The properties of conventional supersonic oxygen jet and coherent jet were simulated by Fluent in this paper. Their velocity field and jet radius were analyzed comparatively. The attenuation of gas jet was slowed down by the coherent jet oxygen lance. Besides, the effects of annular flow rate on the central oxygen jet velocity were also researched. It is showed that the core of the jet is gradually prolonged with the increase of annular gas flow rate. Based on the simulations, the designed coherent jet oxygen lance was experimented in 35 ton converter. It is found that the end-point phosphorus content is decreased from 0.024 to 0.016%, and dephosphorization rate is increased significantly, the average consumption of steel material is reduced by 3.4 kg/t, and iron-loss of slag is also reduced, which is favorable to improve oxygen utilization and metallic yield. This research provides good foundation for coherent jet technology promotion and application in Basic Oxygen Furnace (BOF).
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Zhao, Fei, Tianhao Di, Rong Zhu, and Wenrui Wang. "Supersonic Shrouding Methane Mixtures for Supersonic Combustion Coherent Jets." Metals 13, no. 1 (January 7, 2023): 123. http://dx.doi.org/10.3390/met13010123.
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A coherent jet oxygen supply plays a key role in the process of electric arc furnace steelmaking: it provides the necessary oxygen for the smelting of molten steel and promotes the flow of the molten pool. Compared with coherent jets in current use, the supersonic combustion coherent jet shrouded in supersonic methane gas could improve the impact capacity and stirring intensity of the molten pool. In order to reduce the smelting cost, the characteristics of the supersonic combustion coherent jet shrouding the supersonic methane and nitrogen mixtures must be studied. Computational fluid dynamics software is used to simulate the supersonic combustion coherent jet under various methane–nitrogen mixing conditions. The six-component combustion mechanism of methane and the Eddy Dissipation Concept combustion reaction model are selected. In agreement with thermal experiments, the simulation results show that the inclusion of a small amount of nitrogen has little effect on the combustion of supersonic shrouding methane gas. However, as the nitrogen content increases, the combustion region of supersonic shrouding gas becomes shorter in length, resulting in decreases in the lengths of the high-temperature, low-density region, and the high-turbulence-intensity region. These effects weaken the ability of the shrouding gas to envelop the main oxygen jet. The potential core length of the main oxygen jet decreases significantly; this decrease first accelerates and then decelerates. These results demonstrate the feasibility of including a small amount of nitrogen (about 10 wt%) in the supersonic shrouding methane gas without substantial negative impacts on the characteristics of the supersonic combustion coherent jet.
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Noblesse, Francis, Douglas G. Anthony, and Chi Yang. "Water Waves Radiated by Coherent Vortices in a Submerged Jet." Journal of Ship Research 37, no. 01 (March 1, 1993): 13–15. http://dx.doi.org/10.5957/jsr.1993.37.1.13.
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The physical problem - We consider a jet of water discharging from a nozzle submerged at a depth D below the free surface of a large body of water at rest, as in the experimental study of Bernal and Madnia (1989). The free surface is taken as the plane Z = 0 and the Z-axis points upward. The X-axis is chosen aligned with the jet and pointing in the same direction. The origin of the X-axis is taken directly above the nozzle, which thus is located at the point (X = 0, Y = 0, Z = -D). The jet is unstable to axially symmetric disturbances, which result in the formation of a periodic train of fairly coherent ring-like vortices. These vortices are created at a frequency co, and are convected downstream with a speed U roughly 70% of the jet exit velocity. The vortices grow in amplitude until nonlinear motions destroy their coherence, within 5 to 8 diameters of the jet exit, as is described in several experimental studies noted in Bernal and Madnia (1989), notably Yule (1978), Zaman and Hussain (1980), Hussain and Zaman (1980), Crow and Champagne (1971), and Hussain and Zaman (1981). An understanding of the free-surface disturbance created by a coherent periodic system of traveling vortices and observed in the experimental study of Bernal and Madnia (1989) is sought.
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Deguchi, Kengo, and Philip Hall. "Free-stream coherent structures in a planar jet." Journal of Fluid Mechanics 837 (January 5, 2018): 916–30. http://dx.doi.org/10.1017/jfm.2017.842.
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The free-stream coherent structure theory developed by Deguchi & Hall (J. Fluid Mech., vol. 752, 2014, pp. 602–625), valid in the large-Reynolds-number asymptotic limit, is extended and applied to jet flows. It is shown that a nonlinear exact coherent structure can be supported at the edge of the jet, and the structure induces a much bigger streaky flow in the centre of the jet. The lambda-shaped vortices that characterise the coherent structure are qualitatively consistent with those seen in experimental observations. Here a planar incompressible jet is investigated for the sake of simplicity, but the structure we describe could be used as a basis of more complex theories for incompressible and compressible jets of practical importance.
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Li, Xin, Guangsheng Wei, Rong Zhu, Bohan Tian, Ruimin Zhao, and Xinyi Lan. "Study on the Characteristics of Coherent Supersonic Jet with Superheated Steam." Metals 12, no. 5 (May 13, 2022): 835. http://dx.doi.org/10.3390/met12050835.
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By establishing a mathematical model to simulate a mixed jet of oxygen and superheated steam from a coherent supersonic jet oxygen lance, we studied the effect of superheated steam on the fluid characteristics of the mixed jet. The model was initially verified through laboratory experiments prior to analyzing the fluid characteristics of the mixed jet in detail. These characteristics included the jet velocity, the temperature, the turbulent kinetic energy (TKE), and the mass distribution. The results showed that, at an ambient temperature of 1700 K, the jet velocity measured in the laboratory experiment was consistent with the fluid velocity obtained by numerical simulations, with an error of only 2.7%. In a high-temperature environment, the jet velocity of the mixed oxygen and superheated steam jet was increased, the TKE around the center jet was enhanced, the superheated steam exhibited an inhibitory effect on the combustion reaction of annular methane, and the potential core length of the coherent supersonic jet was reduced, which was conducive to methane combustion and delayed the reduction in the central jet velocity.
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Liu, Kun, Ren Zhi Han, and Chun Yang. "The Experimentation and Imitation Study on Flow Field of Coherent Jet." Advanced Materials Research 150-151 (October 2010): 930–36. http://dx.doi.org/10.4028/www.scientific.net/amr.150-151.930.
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By oxygen lance measuring system, under the normal temperature (cold condition) systematic study is carried on traditional supersonic jet flow field that is simulated by compressed-air and on coherent jet flow flied which is accompanied by low density helium in this paper, By commercial software FLUENT, associated with experimental data, the standard double equation K- model is revised appropriately with C1=1.45，C2=1.88. The behavior of axis symmetric jet can be predicted better by simulated results. The flow state of traditional supersonic jet and the characteristic of coherent jet flow flied under vice-hole helium low density concomitance situation are analyzed systematically.
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Morgan, Michael N., and V. Baines-Jones. "On the Coherent Length of Fluid Nozzles in Grinding." Key Engineering Materials 404 (January 2009): 61–67. http://dx.doi.org/10.4028/www.scientific.net/kem.404.61.
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The delivery of grinding fluid to the contact zone is generally achieved via a nozzle. The nozzle geometry influences the fluid velocity and flow pattern on exit from the nozzle orifice. It is important to the efficiency of the process and to the performance of the operation that the fluid is delivered in a manner that ensures the desired jet velocity has adequate coverage of the contact zone. Often, assumptions about adequate coverage are based on visual inspections of the jet coherence. This paper provides new insight into the internal nozzle flows and the coherent length of a wide range of nozzle designs. The work presents a new analytical model to predict coherent length which is shown to correlate well with measured data from experiment. Recommendations are given to guide a user to optimal design of nozzles to ensure adequate fluid supply to the contact zone.
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Wu, Xuetao, Rong Zhu, Guangsheng Wei, and Kai Dong. "Influence of lance height and angle on the penetration depth of inclined coherent and conventional supersonic jets in electric arc furnace steelmaking." Journal of Mining and Metallurgy, Section B: Metallurgy, no. 00 (2020): 19. http://dx.doi.org/10.2298/jmmb190225019w.
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Nowadays, coherent and conventional supersonic jets are widely used in electric arc furnace (EAF)steelmaking processes. Generally, these jets are installed in the EAF oven wall with a tilt angle of 35-45?. However, limited studies have been conducted on the impact characteristics of these inclined supersonic jets. This study developed an optimized theoretical model to calculate the penetration depth of inclined coherent and conventional supersonic jets by combining theoretical modeling and numerical simulations. The computational fluid dynamics results are validated against water model experiments. A variable k is newly defined to reflect the velocity variation, which is related to the jet exit at the jet free distance. The results of the optimized theoretical model show that the lance height and lance angle influence the penetration depth of the inclined supersonic jet. At the same lance angle, the penetration depth decreases with the increase in the lance height. Similarly, it decreases with the decrease in lance angle at the same lance height. In addition, the penetration depth of an inclined coherent supersonic jet is larger than that of an inclined conventional supersonic jet under the same conditions. An optimized theoretical model can accurately predict the penetration depths of the inclined coherent and conventional supersonic jets.
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Matsuda, Hisashi, Sei-ichi Iida, and Michio Hayakawa. "Coherent Structures in a Three-Dimensional Wall Jet." Journal of Fluids Engineering 112, no. 4 (December 1, 1990): 462–67. http://dx.doi.org/10.1115/1.2909428.
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The formation mechanism of streamwise vortices in the near field of the three-dimensional wall jet discharging from a circular nozzle along a flat plate is studied experimentally using a conditional sampling technique. Ensemble-averages of the lateral velocity component indicate the presence of large-scale horseshoe-like structures, whose legs are inclined and stretched to form the streamwise vortices in the mixing region of the jet. Based on the present result, a coherent structure model for the near field of the wall jet is proposed.
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BASTIN, F., P. LAFON, and S. CANDEL. "Computation of jet mixing noise due to coherent structures: the plane jet case." Journal of Fluid Mechanics 335 (March 25, 1997): 261–304. http://dx.doi.org/10.1017/s0022112096004582.
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A computational approach to the prediction of jet mixing noise is described. It is based on Lighthill's analogy, used together with a semi-deterministic modelling of turbulence (SDM), where only the large-scale coherent motion is evaluated. The features of SDM are briefly illustrated in the case of shear layers, showing that suitable descriptions of the mean flow and of the large-scale fluctuations are obtained. Aerodynamic calculations of two cold fully expanded plane jets at Mach numbers 0.50 and 1.33 are then carried out. The numerical implementation of Lighthill's analogy is described and different integral formulations are compared for the two jets. It is shown that the one expressed in a space–time conjugate (κ, ω)-plane is particularly convenient and allows a simple geometrical interpretation of the computations. Acoustic results obtained with this formulation are compared to relevant experimental data. It is concluded that the radiation of subsonic jets cannot be explained only by the contribution of the turbulent coherent motion. In this case, directivity effects are well recovered but the acoustic spectra are too narrow and limited to the low-frequency range. In contrast at Mach number 1.33, especially in the forward quadrant, results are satisfactory, showing that coherent structures indeed provide the main source of supersonic jet mixing noise.
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Liu, Kun, Li Ming Bao, Ren Zhi Han, and Sheng Tao Qiu. "Hydraulic Model Experimental Study on Coherent Jet Flow Field." Applied Mechanics and Materials 44-47 (December 2010): 1099–109. http://dx.doi.org/10.4028/www.scientific.net/amm.44-47.1099.
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Based on Anshan Iron and Steel Company 180t top-bottom converter prototype, the operating parameters and the structural parameters for best stirring effect of bottom-blowing converter and top-bottom converter was given by the hydraulic model test in this article. Coherent jet oxygen lance converter smelting effect was simulated under the condition of keeping the best top blowing gas flow rate. The experiment result shows that coherent jet oxygen lance may achieve the result of top-bottom converter stirring effect. If coherent jet oxygen lance could be applied in the converter, bottom blowing system of converter could be canceled. In that case, not only the converter equipment can be simplified, but also the converter lining life can be improved, bring steel-making technology transformation.
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Cala, C. E., E. C. Fernandes, M. V. Heitor, and S. I. Shtork. "Coherent structures in unsteady swirling jet flow." Experiments in Fluids 40, no. 2 (November 4, 2005): 267–76. http://dx.doi.org/10.1007/s00348-005-0066-9.
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Drobniak, S., and R. Klajny. "Coherent structures of free acoustically stimulated jet." Journal of Turbulence 3 (January 2002): N1. http://dx.doi.org/10.1088/1468-5248/3/1/001.
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Komori, Satoru, and Hiromasa Ueda. "The large-scale coherent structure in the intermittent region of the self-preserving round free jet." Journal of Fluid Mechanics 152 (March 1985): 337–59. http://dx.doi.org/10.1017/s0022112085000726.
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Large-scale coherent structure in a round free jet injected into a low-speed, co-flowing stream was experimentally investigated using laser-Doppler and cold-wire techniques. Particular attention was paid to the coherent structures in the outer intermittent region of the jet in an almost self-preserving state. Velocity fluctuations u (axial) and v (radial) and temperature fluctuations θ were measured simultaneously at two positions: a reference position and a moving position. In order to clarify the pattern of coherent motion, a pattern-averaging technique was adopted and the characteristics of the turbulent fluctuations were conditionally averaged. The results show that a large-scale coherent structure exists even in the self-preserving region of a round free jet, as well as in the near field. It has a vortical structure which consists of strong outward turbulent motion from inside the jet, turbulent reverse flow and inflow in the irrotational ambient region (entrainment). In the coherent structure, the negative pattern-averaged Reynolds stress occurs at two locations: one in the irrotational ambient region outside the turbulent/irrotational interface and the other in the turbulent jet inside the interface. The former is instantaneously produced in the irrotational inflow outside the interface when the vortical motion is accelerated, and it changes even the sign of conventionally averaged Reynolds stress. The latter is instantaneously produced in the turbulent flow near the high-shear region when the turbulent motion is more strongly directed by the acceleration of the vortical motion towards the centre of the vortical structure than the averaged motion.
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Inoue, Yoshihiro, Jun Funato, Shintaro Yamashita, Haruhisa Yano, and Atsushi Sawada. "A COMPARATIVE STUDY ON THE COHERENT STRUCTURES IN 2D AND 3D WALL JETS(Wall Jet and Wall Flow)." Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2005 (2005): 79–84. http://dx.doi.org/10.1299/jsmeicjwsf.2005.79.
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Liu, Fuhai, Rong Zhu, Guangsheng Wei, and Shiliang Fan. "Effect of Lance Structure on Behavior of Coherent Jet in EAF Steelmaking Process." Materials 13, no. 5 (February 26, 2020): 1043. http://dx.doi.org/10.3390/ma13051043.
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During the electric arc furnace steelmaking process, the coherent jet technology was widely used to protect the kinetic energy of the supersonic oxygen jet and achieve better mixing effects. Comparing with the conventional oxygen lance, the coherent lance could increase the surface area of impaction cavity, resulting in a better stirring effect and higher reaction rate. However, there was limited research about the effect of restriction structure for the coherent lance tip on the flow field characteristic of the main oxygen jet. In this research, three kinds of restriction structures have been investigated by numerical simulation and combustion experiment at room and high ambient temperature conditions. Then an optimum restriction structure would be tested in a 75 t electrical arc furnace steelmaking process to verify its metallurgical property.
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Namgyal, Lhendup, and Joseph W. Hall. "Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet." Fluids 6, no. 1 (January 11, 2021): 35. http://dx.doi.org/10.3390/fluids6010035.
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The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow.
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Namgyal, Lhendup, and Joseph W. Hall. "Coherent Streamwise Vortex Structure of a Three-Dimensional Wall Jet." Fluids 6, no. 1 (January 11, 2021): 35. http://dx.doi.org/10.3390/fluids6010035.
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The dynamics of the coherent structures in a turbulent three-dimensional wall jet with an exit Reynolds number of 250,000 were investigated using the Snapshot Proper Orthogonal Decomposition (POD). A low-dimensional reconstruction using the first 10 POD modes indicates that the turbulent flow is dominated by streamwise vortex structures that grow in size and relative strength, and that are often accompanied by strong lateral sweeps of fluid across the wall. This causes an increase in the bulging and distortions of streamwise velocity contours as the flow evolves downstream. The instantaneous streamwise vorticity computed from the reconstructed instantaneous velocities has a high level of vorticity associated with these outer streamwise vortex structures, but often has a persistent pair of counter-rotating regions located close to the wall on either side of the jet centerline. A model of the coherent structures in the wall jet is presented. In this model, streamwise vortex structures are produced in the near-field by the breakdown of vortex rings formed at the jet outlet. Separate structures are associated with the near-wall streamwise vorticity. As the flow evolves downstream, the inner near-wall structures tilt outward, while the outer streamwise structures amalgamate to form larger streamwise asymmetric structures. In all cases, these streamwise vortex structures tend to cause large lateral velocity sweeps in the intermediate and far-field regions of the three-dimensional wall jet. Further, these structures meander laterally across the jet, causing a strongly intermittent jet flow.
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Shen, Ming Gang, Lei Zhang, and Zhen Shan Zhang. "Simulation Study of Converter Coherent Jet Oxygen Lance." Advanced Materials Research 291-294 (July 2011): 3322–26. http://dx.doi.org/10.4028/www.scientific.net/amr.291-294.3322.
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In this paper, hydraulic model experiment is performed for comparing the agitation ability of the coherent blowing and the top-bottom blowing. And numerical simulation is implemented for studying the influence of the concomitant flow temperature and pressure on the core space of the main jet. And the results show that the agitation ability of the coherent blowing and the top-bottom blowing is considerable. And the core space of the main jet of lance increases along with the increasing of the concomitant flow temperature under a certain pressure.
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Husain, Hyder S., and Fazle Hussain. "Elliptic jets. Part 2. Dynamics of coherent structures: pairing." Journal of Fluid Mechanics 233 (December 1991): 439–82. http://dx.doi.org/10.1017/s0022112091000551.
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The dynamics of coherent structure interactions, in particular the jet column mode of vortex pairing, in the near field of an elliptic jet have been investigated using hotwire measurements and flow visualization. A 2:1 aspect-ratio jet with an initially laminar boundary layer and a constant momentum thickness all around the nozzle exit perimeter is used for this study. While detailed hot-wire measurements were made in air at a Reynolds number ReDe (≡UeDe/ν) = 3.2 × 104, flow visualization was performed in water at a lower ReDe = 1.7 × 104; here Ue is the exit speed and De is the equivalent diameter of the nozzle exit cross-section. Excitation at the stable pairing mode induced successive pairings to occur periodically at the same location, allowing phase-locked measurements using a local trigger sensor. Coherent structures were educed at different phases of pairing in the planes of both the major and minor axes. These are compared with corresponding data in a circular jet, educed similarly.Pairing interactions are found to be quite different from those in a circular jet. Owing to non-planar and non-uniform self-induction of elliptical vortical structures and the consequent effect on mutual induction, pairing of elliptic vortices in the jet column does not occur uniformly around the entire perimeter, unlike in a circular jet. Merger occurs only in the initial major-axis plane through an entanglement process, while in the initial minor-axis plane, the trailing vortex rushes through the leading vortex without pairing and then breaks down violently. These motions produce considerably greater entrainment and mixing than in circular or plane jets. From distributions of dynamical properties over the extent of coherent structures, the production mechanism is explained in terms of the longitudinal vortices (or ribs) connecting the elliptic structures. Time-average measures and their modification by controlled excitation are also discussed in terms of coherent structure dynamics. A significant space in this paper is devoted to documenting phase-dependent and time-average flow measures; these new results should serve as target data for numerical simulations. Further details are given in Husain (1984).
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Kim, S., and A. F. Mills. "Condensation on Coherent Turbulent Liquid Jets: Part I—Experimental Study." Journal of Heat Transfer 111, no. 4 (November 1, 1989): 1068–74. http://dx.doi.org/10.1115/1.3250769.
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Condensation on coherent turbulent liquid jets was investigated experimentally in order to obtain a data base for the liquid side heat transfer coefficient. Jet breakup was identified by means of high-speed photography. Nozzles were formed from smooth and roughened glass tubes to define the initial turbulence level in the jets. Jet diameters of 3–7 mm and lengths of 2–12 cm were tested at jet velocities of 1.4–12 m/s giving Reynolds numbers of 6000–40,000. Viscosity and surface tension were varied by using ethanol, and water from 277–300 K, as test liquids. The Stanton number was found to be essentially independent of jet diameter, but to decrease with length to the power of −0.57, velocity to the power of −0.20, surface tension to the power of −0.30, and viscosity to the power of −0.1.
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Constantinou, Navid C., Brian F. Farrell, and Petros J. Ioannou. "Statistical State Dynamics of Jet–Wave Coexistence in Barotropic Beta-Plane Turbulence." Journal of the Atmospheric Sciences 73, no. 5 (May 1, 2016): 2229–53. http://dx.doi.org/10.1175/jas-d-15-0288.1.
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Abstract Jets coexist with planetary-scale waves in the turbulence of planetary atmospheres. The coherent component of these structures arises from cooperative interaction between the coherent structures and the incoherent small-scale turbulence in which they are embedded. It follows that theoretical understanding of the dynamics of jets and planetary-scale waves requires adopting the perspective of statistical state dynamics (SSD), which comprises the dynamics of the interaction between coherent and incoherent components in the turbulent state. In this work, the stochastic structural stability theory (S3T) implementation of SSD for barotropic beta-plane turbulence is used to develop a theory for the jet–wave coexistence regime by separating the coherent motions consisting of the zonal jets together with a selection of large-scale waves from the smaller-scale motions that constitute the incoherent component. It is found that mean flow–turbulence interaction gives rise to jets that coexist with large-scale coherent waves in a synergistic manner. Large-scale waves that would exist only as damped modes in the laminar jet are found to be transformed into exponentially growing waves by interaction with the incoherent small-scale turbulence, which results in a change in the mode structure, allowing the mode to tap the energy of the mean jet. This mechanism of destabilization differs fundamentally and serves to augment the more familiar S3T instabilities in which jets and waves arise from homogeneous turbulence with the energy source exclusively from the incoherent eddy field and provides further insight into the cooperative dynamics of the jet–wave coexistence regime in planetary turbulence.
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Oberleithner, K., C. O. Paschereit, and I. Wygnanski. "On the impact of swirl on the growth of coherent structures." Journal of Fluid Mechanics 741 (February 7, 2014): 156–99. http://dx.doi.org/10.1017/jfm.2013.669.
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AbstractSpatial linear stability analysis is applied to the mean flow of a turbulent swirling jet at swirl intensities below the onset of vortex breakdown. The aim of this work is to predict the dominant coherent flow structure, their driving instabilities and how they are affected by swirl. At the nozzle exit, the swirling jet promotes shear instabilities and, less unstable, centrifugal instabilities. The latter stabilize shortly downstream of the nozzle, contributing very little to the formation of coherent structures. The shear mode remains unstable throughout generating coherent structures that scale with the axial shear-layer thickness. The most amplified mode in the nearfield is a co-winding double-helical mode rotating slowly in counter-direction to the swirl. This gives rise to the formation of slowly rotating and stationary large-scale coherent structures, which explains the asymmetries in the mean flows often encountered in swirling jet experiments. The co-winding single-helical mode at high rotation rate dominates the farfield of the swirling jet in replacement of the co- and counter-winding bending modes dominating the non-swirling jet. Moreover, swirl is found to significantly affect the streamwise phase velocity of the helical modes rendering this flow as highly dispersive and insensitive to intermodal interactions, which explains the absence of vortex pairing observed in previous investigations. The stability analysis is validated through hot-wire measurements of the flow excited at a single helical mode and of the flow perturbed by a time- and space-discrete pulse. The experimental results confirm the predicted mode selection and corresponding streamwise growth rates and phase velocities.
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Edgington-Mitchell, Daniel, Kilian Oberleithner, Damon R. Honnery, and Julio Soria. "Coherent structure and sound production in the helical mode of a screeching axisymmetric jet." Journal of Fluid Mechanics 748 (May 8, 2014): 822–47. http://dx.doi.org/10.1017/jfm.2014.173.
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AbstractThe structure of a screeching axisymmetric jet in the helical C mode at a nozzle pressure ratio of 3.4 issuing from a convergent nozzle is studied using high-resolution particle image velocimetry. Proper orthogonal decomposition (POD) is used to extract the dominant coherent structures within the jet. The first two modes produced by the POD are used to reconstruct a phase-averaged data sequence. A triple decomposition into mean, coherent and random velocity components is performed. The embedded shock structures within the jet are shown to strongly modulate the coherent axial stresses within the shear layer and to weakly modulate the random axial stresses. Analysis of the third and fourth moments of the velocity probability density function is used as an indicator of possible regions of shock–vortex interaction and thus screech tone generation. Peaks of kurtosis (flatness) occur at the second, third and fourth shock–boundary intersection points, with the radial position shifting towards the centreline with increasing downstream distance. Analysis of the coherent component of vorticity shows that the largest fluctuations in coherent vorticity occur at the high-speed side of the shear layer in an area extending from the second to the fourth shock cell. With reference to prior literature, the argument is made that it is this increased magnitude of coherent vorticity fluctuation that is the primary factor in the determination of which shock cells act as dominant screech sources.
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Husain, Hyder S., and Fazle Hussain. "Elliptic jets. Part 3. Dynamics of preferred mode coherent structure." Journal of Fluid Mechanics 248 (March 1993): 315–61. http://dx.doi.org/10.1017/s0022112093000795.
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The dynamics of the preferred mode structure in the near field of an elliptic jet have been investigated using hot-wire measurements. A 2:1 aspect ratio jet with an initially turbulent boundary layer and a constant momentum thickness all around the nozzle exit perimeter was used for this study. Measurements were made in air at a Reynolds number ReDe (≡ UeDe/v) = 3.5 × 104. Controlled longitudinal excitation at the preferred mode frequency (StDe ≡ fDe/Ue = 0.4) induced periodic formation of structures, allowing phase-locked measurements with a local trigger hot wire. The dynamics of the organized structure are examined from educed fields of coherent vorticity and incoherent turbulence in the major and minor symmetry planes at five successive phases of evolution, and are also compared with corresponding data for a circular jet. Unlike in a circular jet, azimuthally fixed streamwise vortices (ribs) form without the aid of azimuthal forcing. The three-dimensional deformation of elliptic vortical structures and the rib formation mechanism have also been studied through direct numerical simulation. Differential self-induced motions due to non-uniform azimuthal curvature and the azimuthally fixed ribs produce greater mass entrainment in the elliptic jet than in a circular jet. The turbulence production mechanism, entrainment and mixing enhancement, and time-average measures and their modification by excitation are also discussed in terms of coherent structure dynamics and the rib-roll interaction. Various phase-dependent and time-average turbulence measures documented in this paper should serve as target data for validation of numerical simulations and turbulence modelling, and for design and control purposes in technological applications. Further details are given by Husain (1984).
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Liu, Qilin, and Huanxin Lai. "Coherent structures in a compressible turbulent plane jet." Physics of Fluids 33, no. 10 (October 2021): 105109. http://dx.doi.org/10.1063/5.0062963.
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Huang, Rong F., and Jean M. Chang. "Coherent structure in a combusting jet in crossflow." AIAA Journal 32, no. 6 (June 1994): 1120–25. http://dx.doi.org/10.2514/3.12110.
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SATO, Daisaku, and Masamitsu ARITA. "CHARACTERISTICS OF COHERENT STRUCTURE IN SHALLOW WATER JET." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 70, no. 4 (2014): I_1591—I_1596. http://dx.doi.org/10.2208/jscejhe.70.i_1591.
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Tang, S. K., and N. W. M. Ko. "Coherent structure interactions in an unexcited coaxial jet." Experiments in Fluids 17, no. 3 (July 1994): 147–57. http://dx.doi.org/10.1007/bf00190911.
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Tang, Wenbo, Manikandan Mathur, George Haller, Douglas C. Hahn, and Frank H. Ruggiero. "Lagrangian Coherent Structures near a Subtropical Jet Stream." Journal of the Atmospheric Sciences 67, no. 7 (July 1, 2010): 2307–19. http://dx.doi.org/10.1175/2010jas3176.1.
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Abstract Direct Lyapunov exponents and stability results are used to extract and distinguish Lagrangian coherent structures (LCS) from a three-dimensional atmospheric dataset generated from the Weather Research and Forecasting (WRF) model. The numerical model is centered at 19.78°N, 155.55°W, initialized from the Global Forecast System for the case of a subtropical jet stream near Hawaii on 12 December 2002. The LCS are identified that appear to create optical and mechanical turbulence, as evidenced by balloon data collected during a measurement campaign near Hawaii.
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Filippi, Margaux, Irina I. Rypina, Alireza Hadjighasem, and Thomas Peacock. "An Optimized-Parameter Spectral Clustering Approach to Coherent Structure Detection in Geophysical Flows." Fluids 6, no. 1 (January 12, 2021): 39. http://dx.doi.org/10.3390/fluids6010039.
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In Lagrangian dynamics, the detection of coherent clusters can help understand the organization of transport by identifying regions with coherent trajectory patterns. Many clustering algorithms, however, rely on user-input parameters, requiring a priori knowledge about the flow and making the outcome subjective. Building on the conventional spectral clustering method of Hadjighasem et al. (2016), a new optimized-parameter spectral clustering approach is developed that automatically identifies optimal parameters within pre-defined ranges. A noise-based metric for quantifying the coherence of the resulting coherent clusters is also introduced. The optimized-parameter spectral clustering is applied to two benchmark analytical flows, the Bickley Jet and the asymmetric Duffing oscillator, and to a realistic, numerically generated oceanic coastal flow. In the latter case, the identified model-based clusters are tested using observed trajectories of real drifters. In all examples, our approach succeeded in performing the partition of the domain into coherent clusters with minimal inter-cluster similarity and maximum intra-cluster similarity. For the coastal flow, the resulting coherent clusters are qualitatively similar over the same phase of the tide on different days and even different years, whereas coherent clusters for the opposite tidal phase are qualitatively different.
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Wang, Jiabao, Hyemi Kim, Daehyun Kim, Stephanie A. Henderson, Cristiana Stan, and Eric D. Maloney. "MJO Teleconnections over the PNA Region in Climate Models. Part II: Impacts of the MJO and Basic State." Journal of Climate 33, no. 12 (June 15, 2020): 5081–101. http://dx.doi.org/10.1175/jcli-d-19-0865.1.
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AbstractIn an assessment of 29 global climate models (GCMs), Part I of this study identified biases in boreal winter MJO teleconnections in anomalous 500-hPa geopotential height over the Pacific–North America (PNA) region that are common to many models: an eastward shift, a longer persistence, and a larger amplitude. In Part II, we explore the relationships of the teleconnection metrics developed in Part I with several existing and newly developed MJO and basic state (the mean subtropical westerly jet) metrics. The MJO and basic state diagnostics indicate that the MJO is generally weaker and less coherent and propagates faster in models compared to observations. The mean subtropical jet also exhibits notable biases such as too strong amplitude, excessive eastward extension, or southward shift. The following relationships are found to be robust among the models: 1) models with a faster MJO propagation tend to produce weaker teleconnections; 2) models with a less coherent eastward MJO propagation tend to simulate more persistent MJO teleconnections; 3) models with a stronger westerly jet produce stronger and eastward shifted MJO teleconnections; 4) models with an eastward extended jet produce an eastward shift in MJO teleconnections; and 5) models with a southward shifted jet produce stronger MJO teleconnections. The results are supported by linear baroclinic model experiments. Our results suggest that the larger amplitude and eastward shift biases in GCM MJO teleconnections can be attributed to the biases in the westerly jet, and that the longer persistence bias is likely due to the lack of coherent eastward MJO propagation.
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Hart, Neil C. G., Suzanne L. Gray, and Peter A. Clark. "Detection of Coherent Airstreams Using Cluster Analysis: Application to an Extratropical Cyclone." Monthly Weather Review 143, no. 9 (August 31, 2015): 3518–31. http://dx.doi.org/10.1175/mwr-d-14-00382.1.
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Abstract Flow in geophysical fluids is commonly summarized by coherent streams (e.g., conveyor belt flows in extratropical cyclones or jet streaks in the upper troposphere). Typically, parcel trajectories are calculated from the flow field and subjective thresholds are used to distinguish coherent streams of interest. This methodology contribution develops a more objective approach to distinguish coherent airstreams within extratropical cyclones. Agglomerative clustering is applied to trajectories along with a method to identify the optimal number of cluster classes. The methodology is applied to trajectories associated with the low-level jets of a well-studied extratropical cyclone. For computational efficiency, a constraint that trajectories must pass through these jet regions is applied prior to clustering; the partitioning into different airstreams is then performed by the agglomerative clustering. It is demonstrated that the methodology can identify the salient flow structures of cyclones: the warm and cold conveyor belts. A test focusing on the airstreams terminating at the tip of the bent-back front further demonstrates the success of the method in that it can distinguish finescale flow structure such as descending sting-jet airstreams.
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YUAN, LESTER L., ROBERT L. STREET, and JOEL H. FERZIGER. "Large-eddy simulations of a round jet in crossflow." Journal of Fluid Mechanics 379 (January 25, 1999): 71–104. http://dx.doi.org/10.1017/s0022112098003346.
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This paper reports on a series of large-eddy simulations of a round jet issuing normally into a crossflow. Simulations were performed at two jet-to-crossflow velocity ratios, 2.0 and 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow velocity and jet diameter. Mean and turbulent statistics computed from the simulations match experimental measurements reasonably well. Large-scale coherent structures observed in experimental flow visualizations are reproduced by the simulations, and the mechanisms by which these structures form are described. The effects of coherent structures upon the evolution of mean velocities, resolved Reynolds stresses, and turbulent kinetic energy along the centreplane are discussed. In this paper, the ubiquitous far-field counter-rotating vortex pair is shown to originate from a pair of quasi-steady ‘hanging’ vortices. These vortices form in the skewed mixing layer that develops between jet and crossflow fluid on the lateral edges of the jet. Axial flow through the hanging vortex transports vortical fluid from the near-wall boundary layer of the incoming pipe flow to the back side of the jet. There, the hanging vortex encounters an adverse pressure gradient and breaks down. As this breakdown occurs, the vortex diameter expands dramatically, and a weak counter-rotating vortex pair is formed that is aligned with the jet trajectory.
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Zhou, M. D., C. Heine, and I. Wygnanski. "The effects of excitation on the coherent and random motion in a plane wall jet." Journal of Fluid Mechanics 310 (March 10, 1996): 1–37. http://dx.doi.org/10.1017/s0022112096001711.
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Three components of velocity fluctuations were measured in a plane turbulent wall jet which was modulated periodically by a sinusoidal pressure fluctuation in its settling chamber. The experiment was carried out in a closed-loop wind tunnel in the absence of an external stream at Reynolds number Rej = Ujb/v = 6900 and Strouhal number Stj = fb/Uj = 9.5 × 10−3, where b is the width of the slot from which the jet emerges at an efflux velocity Uj. A detailed comparison is provided with similar measurements made in a natural, unexcited turbulent wall jet. One of the purposes of this experiment was to establish the kinetic energy transfers which take place in the wall jet under controlled perturbations. More specifically, we were interested in determining the interactions occurring between the steady mean flow, the coherent eddies and the ‘random’ turbulent fluctuations. We used the triple decomposition of the equations of motion as suggested by Hussain (1983) and quickly observed that the usefulness of this decomposition depends on the definition of coherent motion, which is ambiguous in the presence of phase jitter. Two such definitions were considered and the results are discussed in the experimental case-study provided. An attempt is made to define quantitatively the intensities of the coherent motion in externally excited, wallbounded flows. It is a case-study and not a parametric investigation aimed at maximizing the effects of period oscillations on the wall jet.
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Lv, Zi Qiang, Qing Yuan Ma, and Xiao Jun Su. "A Study on Flow Characteristics of Coherent Jet Oxygen Injector." Advanced Materials Research 194-196 (February 2011): 347–50. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.347.
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Oxygen injector is oxygen supply equipment for steelmaking process. Based on the numerical simulation of the flow field of a new coherent jet oxygen injector and traditional supersonic oxygen injector, the authors contrasted the axial and radial velocity decay of them. After a discussion on the influence of structural parameters on the jets, the authors pointed the impact of the jet characteristics of oxygen injector due to structural wear from the angle of practical operation.
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Brandner, P. A., B. W. Pearce, and K. L. de Graaf. "Cavitation about a jet in crossflow." Journal of Fluid Mechanics 768 (March 4, 2015): 141–74. http://dx.doi.org/10.1017/jfm.2015.73.
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Cavitation occurrence about a jet in crossflow is investigated experimentally in a variable-pressure water tunnel using still and high-speed photography. The 0.012 m diameter jet is injected on the centreplane of a 0.6 m square test section at jet to freestream velocity ratios ranging from 0.2 to 1.6, corresponding to jet-velocity-based Reynolds numbers of $25\times 10^{3}$ to $160\times 10^{3}$ respectively. Measurements were made at a fixed freestream-based Reynolds number, for which the ratio of the undisturbed boundary layer thickness to jet diameter is 1.18. The cavitation number was varied from inception (up to about 10) down to 0.1. Inception is investigated acoustically for bounding cases of high and low susceptibility to phase change. The influence of velocity ratio and cavitation number on cavity topology and geometry are quantified from the photography. High-speed photographic recordings made at 6 kHz provide insight into cavity dynamics, and derived time series of spatially averaged pixel intensities enable frequency analysis of coherent phenomena. Cavitation inception was found to occur in the high-shear regions either side of the exiting jet and to be of an intermittent nature, increasing in occurrence and duration from 0 to 100 % probability with decreasing cavitation number or increasing jet to freestream velocity ratio. The frequency and duration of individual events strongly depends on the cavitation nuclei supply within the approaching boundary layer. Macroscopic cavitation develops downstream of the jet with reduction of the cavitation number beyond inception, the length of which has a power-law dependence on the cavitation number and a linear dependence on the jet to freestream velocity ratio. The cavity closure develops a re-entrant jet with increase in length forming a standing wave within the cavity. For sufficiently low cavitation numbers the projection of the re-entrant jet fluid no longer reaches the cavity leading edge, analogous to supercavitation forming about solid cavitators. Hairpin-shaped vortices are coherently shed from the cavity closure via mechanisms of shear-layer roll-up similar to those shed from protuberances and jets in crossflow in single-phase flows. These vortices are shed at an apparently constant frequency, independent of the jet to freestream velocity ratio but decreasing in frequency with reducing cavitation number and cavity volume growth. Highly coherent cavitating vortices form along the leading part of the cavity due to instability of the jet upstream shear layer for jet to freestream velocity ratios greater than about 0.8. These vortices are cancelled and condense as they approach the trailing edge in the shear layer of opposing vorticity associated with the cavity closure and the hairpin vortex formation. For lower velocity ratios, where there is decreased jet penetration, the jet upstream shear velocity gradient reverses and vortices of the opposite sense form, randomly modulated by boundary layer turbulence.
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Wei, Guang-sheng, Rong Zhu, Ling-zhi Yang, Kai Dong, and Run-zao Liu. "Modeling on impact zone volume generated by coherent supersonic jet and conventional supersonic jet." Journal of Iron and Steel Research International 25, no. 7 (June 25, 2018): 681–91. http://dx.doi.org/10.1007/s42243-018-0098-z.
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CAMUSSI, R., and G. GUJ. "Orthonormal wavelet decomposition of turbulent flows: intermittency and coherent structures." Journal of Fluid Mechanics 348 (October 10, 1997): 177–99. http://dx.doi.org/10.1017/s0022112097006551.
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Experimental data obtained in various turbulent flows are analysed by means of orthogonal wavelet transforms. Several configurations are analysed: homogeneous grid turbulence at low and very low Reλ, and fully developed jet turbulence at moderate and high Reλ. It is shown by means of the wavelet decomposition in combination with the form of scaling named extended self-similarity that some statistical properties of fully developed turbulence may be extended to low-Reλ flows. Indeed, universal properties related to intermittency are observed down to Reλ≃10. Furthermore, the use of a new conditional averaging technique of velocity signals, based on the wavelet transform, permits the identification of the time signatures of coherent structures which may or may not be responsible for intermittency depending on the scale of the structure itself. It is shown that in grid turbulence, intermittency at the smallest scales is related to structures with small characteristic size and with a shape that may be related to the passage of vortex tubes. In jet turbulence, the longitudinal velocity component reveals that intermittency may be induced by structures with a size of the order of the integral length. This effect is interpreted as the signature of the characteristic jet mixing layer structures. The structures identified on the transverse velocity component of the jet case turn out on the other hand not to be affected by the mixing layer and the corresponding shape is again correlated with the signature of vortex tubes.
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Chen, Yuchao, Armin K. Silaen, and Chenn Q. Zhou. "3D Integrated Modeling of Supersonic Coherent Jet Penetration and Decarburization in EAF Refining Process." Processes 8, no. 6 (June 17, 2020): 700. http://dx.doi.org/10.3390/pr8060700.
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The present study proposes a complete 3D integrated model to simulate the top-blown supersonic coherent jet decarburization in the electric arc furnace (EAF) refining process. The 3D integrated model avoids the direct simulation of the supersonic coherent jet interacting with the liquid steel bath and provides a feasible way to simulate the decarburization in the liquid steel-oxygen two-phase reacting flow system with acceptable computational time. The model can be used to dynamically predict the details of the molten bath, including 3D distribution of in-bath substances, flow characteristics and bath temperature and provide a basis for optimizing the decarburization rate or other required parameters during the refining process.
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GUJ, G., M. CARLEY, R. CAMUSSI, and A. RAGNI. "ACOUSTIC IDENTIFICATION OF COHERENT STRUCTURES IN A TURBULENT JET." Journal of Sound and Vibration 259, no. 5 (January 2003): 1037–65. http://dx.doi.org/10.1006/jsvi.2002.5130.
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Yu, Mingzhou, Lihua Chen, Hanhui Jin, and Jianren Fan. "Large eddy simulation of coherent structure of impinging jet." Journal of Thermal Science 14, no. 2 (June 2005): 150–55. http://dx.doi.org/10.1007/s11630-005-0026-y.
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Lobasov, A. S. "Effect of coherent structures on convective heat transfer in a swirling impinging jet." Journal of Physics: Conference Series 2119, no. 1 (December 1, 2021): 012014. http://dx.doi.org/10.1088/1742-6596/2119/1/012014.
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Abstract The present paper reports on the detailed investigation of the flow dynamics and unsteady heat transfer in an impinging jet in regimes with high swirl and vortex breakdown. A combination of the time-resolved stereoscopic PIV, time-resolved PLIF and high-speed IR-thermometry methods is used. Two cases of distances between the jet nozzle and impingement surface are considered, H = d and H = 2d. The Reynolds number is fixed as Re = 5000. The temperature distribution in the flow has a maximum on the jet axis near the surface in the region of the central recirculation zone. The data are processed using the POD method to extract coherent flow structures and quantify temperature fluctuations on the impact surface. The helical vortex structure in the case of H = d influences heat transfer between the swirling jet and the surface, the temperature fluctuations on the surface reach 0.05 degrees.
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Ghassemieh, E., H. K. Versteeg, and M. Acar. "The effect of nozzle geometry on the flow characteristics of small water jets." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 220, no. 12 (December 1, 2006): 1739–53. http://dx.doi.org/10.1243/0954406jmes430.
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A wide variety of processes make use of plain orifice nozzles. Fuel injectors for internal combustion engines incorporate these nozzles to generate finely atomized sprays. Processes such as jet cutting, jet cleaning, and hydroentanglement, on the other hand, use similar nozzles, but require coherent jets. The spray or jet characteristics depend on the stability of the flow emerging from the orifice. This problem has been extensively researched for nozzles with diameters above 300 μm. Much less is known about the characteristics of jets produced by nozzles with smaller diameters, where viscous effects and small geometric variations due to manufacturing tolerances are likely to play an increasing role. Results are presented of a wide-ranging investigation of geometry effects on the flow parameters and jet characteristics of nozzles with diameters between 120 and 170 μm. Nozzles with circular cross-section and conical, cone-capillary and capillary axial designs were investigated. For conical and cone-capillary nozzles, the effect of cone angle and effects due to interactions between adjacent nozzles in the multi-hole cone-capillary nozzles were studied. For capillary nozzles, the effects of diameter variations and inlet edge roundness for capillary nozzles were considered. Furthermore, the effect of varying the aspect ratio (ratio of major and minor axes) of elliptical nozzles was studied. Flowrate and jet impact force measurements were carried out to determine the discharge coefficient Cd, velocity coefficient Cv, and contraction coefficient Cc of the nozzles for supply pressures between 3 and 12 MPa. Visualizations of the jet flow were carried out in the vicinity of the nozzle exit in order to identify near-nozzle flow regimes and to study jet coherence. The relationship between nozzle geometry, discharge characteristics, and jet coherence is examined.
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Brazier, Jean-Philippe, Maxime Huet, Olivier Léon, and Maxime Itasse. "Modal analysis of jet near-field pressure fluctuation." International Journal of Numerical Methods for Heat & Fluid Flow 26, no. 7 (September 5, 2016): 2000–2012. http://dx.doi.org/10.1108/hff-07-2015-0289.
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Purpose Unstable Kelvin-Helmholtz waves are suspected to be responsible for a large part of low-frequency noise radiation in high-speed jets. The purpose of this paper is to check the coherence of numerical and experimental data concerning this phenomenon, in the particular case of a cold subsonic jet. Design/methodology/approach In the present work, a cross-investigation of the near pressure field is performed on three different data sets: large-eddy simulation (LES) computations, parabolised stability equations (PSE) semi-modal computations and microphone measurements, in order to determine the local amplitudes of unstable waves. Findings The large coherent structures are found in both LES and experimental results and they are also in good agreement with direct semi-modal computations carried out with the PSE approach. Originality/value This work confirms that the unstable wave packets can be extracted from both LES and experimental results, provided that an appropriate modal decomposition is performed.
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Hsiao, Fei-Bin, I.-Che Hsu, and Cheng-Chiang Hsu. "Instability Modal Behavior of the Acoustically Excited Impinging Plane Jet With a Small Cylinder." Journal of Mechanics 20, no. 2 (June 2004): 145–57. http://dx.doi.org/10.1017/s1727719100003361.
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AbstractThe Instability modal behavior of coherent structures in a jet-small cylinder impinging flow field is extensively studied by hot-wire anemometry measurements. The free jet is employed with a small cylinder of 3 mm in diameter located in the potential core region at the impinging length of L/H = 1.5 for the near field impingement and L/H = 4 for the far field impingement. The jet exit velocity is operated at 10 m/sec with the Reynolds number of 1.03 × 104 based on the nozzle exit width H = 15mm. The impinging jet is locally excited at the nozzle exit with varicose mode (m =0) and sinuous mode (m = 1) disturbances at the fundamental frequency of the natural jet flow. Data indicate that the jet flow is greatly altered and significantly enhanced by strengthening the coherent structures of the flow due to resonance according to the feedback mechanism. Although the original natural jet preferably exhibits the varicose mode, the strong sinuous mode is dominant in the flow field owing to the presence of the small cylinder in the potential core region. In the near field impingement, the wake region behind the cylinder preserves the pure sinuous mode to where the jet vortices merge and then mildly fades out. Whereas in the jet shear layer, the sinuous mode exists in the initial portion and gradually transforms to the varicose mode. In the far field impingement, the alternate mode dominates in each frequency stage in pure impinging case and the modal behavior follows the selected mode with the introducing acoustic waves in the acoustic excitation cases.
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EIFF, OLIVIER S., and JAMES F. KEFFER. "On the structures in the near-wake region of an elevated turbulent jet in a crossflow." Journal of Fluid Mechanics 333 (February 25, 1997): 161–95. http://dx.doi.org/10.1017/s0022112096004314.
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A pattern-recognition technique, applied to multi-point simultaneous velocity measurements obtained with 45° X-wire anemometer probes, is used to extract and characterize the underlying organized motions, i.e. coherent structures, within the near-wake region of a turbulent round jet discharged perpendicularly from a pipe into a crossflow. This flow has been found to be quite complex owing to its three-dimensional nature and the interactions between several flow regions. Analyses of the underlying coherent structures, which play an important role in the physics of the flow, are still rare and are mostly based on flow-visualization techniques. Using a pattern-recognition technique in conjunction with hot-wire measurements, we recently examined the wake regions of the pipe and jet at levels near the tip of the pipe, and found that Kármán-like vortex structures in the wake of the pipe are locked to similar structures in the jet-wake. In this paper we expand upon our previous work and characterize these structures throughout the wake of the jet up into the region of the bent-over jet – a region where they have not been identified previously. The complex geometry of these structures in the wake of the jet as well as their interaction with the bent-over jet are discussed. The results show that these structures split before they link to similar structures on the opposite side of the symmetry plane in the jet region. The results further suggest that the vorticity due to the structures in the wake of the jet contributes to the motion of the well-known counter-rotating vortex pair.
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Abdurakipov, Sergey, Vladimir Dulin, and Dmitriy Markovich. "Experimental Investigation of Coherent Structure Dynamics in a Submerged Forced Jet." Siberian Journal of Physics 8, no. 1 (March 1, 2013): 56–64. http://dx.doi.org/10.54362/1818-7919-2013-8-1-56-64.
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The present work investigates the dynamics of coherent structures, including their scales and intensity, in an initial region of a submerged round forced jet by a Particle Image Velocimetry (PIV) technique for measurements of instantaneous velocity fields and statistical analysis tool Dynamic Mode Decomposition (DMD). The PIV measurements were carried out with 1,1 kHz acquisition rate. Application of DMD to the measured set of the velocity fields provided information about dominant frequencies, contained in DMD spectrum, of velocity fluctuations in different flow regions and about scales of the corresponding spatial coherent structures, contained in DMD modes. Additional calculations of time-spectra from turbulent fluctuations showed good agreement between frequencies of the main harmonics and characteristic frequencies of the dominant dynamic modes. Superposition of relevant DMD modes approximately described nonlinear interaction of coherent structures: vortex formation, their quasi-periodic pairing with modulation amplitude of generated harmonics