Drag reduction of a heavy duty: preliminary study on a 1 ... · 1 Drag reduction of a heavy duty: preliminary study on a 1:43 scale simplified truck model GDR Contrôle des décollements

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



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



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



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.



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



Slide

Introduction


• Objectives

Experimental setup


• Test facilities

Results



• Bi-stability phenomenum


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



Slide

Flow

Nose

Skirt

8

Test facilities

Passive control with boat tails:

Rear base configuration Boat-tail configuration

25 base static pressure taps



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



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.



Slide

11



Slide

Introduction


• Objectives

Experimental setup


• Test facilities

Results



• Bi-stability phenomenum


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



Slide

𝑦0/𝐻

𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎

𝑥0/𝐻 𝑥0/𝐻

13


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


The fluctuations are either localized in the upper shear

layer or in the under shear layer.



Slide

𝑦0/𝐻

𝝀 = 𝟎. 𝟓𝟖 𝝀 = 𝟎. 𝟕𝟎


14


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



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


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



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



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]



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



Slide

Time [s]

a1

19


It’s a top/down mode

Mode 1



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


The unsteady data are

sorted according the sign

of the first coefficient.

𝑦0/𝐻

𝑧0/𝐻

𝜆 = 0.58

𝑦0/𝐻

𝑧0/𝐻



Slide

𝜆 = 0.70𝑎1 > 0

𝑎1 < 0

21


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



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.




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.


Correlation between pressure and SPIV data:



Slide

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


𝑦0/𝐻


Mean velocity fields:



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.



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



Slide

Department, Name, Document name, Security Class

27 Date

Thank you for your attention

Questions ?

Congrès Français de Mécanique – 27/08/2015


Slide

Documents

Drag reduction of a heavy duty: preliminary study on a 1 ... · 1 Drag reduction of a heavy duty: preliminary study on a 1:43 scale simplified truck model GDR Contrôle des décollements