One of the main features of the backward-facing step (BFS) low frequency pulsatile flow is the unsteadiness due to the convection of vortical (coherent) structures, which characterize the flow dynamics in the shear layer. The physics of the flow field is analyzed by looking at energy redistribution between the mean and pulsating flow field obtained via a particle image velocimeter (PIV) using the concept of a triple decomposition. The total fluctuating kinetic budget is calculated and discussed for a mean Reynolds number of 100 and for 0.035 ≤ St ≤ 2.19. The effects that these coherent structures have on the fluctuating kinetic energy production, dissipation, and transport mechanism are examined. The results provide insight into the physics of the flow and suggest reasons for vortex growth and decay. Fluctuating kinetic energy is generally produced at the separated shear layers and transported towards the core flow and then to the upper and lower walls where viscosity dissipates the energy. The remaining energy is transported streamwise and decays as it is convected downstream (St = 0.4 and 1 cases). It was also found that the pressure-velocity correlation diffusion plays a significant role in the transport of kinetic energy and Reynolds stresses, especially in the separated shear layer. More energy was dissipated at the walls for the high Strouhal number case St = 2.19 due to the transverse pressure diffusion term being increasingly dominant. This could be the reason why the convected primary vortices were much smaller in size and weaker with no upper wall vortices formed at this pulsation Strouhal number. The shear production for St = 0.035 was very minimal; thus, the vortices died down quickly even before the shedding could happen. Finally, the pressure-strain correlation term was found to be significant in redistributing the kinetic energy from u-component to v-component.

References

References
1.
Pedley
,
T. J.
, and
Stephanoff
,
K. D.
,
1985
, “
Flow Along a Channel With a Time-Dependent Indentation in One Wall: The Generation of Vorticity Waves
,”
J. Fluid Mech.
,
160
, pp.
337
367
.10.1017/S0022112085003512
2.
Ralph
,
M. E.
, and
Pedley
,
T. J.
,
1988
, “
Flow in a Channel With a Moving Indentation
,”
J. Fluid Mech.
,
190
, pp.
87
112
.10.1017/S0022112088001223
3.
Sobey
,
I. J.
,
1985
, “
Observation of Waves During Oscillatory Channel Flow
,”
J. Fluid Mech.
,
151
, pp.
395
426
.10.1017/S0022112085001021
4.
Tutty
,
O. R.
,
1992
, “
Pulsatile Flow in a Constricted Channel
,”
ASME J. Biomech. Eng.
,
114
, pp.
50
54
.10.1115/1.2895449
5.
Tutty
,
O. R.
, and
Pedley
,
T. J.
,
1993
, “
Oscillatory Flow in a Stepped Channel
,”
J. Fluid Mech.
,
247
, pp.
179
204
.10.1017/S0022112093000436
6.
Rosenfeld
,
M.
,
1995
, “
A Numerical Study of Pulsating Flow Behind a Constriction
,”
J. Fluid Mech.
,
301
, pp.
203
223
.10.1017/S0022112095003867
7.
Malek
,
A. M.
,
Alper
,
S. L.
, and
Izumo
,
S.
,
1999
, “
Hemodynamic Shear Stress and its Role in Atherosclerosis
,”
J. Am. Med. Assoc.
,
282
, pp.
2035
2042
.10.1001/jama.282.21.2035
8.
Salek
,
M. M.
,
Dol
,
S. S.
, and
Martinuzzi
,
R. J.
,
2009
, “
Analysis of Pulsatile Flow in a Separated Flow Region
,” Proceedings of the
ASME
2009 Fluids Engineering Division Summer Meeting, FEDSM2009
,
Vail, CO
, August 2–6, pp.
1429
1438
. 10.1115/FEDSM2009-78302
9.
Dol
,
S. S.
,
Salek
,
M. M.
, and
Martinuzzi
,
R. J. M.
,
2014
, “
Effects of Pulsation to the Mean Field and Vortex Development in a Backward-Facing Step Flow
,
ASME J. Fluids Eng.
,
136
(
1
), p.
011001
.10.1115/1.4025608
10.
de Brederode
,
V.
, and
Bradshaw
,
P.
,
1972
, “
Three-Dimensional Flow in Nominally Two-Dimensional Separation Bubbles, I. Flow Behind a Rearward-Facing Step
,” Imperial College of Science and Technology, London, Aero Report No. 72-19.
11.
Dol
,
S. S.
,
2011
, “
Particle Image Velocimetry Investigation of Pulsatile Flow Over a Backward-Facing Step
,” Ph.D. thesis, University of Calgary, Calgary, Canada.
12.
Hussain
,
A. K. M. F.
,
1986
, “
Coherent Structures and Turbulence
,”
J. Fluid Mech.
,
173
, pp.
303
356
.10.1017/S0022112086001192
13.
Rinoie
,
K.
,
Shirai
,
Y.
, and
Sunada
,
Y.
,
2002
, “
Behavior of Separated and Reattaching Flow Formed Over a Backward-Facing Step
,”
Trans. Jpn. Soc. Aero. Space Sci.
,
45
(
147
), pp.
20
27
.10.2322/tjsass.45.20
14.
Beratlis
,
N.
,
Balaras
,
E.
, and
Kiger
,
K.
,
2007
, “
Direct Numerical Simulations of Transitional Pulsatile Flow Through a Constriction
,”
J. Fluid Mech.
,
587
, pp.
425
451
.10.1017/S0022112007007380
15.
Speziale
,
C. G.
,
Sarkar
,
S.
, and
Gatski
,
T. B.
,
1991
, “
Modeling the Pressure-Strain Correlation of Turbulence: An Invariant Dynamical Systems Approach
,”
J. Fluid Mech.
,
227
, pp.
245
272
.10.1017/S0022112091000101
You do not currently have access to this content.