Flow inside an unbaffled Rushton-impeller stirred tank reactor (STR) is perturbed using a time dependent impeller rotational speed. Large eddy simulation (LES) revealed that the perturbation increased the width of impeller jet compared to the constant rotational speed cases. The turbulent fluctuations were also observed to be enhanced in the perturbed flow and showed higher values of production and convection of turbulent kinetic energy. Changes in the mean flow-field during the perturbation cycle are investigated. The trailing edge vortices were observed to propagate farther both in the radial and azimuthal direction in the perturbed case. Production of turbulent kinetic energy is observed to be related to the breakup of the impeller jet in the perturbed case. Dissipation of turbulent kinetic energy is augmented due to the perturbation ensuring a better mixing at the molecular scale.

References

References
1.
Tatterson
,
G. B.
,
Brodkey
,
R. S.
, and
Calbrese
,
R. V.
, 1991, “
Move Mixing Technology Into the 21st Century
,”
Chem. Eng. Prog.
,
87
(
6
), pp.
45
48
. Available at: http://www.scopus.com/record/display.url?eid=2-s2.0-0026174333&origin=inward&txGid=_ScQvhcErplhjjJIiUYoSK1%3a2http://www.scopus.com/record/display.url?eid=2-s2.0-0026174333&origin=inward&txGid=_ScQvhcErplhjjJIiUYoSK1%3a2
2.
Paul
,
E. L.
,
Atiemo-Obeng
,
V. A.
, and
Kresta
,
S. M.
, 2004,
Introduction of the Handbook of Industrial Mixing
,
Wiley, Hoboken
,
NJ
.
3.
Metzenar
,
A. B.
, and
Taylor
,
J. S.
, 1960, “
Flow Patterns in Agitated Vessels
,”
AIChE J.
,
6
, pp.
432
437
.
4.
Dong
,
L.
,
Johansen
,
S. T.
, and
Engh
,
T. A.
, 1994, “
Flow Induced by an Impeller in an Unbaffled Tank-I. Experimental
,”
Chem. Eng. Sci
,
49
, pp.
549
560
.
5.
Desouza
,
A.
, and
Pike
,
R. W.
, 1972, “
Fluid Dynamics and Flow Patterns in Stirred Tanks With a Turbine Impeller
,”
Can. J. Chem. Eng.
,
50
, pp.
15
27
.
6.
Perng
,
Y.
, and
Murthy
,
J. Y.
, 1993, “
A Sliding-Mesh Technique for Simulation of Flow in Mixing Tank
,” ASME Winter Annual Meeting, New Orleans, LA.
7.
Harvey
,
A. D.
, III
, and
Rogers
,
S. E.
, 1996, “
Steady and Unsteady Computation of Impeller Stirred Reactors
,”
AIChE J.
,
42
, pp.
2701
2712
.
8.
Lamberto
,
D. J.
,
Muzzio
,
F. J.
,
Swadsom
,
P. D.
, and
Tonchovich
,
A.L.
, 1996, “
Using Time Dependent RPM to Enhance Mixing in Stirred Vessels
,”
Chem. Eng. Sci.
,
51
, pp.
733
746
.
9.
Lamberto
,
D. J.
,
Alvarez
,
M. M.
, and
Muzzio
,
F. J.
, 2001, “
Computational Analysis of Regular and Chaotic Mixing in a Stirred Tank Reactor
,”
Chem. Eng. Sci.
,
56
, pp.
4887
4899
.
10.
Ascanio
,
G.
,
Brito-Bazan
,
M.
,
La Fuente
,
E. B.-L.
,
Carreau
,
P. J.
, and
Tanguy
,
P. A.
, 2002, “
Unconventional Configuration Studies to Improve Mixing Time in Stirred Tanks
,”
Can. J. Chem. Eng.
,
80
, pp.
558
565
.
11.
Distelhoff
,
M. F. W.
,
Laker
,
J.
,
Marquis
,
A. J.
, and
Nouri
J. M.
, 1995, “
The Application of a Strain Gauge Technique to Measurement of the Power Characteristics of Five Impellers
,”
Exp. Fluid
,
20
, pp.
56
58
.
12.
Roy
,
S.
,
Acharya
,
S.
, and
Cloeter
,
M. D.
, 2010, “
Flow Structures and Effects of Macro-Instabilities in a Pitched-Blade Stirred Tank
,”
Chem. Eng. Sci.
,
65
(
10
), pp.
3009
3024
.
13.
Gao
,
D. R.
,
Acharya
,
S.
,
Wang
,
Y. Q.
, and
Uhm
,
J. H.
, 2004, “
Flow Field Around Rushton Turbine in Stirred Tank by Particle Image Velocimetry Measurement
,”
Chin. J. Chem. Eng.
,
12
(
6
), pp.
843
850
. Available at: http://scholar.googleusercontent.com/scholar?q=cache:D2oQYk8g7y8J:scholar.google.com/+gao+acharya+uhm&hl=en&as_sdt=0,5http://scholar.googleusercontent.com/scholar?q=cache:D2oQYk8g7y8J:scholar.google.com/+gao+acharya+uhm&hl=en&as_sdt=0,5
14.
Roy
,
S.
, and
Acharya
,
S.
, 2011, “
Perturbed Turbulent Stirred Tank Flows With Amplitude and Mode-Shape Variations
,”
Chem. Eng. Sci.
,
66
, pp.
5703
5722
.
15.
Fiedler
,
H. E.
, and
Mensing
,
P.
, 1985, “
The Plane Turbulent Shear Layer With Periodic Excitation
,”
J.Fluid Mech.
,
150
, pp.
281
309
.
16.
Hussain
,
A. K. M. F.
, 1970, “
The Mechanism of a Perturbation Wave in Turbulent Shear Flow
,” Ph.D. thesis, Stanford University, Stanford, CA.
17.
Roy
,
S.
, and
Acharya
,
S.
, 2011, “
Scalar Mixing in a Turbulent Stirred Tank With Pitched Blade Turbine: Role of Impeller Speed Perturbation
,”
Chem. Eng. Res. Des.
, in press.
18.
Kresta
,
S. M.
, and
Roussinova
,
V. T.
, 2004, “
Comments to ‘On the Origin, Frequency and Magnitude of Macro–Instabilities of the Flows in Stirred Vessles’ by Nikiforaki et al.
,”
Chem. Eng. Sci.
,
59
, pp.
951
953
.
19.
Galletti
,
A.
,
Paglianti
,
A.
,
Lee
,
K. C.
, and
Yianneskis
M.
, 2004, “
Reynolds Number and Impeller Diameter Effects on Instabilities in Stirred Vessels
,”
AIChE J.
,
50
, pp.
2050
2063
.
20.
Roussinova
,
V.
,
Grgic
,
B.
, and
Kresta
,
S. M.
, 2000, “
Study of Macroinstabilities in Stirred Tanks Using a Velocity Decomposition Technique
,”
Trans. IChemE
,
78
, pp.
1040
1048
.
21.
Fan
,
J.
,
Wang
,
Y.
, and
Fei
,
W.
, 2007, “
Large Eddy Simulations of Flow Instabilities in a Stirred Tank Generated by a Rushton Turbine
,”
Chin. J. Chem. Eng.
,
15
, pp.
200
208
.
22.
Hasal
,
P.
,
Fort
,
I.
, and
Kratena
,
J.
, 2004, “
Force Effects of the Macro-Instability of Flow Pattern on Radial Baffles in a Stirred Vessel With Pitched-Blade and Rushton Turbine Impellers
,”
Trans. IChemE
,
82
, pp.
1268
1281
.
23.
Yianneskis
,
M.
,
Popiolek
,
Z.
, and
Whitelaw
,
Z. H.
, 1987, “
An Experimental Study of Steady and Unsteady Flow Characteristics of Stirred Tanks
,”
J.Fluid Mech.
,
175
, pp.
537
555
.
24.
Tyagi
,
M.
,
Roy
,
S.
,
Harvey
,
A. D.
, III
, and
Acharya
,
S.
, 2007, “
Simulation of Laminar and Turbulent Flows in Impeller Stirred Tanks Using Immersed Boundary Method and Large Eddy Simulation With Multi-Block Curvilinear Geometry
,”
Chem. Eng. Sci.
,
62
, pp.
1351
1363
.
25.
Weiss
,
J. M.
, and
Smith
,
W. A.
, 1995, “
Preconditioning Applied to Variable and Constant Density Flows
,”
AIAA J.
,
33
, pp.
2050
2057
.
26.
Edwards
,
J. R.
, 1997, “
A Low-Diffusion Flux-Splitting Scheme for Navier-Stokes Calculations
,”
Comput. Fluids
,
26
, pp.
635
659
.
27.
Karypis
,
G.
, and
Kumar
,
V.
, 1998, “
METIS, A Software Package for Partitioning Unstructured Graphs, Partitioning Meshes, and Computing Fill-Reducing Orderings of Sparse Matrices
,” University of Minnesota, MN.
28.
Gropp
,
W.
,
Lusk
,
E.
, and
Skjellum
,
A.
, 1999,
Using MPI: Portable Parallel Programming with the Message-Passing Interface
,
The MIT Press
,
MA
.
29.
Gilmanov
,
A.
, and
Acharya
,
S.
, 2008, “
A Computational Strategy for Simulating Heat Transfer and Flow Past Deformable Objects
,”
Int. J. Heat Mass Transfer
,
51
, pp.
4415
4426
.
30.
Franke
,
R.
, 1982, “
Scattered Data Interpolation: Tests of Some Methods
,”
Math. Comput.
,
38
(
157
), pp.
181
200
. Available at: http://www.jstor.org/stable/2007474http://www.jstor.org/stable/2007474
31.
Tyagi
,
M.
, and
Acharya
,
S.
, 2005, “
Large Eddy Simulation in Complex Geometries Using the Immersed Boundary Method
,”
Int. J. Numer. Methods Fluids
,
48
, pp.
691
722
.
32.
Sagaut
,
P.
, 2001,
Large Eddy Simulation for Incompressible Flows
,
Springer-Verlag
,
Berlin, Germany
.
33.
Tyagi
,
M.
, 2003, “
Large Eddy Simulations of Complex Turbulent Flows
,” Ph.D. thesis, Louisiana State University, Baton Rouge, LA.
34.
Jordan
,
S. A.
, 1999, “
A Large Eddy Simulation Methodology in Generalized Curvilinear Coordinate
,”
J.Comput. Phys.
,
148
, pp.
322
340
.
35.
Smagorinsky
,
J.
, 1963, “
General Circulation Experiments With the Primitive Equations. I: The Basic Experiment
,”
Mon. Weather Rev.
,
91
, pp.
99
165
.
36.
Germano
,
M.
,
Piomelli
,
U.
,
Moin
,
P.
, and
Cabot
,
W. H.
, 1991, “
A Dynamic Subgrid-Scale Eddy Viscosity Model
,”
Phys. Fluids A.
,
3
, pp.
1760
1765
.
37.
Yapici
,
K.
,
Karasozen
,
B.
,
Scafer
,
M.
, and
Uludag
,
Y.
, 2008, “
Numerical Investigation of the Effect of the Rushton Type Turbine Design Factors on Agitated Tank Flow Characteristics
,”
Chem. Eng. Proc.
,
47
, pp.
1340
1349
.
38.
Piomelli
,
U.
,
Moin
,
P.
, and
Ferziger
,
J. H.
, 1988, “
Model Consistency in Large Eddy Simulation of Turbulent Channel Flows
,”
Phys. Fluids
,
34
, pp.
1884
1891
.
39.
Balaras
,
E.
,
Benocci
,
C.
, and
Piomelli
,
U.
, 1996, “
Finite-Difference Computations of High Reynolds Number Flows Using the Dynamic Subgrid-Scale Models
,”
Theor. Comput. Fluid Dyn.
,
7
, pp.
207
216
.
40.
Jeong
,
J.
, and
Hussain
,
F.
, 1995, “
On Identification of a Vortex
,”
J.Fluid Mech.
,
285
, pp.
69
94
.
41.
Tay
,
M.
, and
Tatterson
,
G. B.
, 1985, “
Form and Skin Drag Contribution to Power Consumption for the Pitched Blade Turbine
,”
AIChE J.
,
31
, pp.
1915
1918
.
42.
Yoon
,
S. H.
,
Balachandar
,
S.
, and
Ha
,
M. Y.
, 2009, “
Large-Eddy Simulation of Flow in an Unbaffled Stirred Tank for Different Reynolds Number
,”
Phys. Fluids
,
21
, p.
085102
.
43.
Hoogendoorn
,
C. J.
, and
Den Hartog
,
A. P.
, 1967, “
Model Studies in the Viscous Flow Region
,”
Chem. Eng. Sci.
,
22
, pp.
1689
1699
.
44.
Ho
,
C. M.
, and
Huerre
,
P.
, 1984, “
Perturbed Free Shear Layer,”
Ann. Rev. Fluid Mech.
,
16
, pp.
365
422
.
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