scholarly journals Numerical Simulation of Mixed Convective Flow Over a Three-Dimensional Horizontal Backward Facing Step

2005 ◽  
Vol 127 (9) ◽  
pp. 1027-1036 ◽  
Author(s):  
J. G. Barbosa Saldana ◽  
N. K. Anand ◽  
V. Sarin
Keyword(s):  
Convective Flow ◽  
Three Dimensional ◽  
Step Length ◽  
Expansion Ratio ◽  
Step Height ◽  
Streamwise Direction ◽  
Backward Facing Step ◽  
Thermal Features ◽  
Mixed Convective Flow ◽  
Thermally Conducting

Laminar mixed convective flow over a three-dimensional horizontal backward-facing step heated from below at a constant temperature was numerically simulated using a finite volume technique and the most relevant hydrodynamic and thermal features for air flowing through the channel are presented in this work. The channel considered in this work has an aspect ratio AR=4, and an expansion ratio ER=2, while the total length in the streamwise direction is 52 times the step height (L=52s) and the step length is equal to 2 times the step height (l=2s). The flow at the duct entrance was considered to be hydrodynamically fully developed and isothermal. The bottom wall of the channel was subjected to a constant high temperature while the other walls were treated to be adiabatic. The step was considered to be a thermally conducting block.

scholarly journals Numerical Simulation for Mixed Convective Flow Over a Three-Dimensional Horizontal Backward Facing Step

2004 ◽  
Author(s):  
J. G. Barbosa Saldana ◽  
N. K. Anand ◽  
V. Sarin
Keyword(s):  
Convective Flow ◽  
Three Dimensional ◽  
Step Length ◽  
Expansion Ratio ◽  
The Other ◽  
Step Height ◽  
Streamwise Direction ◽  
Backward Facing Step ◽  
Thermal Features ◽  
Mixed Convective Flow

Laminar mixed convective flow over a three-dimensional horizontal backward-facing step heated from below at a constant temperature was numerically simulated using a finite volume technique and the most relevant hydrodynamic and thermal features for air flowing through the channel are presented in this work. The channel considered in this work has an aspect ratio AR = 4, and an expansion ratio ER = 2, while the total length in the streamwise direction is 52 times the step height (L = 52s) and the step length is equal to 2 times the step height (l = 2s). The flow at the duct entrance was considered to be hydro-dynamically fully developed and isothermal. The bottom wall of the channel was subjected to a constant high temperature while the other walls were treated to be adiabatic. The step was considered to be a thermal conductive block.

Eddy structures in a transitional backward-facing step flow

2007 ◽  
Vol 588 ◽  
pp. 43-58 ◽  
Author(s):  
H. P. RANI ◽  
TONY W. H. SHEU ◽  
ERIC S. F. TSAI
Keyword(s):  
Three Dimensional ◽  
Flow Simulation ◽  
Simulated Data ◽  
Numerical Data ◽  
Expansion Ratio ◽  
Transitional Flow ◽  
Backward Facing Step ◽  
Longitudinal Vortices ◽  
Eddy Structures ◽  
Spanwise Flow

In the present study, flow simulation has been carried out in a backward-facing step channel defined by an expansion ratio of 2.02 and a spanwise aspect ratio of 8 to provide the physical insight into the longitudinal and spanwise flow motions and to identify the presence of Taylor–Görtler-like vortices. The Reynolds numbers have been taken as 1000 and 2000, which fall in the category of transitional flow. The present simulated results were validated against the experimental and numerical data and the comparison was found to be satisfactory. The simulated results show that the flow becomes unsteady and exhibits a three-dimensional nature with the Kelvin–Helmholtz instability oscillations and Taylor–Görtler-Like longitudinal vortices. The simulated data were analysed to give an in-depth knowledge of the complex interactions among the floor and roof eddies, and the spiralling spanwise flow motion. Destabilization of the present incompressible flow system, with the amplified Reynolds number due to the Kelvin–Helmholtz and Taylor–Görtler instabilities, is also highlighted. A movie is available with the online version of the paper.

Global stability of the two-dimensional flow over a backward-facing step

2011 ◽  
Vol 693 ◽  
pp. 1-27 ◽  
Author(s):  
Daniel Lanzerstorfer ◽  
Hendrik C. Kuhlmann
Keyword(s):  
Three Dimensional ◽  
Physical Nature ◽  
Expansion Ratio ◽  
Two Dimensional ◽  
Backward Facing Step ◽  
Critical Mode ◽  
Large Step ◽  
Large Expansion ◽  
Amplification Process ◽  
Two Dimensional Flow

AbstractThe two-dimensional, incompressible flow over a backward-facing step is considered for a systematic variation of the geometry covering expansion ratios (step to outlet height) from 0.25 to 0.975. A global temporal linear stability analysis shows that the basic flow becomes unstable to different three-dimensional modes depending on the expansion ratio. All critical modes are essentially confined to the region behind the step extending downstream up to the reattachment point of the separated eddy. An energy-transfer analysis is applied to understand the physical nature of the instabilities. If scaled appropriately, the critical Reynolds number approaches a finite asymptotic value for very large step heights. In that case centrifugal forces destabilize the flow with respect to an oscillatory critical mode. For moderately large expansion ratios an elliptical instability mechanism is identified. If the step height is further decreased the critical mode changes from oscillatory to stationary. In addition to the elliptical mechanism, the strong shear in the layer emanating from the sharp corner of the step supports the amplification process of the critical mode. For very small step heights the basic state becomes unstable due to the lift-up mechanism, which feeds back on itself via the recirculating eddy behind the step, resulting in a steady critical mode comprising pronounced slow and fast streaks.

Buoyancy-assisted mixed convective flow over backward-facing step in a vertical duct using nanofluids

2012 ◽  
Vol 19 (1) ◽  
pp. 33-52 ◽  
Author(s):  
H. A. Mohammed ◽  
A. A. Al-aswadi ◽  
M. Z. Yusoff ◽  
R. Saidur
Keyword(s):  
Convective Flow ◽  
Backward Facing Step ◽  
Mixed Convective Flow ◽  
Vertical Duct

scholarly journals Convective instability and transient growth in flow over a backward-facing step

2008 ◽  
Vol 603 ◽  
pp. 271-304 ◽  
Author(s):  
H. M. BLACKBURN ◽  
D. BARKLEY ◽  
S. J. SHERWIN
Keyword(s):  
Convective Instability ◽  
Three Dimensional ◽  
Nonlinear Effects ◽  
Expansion Ratio ◽  
Base Flow ◽  
Time Interval ◽  
Transient Growth ◽  
Two Dimensional ◽  
Backward Facing Step ◽  
Transient Energy

Transient energy growths of two- and three-dimensional optimal linear perturbations to two-dimensional flow in a rectangular backward-facing-step geometry with expansion ratio two are presented. Reynolds numbers based on the step height and peak inflow speed are considered in the range 0–500, which is below the value for the onset of three-dimensional asymptotic instability. As is well known, the flow has a strong local convective instability, and the maximum linear transient energy growth values computed here are of order 80×103 at Re = 500. The critical Reynolds number below which there is no growth over any time interval is determined to be Re = 57.7 in the two-dimensional case. The centroidal location of the energy distribution for maximum transient growth is typically downstream of all the stagnation/reattachment points of the steady base flow. Sub-optimal transient modes are also computed and discussed. A direct study of weakly nonlinear effects demonstrates that nonlinearity is stablizing at Re = 500. The optimal three-dimensional disturbances have spanwise wavelength of order ten step heights. Though they have slightly larger growths than two-dimensional cases, they are broadly similar in character. When the inflow of the full nonlinear system is perturbed with white noise, narrowband random velocity perturbations are observed in the downstream channel at locations corresponding to maximum linear transient growth. The centre frequency of this response matches that computed from the streamwise wavelength and mean advection speed of the predicted optimal disturbance. Linkage between the response of the driven flow and the optimal disturbance is further demonstrated by a partition of response energy into velocity components.

Heat Transfer Analysis of Three-Dimensional Mixed Convective Flow of an Oldroyd-B Nanoliquid over a Slippery Stretching Surface

2020 ◽  
Vol 401 ◽  
pp. 164-182
Author(s):  
K.V. Prasad ◽  
Hanumesh Vaidya ◽  
K. Vajravelu ◽  
Gudekote Manjunatha ◽  
M. Rahimi-Gorji ◽  
...  
Keyword(s):  
Convective Flow ◽  
Three Dimensional ◽  
Velocity Slip ◽  
Heat Transfer Analysis ◽  
Soret And Dufour Effects ◽  
Flux Boundary Condition ◽  
Thermal Buoyancy ◽  
Mixed Convective Flow ◽  
Dufour Number ◽  
The Impact

The present article examines Soret and Dufour effects on the three-dimensional mixed convective flow of an Oldroyd-B nanoliquid. The flow is caused due to bidirectional stretching of the surface in the presence of an induced magnetic field and heat generation/absorption. Besides, concentration and thermal buoyancy impacts are inspected. The velocity slip, convective and zero nanoparticle mass flux boundary condition at the surface are taken into account. Nonlinear system of equations which are highly coupled is solved via optimal homotopy algorithm. The influence of pertinent parameters on velocity, temperature, and concentration are analyzed graphically. The impact of Dufour number is quite substantial on temperature whereas Soret number increases the concentration. To see the legitimacy of the present work, the present results are compared with the results available in the literature and noted an excellent agreement for the limiting cases.

Numerical Simulation of Two-Dimensional Laminar Incompressible Wall Jet Flow Under Backward-Facing Step

2006 ◽  
Vol 128 (5) ◽  
pp. 1023-1035 ◽  
Author(s):  
P. Rajesh Kanna ◽  
Manab Kumar Das
Keyword(s):  
Linear Trend ◽  
Step Length ◽  
Jet Flow ◽  
Step Height ◽  
Jet Flows ◽  
Wall Jet ◽  
Two Dimensional ◽  
Backward Facing Step ◽  
Navier Stokes Equation ◽  
Wall Jet Flow

Two-dimensional laminar incompressible wall jet flow over a backward-facing step is solved numerically to gain insight into the expansion and recirculation of flow processes. Transient streamfunction vorticity formulation of the Navier-Stokes equation is solved with clustered grids on the physical domain. The behavior of the jet has been studied for different step geometry (step length, l, step height, s) and Reynolds number (Re). It is found that the presence of a step in the wall jet flow creates recirculation and the reattachment length follows an almost linear trend within the range considered for both parameters Re and step geometry. Simulations are made to show the effect of entrainment on recirculation eddy. Detailed study of u velocity decay is reported. The velocity profile in the wall jet region shows good agreement with experimental as well as similarity results. The distance where the similarity profile forms is reduced by increasing the step geometry whereas an increment in Re increases this distance. The effects of Re, step length, and step height on wall vorticity are presented. The parametric study is helpful to predict the reattachment location for wall jet flows over step.

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