drag reduction of a heavy duty: preliminary study on a 1 ... · 1 drag reduction of a heavy duty:...
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1
Drag reduction of a heavy duty: preliminary
study on a 1:43 scale simplified truck model
GDR Contrôle des décollements – Nantes 2015
M. Szmigiel1,2, T. Castelain2, M. Michard2, D. Chacaton1, D. Juvé2
1 - Volvo Group Truck Technology, Renault Trucks SAS, Cab Engineering Lyon, 99 route de Lyon, 69806 Saint-Priest Cedex
2 - LMFA UMR CNRS 5509, Ecole Centrale de Lyon, 36 Avenue Guy-de-Collongue, 69134 Ecully Cedex
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
2
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Introduction
• Scientific and industrial context
• Objectives
Experimental setup
• 1/43 scale simplified truck model
• Test facilities
Results
• Wake flow velocity measurements by Stereo-PIV
• Base pressure maps
• Bi-stability phenomenon
Conclusion/Perspectives
Outline
Various velocity scales (free/underbody velocity)
3
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Trailer wake flow specificities
The aspect ratio H/W > 1 (various geometry scales)
Streamlines relative to mean flow in the symmetry plane (left) and Pressure coefficient
at the rear base (right), RANS simulations – D. Chacaton - VOLVO
Wake is strongly asymmetrical - Stratified base-pressure distribution
Renault Trucks T (left), D (middle) and Master (right)
𝑈∞
𝑈𝑠
4
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Context
Study the feasibility of drag reduction of (heavy or medium) trucks by
fluidic injection combined with rear passive devices for various aspect
ratios.
Objective of the thesis:
Boat-tails on Optifuel Lab 2
Renault Trucks
Parameters to study:
• Angle: boat-tails are easily mountable but it’s
not a robust system (requires a small angle, a
small variation of the wind speed…) Browand et al.
SAE paper 2005-01-1016
• Actuation frequency 𝑓𝑎𝑐𝑡 - jet velocity 𝐶𝜇 :
unsteady jets is a good way to reduce the
drag. Englar et al. SAE paper 2005-01-3627
• Underbody velocity 𝜆 = 𝑈𝑠/𝑈∞: in function of
this velocity the previous systems can not
have the same efficiency.
5
The flow along a boat-tail :
Natural flow is either attached or separated from the inclined flaps.
?One aim of the thesis
Context
In this study, the natural flow is attached to the flaps even for several
Reynolds numbers and only passive control is used.
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Chaligné et al. (Aerovehicles 1 - 2014 and thesis)
Objectives: study the influence of underbody velocity and passive control
(use of boat-tails) on the trailer wake and the rear base pressure.
6
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Introduction
• Scientific and industrial context
• Objectives
Experimental setup
• 1/43 scale simplified truck model
• Test facilities
Results
• Wake flow velocity measurements by Stereo-PIV
• Base pressure maps
• Bi-stability phenomenum
Conclusion/Perspectives
Outline
7
Experimental setup
1:43 scale simplified truck model:
Square back geometry associated with inclined flaps
Model main dimensions:
𝐿[mm]
𝐻[mm]
𝐺[mm]
𝑊[mm]
𝑈∞[m/s]
𝑅𝑒𝐻
320 74 19 66 25 1,3.105
Several pressure losses
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Flow
Nose
Skirt
8
Test facilities
Passive control with boat tails:
Rear base configuration Boat-tail configuration
25 base static pressure taps
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Metrology:
Wall pressure
(f = 20 Hz or f = 1 kHz)
Hot wire anemometry
(20s at f = 51.2 kHz)
Stereoscopic PIV
(1000 samples at f = 100 Hz) Stereoscopic PIV facilities
Light sheet
Flow
Top side
Model
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
9
Results
The ratio 𝜆 between the velocity under the body 𝑈𝑠 and the free stream
flow velocity 𝑈∞ is adjustable thanks to pressure loss system.
Pressure loss configurations
𝜆 =𝑈𝑠𝑈∞ Configurations:
12 𝜆=0.58
13 𝜆=0.65
14 𝜆=0.70
The underbody velocity:
Chaligné et al.
Present study
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Bi-stability
Pressure losses
10
Velocity fields from PIV measurements for different ground clearances - Grandemange et al., Physics of Fluids 2013
Bibliography
Grandemange et al. have study the impact of the ground clearance on
the wake and on the rear base pressure.
Grandemange et al. have shown some bi-
stability effects. Grandemange et al., Physics of Fluids 2013
Vertical gradient for H/W=1.34
When Grandemange et al. change the ground clearance, they also change
the interaction of the model with the ground, the momentum and the shear
layers.
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
11
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Introduction
• Scientific and industrial context
• Objectives
Experimental setup
• 1/43 scale simplified truck model
• Test facilities
Results
• Wake flow velocity measurements by Stereo-PIV
• Base pressure maps
• Bi-stability phenomenum
Conclusion/Perspectives
Outline
The flow is not separated from the boat-tail
Two counter-rotating bubbles detached from the ground
For 𝜆 = 0.58 the under bubble is closer to the rear base. For 𝜆 > 0.65the upper bubble is closer to the rear base.
12
Results - Wake flow velocity measurements in the mid plane
Mean velocity fields:
𝑈/𝑈∞
𝑦0/𝐻
𝑥0/𝐻
𝝀 = 𝟎. 𝟓𝟖
𝑥0/𝐻
𝝀 = 𝟎. 𝟕𝟎
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝑦0/𝐻
𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎
𝑥0/𝐻 𝑥0/𝐻
13
Results - Wake flow velocity measurements in the mid plane
Reynolds stress < 𝑢′𝑢′ >/𝑈∞2 Reynolds stress < 𝑣′𝑣′ >/𝑈∞
2
Reynolds stress < 𝑢′𝑣′ >/𝑈∞2
𝑦0/𝐻
𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎
𝑥0/𝐻 𝑥0/𝐻
The fluctuations are either localized in the upper shear
layer or in the under shear layer.
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝑦0/𝐻
𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎
𝑥0/𝐻 𝑥0/𝐻
14
Results - Wake flow velocity measurements in the mid plane
Production of turbulent kinetic energy:
𝑃𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛 = −𝜌 < 𝑢𝑖′𝑢𝑗′ >𝜕 < 𝑈𝑖 >
𝜕𝑥𝑗
The production of turbulent kinetic energy is mainly localized in the shear
layers but the repartition is not symmetric.
The value of production is due to the shear.
𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝑃 = −𝜌(< 𝑢′2>𝜕 < 𝑈 >
𝜕𝑥+< 𝑢′𝑣′ >
𝜕 < 𝑈 >
𝜕𝑦+< 𝑢′𝑣′ >
𝜕 < 𝑉 >
𝜕𝑥+< 𝑣′
2>𝜕 < 𝑉 >
𝜕𝑦)
𝑊𝑒 𝑠𝑢𝑝𝑝𝑜𝑠𝑒𝜕
𝜕𝑧= 0 𝑎𝑛𝑑 𝑊 ≪ 𝑈, 𝑉
𝑃𝐻
𝑈∞3
𝑥0/𝐻 𝑥0/𝐻
𝑦0/𝐻 < 𝑢′𝑣′ >
𝜕 < 𝑈 >
𝜕𝑦𝐻/𝑈∞
3
Frequency analysis in 𝑥0/H=2:
No peak associated to a natural frequency in the mid plane behind the
recirculation bubble.
The boat-tails decrease the global instability relative to the base
configuration.
𝑆𝑡𝐻
𝑃𝑆𝐷
15
Results – Hot Wire measurements
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Important pressure
fluctuations for 𝜆=0.65
Up to 50% of the mean
coefficient value
16
Results – Pressure measurements
Mean static pressure:
Reversal vertical
pressure gradient
Pressure fluctuations:
𝜆 = 0.58 𝜆 = 0.65 𝜆 = 0.70
𝜆 = 0.58 𝜆 = 0.65 𝜆 = 0.70
𝑧0/𝐻 𝑧0/𝐻 𝑧0/𝐻
𝑧0/𝐻 𝑧0/𝐻 𝑧0/𝐻
𝑦0/𝐻
𝑦0/𝐻
𝝀 𝑪𝒑
0.58 -0.089
0.70 -0.094
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
The high fluctuation values result mainly from the
bi-stable behavior of the flow.
17
Results – Bi-stability study
The sequence of the two states is random
Ratio: State 1: ~ 82% / State 2: ~ 18%
Transition time 𝑇𝑡: 0.1s < 𝑇𝑡 < 0.3s = ~ 65𝐻/𝑈∞This timescale is much smaller than the timescale of the bi-stability
phenomenon: ~1500𝐻/𝑈∞ Grandemange et al. - 2013 - J Fluid Mech 722:51–84
Bi-stability observed for 𝜆=0.65 :
State 1
State 2
𝜕𝐶𝑝
𝜕𝑦0∗
𝑇𝑖𝑚𝑒 [𝑠]
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝜕𝐶𝑝
𝜕𝑦0∗ =𝐶𝑝 𝐴 − 𝐶𝑝(𝐵)
Δy0/H
𝜆 = 0.65
𝑧0/𝐻
𝑦0/𝐻
A
B
Δ𝑦0
Are the two states consistent with the two
neighboring configurations?
18
Results - Bi-stability study
Idea of this method: Find an optimal basis of the energy point of view to
represent the flow.
𝑝′ 𝑥, 𝑡 =
𝑛=1
𝑁
𝑎𝑛 𝑡 𝜙𝑛(𝑥) = 𝑎1 𝑡 𝜙
1 𝑥 + 𝑎2 𝑡 𝜙2 𝑥 + . . .
1st mode 2nd mode
POD method:
ModeEnergy
contribution [%]
1 52.8
2 11.5
3 8.3E
ige
nva
lue
s
Mode number
Mode 1
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Time [s]
a1
19
Results – Bi-stability study
It’s a top/down mode
Mode 1
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝜕𝐶𝑝
𝜕𝑦0∗
Time [s]
Strong resemblance between the
evolution of the first coefficient and
the vertical gradient.
POD seems to be a good signal
processing tool to analyze the bi-
stability phenomenon
20
The two conditional averaging are respectively similar to the
pressure fields of the cases 𝜆=0.70 and 𝜆=0.58.
Time (s)
a1
Results – Bi-stability study
The unsteady data are
sorted according the sign
of the first coefficient.
𝑦0/𝐻
𝑧0/𝐻
𝜆 = 0.58
𝑦0/𝐻
𝑧0/𝐻
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝜆 = 0.70𝑎1 > 0
𝑎1 < 0
21
Results – Bi-stability study
The 3rd mode is independant from bi-stability phenomenon and has small
impact on the mean pressure field.
Mode 1 in study of Volpe et al. is like our mode 3 and their mode 4 looks
like our mode 1.
Two instantaneous pressure fields of the
same state for 𝜆 = 0.65
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝜆 = 0.65𝜆 = 0.58 𝜆 = 0.70
Mode 3: left/right
Mode 1Volpe et al. 2015
Mode 3 Mode 4Volpe et al. 2015
Mode 1
22
Whatever the 𝜆 values, the time scale of pressure fluctuations
of the 𝑎2 and 𝑎3 coefficients is smaller than the 𝑎1 coefficient.
Results – Bi-stability study
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Mode 1
Mode 3
Time (s)
a1
a2
Coef 1
Coef 3
Autocorrelation
Autocorrelation
Time (s)
𝑇𝑖 ~ 100𝐻/𝑈∞
Time (s)
𝑎1/ 𝜆1
23
Use of POD method to separate the PIV data in two states according
the first coefficient value .
Bi-stability is visible on both the pressure and PIV data
synchronously using the POD coefficients.
Results – Bi-stability study
Correlation between pressure and SPIV data:
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
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ModeEnergy
contribution [%]
1 20.3
2 4.7
3 4.5
𝜆 = 0.70
𝜆 = 0.58
24
The two states are
respectively similar to
the mean velocity fields
of the cases 𝜆=0.70 and
𝜆=0.58
𝑦0/𝐻
𝑥0/𝐻 𝑥0/𝐻
𝑦0/𝐻
Results – Bi-stability study
Mean velocity fields:
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
𝑎1 > 0
𝑎1 < 0
25
Conclusions
Bi-stability phenomenon is:
• observed for only one configuration (with the boat-tails) among 30
cases.
• analyzed here by use of POD applied both on back pressure and
velocity fields in the wake.
It’s characterized by:
• a change of the vertical pressure gradient sign and a change of the
wake structure where the two states cannot be symmetrical because
of ground effects.
• a transition timescale much smaller than the timescale of the bi-
stability phenomenon.
Bi-stability is sensitive to small changes:
• ground clearance (Grandemange et al.), yaw angle (Volpe et al.)
• underbody velocity in this study.
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
Slide
Study the transition phase for the phenomenon of bi-stability.
Increase the Reynolds number either increasing the free velocity or
the height of the model.
Add a blowing system.
26
Perspectives
GDR Contrôle des décollements – 18/19 Novembre 2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
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Department, Name, Document name, Security Class
27 Date
Thank you for your attention
Questions ?
Congrès Français de Mécanique – 27/08/2015
M. Szmigiel / T. Castelain / M. Michard / D. Chacaton / D. Juvé
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