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Ming Zhao - One of the best experts on this subject based on the ideXlab platform.

  • flow induced by an oscillating Circular Cylinder close to a plane boundary in quiescent fluid
    Journal of Fluid Mechanics, 2020
    Co-Authors: Ming Zhao
    Abstract:

    Flow induced by an oscillating Circular Cylinder close to a plane boundary in quiescent fluid is simulated numerically by solving the two-dimensional Navier–Stokes equations. The aim of this study is to investigate the effects of the gap ratio between the Cylinder and plane boundary ( number is sufficiently small and vortex shedding does not exist.

  • numerical investigation of vortex induced vibration of Circular Cylinder with multiple control rods at low reynolds number
    Symposium on Fluid-Structure-Sound Interactions and Control, 2017
    Co-Authors: Mingming Liu, Ming Zhao, Bin Teng, Guoqiang Tang
    Abstract:

    Vortex induced vibration of a Circular Cylinder with multiple small-diameter control rods at a relatively low Reynolds number Re = 200 is numerically investigated in this study. The numerical model is based on the Reynolds-Averaged Navier-Stokes equations. The Arbitrary Lagrangian-Eulerian (ALE) method is employed to consider the motion of the Circular Cylinders. The Petrove Galerkin Finite Element Method (PG-FEM) is used to discretize the governing equations. The numerical results show that the maximum oscillation amplitude for the small gap ratio of G/D = 0.1 is almost the same as that of an isolated Circular Cylinder. However, for larger gap ratios, the maximum oscillation amplitudes are much smaller. Therefore, the VIV response of the Circular Cylinder can be successfully suppressed by the six control rods in present study.

  • Numerical simulation of two-degree-of-freedom vortex-induced vibration of a Circular Cylinder close to a plane boundary
    Journal of Fluids and Structures, 2011
    Co-Authors: Ming Zhao
    Abstract:

    Abstract Two-degree-of-freedom vortex-induced vibrations (VIV) of a Circular Cylinder close to a plane boundary are investigated numerically. The Reynolds-Averaged Navier–Stokes (RANS) equations are solved using the Arbitrary Lagrangian Eulerian (ALE) scheme with a k–ω turbulence model closure. The numerical model is validated against experimental data of VIV of a Cylinder in uniform flow and VIV of a Cylinder close to a plane boundary at low mass ratios. The numerical results of the vibration mode, vibration amplitude and frequency agree well with the experimental data. VIV of a Circular Cylinder close to a plane boundary is simulated with a mass ratio of 2.6 and gap ratios of e/D=0.002 and 0.3 (gap ratio is defined as the ratio of gap between the Cylinder and the bed (e) to Cylinder diameter (D)). Simulations are carried out for reduced velocities ranging from 1 to 15 and Reynolds numbers ranging from 1000 to 15 000. It is found that vortex-induced vibrations occur even if the initial gap ratio is as small as e/D=0.002, although reported research indicated that vortex shedding behind a fixed Circular Cylinder is suppressed at small gap ratios (e/D

Atul Srivastava - One of the best experts on this subject based on the ideXlab platform.

  • flow and heat transfer measurements in the laminar wake region of semi Circular Cylinder embedded within a rectangular channel
    International Communications in Heat and Mass Transfer, 2020
    Co-Authors: Apoorv Vyas, Aishwarya Yadav, Atul Srivastava
    Abstract:

    Abstract Flow and heat transfer in the wake region of a semi-Circular Cylinder embedded within a rectangular channel have been studied experimentally using non-intrusive techniques. The semi-Circular Cylinder embedded within the channel with a blockage ratio of 0.45 (d/H) acts as an obstacle to the incoming fully developed laminar flow and creates a wake region in its downstream side. The velocity field in the downstream wake region is mapped using PIV (particle image velocimetry) technique with water as the working medium. The fluctuating shear layers and the vortices shed by the Cylinder interact with the bottom heated wall of the channel. The influence of the wake region of the Cylinder manifests on the heat transfer characteristics of the bottom wall of the channel and acts in a way to passively improve the overall heat transfer characteristics. The resulting whole field temperature values are captured using interferometry and augmentation in heat transfer rates vis-a-vis a channel without Cylinder are compared. The dominant frequencies of the downstream unsteady flow in the wake of the Cylinder are captured using schlieren technique. Heat transfer enhancement up to 42 percentage is observed in the case of the presence of the semi-Circular Cylinder in the channel in comparison with the flow in a plain channel for the Reynolds number range of 75–200 under which the experiments are performed.

  • non intrusive investigation of flow and heat transfer characteristics of a channel with a built in Circular Cylinder
    Physics of Fluids, 2018
    Co-Authors: Apoorv Vyas, Biswajit Mishra, Atul Agrawal, Atul Srivastava
    Abstract:

    Interferometry-based experimental investigation of heat transfer phenomena associated with a channel fitted with a Circular Cylinder has been reported. Experiments have been performed with water as the working fluid, and the range of Reynolds number considered is 75 ≤ Re ≤ 165. The Circular Cylinder, placed at the inlet section of the channel, provides a blockage ratio of 0.5. The experimental methodology has been benchmarked against the results of transient numerical simulations. In order to assess the performance of the channel fitted with a Circular Cylinder for possible heat transfer enhancement from the channel wall(s), experiments have also been performed on a plane channel (without a Cylinder). The interferometry-based experiments clearly highlighted the influence of the built-in Cylinder in generating the flow instabilities and alterations in the thermal boundary layer profile along the heated wall of the channel. The phenomenon of vortex shedding behind the Cylinder was successfully captured. A g...

Apoorv Vyas - One of the best experts on this subject based on the ideXlab platform.

  • flow and heat transfer measurements in the laminar wake region of semi Circular Cylinder embedded within a rectangular channel
    International Communications in Heat and Mass Transfer, 2020
    Co-Authors: Apoorv Vyas, Aishwarya Yadav, Atul Srivastava
    Abstract:

    Abstract Flow and heat transfer in the wake region of a semi-Circular Cylinder embedded within a rectangular channel have been studied experimentally using non-intrusive techniques. The semi-Circular Cylinder embedded within the channel with a blockage ratio of 0.45 (d/H) acts as an obstacle to the incoming fully developed laminar flow and creates a wake region in its downstream side. The velocity field in the downstream wake region is mapped using PIV (particle image velocimetry) technique with water as the working medium. The fluctuating shear layers and the vortices shed by the Cylinder interact with the bottom heated wall of the channel. The influence of the wake region of the Cylinder manifests on the heat transfer characteristics of the bottom wall of the channel and acts in a way to passively improve the overall heat transfer characteristics. The resulting whole field temperature values are captured using interferometry and augmentation in heat transfer rates vis-a-vis a channel without Cylinder are compared. The dominant frequencies of the downstream unsteady flow in the wake of the Cylinder are captured using schlieren technique. Heat transfer enhancement up to 42 percentage is observed in the case of the presence of the semi-Circular Cylinder in the channel in comparison with the flow in a plain channel for the Reynolds number range of 75–200 under which the experiments are performed.

  • non intrusive investigation of flow and heat transfer characteristics of a channel with a built in Circular Cylinder
    Physics of Fluids, 2018
    Co-Authors: Apoorv Vyas, Biswajit Mishra, Atul Agrawal, Atul Srivastava
    Abstract:

    Interferometry-based experimental investigation of heat transfer phenomena associated with a channel fitted with a Circular Cylinder has been reported. Experiments have been performed with water as the working fluid, and the range of Reynolds number considered is 75 ≤ Re ≤ 165. The Circular Cylinder, placed at the inlet section of the channel, provides a blockage ratio of 0.5. The experimental methodology has been benchmarked against the results of transient numerical simulations. In order to assess the performance of the channel fitted with a Circular Cylinder for possible heat transfer enhancement from the channel wall(s), experiments have also been performed on a plane channel (without a Cylinder). The interferometry-based experiments clearly highlighted the influence of the built-in Cylinder in generating the flow instabilities and alterations in the thermal boundary layer profile along the heated wall of the channel. The phenomenon of vortex shedding behind the Cylinder was successfully captured. A g...

Li Hao Feng - One of the best experts on this subject based on the ideXlab platform.

  • suppression of lift fluctuations on a Circular Cylinder by inducing the symmetric vortex shedding mode
    Journal of Fluids and Structures, 2015
    Co-Authors: Yaguang Liu, Li Hao Feng
    Abstract:

    Abstract The flow around a stationary Circular Cylinder modified by two synthetic jets positioned at the mean separation points is numerically studied. The Reynolds number based on the free-stream velocity and the Circular Cylinder diameter is Re=500. The focus is to present a novel way to suppress the lift fluctuations by changing the vortex shedding mode, and thus particular attention is paid to the interactions between the synthetic jets and wake shear layers and the resulting vortex dynamics. The overall influences of both momentum coefficient and excitation frequency are discussed. In some simulated cases, the vortex lock-on phenomenon is discovered, which causes the typical Karman type vortex shedding to be converted into the symmetric shedding modes, leading to the complete suppression of lift fluctuations. In other cases, the asymmetric shedding mode still dominates the wake evolution. Detailed vortical evolution for each typical wake pattern is analyzed to reveal the control mechanism. Additionally, the control effectiveness is evaluated, indicating that the present control strategy contributes an effective way to suppress the lift fluctuations and reduce the mean drag.

  • modification of a Circular Cylinder wake with synthetic jet vortex shedding modes and mechanism
    European Journal of Mechanics B-fluids, 2014
    Co-Authors: Li Hao Feng, Jinjun Wang
    Abstract:

    Abstract The wake behind a Circular Cylinder is modified by a synthetic jet positioned at the front stagnation point. The flow field is measured with a time-resolved particle image velocimetry (PIV) system, and the proper orthogonal decomposition (POD) and λ c i methods are used to analyze the vortex dynamics. The synthetic jet vortex pair is induced near the exit orifice periodically and then moves upstream. The interaction between the synthetic jet and the oncoming flow gives rise to an envelope formed upstream of the Circular Cylinder, which acts as a virtual aerodynamic shape. It is found that the envelope can be categorized into the periodic closed envelope and the quasi-steady open envelope, leading to different shedding modes for the wake around the Circular Cylinder. In the present investigation, six kinds of vortex shedding modes under synthetic jet control have been classified as natural Karman vortex mode, bistable state mode I, symmetric mode, bistable state mode II, antisymmetric mode with shortened vortex formation length, vortex generation close to the rear stagnation point. The vortex dynamics analysis indicates that the wake vortex trajectory, vortex circulation, and convection velocity at the vortex core all exhibit regular variations for these typical shedding modes. The formation mechanisms for these shedding modes have been further revealed, which present some novel formation processes in comparison with the natural Karman vortex street. Moreover, the effects of the synthetic jet momentum coefficient and excitation frequency on the control are also compared, which suggests that the type of the front envelope is most important for the vortex shedding modes.

  • proper orthogonal decomposition analysis of vortex dynamics of a Circular Cylinder under synthetic jet control
    Physics of Fluids, 2011
    Co-Authors: Li Hao Feng, Jinjun Wang, Chong Pan
    Abstract:

    Vortex dynamics of a Circular Cylinder controlled by a synthetic jet positioned at the back stagnation point is experimentally investigated using particle image velocimetry (PIV) technique. The proper orthogonal decomposition (POD) method is adopted to present the variations of the POD energy, mode, coefficient, corresponding dominant frequency, and the reconstructed spanwise vorticity. It is found that the dominant dimensionless control parameters should be the synthetic jet stroke length L0/D, where D is the diameter of the experimental Circular Cylinder, and the equivalent momentum coefficient Cμ. For the same stroke length L0/D=3.3, the states of the wake vortex shedding are determined by the momentum coefficient. They can be categorized into three groups summarizing all the parameters tested: antisymmetric Karman vortex shedding mode (Cμ≤0.027), vortex synchronization with shedding modes varying between the symmetric and antisymmetric ones (0.061≤Cμ≤0.109), and vortex synchronization with symmetric s...

Ali Beskok - One of the best experts on this subject based on the ideXlab platform.

  • mixing induced by a transversely oscillating Circular Cylinder in a straight channel
    Physics of Fluids, 2009
    Co-Authors: Bayram Celik, Ali Beskok
    Abstract:

    Flow past a transversely oscillating Circular Cylinder in a channel can be used as an active mesoscale mixer, kinematics of which was investigated by Celik et al. [“Flow past an oscillating Circular Cylinder in a channel with an upstream splitter plate,” Phys. Fluids 20, 103603 (2008)] at Re=100. This study presents numerical simulations of species transport in the mixer, obtained for various Cylinder excitation frequencies and the species inlet configurations for a wide range of Peclet numbers. Mixing indices are calculated on the vortex spacing based mixing blocks, which is a newly introduced concept that utilizes periodicity of the vorticity field. Mixing index comparisons show that mixing efficiency is strongly dependent on the identity of the species within wall shear layers and vortex cores. For the Cylinder excitation frequency of 25% higher than the natural vortex shedding frequency, 60% and 46% mixing enhancements relative to the straight channel and the stationary Cylinder cases are observed at ...

  • flow past an oscillating Circular Cylinder in a channel with an upstream splitter plate
    Physics of Fluids, 2008
    Co-Authors: Bayram Celik, Unal Akdag, Sibel Gunes, Ali Beskok
    Abstract:

    A transversely oscillating Circular Cylinder confined in a channel has the potential to promote mixing and heat transfer at moderate Reynolds number flows. In the present study, simulation results for flow past a Circular Cylinder subjected to forced cross-flow oscillations in a straight channel with an upstream splitter plate are presented in a wide range of Cylinder oscillation frequencies, including the subharmonic, superharmonic, and primary lock-in regimes. Simulations are performed at Re=100, with Cylinder oscillation amplitude of 0.4 diameters and a blockage ratio of 1/3. A spectral element algorithm based on the arbitrary Lagrangian Eulerian formulation is utilized. The numerical method exhibits spectral accuracy and allows large mesh deformation in the computational domain without mesh refinements. The main objective of this study is systematic investigations of the Cylinder oscillation on the vortex shedding mechanism, downstream vortex patterns, and forces exerted on the Cylinder.