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Aerodynamic coastdown analysis of a passenger car for various configurations

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Abstract

Experimental coastdown analysis were performed on a full scale passenger car model FIAT Linea to obtain the drag coefficients for three different test configurations as engine-cooling airflow closed with smooth underbody, enginecooling airflow closed with detailed underbody, and engine-cooling airflow open with detailed underbody. The comparison of the drag coefficients for all three coastdown configurations were in good agreement with the CFD results and FIAT wind tunnel results. The coastdown tests predicted the model drag coefficients 5.3 % to 7.8 % less than FIAT wind tunnel drag coefficients for three test configurations. The contribution of the engine-cooling airflow and the detailed underbody configuration on the total drag coefficient were measured as 9.6 % ~ 10.4 % and 14.6 % ~ 16.7 %, respectively in the coastdown, FIAT wind tunnel tests and CFD analysis. In the CFD analysis,steady RANS equations were solved by STAR-CCM+ code. The turbulence model was selected as realizable k-ε two layer model. Model surface pressure contours were compared for all three test.

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Abbreviations

M e :

total effective vehicle mass, kg

V :

vehicle speed, km/h

t :

time, second

µ :

coefficient of rolling resistance, dimensionless

W :

vehicle test weight, N or lb

?:

air mass density, kg/m3

C ′d :

aerodynamic drag coefficient for nonzero yaw, dimensionless

A :

vehicle frontal area, m2

S :

+1 or -1, depending on vehicle coastdown direction

v x :

component of wind parallel to track, km/h

v y :

component of wind perpendicular to track, km/h

µ 0 :

velocity-independent coefficient of rolling resistance, dimensionless

µ′:

velocity-dependent coefficient of rolling resistance, (km/h)-2

C d :

aerodynamic drag coefficient, dimensionless

φ :

aerodynamic yaw angle, radians

k :

drag coefficient dependence on yaw angle φ

a 0, a 2 :

constants for trend line equation

f 0, f 2 :

coefficients of the zeroth and second order terms (respectively) in the road load force equation, N and N/[km/h2]

f ′0 , f ′2 :

coefficients of the zeroth and second order terms (respectively) in the road load force equation corrected to standard conditions

t-t 0 :

coastdown time interval, seconds

P 0 :

reference atmospheric pressure 736.6 mm Hg (29.0 in Hg)

T 0 :

standard temperature, (20 °C = 293.15 K, 68 °F = 527.67 °R)

C ɛ1, C ɛ2, C ɛ3, σ k , σ ɛ :

realizable k-ɛ constants

A 0, A s, U*:

functions of velocity gradients

G k, G b :

turbulence production terms

S k, S ɛ :

user defined source terms

S :

modulus of the mean strain rate tensor

y + :

wall function

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Authors and Affiliations

  1. FCA/TOFAS, Production Quality, Yeni Yalova Yolu Cad. No. 574, 16369, Bursa, Turkey

    A. Altinisik

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  1. A. Altinisik
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Altinisik, A. Aerodynamic coastdown analysis of a passenger car for various configurations. Int.J Automot. Technol. 18, 245–254 (2017). https://doi.org/10.1007/s12239-017-0024-6

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  • DOI: https://doi.org/10.1007/s12239-017-0024-6

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