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Time-resolved visualization of coherent structures during supersonic boundary layer transition

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Chinese Journal of Aeronautics 2023年第4期36卷 190-200页

作者： Lin HE Xiaoge LU Junhao HAN Zhengbang WU Shihe YI College of Aerospace Science and Engineering National University of Defense TechnologyChangsha 410073China

The coherent structures arising during flat-plate boundary layer transition at Mach num-ber 3.4 are investigated using a custom-built hyper-rate imaging system.The evolution of transi-tional structures is investigated in the Eulerian and Lagrangian reference frames.The upstream evolution of transition is dominated by the generation of new hairpin structures,while the interac-tion among multiple structural types dominates the evolution downstream.The breakdown of the existing structure,which may be caused by interactions among multiple types of structures with sim-ilar scales,is also visualized.

关键词： coherent structures Flow visualization Supersonic boundary layer Time-resolved Transition

Numerical study of flow and thermal characteristics of pulsed impinging jet on a dimpled surface

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Theoretical & Applied Mechanics Letters 2024年第2期14卷 106-117页

作者： Amin Bagheri Kazem Esmailpour Morteza Heydari Renewable Energy Research Center Damavand BranchIslamic Azad UniversityDamavandIran

This research comprehensively investigates the flow and thermal characteristics of a pulsating impinging jet over a dimpled surface.It analyzes the impact of key parameters(e.g.,inlet velocity pulsation functions,pulsation frequency,amplitude,dimple pitch,dimple depth,Reynolds number)on flow patterns and heat transfer.Validated computational fluid dynamics and the Re-normalization group turbulence model are employed to accurately simulate complex turbulent flow behavior.Local and average heat transfer coefficients are calculated and compared to steady impingement cases,revealing the potential benefits of pulsation for heat transfer enhancement.The study also examines how pulsation-induced flow modulation and thermal mixing affect heat transfer mechanisms.Results indicate that combining fluctuating flow with a dimpled surface can improve heat transfer rates.In summary,increasing pulsation amplitude consistently enhances heat transfer,while the effect of frequency varies between impinging and wall jet zones.

关键词： Pulsating impinging jet Dimpled surface Heat transfer enhancement Pulsation frequency and amplitude coherent structures

Tomographic particle image velocimetry measurement on three-dimensional swirling flow in dual-stage counter-rotating swirler

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Chinese Journal of Aeronautics 2024年第3期37卷 7-20页

作者： Yuyang ZHOU Ling DONG Mingtao SHANG Jibao LI Akira RINOSHIKA Key Laboratory of Fluid Mechanics of Ministry of Education Beihang UniversityBeijing 100191China School of Mechanical and Automotive Engineering Shanghai University of Engineering ScienceShanghai 201620China AECC Commercial Aircraft Engine Co. Ltd.Shanghai 200241China Department of Mechanical Systems Engineering Yamagata UniversityYamagata 992-8510Japan

Three-Dimensional(3D)swirling flow structures,generated by a counter-rotating dualstage swirler in a confined chamber with a confinement ratio of 1.53,were experimentally investigated at Re=2.3×10^(5)using Tomographic Particle Image Velocimetry(Tomo-PIV)and planar Particle Image Velocimetry(PIV).Based on the analysis of the 3D time-averaged swirling flow structures and 3D Proper Orthogonal Decomposition(POD)of the Tomo-PIV data,typical coherent flow structures,including the Corner Recirculation Zone(CRZ),Central Recirculation Zone(CTRZ),and Lip Recirculation Zone(LRZ),were extracted.The counter-rotating dual-stage swirler with a Venturi flare generates the independence process of vortex breakdown from the main stage and pilot stage,leading to the formation of an LRZ and a smaller CTRZ near the nozzle outlet.The confinement squeezes the CRZ to the corner and causes a reverse rotation flow to limit the shape of the CTRZ.A large-scale flow structure caused by the main stage features an explosive breakup,flapping,and Precessing Vortex Core(PVC).The explosive breakup mode dominates the swirling flow structures owing to the expansion and construction of the main jet,whereas the flapping mode is related to the wake perturbation.Confinement limits the expansion of PVC and causes it to contract after the impacting area.

关键词： coherent structures Dual-stage counter-rotating swirler cup Precessing vortex core Proper orthogonal decomposition Swirling flow Tomographic particle image velocimetry

The spatial-temporal evolution of coherent structures in log law region of turbulent boundary layer

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Acta Mechanica Sinica 2015年第1期31卷 16-24页

作者： Xiao-Bo Zheng Nan.Jiang Department of Mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering Mechanics The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

The spatial-temporal evolution of coherent structures （CS） is significant for turbulence control and drag re- duction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component （3D-3C） velocity fields of the flat plate turbulent boundary layer （TBL） measured by a Tomographic and Time-resolved PIV （Tomo TRPIV） system. Using multi-resolution wavelet transform and conditional sampling method, we extracted the intrinsic topologies and found that the streak structures appear in bar-like patterns. Furthermore, we seized locations and velocity information of transient CS, and then calculated the propagation velocity of CS based on spatial-temporal cross-correlation scanning. This laid a foundation for further studies on relevant dynamics properties.

关键词： Log law region in TBL. Spatial-temporal cross-correlation Tomographic TRPIV coherent structures Low and high speed streaks Multi-resolution wavelet de-composition

Tomographic PIV investigation of coherent structures in a turbulent boundary layer flow

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Acta Mechanica Sinica 2012年第3期28卷 572-582页

作者： Zhan-Qi Tang Nan Jiang Andreas Schroder Reinhard Geisler Department of Mechanics Tianjin University300072 TianjinChina Tianjin Key Laboratory of Modern Engineering Mechanics 300072 TianjinChina Institute of Aerodynamics and Flow Technology Department of Experimental MethodsBunsenstrasse 1037073 GiSttingenGermany

Tomographic particle image velocimetry was used to quantitatively visualize the three-dimensional co- herent structures in the logarithmic region of the turbulent boundary layer in a water tunnel. The Reynolds number based on momentum thickness is Reo = 2 460. The in- stantaneous velocity fields give evidence of hairpin vortices aligned in the streamwise direction forming very long zones of low speed fluid, which is flanked on either side by high- speed ones. Statistical support for the existence of hairpins is given by conditional averaged eddy within an increasing spanwise width as the distance from the wall increases, and the main vortex characteristic in different wall-normal re- gions can be reflected by comparing the proportion of ejec- tion and its contribution to Reynolds stress with that of sweep event. The pre-multiplied power spectra and two-point cor- relations indicate the presence of large-scale motions in the boundary layer, which are consistent with what have been termed very large scale motions （VLSMs）. The three dimen-sional spatial correlations of three components of veloc- ity further indicate that the elongated low-speed and high- speed regions will be accompanied by a counter-rotating roll modes, as the statistical imprint of hairpin packet structures, all of which together make up the characteristic of coherent structures in the logarithmic region of the turbulent boundary layer （TBL）.

关键词： Tomographic particle image velocimetry Tur-bulent boundary layer coherent structures Hairpin vortex Very large scale motion

AN EXPERIMENTAL STUDY ON TURBULENT coherent structures NEAR A SHEARED AIR-WATER INTERFACE

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Acta Mechanica Sinica 1999年第4期15卷 289-298页

作者：王双峰贾复钮珍南吴彰植 Institute of Mechanics Chinese Academy of Sciences Beijing China 100080 State Key Laboratory for Turbulence Research Peking University Beijing China 100871

The turbulence structures near a sheared air-water interface were experimentally investigated with the hydrogen bubble visualization technique. Surface shear was imposed by an airflow over the water flow which was kept free from surface waves. Results show that the wind shear has the main influence on coherent structures under air-water interfaces. Low- and high- speed streaks form in the region close to the interface as a result of the imposed shear stress. When a certain airflow velocity is reached, “turbulent spots” appear randomly at low-speed streaks with some characteristics of hairpin vortices. At even higher shear rates, the flow near the interface is dominated primarily by intermittent bursting events. The coherent structures observed near sheared air-water interfaces show qualitative similarities with those occurring in near-wall turbulence. However, a few distinctive phenomena were also observed, including the fluctuating thickness of the instantaneous boundary layer and vertical vortices in bursting processes, which appear to be associated with the characteristics of air-water interfaces.

关键词： air-water interface surface shear coherent structures flow visualization

Diffusive Lorenz dynamics: coherent structures and spatiotemporal chaos

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Communications in Nonlinear Science and Numerical Simulation 2000年第2期5卷 49-57页

作者： Yuehong QIAN Hudong CHEN and Da-Hsuan FENG (Exa Corporation, 450 Bedford Street, Lexington, MA 02420, USA email: qian@***, hudong@exa. Com Department of Physics, Drexel University, Philadelphia, PA 19104, USA email: da.hsuan.feng@***) Exa Corporation 450 Bedford Street Lexington MA 02420 USA Department of Physics Drexel University Philadelphia PA 19104 USA

In this paper, we are interested in collective behaviors of many interacting Lorenz strange attractors. With an intermediate chion coupling between the attractors,a new remarkable synchronization of well orgtried structuxes merges as a result of two competing mechanisms: temporal chaos and spatial chsive stabilization. A window of the coupling parazneter for coherent structures is found numerically. Different from all exist ing scenarios of routes to chaos (period doubling, intermittency and strange attractors), an algorithmetic increase of wavenumbers before an abrupt change to chaos (compared to the periodic doubling geometrical) is unexpectedly discovered. Metastable states are also ob served in simulations.

关键词： synchronizied chaos coherent structures intermittency reaction-diffusion

RESEARCH ON coherent structures IN A MIXING LAYER OF THE FENE-P POLYMER SOLUTION

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Applied Mathematics and Mechanics(English Edition) 2001年第3期22卷 304-311页

作者：邵雪明林建忠余钊圣 Department of Mechanics Zhejiang University Hangzhou 310027 P R ChinaState Key Laboratory of Fluid Transmission and Control Hangzhou 310027 P R ChinaPaper from LIN Jian-zhong Member of Editorial Committee AMM Department of Mechanics Zhejiang University Hangzhou 310027 P R China

The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteristics of the coherent structures at high b were obtained, which Azaiez and Homsy did not address. The results indicate that adding polymer to the Newtonian fluids will cause stronger vorticity diffusion, accompanied with weaker fundamental and subharmonical perturbations and slower rotational motion of neighbouring vortices during pairing. This effect decreases with the Weissenberg number, but increases with b. In addition, the time when the consecutive rollers are completely coalesced into one delays in the viscoelastic mixing layer compared with the Newtonian one of the same total viscosity.

关键词： mixing layer coherent structures FENE-P model pseudo-spectral method

A MECHANISM FOR EXCITATION OF coherent structures IN WALL REGION OF A TURBULENT BOUNDARY LAYER

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Applied Mathematics and Mechanics(English Edition) 2005年第4期26卷 415-422页

作者：张东明罗纪生周恒 Department of Mechanics Tianjin University Tianjin 300072 P.R.China

The problem of how the coherent structures in the wall region of a turbulent boundary layer could be excited by the disturbances from the outer region was investigated by using direct numerical simulation (DNS) method. The results show that velocity disturbances at the upper boundary of the wall region could excite coherent structures in the wall region, thus offering a more comprehensive model for individual coherent structures.

关键词： turbulent boundary layer coherent structures excitation