Effects of Unsteady Coanda Blowing on the Wake and Drag of a Simplified Blunt Vehicle
The impact of periodic forcing on the wake past a square back bluff body is experimentally studied. By the use of pulsed jets in combination with a Coanda effect, shear layer forcing allows to recover over 30 % of the model’s base pressure. The actuation
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Effects of Unsteady Coanda Blowing on the Wake and Drag of a Simplified Blunt Vehicle D. Barros, J. Borée, B.R. Noack, A. Spohn, and T. Ruiz
19.1 Introduction An ongoing challenge for manufacturers worldwide concerns the reduction of road vehicles’ drag due to increasing need for fuel saving and diminution of greenhouse gas emissions. The aerodynamic drag of such vehicles is mainly the result of significant pressure differences between their front and rear surfaces. In particular, square back geometries like cars with vertical rear hatch panels, buses, or trucks have been extensively studied in the past [1] and are still subject of intense research to elucidate the main flow features [2, 3]. The domain of recirculating flow formed behind these geometries is surrounded by free shear layers, which act as a noise amplifier developing through the Kelvin–Helmholtz instabilities, while the absolute wake instability results in self-sustained oscillations [4].
D. Barros () Institut Pprime UPR-3346, CNRS – Université de Poitiers – ENSMA, Futuroscope, Chasseneuil, 86360, France PSA Peugeot Citroën, Centre Technique de Vélizy, 78943 Vélizy-Villacoublay Cedex, France e-mail: [email protected] J. Borée • A. Spohn Institut Pprime UPR-3346, CNRS – Université de Poitiers – ENSMA, Futuroscope, Chasseneuil 86360, France B.R. Noack LIMSI – CNRS, UPR 3251, Campus Universitare dÓrsay, Rue John Von Neumann, Bat 508, F-91405 Orsay Cedex, France Institut für Strömungsmechanik, Technische Universität Braunschweig, Hermann-Blenck-Straße 37, 38108 Braunschweig, Germany T. Ruiz PSA Peugeot Citroën, Centre Technique de Vélizy, 78943 Vélizy-Villacoublay Cedex, France © Springer International Publishing Switzerland 2017 A. Pollard et al. (eds.), Whither Turbulence and Big Data in the 21st Century?, DOI 10.1007/978-3-319-41217-7_19
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In recent years, flow control turned out to be an efficient way to modify bluff body wakes with the aim to decrease drag [5]. In fully 3D flows past rectangular bluff bodies, for example, base pressure recovery can be obtained by the use of boat-tailing surfaces installed on the trailing edges [3] or by producing flow deflection through steady jets associated or not with a Coanda effect [6–8]. The combination of fluidic actuation with boat-tailing has been recently tested to improve flow attachment along the extended surface and better deviating the separated flow [9, 10]. For practical applications, the tested control techniques show limitations related to power cost and geometrical constraints. Here we explore the possibility to reduce both constraints by coupling unsteady pulsed jets with a Coanda effect to deviate more efficiently the flow. Recent studies applied fluidic actuation to virtually manipulate the flow consequently increasing the blunt body base pressure [11, 12]. Depending on the forcing frequency and amplitude of periodic jets, which are released in the downstream direction along the four trailing edges, the time-averaged wake can be virtually shaped with reduced cr
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