This content is not included in your SAE MOBILUS subscription, or you are not logged in.
Assessment of a Vehicle's Transient Aerodynamic Response
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 16, 2012 by SAE International in United States
Annotation ability available
A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, due to the unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. There is increasing concern about potential differences between the steady flow conditions used for development and the transient conditions that occur on the road. This paper seeks to determine if measurements made under steady state conditions can be used to predict the aerodynamic behaviour of a vehicle on road in a gusty environment.
The project has included measurements in two full size wind tunnels, including using the Pininfarina TGS, steady-state and transient inlet simulations in Exa Powerflow, and a campaign of testing on-road and on-track. The particular focus of this paper is on steady wind tunnel measurements and on-road tests, representing the most established development environment and the environment experienced by the customer, respectively. Measurements of the surface pressure on the front sideglass were used for comparisons as this area exhibits a complex flow which is highly sensitive to yaw angle and which is also an important region, for wind noise considerations in particular.
It was found that, if the transient on-road environment is known then steady-state wind tunnel measurements can be used to predict accurately the transient surface pressures, provided the methodology is sufficiently rigorous. Admittance or transfer function techniques are commonly used to compare transient and steady-state results and the limitations of these methods are shown here when the spectra of self-excited and externally imposed unsteadiness overlap. A new method is introduced to obtain a “true” transfer or admittance function, unconfused by the presence of self-excited unsteadiness. The aerodynamic admittance was found to be close to unity up to a frequency of 2-10 Hz and it then drops progressively.
CitationOettle, N., Mankowski, O., Sims-Williams, D., Dominy, R. et al., "Assessment of a Vehicle's Transient Aerodynamic Response," SAE Technical Paper 2012-01-0449, 2012, https://doi.org/10.4271/2012-01-0449.
- Watkins, S Wind-Tunnel Modelling of Vehicle Aerodynamics: With Emphasis on Turbulent Wind Effects on Commercial Vehicle Drag PhD Thesis Victorian University of Technology 1990
- Watkins, S Saunders, J Hoffmann, P Turbulence Experienced by Moving Vehicles. Part 1. Introduction and Turbulence Intensity Journal of Wind Engineering and Industrial Aerodynamics 1995 57 1-17
- Wordley, S On-Road Turbulence PhD Thesis Monash University 2009
- Wordley, S. Saunders, J. “On-road Turbulence,” SAE Int. J. Passeng. Cars - Mech. Syst. 1 1 341 360 2009 10.4271/2008-01-0475
- Wordley, S. Saunders, J. “On-road Turbulence: Part 2,” SAE Int. J. Passeng. Cars - Mech. Syst. 2 1 111 137 2009 10.4271/2009-01-0002
- Wojciak, J Indinger, T Adams, N Theissen, P Demuth, R. Experimental Study of on-Road Aerodynamics During Crosswind Gusts MIRA Vehicle Aerodynamics Conference Grove, UK 2010
- Howell, J. Real Environment for Vehicles on the Road Euromotor - Progress in Vehicle Aerodynamics Stuttgart 2000
- Cooper, K. Watkins, S. “The Unsteady Wind Environment of Road Vehicles, Part One: A Review of the On-road Turbulent Wind Environment,” SAE Technical Paper 2007-01-1236 2007 10.4271/2007-01-1236
- Sims-Williams, D. “Cross Winds and Transients: Reality, Simulation and Effects,” SAE Int. J. of Passeng. Cars - Mech. Syst. 4 1 172 183 2011 10.4271/2011-01-0172
- He, L Modelling Issues for Computation of Unsteady Turbomachinery Flows Lecture Series 1996-05, Unsteady Flows in Turbomachines Von Karman Institute for Fluid Dynamics 1996
- Oettle, N. Sims-Williams, D. Dominy, R. Darlington, C. et al. “The Effects of Unsteady On-Road Flow Conditions on Cabin Noise,” SAE Technical Paper 2010-01-0289 2010 10.4271/2010-01-0289
- Oettle, N. Sims-Williams, D. Dominy, R. Darlington, C. et al. “The Effects of Unsteady On-Road Flow Conditions on Cabin Noise: Spectral and Geometric Dependence,” SAE Int. J. of Passeng. Cars - Mech. Syst. 4 1 120 130 2011 10.4271/2011-01-0159
- Irwin, H Cooper, K Girard, R Correction of Distortion Effects Caused by Tubing Systems in Measurements of Fluctuating Pressures Journal of Industrial Aerodynamics 1979 5 1-2 93 107
- Sims-Williams, D. Dominy, R. “Experimental Investigation into Unsteadiness and Instability in Passenger Car Aerodynamics,” SAE Technical Paper 980391 1998 10.4271/980391
- Cogotti, A. “Generation of a Controlled Level of Turbulence in the Pininfarina Wind Tunnel for the Measurement of Unsteady Aerodynamics and Aeroacoustics,” SAE Technical Paper 2003-01-0430 2003 10.4271/2003-01-0430
- Cogotti, A. “Update on the Pininfarina “Turbulence Generation System” and its Effects on the Car Aerodynamics and Aeroacoustics,” SAE Technical Paper 2004-01-0807 2004 10.4271/2004-01-0807
- Lietz, R. Mallick, S. Kandasamy, S. Chen, H. “Exterior Airflow Simulations Using a Lattice Boltzmann Approach,” SAE Technical Paper 2002-01-0596 2002 10.4271/2002-01-0596