Reduction of the Flow Separation Zone at Combining Open-Channel Junction by Applying Alternate Suction and Blowing

2021 ◽  
Vol 147 (10) ◽  
pp. 06021011
Author(s):  
Abhishek K. Pandey ◽  
Pranab K. Mohapatra
Keyword(s):  
Flow Separation ◽  
Open Channel ◽  
Separation Zone ◽  
Suction And Blowing

Magnetohydrodynamic Viscous Flow Separation in a Channel With Constrictions

2003 ◽  
Vol 125 (6) ◽  
pp. 952-962 ◽  
Author(s):  
C. Midya ◽  
G. C. Layek ◽  
A. S. Gupta ◽  
T. Ray Mahapatra
Keyword(s):  
Magnetic Field ◽  
Flow Separation ◽  
Separation Zone ◽  
Transverse Magnetic ◽  
Mhd Equations ◽  
Staggered Grid ◽  
Solution Technique ◽  
Computational Domain ◽  
Pressure Poisson Equation ◽  
The Magnetic Field

An analysis is made of the flow of an electrically conducting fluid in a channel with constrictions in the presence of a uniform transverse magnetic field. A solution technique for governing magnetohydrodynamic (MHD) equations in primitive variable formulation is developed. A coordinate stretching is used to map the long irregular geometry into a finite computational domain. The governing equations are discretized using finite difference approximations and the well-known staggered grid of Harlow and Welch is used. Pressure Poisson equation and pressure-velocity correction formulas are derived and solved numerically. It is found that the flow separates downstream of the constriction. With increase in the magnetic field, the flow separation zone diminishes in size and for large magnetic field, the separation zone disappears completely. Wall shear stress increases with increase in the magnetic field strength. It is also found that for symmetrically situated constrictions on the channel walls, the critical Reynolds number for the flow bifurcation (i.e., flow asymmetry) increases with increase in the magnetic field.

Control of Heat Transfer in Separated Flows With the Help of Miniturbulators

2010 ◽  
Author(s):  
T. V. Bogatko ◽  
A. Yu. D’yachenko ◽  
V. I. Terekhov ◽  
N. I. Yarygina
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Separation ◽  
Separation Zone ◽  
Cross Flow ◽  
Separated Flow ◽  
Separation Point ◽  
Upstream Region ◽  
Maximum Heat

In the present paper, the influence of vorticity layer on the turbulent separated flow and heat transfer in a cross-flow cavity was experimentally examined. The vorticity layer was generated by a miniturbulator installed in the upstream region of the flow separation point. As the miniturbulator, a small cross-flow rib was used whose height was one order of magnitude smaller than the cavity depth. The variable parameters were the angle of wall inclination in the cavity, the rib height, and the rib-to-cavity separation. The additional vortical disturbances introduced into the recirculation zone were found to exert an appreciable influence on the vortex formation pattern and on the distribution of pressure and heat-transfer coefficients. The experimental data were compared to computation data obtained with the Fluent 6 software. Numerical data on the dynamic and thermal characteristics of flows past a system comprising a sudden pipe expansion and a low-height diaphragm installed in the upstream region of the flow separation point are also presented. It is found that such a diaphragm, used to modify the characteristics of the separated flow, results in a change of the length and intensity of the eddying flow in the separation zone. The vortex sheet produced by the diaphragm interacts with the primary eddy, makes the separation zone more extended, and shifts, even to a greater extent, the point at which the heat-transfer coefficient attains its maximum in the downstream direction. The maximum heat-transfer coefficient turns out to be increased in comparison with undisturbed flow. Both the location of the diaphragm and the diaphragm height strongly affect the heat-transfer characteristics.

scholarly journals Flow-field Near Forty-Five Degree Dividing Open Channel

2019 ◽  
Vol 8 (3) ◽  
pp. 2768-2773
Keyword(s):  
Turbulent Flows ◽  
Open Channel ◽  
Separation Zone ◽  
Irrigation System ◽  
Effective Length ◽  
Water Diversion ◽  
Engineering System ◽  
Main River ◽  
Water Conveyance ◽  
Fluent Software

Dividing flows are most common in open channel flow in hydraulic engineering system. Turbulent flows are most common through lateral intakes adjoining rivers and canals. Lateral intakes are used for the distribution of water for irrigation system, power plant, public supply etc. Sedimentation remains the most prominent problem in and around the intake structures in water diversion engineering. Sediment entering the water conveyance system leads to reducing the effective length of the waterway and also the closure of entrances of intake structures. Diversion works or intake works are structures provided to draw in water from the main river or channel into conveyance systems for meeting different uses such a irrigation, drinking water requirements etc. In the present study, experimental and numerical modelling study has been made to model an intake at 450 and velocity is measured experimentally. These velocities are then compared with the velocity obtained using the FLUENT software in the main and branch channel along with the junction point. The study shows good agreement between the numerical simulation and experimental data. And found the variation in separation zone at different discharge ratio and compare with the separation zone which is found by the previous study around 900 water intakes

Flow Separation at 90-Degree Junctions With Opposing Flows

2003 ◽  
Author(s):  
Carl Frizzell ◽  
David Werth
Keyword(s):  
Flow Separation ◽  
Cooling Tower ◽  
Hydraulic Structure ◽  
Separation Zone ◽  
Theoretical Method ◽  
Conservation Of Energy ◽  
3 Dimensional ◽  
Theoretical Predictions ◽  
Energy And Momentum ◽  
Separation Zones

Sumps located on the side of cooling tower basins, or any other type of hydraulic structure where opposing flows combine and turn 90-degrees can result in a significant amount of flow separation and energy dissipation at the junction. These separation zones can result in localized regions of higher velocity. If the separation zone is large enough, the flow can approach critical depth. A theoretical method of predicting the size of these separation zones is presented based on the conservation of energy and momentum. To validate the model, the results of an ongoing experimental study are compared to the theoretical predictions. A physical model was constructed and an Acoustic Doppler Velocimeter was used to collect 3-dimensional velocity data within each leg of the junction.

Active Flow Control With an Oscillating Backward Facing Step in a Shallow Open Channel

2012 ◽  
Author(s):  
Sertac Cadirci ◽  
Hasan Gunes
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Flow Separation ◽  
Open Channel ◽  
Recirculation Zone ◽  
Active Flow Control ◽  
Computational Domain ◽  
Backward Facing Step ◽  
Induced Flow ◽  
Active Flow

An oscillatory, zero-net-mass flux actuator system, Jet and Vortex Actuator (JaVA), is implemented on the step wall of a backward facing step. JaVA can energize the boundary layer by creating jets or vortices thus it may delay flow separation when used properly. The main part of JaVA is a rectangular cavity with a moving actuator plate. The actuator plate is mounted asymmetrically inside the cavity of the JaVA box, such that there are one narrow and one wide gap between the plate and the box. The main governing parameters are the actuator plate’s width (b), the amplitude (a) and the operating frequency (f). The main target of the control with active jets on the step wall is to influence directly the main recirculation zone, thus as the actuator plate or the step’s vertical wall moves periodically in horizontal direction, a jet emerges into the recirculation zone. Non-dimensional numbers such as the scaled amplitude (Sa = 2πa/b) and the jet Reynolds number (ReJ = 4abf/ν) as well as the cross flow parameter characterize the JaVA-induced flow types and the effects on the recirculation zone. One period consists of one blowing and one suction phase into the recirculation zone. Boundary layer profiles extracted from time-averaged flow fields of the not actuated (f = 0) and actuated cases at various operating frequencies indicate the effect of active flow control. The interaction between JaVA-induced flow regimes and the boundary layer is investigated numerically in an open channel with a BFS. The computational domain consists of a moving zone along the channel and the motion of the actuator plate is generated by a moving grid imposing appropriate boundary conditions with User-Defined-Functions and the calculations are carried out by a commercial finite-volume-based unsteady, laminar, incompressible Navier-Stokes solver. Numerical simulations and comparisons reveal the JaVA-boundary layer interaction for various governing parameters. Reynolds numbers based on the step height for the shallow open channel flow are Reh = 225 and 450. The proposed control method based on suction and blowing with an oscillating vertical step seems to be effective in shortening the recirculation zone length and delaying the flow separation downstream of the backward facing step.

Separation Zone at Open‐Channel Junctions

1984 ◽  
Vol 110 (11) ◽  
pp. 1588-1594 ◽  
Author(s):  
James L. Best ◽  
Ian Reid
Keyword(s):  
Open Channel ◽  
Separation Zone

Numerical Research on the Flow Field and Performance of a Ram-Rotor and a Scrampressor

2012 ◽  
Author(s):  
Ling Yang ◽  
Jingjun Zhong ◽  
Ji-ang Han
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Flow Separation ◽  
Rotational Speed ◽  
Separation Zone ◽  
Back Pressure ◽  
Wave Number ◽  
Typical Structure ◽  
Total Performance ◽  
Subsonic Diffuser

The design methods of typical supersonic aircraft intakes and shock wave compression technology have been applied to ram-rotor, a new attractive compression system. A ram-rotor is a typical structure including the compression ramp, the throat and the subsonic diffuser; a scrampressor is similar to ram-rotor, the only different is that scrampressor has no subsonic diffuser. Base on the preparatory work, it has been found that these two structures have different advantages respectively. So, in this paper, the three dimensional Reynolds-averaged Navier-Stokes equations and the Spalart-Allmaras turbulent model are used to simulate numerically the flow field of the ram-rotor and the scrampressor at the design and at the off-design conditions. The back pressure and rotational speed are mainly considered which may affect the flow field and the total performance. It has been found that back pressure can not have influence on the flow field before the throat outlet obviously. With increasing of the back pressure, the position of the flow separation zone and shock train move forwards to the inlet. The rotational speed changes the shock wave structure of the ram-rotor and scrampressor evidently. With the rotational speed increasing, each shock wave moves to the outlet and the shock wave number decreases. The ram-rotor and scrampressor structure is similar, except the ram-rotor flow structure has a large flow separation zone after the throat outlet. The compression capability of the ram-rotor is higher than that of the scrampressor. The total performance of the scrampressor is better than the ram-rotor.

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