We investigate experimentally and numerically the transient development of the wake induced by a constant acceleration of a D-shaped bluff body, starting from rest and reaching a permanent regime of Reynolds number Re = 2000, under different values of acceleration and implementing three distinct rear geometrical configurations. Thus, alongside the classical blunt base, two control passive devices, namely, a straight cavity and an optimized, curved cavity, recently designed using adjoint optimization techniques, have also been used to assess their performance in transient flow conditions. Particle image velocimetry measurements were performed in a towing tank to characterize the near wake development in the early transient stages. It has been observed that the flow first develops symmetric shear layers with primary eddies attracted toward the base of the body due to the flow suction generated by the accelerated motion. Eventually, the interaction between the upper and lower shear layers provokes the destabilization of the flow and the symmetry breaking of the wake, finally giving rise to an alternate transitional vortex shedding regime. The transition between these phases is sped-up when the optimized cavity is used, reaching earlier the permanent flow conditions. In particular, the use of the optimized geometry has been shown to limit the growth of the primary eddies, decreasing both the recirculation and vortex formation length and providing with a more regularized, more organized vortex shedding. In addition, numerical simulations have been performed to evaluate the distribution of forces induced by the addition of rear cavities. In general, the aforementioned smoother and faster transition related to the use of optimized cavity translates into a lower averaged value of the drag coefficient, together with less energetic force fluctuations, regardless of the acceleration value.

1.
H.
Choi
,
J.
Lee
, and
H.
Park
, “
Aerodynamics of heavy vehicles
,”
Annu. Rev. Fluid Mech.
46
,
441
468
(
2014
).
2.
R.
Bradley
, “
Technology roadmap for the 21st century truck program
,” Technical Report No. 21CT-001,
US Department of Energy
,
Washington, D.C.
,
2000
.
3.
R. M.
Wood
, “
A discussion of a heavy truck advanced aerodynamic trailer system
,” presented at
9th International Symposium on Heavy Vehicle Weights and Dimensions
(
University Park
,
PA
,
2006
).
4.
S.
Ahmed
,
G.
Ramm
, and
G.
Faitin
, “
Some salient features of the time averaged ground vehicle wake
,”
SAE Trans.
93
,
473
503
(
1984
)
5.
T.
Han
,
V.
Sumantran
,
C.
Harris
,
T.
Kuzmanov
,
M.
Huebler
, and
T.
Zak
, “
Flow-field simulations of three simplified vehicle shapes and comparisons with experimental measurements
,” Technical Report No. 960678, SAE Technical Paper,
1996
.
6.
M.
Pastoor
,
L.
Henning
,
B. R.
Noack
,
R.
King
, and
G.
Tadmor
, “
Feedback shear layer control for bluff body drag reduction
,”
J. Fluid Mech.
608
,
161
196
(
2008
).
7.
M.
Grandemange
,
O.
Cadot
,
A.
Courbois
,
D.
Herbert
,
T.
Ricot
,
R.
Ruiz
, and
A.
Vigneron
, “
A study of wake effects on the drag of Ahmed’s squareback model at the industrial scale
,”
J. Wind Eng. Ind. Aerodyn.
145
,
282
291
(
2015
).
8.
G.
Bonnavion
,
O.
Cadot
,
A.
Evrard
,
V.
Herbert
,
S.
Parpais
,
R.
Vigneron
, and
J.
Délery
, “
On multistabilities of real car’s wake
,”
J. Wind Eng. Ind. Aerodyn.
164
,
22
33
(
2017
).
9.
P.
Bohorquez
,
E.
Sanmiguel-Rojas
,
A.
Sevilla
,
J. I.
Jiménez-González
, and
C.
Martínez-Bazán
, “
Stability and dynamics of the laminar wake past a slender blunt-based axisymmetric body
,”
J. Fluid Mech.
676
,
110
144
(
2011
).
10.
E.
Sanmiguel-Rojas
,
J. I.
Jiménez-González
,
P.
Bohorquez
,
G.
Pawlak
, and
C.
Martínez-Bazán
, “
Effect of base cavities on the stability of the wake behind slender blunt-based axisymmetric bodies
,”
Phys. Fluids
23
,
114103
(
2011
).
11.
A.
Evrad
,
O.
Cadot
,
C.
Sicot
,
V.
Herbert
,
D.
Ricot
, and
R.
Vigneron
, “
Comparative effects of vortex generators on Ahmed’s squareback and minivan car models
,”
Proc. Inst. Mech. Eng., Part D: J. Automot. Eng.
231
,
1287
1293
(
2016
).
12.
R. D.
Brackston
,
J. M.
García de la Cruz
,
W. A. G.
Rigas
, and
J. F.
Morrison
, “
Stochastic modelling and feedback control of bistability in a turbulent bluff body wake
,”
J. Fluid Mech.
802
,
726
749
(
2016
).
13.
P.
Meliga
,
E.
Boujo
,
G.
Pujals
, and
F.
Gallaire
, “
Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder
,”
Phys. Fluids
26
,
104101
(
2014
).
14.
P.
Meliga
,
O.
Cadot
, and
E.
Serre
, “
Experimental and theoretical sensitivity analysis of turbulent flow past a square cylinder
,”
Flow, Turbul. Combust.
97
,
987
1015
(
2016
).
15.
C.
Othmer
, “
Adjoint methods for car aerodynamics
,”
J. Math. Ind.
4
,
1
23
(
2014
).
16.
M.
Lorite-Díez
,
J. I.
Jiménez-González
,
C.
Gutiérrez-Montes
, and
C.
Martínez-Bazán
, “
Drag reduction of slender blunt-based bodies using optimized rear cavities
,”
J. Fluids Struct.
74
,
158
177
(
2017
).
17.
L.
Liu
,
Y.
Sun
,
X.
Chi
,
G.
Du
, and
M.
Wang
, “
Transient aerodynamic characteristics of vans overtaking in crosswinds
,”
J. Wind Eng. Ind. Aerodyn.
170
,
46
55
(
2017
).
18.
F.
Odar
and
W.
Hamilton
, “
Forces on a sphere accelerating in a viscous fluid
,”
J. Fluid Mech.
18
,
302
314
(
1964
).
19.
F.
Roos
and
W.
Willmarth
, “
Some experimental results on sphere and disk drag
,”
J. Fluid Mech.
9
,
285
291
(
1971
).
20.
R.
Bouard
and
M.
Coutanceau
, “
The early stage of development of the wake behind an impulsively started cylinder for 40 < Re < 104
,”
J. Fluid Mech.
101
,
583
607
(
1980
).
21.
T.
Sarpkaya
and
H. K.
Kline
, “
Impulsively-started flow about four types of bluff body
,”
ASME J. Fluids Eng.
104
,
207
213
(
1982
).
22.
C. C.
Chang
and
R. L.
Chern
, “
A numerical study of flow around an impulsively started circular cylinder by a deterministic vortex method
,”
J. Fluid Mech.
223
,
243
263
(
1991
).
23.
F.
Finaish
, “
On vortex structures and processes over bluff bodies in impulsive flow
,”
Exp. Fluids
11
,
262
267
(
1991
).
24.
C. C.
Chu
and
Y. Y.
Liao
, “
A quantitative study of the flow around an impulsively started circular cylinder
,”
Exp. Fluids
13
,
137
146
(
1992
).
25.
N.
Tonui
and
D.
Sumner
, “
Flow around impulsively started square prisms
,”
J. Fluids Struct.
27
,
62
75
(
2011
).
26.
J. N.
Fernando
and
D. E.
Rival
, “
On vortex evolution in the wake of axisymmetric and non-axisymmetric low-aspect-ratio accelerating plates
,”
Phys. Fluids
28
,
017102
(
2016
).
27.
J. N.
Fernando
,
M.
Marzanek
,
C.
Bond
, and
D. E.
Rival
, “
On the separation mechanics of accelerating spheres
,”
Phys. Fluids
29
,
037102
(
2017
).
28.
W.
Thielicke
and
E.
Stamhuis
, “
PIVlab - Towards user-friendly, affordable and accurate digital particle image velocimetry in MATLAB
,”
J. Open Res. Software
2
,
e30
(
2014
).
29.
R. I.
Issa
, “
Solution of the implicitly discretised fluid flow equations by operator-splitting
,”
J. Comput. Phys.
62
,
40
65
(
1986
).
30.
G.
Pawlak
,
C.
Marugan-Cruz
,
C.
Martínez-Bazán
, and
P.
García-Hrdy
, “
Experimental characterization of starting jet dynamics
,”
Fluid Dyn. Res.
39
,
711
730
(
2007
).
You do not currently have access to this content.