Browse Publications Technical Papers 2018-37-0017
2018-05-30

FCA Full Scale Wind Tunnel : WLTP and coast down test performed with wind tunnel method 2018-37-0017

The effect of pollutants emission on health and environment is a problem that has become even more important with time: WLTP represents the harmonization of test procedures that aims to characterize all vehicles predicting their emissions, depending on coast down road test results and new different driving cycles. UN GTR technical regulation allows the use of wind tunnel to perform a bench coast down with the use of dynamometer or flat belt to calculate the whole vehicle drag (aerodynamic, mechanic and rolling resistance). During 2013, FCA made an upgrade to wind tunnel facility installing a new balance with 5 moving belts: one central belt e four wheels flat belts, each one connected to a specific balance. This upgrade is very important because wheel spinning unit balances allow the calculation of rolling resistance as required by UN GTR. Moreover UN GTR prescribes several criteria that must be respected from facility to allow wind tunnel to be used instead of road test: nowadays FCA is working on an auto-certification of facility but the aim is to reach an ISO9001 certification. Wind tunnel coast down test requires two in-parallel measurements to be done: aerodynamic force is measured by main balance, while forces on wheels are obtained by wheel spinning unit balances. Thus coast down coefficients are known, letting possible the calculation of emitted CO2. Comparison between wind tunnel and road test results has been performed and a very good correlation has been obtained with a percent difference of cycle energy under 5% as required by UN GTR. The possibility to perform a wind tunnel coast down has many advantages: controlled environment condition, fixed ground condition, no relative wind but above all it takes less than one hour to perform test and find results in terms of coast down coefficients. Moreover this procedure allows to calculate wheel ventilation drag, thus characterizing aerodynamic impact of different rims and wheel caps.

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