1. Improvement of Wind tunnel Measurement Process Status report
Introduction:
Japan and BMW introduced proposals on improvements for the wind tunnel method during the last IWG meetings.
Within the New Issues Task Force the content was agreed and a common proposal shall be developed.
A first text proposal was developed via exchange.
That proposals have been discussed in the New Issues Task Force on the
Status:
A major part is agreed, but some important points are open, these are:
How to handle different cd*A over velocity (if that is the case) and if measuring more than one wind speed is a requirement or a recommendation.
The text proposal is presented in the following slides and includes the following improvements:
Clarifying the measurement speed and process.
Adding a recommendation on measurement at more wind speeds – this is still open.
WLTP Improvements And Proposals | Japan and BMW |

2. WLTP Road Load – Annex 4 Improvement of Wind tunnel Measurement Process 1/4
Text proposal: Add a new paragraph at the end within the wind tunnel criteria in Annex 4, §3.2:
Wind tunnel measurement procedure
The vehicle shall be placed parallel to the longitudinal centre line of the tunnel with a maximum deviation of 10 mm. The vehicle shall be placed with a yaw angle of 0° and with a tolerance of ±0.1°.
Prior to a test it shall be checked, that at 0 kph wind speed the measurement system delivers a result equal to 0.
Aerodynamic drag shall be measured for at least 60 seconds and at a minimum frequency of 5 Hz. Alternatively, the drag may be measured at a minimum frequency of 1 Hz and with at least 300 subsequent samples. The result shall be the arithmetic average of the drag.
…please continue on next slide…
Text moved from
: OK
New. Japanese proposal, modified.
4.9.17: Under discussion.
Text moved from
: OK
WLTP Improvements And Proposals | Japan and BMW |

3. WLTP Road Load – Annex 4 Improvement of Wind tunnel Measurement Process 2/4
Text proposal: …continuation from previous slide…
Aerodynamic drag shall be measured at a wind speed of at least 80 km/h, or higher, up to a maximum of 150 km/h such, that the wind speed in the wind tunnel is stable.
If for the wind tunnel concerned the accuracy can be improved, it is recommended to take the average of measurements at two or more different wind speeds. In that case one measurement point should be below 100 km/h, and one above.
It is recommended to perform the measurement of aerodynamic drag according to of ISO or of JIS D1012_2005.
New. BMW proposal.
: OK
New. It is under discussion, whether there should be a rule, when 2 or more points are required.
 See presentation from Japan.
New. Japanese proposal, modified.
: OK
WLTP Improvements And Proposals | Japan and BMW |

4. WLTP Road Load – Annex 4 Improvement of Wind tunnel Measurement Process 3/4
Text proposal: Add a sentence within§ of Annex 4.
Measurement with the wind tunnel method according to paragraphs to 6.7. inclusive of this annex shall be performed on the same three vehicles as selected in paragraph of this annex and in the same conditions, and the resulting road load coefficients, f0, f1 and f2, shall be determined.
The certification tests shall be performed with the procedure used at the wind tunnel approval, e.g. wind speed(s) described in paragraph of this annex.
If the manufacturer chooses to use one or more of the available alternative procedures within the wind tunnel method (i.e. paragraph on preconditioning, paragraphs and on the procedure, including paragraph on dynamometer setting), these procedures shall also be used also for the approval of the facilities.
New. Japanese proposal.
: OK
WLTP Improvements And Proposals | Japan and BMW |

5. WLTP Road Load – Annex 4 Improvement of Wind tunnel Measurement Process 4/4
Text proposal: Modify§ of Annex 4:
Wind tunnel measurement
The vehicle shall be in the condition described in paragraph 6.3. of this annex.
The vehicle shall be placed parallel to the longitudinal centre line of the tunnel with a maximum deviation of 10 mm. The vehicle shall be placed with a yaw angle of 0° and with a tolerance of ±0.1°. Aerodynamic drag shall be measured for at least for 60 seconds and at a minimum frequency of 5 Hz. Alternatively, the drag may be measured at a minimum frequency of 1 Hz and with at least 300 subsequent samples. The result shall be the arithmetic average of the drag.
The air drag shall be measured as described in paragraph of this annex.
In the case that the vehicle has movable aerodynamic body parts, paragraph of this annex shall apply. Where movable parts are velocity-dependent, every applicable position shall be measured in the wind tunnel and evidence shall be provided to the responsible authority indicating the relationship between reference speed, movable part position, and the corresponding (CD × Af).
The wind speed of the wind tunnel measurement shall not be switched to the reference speed of the reference speed point concerned, but still shall fulfill paragraph of this annex.
Text is moved to
: OK
New. BMW and Japanese proposal.
: OK
New. BMW proposal. Can be skipped, if clarification not necessary.
: OK
WLTP Improvements And Proposals | Japan and BMW |

6. Thank you!

7. Appendix to WLTP-18-19e, from Japan
Relevant area for WLTP (low speed cannot be measured in wind tunnel and not relevant for CO2). Example for red vehicle is approx. 0.5% delta in Cd. That refers for a typical vehicle to a difference of m² Cd*A and a CO2 of < 0.2 g/km.
WLTP Improvements And Proposals | Japan and BMW |

8. WLTP Road Load – Annex 4 Issues Speeds and wind tunnel measurement
There are some misunderstandings on speeds with the wind tunnel measurement.
The target, that should be reflected in the GTR text, is presented here:
reference speed
wind tunnel speed
vehicle with movable aero parts, e.g. spoiler
20 kph
140 kph
position 1
cd*A = 0.567
measurement #1 for pos. #1
30, 40, 50 kph
60 kph
70 kph
position 2
cd*A = 0.589
measurement #2 for pos. #2
80, 90, … 120
130 kph
reference speed
wind tunnel speed
vehicle without movable aero parts
20 kph
140 kph
only one configuration
cd*A = 0.600
one
measurement for that vehicle configuration …
130 kph
vs.
Explanations:
The cd*A value does not depend on the velocity in that area, that is relevant for the WLTC.
A wind tunnel typically cannot measure at lower speeds, as then the velocity is not constant enough to produce good results. Therefore that 140kph requirement is included in the criteria in the GTR.
Movable aerodynamic parts are addressed correctly, as every position is to be measured, and then applied to the reference speed, where it is relevant.
WLTP Improvements And Proposals | BMW |