1. WLTP wind tunnel concept
WLTP rev1e
BMW,
WLTP wind tunnel concept
Definition of wind tunnel for road load determination
OIT #10 and #18

2. from WLTP-DTP-LabProcICE-172 - Comparison RLD flatbelt_VW.pdf
WLTP wind tunnel concept
measurement for road load determination
Within WLTP a state-of-the-art road load determination method should be implemented in parallel to coast down and torque meter method: "Wind tunnel and flat belt". OIT #10 and #18.
Wind tunnel measurement contains three main elements:
Description of wind tunnel  same as for delta-measurements for combined approach
Description of measurements  same as for delta-measurements PLUS additional criteria, e.g. vehicle level (defined by EADE)
Calibration / certification of wind tunnel: (A) Comparison of wind tunnel  with vehicles or standard-bodies: study of TU Munich*?  with coast down testing? (B) Certification? (ISO 9001)
Description and measurement procedure of flat belt is discussed separately.
from WLTP-DTP-LabProcICE Comparison RLD flatbelt_VW.pdf
* Angelina I. Heft, Thomas Indinger and Nikolaus A. Adams: Introduction of a New Realistic Generic Car Model for Aerodynamic Investigations , Published 04/16/2012
WLTP wind tunnel concept, BMW,

3. WLTP wind tunnel concept Next steps wind tunnel in WLTP
Proceeding:  Agreement on concept and direction of development?  If yes:  Start work on details within the defined group…
Check, if wind tunnel requirements for the combined approach are sufficient.  It is assumed, that this is the case.
Definition of additional criteria for measuring cd*A as an absolute input for road load:  level of vehicle, mounting  velocity  …
Definition of calibration method:  how to compare coast down with wind tunnel results? Procedure an tolerances?  how to describe these standard-bodies or vehicles for the comparison, tolerances  which and how many bodies to be used (e.g. small car, van, …)?  how to apply these bodies in the wind tunnel?  how often should this calibration be performed?  certification useful?
This discussion will take place within this group:
Contact Persons:
Rob Cuelenaere (TNO), Christoph Lueginger (BMW)
Experts:
Thomas Schütz (BMW), Gerhard Wickern (Audi), Annette Feucht (Audi), Lothar Krueger (Ford), Kai Behlau (VW), Norbert Ligterink (TNO), Yamaguchi (Japan), Klaus Steininger (EU), Celine Vallaude (UTAC), Bertrand Mercier (PSA), Bob Latu (Renault), Iddo Riemersma (T&E)
Time frame:
Initial proposal expected at WLTP meeting #8, decision in meeting #12.
WLTP wind tunnel concept, BMW,

4. compare overall result
WLTP wind tunnel concept
Two steps procedure for validation
For validation of the method:
Measure a vehicle – with different aerodynamic setups – both in wind tunnel and flat belt and on road. On road many measurements under perfect conditions are required.  Aerodynamics cannot be reverse calculated accurately enough from coast down, only overall comparison possible.  Assumption: If delta-cd*A and the overall result are matching, wind tunnel + flat belt delivers correct results.**
If necessary: Measure standard-bodies (TBD!) in the wind tunnel to gain the information, which cd*A value shall apply for them.
compare deltas
compare overall result
DrivAer Model TUM*
coast down
wind tunnel + flat belt
* Angelina I. Heft, Thomas Indinger and Nikolaus A. Adams: Introduction of a New Realistic Generic Car Model for Aerodynamic Investigations , Published 04/16/2012
** Clarification: Whole curve is compared, not only
WLTP wind tunnel concept, BMW,

5. WLTP wind tunnel concept Details on wind tunnel, Main concept
Optional, if during discussion it turns out, that we need it: Additional periodical tests with standard-bodies / vehicles to compare wind tunnels between different labs (EADE prescriptions) supervised by the type approval authority?
Out of a big group of vehicles (TBD, "road load family"?) a coast down has to be performed and has to be within a certain tolerance (TBD) to wind tunnel + flat belt. These measurements to be performed with the identical vehicle and identical configured vehicle. Achieving this accuracy, the cd*A value from the wind tunnel for this vehicle group can be determined in the wind tunnel.
Wind tunnel description (GTR definition Annex 4, 3.2)
Wind tunnel criteria
Wind tunnel comparison
Wind tunnel validation
Preparation of measurement
cd*A measurement
 Measurement definitions to be developed (e.g. vehicle condition).
 EADE definitions?
WLTP wind tunnel concept, BMW,

6. WLTP wind tunnel concept Next steps
Next steps and main questions to be discussed in the wind tunnel task force:
Remark: Until now no expert discussion has taken place.
Do we need absolute values, or does it work with big families and deltas (like combined approach)?
Do we need a kind of comparison or certification?
Time schedule for testing to be developed until Geneva meeting.
WLTP wind tunnel concept, BMW,