A Numerical Study on Mixing In Turbulent Flow Behind a Backward-Facing Step

2005 ◽  
Author(s):  
R. Veturi ◽  
K. Aung
Keyword(s):  
Turbulent Flow ◽  
Mass Concentration ◽  
Numerical Study ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Backward Facing Step ◽  
Computational Fluid Dynamics Analysis ◽  
Circular Jets ◽  
Contour Plots ◽  
The Cross

Present work studies the mixing in turbulent flow behind a backward-facing step, which is a classical example of mixing of jet in cross flow. In this study the cross flow was an unconfined cross flow flowing through a duct, which has geometry of backward-facing step with varying cross section. Three jet geometries, a slot jet, a single circular jet and three circular jets with different injection angles were studied. Spatial unmixedness based on helium mass concentration was used as an indicator for determining the degree of mixing. Velocity ratio, defined as ratio of jet velocity to the cross flow velocity, was varied during the analysis. Three different values of velocity ratio were considered during the study. Computational fluid dynamics analysis was performed using commercial CFD software CFX 5.6. Results were extracted in the form of helium mass concentration fields, concentration profiles, concentration contour plots and velocity vector plots. From the results obtained it can be concluded that, angle of jet inclination is the important controlling parameter in mixing in flow behind a backward-facing step. Single jet geometry gives better mixing for the given conditions.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

scholarly journals Numerical Study on Heat and Mass Transfer of the Cross-flow Liquid Desiccant Regenerator

2017 ◽  
Vol 205 ◽  
pp. 2647-2654 ◽  
Author(s):  
Yang Li ◽  
Zhibo Fu ◽  
Xiaohu Yang ◽  
Lianying Zhang ◽  
Qunli Zhang ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Numerical Study ◽  
Cross Flow ◽  
Liquid Desiccant ◽  
The Cross

scholarly journals Prediction of side thermal buoyant discharge in the cross flow using multi-objective evolutionary polynomial regression (EPR-MOGA)

2019 ◽  
Vol 21 (6) ◽  
pp. 980-998
Author(s):  
Milad Khosravi ◽  
Mitra Javan
Keyword(s):  
Polynomial Regression ◽  
Velocity Ratio ◽  
Three Dimensional ◽  
Cross Flow ◽  
Temperature Profiles ◽  
Cfd Model ◽  
Multi Objective ◽  
Evolutionary Polynomial Regression ◽  
The Cross ◽  
Thermal Cross Section

Abstract The capability to predict the distribution of pollutants in water bodies is one of the most important issues in the design of jet outfalls. Three-dimensional computational fluid dynamics (CFD) model and multi-objective evolutionary polynomial regression (EPR-MOGA) are used and compared in modeling the temperature field in the side thermal buoyant discharge in the cross flow. The input variables used for training the EPR-MOGA models are spatial coordinates (x, y, z), jet to cross flow velocity ratio (R), depth of the channel (d), and the temperature excess (T0). A previous experimental study is used to verify and compare the performance of the EPR-MOGA and CFD models. The results show that the EPR-MOGA model predicts the thermal cross section of the flow and the spread of pollutants at the surface with a better accuracy than the CFD model. However, the CFD method performs significantly better than EPR-MOGA in predicting temperature profiles. The uncertainty analysis indicated that the EPR-MOGA model had lower mean prediction error and smaller uncertainty band than the CFD model. The relationships achieved by the EPR-MOGA model are very useful to predict temperature profiles, temperature half-thickness, and temperature spread on surface in practice.

scholarly journals Design and Numerical Study of Micropump Based on Induced Electroosmotic Flow

2018 ◽  
Vol 2018 ◽  
pp. 1-6 ◽  
Author(s):  
Kai Zhang ◽  
Lengjun Jiang ◽  
Zhihan Gao ◽  
Changxiu Zhai ◽  
Weiwei Yan ◽  
...  
Keyword(s):  
Electroosmotic Flow ◽  
Stokes Equations ◽  
Numerical Study ◽  
Cross Flow ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Driving Mode ◽  
Electric Driving ◽  
Induced Charge ◽  
The Cross

Induced charge electroosmotic flow is a new electric driving mode. Based on the Navier–Stokes equations and the Poisson–Nernst–Planck (PNP) ion transport equations, the finite volume method is adopted to calculate the equations and boundary conditions of the induced charge electroosmotic flow. In this paper, the formula of the induced zeta potential of the polarized solid surface is proposed, and a UDF program suitable for the simulation of the induced charge electroosmotic is prepared according to this theory. At the same time, on the basis of this theory, a cross micropump driven by induced charge electroosmotic flow is designed, and the voltage, electric potential, charge density, and streamline of the induced electroosmotic micropump are obtained. Studies have shown that when the cross-shaped micropump is energized, in the center of the induction electrode near the formation of a dense electric double layer, there exist four symmetrical vortices at the four corners, and they push the solution towards both outlets; it can be found that the average velocity of the solution in the cross-flow microfluidic pump is nonlinear with the applied electric field, which maybe helpful for the practical application of induced electroosmotic flow in the field of micropump.

scholarly journals Mixing Performance of a Passive Micro-Mixer with Mixing Units Stacked in Cross Flow Direction

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1530
Author(s):  
Makhsuda Juraeva ◽  
Dong-Jin Kang
Keyword(s):  
Numerical Study ◽  
Volume Flow Rate ◽  
Flow Direction ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
High Concentration ◽  
Mixing Performance ◽  
Wall Impingement ◽  
The Cross ◽  
Micro Mixer

A new passive micro-mixer with mixing units stacked in the cross flow direction was proposed, and its performance was evaluated numerically. The present micro-mixer consisted of eight mixing units. Each mixing unit had four baffles, and they were arranged alternatively in the cross flow and transverse direction. The mixing units were stacked in four different ways: one step, two step, four step, and eight step stacking. A numerical study was carried out for the Reynolds numbers from 0.5 to 50. The corresponding volume flow rate ranged from 6.33 μL/min to 633 μL/min. The mixing performance was analyzed in terms of the degree of mixing (DOM) and relative mixing energy cost (MEC). The numerical results showed a noticeable enhancement of the mixing performance compared with other micromixers. The mixing enhancement was achieved by two flow characteristics: baffle wall impingement by a stream of high concentration and swirl motion within the mixing unit. The baffle wall impingement by a stream of high concentration was observed throughout all Reynolds numbers. The swirl motion inside the mixing unit was observed in the cross flow direction, and became significant as the Reynolds number increased to larger than about five. The eight step stacking showed the best performance for Reynolds numbers larger than about two, while the two step stacking was better for Reynolds numbers less than about two.

scholarly journals Effect of Jet Inclination Angle and Hole Exit Shape on Vortical Flow Structures in Low-Reynolds Number Jet in Cross-Flow

2012 ◽  
Vol 2012 ◽  
pp. 1-7
Author(s):  
Yufeng Yao ◽  
Mohamad Maidi ◽  
Jun Yao
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Inclination Angle ◽  
Qualitative Agreement ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Vortical Flow ◽  
Flow Structures ◽  
Good Qualitative Agreement ◽  
The Cross

Numerical studies have been performed to visualize vortical flow structures emerged from jet cross-flow interactions. A single square jet issuing perpendicularly into a cross-flow was simulated first, followed by two additional scenarios, that is, inclined square jet at angles of 30° and 60° and round and elliptic jets at an angle of 90°, respectively. The simulation considers a jet to cross-flow velocity ratio of 2.5 and a Reynolds number of 225, based on the free-stream flow quantities and the jet exit width in case of square jet or minor axis length in case of elliptic jet. For the single square jet, the vortical flow structures simulated are in good qualitative agreement with the findings by other researchers. Further analysis reveals that the jet penetrates deeper into the cross-flow field for the normal jet, and the decrease of the jet inclination angle weakens the cross-flow entrainment in the near-wake region. For both noncircular and circular jet hole shapes, the flow field in the vicinity of the jet exit has been dominated by large-scale dynamic flow structures and it was found that the elliptic jet hole geometry has maximum “lifted-off” effect among three hole configurations studied. This finding is also in good qualitative agreement with existing experimental observations.

scholarly journals Trajectory of a synthetic jet issuing into high-Reynolds-number turbulent boundary layers

2018 ◽  
Vol 856 ◽  
pp. 531-551 ◽  
Author(s):  
Tim Berk ◽  
Nicholas Hutchins ◽  
Ivan Marusic ◽  
Bharathram Ganapathisubramani
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
High Reynolds Number ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Turbulent Boundary Layers ◽  
Synthetic Jet ◽  
Actuation Frequency ◽  
The Cross ◽  
High Reynolds

Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For some applications, the scaling of the trajectory of the jet with actuation and cross-flow parameters is important. This scaling is investigated for changes in the friction Reynolds number, changes in the velocity ratio (defined as the ratio between the mean jet blowing velocity and the free-stream velocity) and changes in the actuation frequency of the jet. A distinctive aspect of this study is the high-Reynolds-number turbulent boundary layers (up to $Re_{\unicode[STIX]{x1D70F}}=12\,800$) of the cross-flow. To our knowledge, this is the first study to investigate the effect of the friction Reynolds number of the cross-flow on the trajectory of an (unsteady) jet, as well as the first study to systematically investigate the scaling of the trajectory with actuation frequency. A broad range of parameters is varied (rather than an in-depth investigation of a single parameter) and the results of this study are meant to indicate the relative importance of each parameter rather than the exact influence on the trajectory. Within the range of parameters explored, the critical ones are found to be the velocity ratio as well as a non-dimensional frequency based on the jet actuation frequency, the cross-flow velocity and the jet dimensions. The Reynolds number of the boundary layer is shown to have only a small effect on the trajectory. An expression for the trajectory of the jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow.

Sign in / Sign up

Export Citation Format

Share Document