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Wake and Unsteady Surface-Pressure Measurements on an SUV with Rear-End Extensions
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 14, 2015 by SAE International in United States
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Previous research on both small-scale and full-scale vehicles shows that base extensions are an effective method to increase the base pressure, enhancing pressure recovery and reducing the wake size. These extensions decrease drag at zero yaw, but show an even larger improvement at small yaw angles.
In this paper, rear extensions are investigated on an SUV in the Volvo Cars Aerodynamic Wind Tunnel with focus on the wake flow and on the unsteady behavior of the surface pressures near the base perimeter. To increase the effect of the extensions on the wake flow, the investigated configurations have a closed upper- and lower grille (closed-cooling) and the underbody has been smoothed with additional panels.
This paper aims to analyze differences in flow characteristics on the wake of an SUV at 0° and 2.5° yaw, caused by different sets of extensions attached to the base perimeter. Extensions with several lengths are investigated with and without a kick. Unsteady pressure sensors attached to the base perimeter of the vehicle are used. The fluctuations are examined for the reference vehicle and the vehicle with extensions for different freestream velocities and under a yaw angle ranging from 0° to 7.5° yaw.
The current investigation indicates that the drag reduction obtained at 2.5° yaw with a “kick” mounted at the rear edge of the extensions have an effect on the size of the wake and enhance the pressure recovery behind the vehicle. The addition of the kick alters the wake distribution and changes the corresponding flow pattern with the largest effect under yaw conditions.
For the unsteady surface pressure measurements, a technique based on Empirical Mode Decomposition (EMD) is applied that results in instantaneous frequencies of the signal. It gives the option of signal reconstruction limited to the frequency area of interest. A Proper Orthogonal Decomposition (POD) on the signals is also conducted, showing large variance in the area below the catwalk for the first two modes. To enhance the correlation, this paper investigates the combination of both mode decompositions, where the POD is applied to EMD-filtered signals.
CitationSterken, L., Sebben, S., Lofdahl, L., Walker, T. et al., "Wake and Unsteady Surface-Pressure Measurements on an SUV with Rear-End Extensions," SAE Technical Paper 2015-01-1545, 2015, https://doi.org/10.4271/2015-01-1545.
- Viswanath , P.R. Flow Management Techniques for Base and Afterbody Drag Reduction Progress Aerospace Science 32 1996 79 129
- Tanner , M. Reduction of Base Drag Progress Aerospace Science 16 1975 369 384
- Irving Brown , Y. , Windsor , S. , and Gaylard , A. The Effect of Base Bleed and Rear Cavities on the Drag of an SUV SAE Technical Paper 2010-01-0512 2010 10.4271/2010-01-0512
- Howell , J. , Sims-Williams , D. , Sprot , A. , Hamlin , F. et al. Bluff Body Drag Reduction with Ventilated Base Cavities SAE Int. J. Passeng. Cars - Mech. Syst . 5 1 152 160 2012 10.4271/2012-01-0171
- Khalighi , B. , Balkanyi , S.R. , and Bernal , L.P. Experimental investigation of aerodynamic flow over a bluff body in ground proximity with drag reduction devices Int. J. Aerodynamics 3 4 217 233 2013
- Hong , S. A Study on the Modeling Technique of Airbag Cushion Fabric SAE Technical Paper 2003-01-0512 2003 10.4271/2003-01-0512
- Gilliéron , P. , Kourta , A. Aerodynamic drag reduction by vertical splitter plates Exp Fluids 48 1 16 2010
- Banister , M. Summary of Results from FU Aerodynamic Tests on a 1:5 Scale Model of a Modified XC90 in MWT Volvo Internal Report 2006
- Sebben , S. AE Project on Advanced Flow Control, Part II: 3D CFD Simulations Volvo Internal Report 2006
- Sterken , L. , Lofdahl , L. , Sebben , S. , and Walker , T. Effect of Rear-End Extensions on the Aerodynamic Forces of an SUV SAE Technical Paper 2014-01-0602 2014 10.4271/2014-01-0602
- Duell , E. and George , A. Experimental Study of a Ground Vehicle Body Unsteady Near Wake SAE Technical Paper 1999-01-0812 1999 10.4271/1999-01-0812
- Huang , N.E. , Shen , Z. , Long , S.R. et. al. The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time-series analysis Proc. Royal Society London 1998
- Clifford , G.D. Singular Value Decomposition & Independent Component Analysis for Blind Source Separation Biomedical Signal and Image Processing 2005
- Beaudoin , J.F. , and Aider , J.-L. Drag and lift reduction of a 3D bluff body using flaps Exp. Fluids (2008) 44 491 501 10.1007/s00348-0070392-1
- Sternéus , J. , Walker , T. , and Bender , T. Upgrade of the Volvo Cars Aerodynamic Wind Tunnel SAE Technical Paper 2007-01-1043 2007 10.4271/2007-01-1043
- Sterken , L. , Sebben , S. , Walker , T. and Löfdahl , L. Traversing unit effect on the flow structures behind a passenger vehicle International Vehicle Aerodynamics Conference, IMechE 2014
- Cogotti , A. A Strategy for Optimum Surveys of Passenger-Car Flow Fields SAE Technical Paper 890374 1989 10.4271/890374
- Ivaníc , T. , and Gilliéron , P. Aerodynamic drag and ways to reduce it Lecture Series VKI Institute Brussels 2005
- Bergh , H. , and Tijdeman , H. Theoretical and experimental results for the dynamic response of pressure measuring systems Nationaal Lucht- en Ruimtevaartlaboratorium 1965