Unsteady Structure and Development of a Row of Impingement Jets, Including Shear Layer and Vortex Development: Part 2 — Laminar Jets

2015 ◽  
Author(s):  
L. Yang ◽  
J. Ren ◽  
H. Jiang ◽  
P. M. Ligrani
Keyword(s):  
Broad Band ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Axial Direction ◽  
Impinging Jets ◽  
Laminar Jet ◽  
Laminar Jets ◽  
Spectral Peaks ◽  
Unsteady Rans ◽  
Band Mixing

Considered is a cylinder channel with a single row of 10 aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, each jet is laminar with a Reynolds number of 200. An unsteady RANS solver is employed for predictions of flow characteristics within and nearby the 10 impingement jets. Spectrum analysis of different flow quantities shows frequencies associated with laminar jet and vortex oscillations, and evidence more orderly flow for Re=200, without the chaos and broad-band mixing associated with the turbulent flow when Re=15,000. Laminar flow spectra also evidence increased flow unsteadiness as cross-flows accumulate within the impingement channel with streamwise development as Z/D increases. In some cases, this increased unsteadiness manifests itself through the formation of multiple spectral peaks, in place of single peak spectra. As for the turbulent jet arrangements, unsteady, local static pressure gradient variations along interfaces between laminar jets and cross flow are also a key flow feature, which is connected to the initiation and development of the Kelvin-Helmholtz instability induced vortices.

Unsteady Structure and Development of a Row of Impingement Jets, Including Shear Layer and Vortex Development: Part 1 — Turbulent Jets

2015 ◽  
Author(s):  
L. Yang ◽  
P. M. Ligrani ◽  
J. Ren ◽  
H. Jiang
Keyword(s):  
Shear Layer ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Turbulent Jets ◽  
Axial Direction ◽  
Impinging Jets ◽  
Local Flow ◽  
Layer Parameter ◽  
Unsteady Rans

Considered is a cylinder channel with a single row of 10 aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady RANS solver is employed for predictions of flow characteristics within and nearby the 10 impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component of vorticity, three-dimensional streamlines, a shear layer parameter, and local static pressure. Kelvin-Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin-Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.

Unsteady Structure and Development of a Row of Impingement Jets, Including Kelvin–Helmholtz Vortex Development

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Li Yang ◽  
Phillip Ligrani ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Static Pressure ◽  
Structural Characteristics ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Impinging Jets ◽  
Navier Stokes ◽  
Vortex Generation ◽  
Local Flow ◽  
Layer Parameter

Considered is a cylinder channel with a single row of ten aligned impinging jets, with exit flow in the axial direction at one end of the channel. For the present predictions, an unsteady Reynolds-Averaged Navier–Stokes (RANS) solver is employed for predictions of flow characteristics within and nearby the ten impingement jets, where the jet Reynolds number is 15,000. Spectrum analysis of different flow quantities is also utilized to provide data on associated frequency content. Visualizations of three-dimensional, unsteady flow structural characteristics are also included, including instantaneous distributions of Y-component vorticity, three-dimensional streamlines, shear layer parameter ψ, and local static pressure. Kelvin–Helmholtz vortex development is then related to local, instantaneous variations of these quantities. Of particular importance are the cumulative influences of cross flows, which result in locally increased shear stress magnitudes, enhanced Kelvin–Helmholtz vortex generation instabilities, and increased magnitudes and frequencies of local flow unsteadiness, as subsequent jets are encountered with streamwise development.

Numerical Study of Counter Jet Formed by Impinging Jets in Cross-Flow and its Effect on Mixing

2017 ◽  
Author(s):  
Thomas A. Epalle ◽  
Fabien Gaugain ◽  
Vincent Melot ◽  
Nasser Darabiha ◽  
Olivier Gicquel
Keyword(s):  
Numerical Study ◽  
Velocity Ratio ◽  
Flow Characteristics ◽  
Cross Flow ◽  
Passive Scalar ◽  
Impinging Jets ◽  
Mean Velocity ◽  
Plane Flow ◽  
Flow Mixing ◽  
Mixing Chambers

In this paper we will numerically analyse flow mixing in multiple jets in a crossflow. The system comprises a row of six radially-distributed injectors around the main pipe. The configuration represents mixing zones in industrial systems where a counter jet can be formed in the injection plane. Flow mixing can be modified as a result of geometry and injection velocities. We propose a simple model to describe the counter jet length as a function of injection flow characteristics. We also develop empirical laws to help engineers design practical test facilities. We then vary the velocity ratio to obtain both impinging and non-impinging jets in the injection plane. The focus is mainly on flow characteristics around the radial injection plane in the case of impinging jets, examining the mixing quality and efficiency by introducing a passive scalar discharge in a nitrogen flow. The mean velocity and width of the counter jet are finally analyzed by changing the injection velocities. These results are compared to those of non-impinging jets. It is found that the non-impinging jet configurations are convenient for short length mixing chambers, while the impinging ones should be considered in the case of longer mixing chambers.

scholarly journals Random pore structure and REV scale flow analysis of engine particulate filter based on LBM

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 881-896
Author(s):  
Chunrui Wu ◽  
Tiechen Zhang ◽  
Jiale Fu ◽  
Xiaori Liu ◽  
Boxiong Shen
Keyword(s):  
Single Channel ◽  
Flow Analysis ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Particulate Filter ◽  
Random Structure ◽  
Structure Generation ◽  
Inlet Flow ◽  
Random Structures ◽  
Boltzmann Method

Abstract In this article, lattice Boltzmann method (LBM) is used to simulate the multi-scale flow characteristics of the engine particulate filter at the pore scale and the representative elementary volume (REV) scale, respectively. Four kinds of random wall-pore structures are considered, which are circular random structure, square random structure, isotropic quartet structure generation set (QSGS), and anisotropic QSGS, with difference analysis done. In terms of the REV scale, the influence of different inlet flow velocities and wall permeabilities on the flow in single channel is analyzed. The result indicates that the internal seepage laws of random structures constructed in this article and single channel are in accordance with Darcy’s law. Circular random structure has better permeability than square random structure. Isotropic QSGS has better fluidity than anisotropic one. The flow in single channel is similar to Poiseuille flow. The flow lines in the channel are complicated and a large number of vortices appear at the ends of channel with high inlet flow rate. With the increase of inlet velocity, the static pressure in channel gradually increases along the axial direction as well as the seepage velocity. The temperature field in the channel becomes more uniform as the flow velocity increases, and the higher temperature distribution appears on the wall of the porous media.

Theoretical and Experimental Characterization of Emulsion Flow in a Cavity Transfer Mixer

2003 ◽  
Author(s):  
A. H. Raza ◽  
R. A. Lai-Fook ◽  
C. J. Lawrence
Keyword(s):  
Flow Characteristics ◽  
Axial Direction ◽  
Solution Procedure ◽  
Modes Of Operation ◽  
Flow Equations ◽  
Recirculating Flow ◽  
Rectangular Pattern ◽  
Mean Pressure ◽  
Emulsion Processing ◽  
Dependent Flow

A theoretical model of time-dependent flow based on Reynolds equation using emulsion processing in a Cavity Transfer Mixer (CTM) has been developed in Mathematica and is presented in this work. It is a continuum model, which allows the study of materials undergoing rapid deformation. The flow of a fluid in a CTM is examined using a finite difference analysis (FDA) to solve the flow equations for an unwound section with cavities arranged in a rectangular pattern. Periodic boundary conditions are included in the model to predict the pressure distribution, which allows subsequent determination of the flow field. The solution procedure gives a smooth function for the pressure field, with equal pressures at the boundaries in the y-direction and an overall mean pressure gradient in the x-direction. Once the pressure has been found, several flow properties follow directly. The flow in the downstream axial direction is seen to consist of purely pressure-driven flow. In contrast, the flow in the cross-cavity direction is a recirculating flow driven by the drag velocity of the moving rotor surface. These two flows taken together combine into a helical flow travelling through the cavity. Because of this, there is likely to bre a high degree of laminar and distributive flow in this type of machine. The experimental part of this work addresses the processing of an emulsion in the CTM when it is run under batch and continuous modes of operation. The flow characteristics have been studied for varying rotor speeds of 0 rpm, 16 rpm, 32 rpm, 48 rpm and 64 rpm. Also studied were the changes that the emulsion exhibits along the mixer length and with time in the mixer. The experiments indicate that increase in the rotational speed causes the viscosity to reduce systematically in both batch and continuous modes of operation.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

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