Abstract
A large contribution to the aerodynamic drag of a vehicle arises from the failure to fully recover pressure in the wake region, especially on squareback configurations. A degree of base pressure recovery can be achieved through careful shape optimisation, but the freedom of an automotive aerodynamicist to implement significant shape changes is limited by a variety of additional factors such styling, ergonomics and loading capacity. Active flow control technologies present the potential to create flow field modifications without the need for external shape changes and have received much attention in previous years within the aeronautical industry and, more recently, within the automotive industry. In this work the influence of steady blowing applied at a variety of angles on the roof trailing edge of a simplified ¼ scale squareback style vehicle has been investigated. Hot-wire anemometry, force balance measurements, surface pressure measurements and PIV have been used to investigate the effects of the steady blowing on the vehicle wake structures and the resulting body forces. The energy consumption of the steady jet is calculated and is used to deduce an aerodynamic drag power change. Results show that overall gains can be achieved; however, the large mass flow rate required restricts the applicability of the technique to road vehicles. Means by which the mass flow rate requirements of the jet may be reduced are discussed and suggestions for further work put forward.
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Abbreviations
- C d :
-
Aerodynamic drag coefficient
- C μ :
-
Momentum coefficient
- l :
-
Measured length (mm)
- w :
-
Measured width (mm)
- h :
-
Measured height (mm)
- L :
-
Model length (mm)
- W :
-
Model width (mm)
- H :
-
Model height (mm)
- l/L :
-
Non-dimensional length
- w/W :
-
Non-dimensional width
- h/H :
-
Non-dimensional ride height
- m j :
-
Mass flow rate exiting jet (kg/s)
- V j :
-
Mean jet exit velocity (m/s)
- Q :
-
Freestream dynamic pressure (Pa)
- A :
-
Model frontal area (m2)
- E :
-
Ratio of model frontal area to wind tunnel cross-sectional area
- Δt :
-
PIV inter-frame time
- L :
-
Model length (m)
- R e :
-
Reynolds number
- C p :
-
Coefficient of pressure
- \( \bar{C}_{p} \) :
-
Area-weighted pressure coefficient
- l/L :
-
Non dimensional length
- APNET :
-
Net change in aerodynamic power (Watts)
- ΔF D :
-
Change in drag force (N)
- V :
-
Freestream velocity (m/s)
- η j :
-
Blowing system efficiency
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Acknowledgments
The authors would like to thank Rob Hunter and Stacey Prentice with all their help in preparing the models for the tests carried out in this paper.
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Littlewood, R.P., Passmore, M.A. Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing. Exp Fluids 53, 519–529 (2012). https://doi.org/10.1007/s00348-012-1306-4
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DOI: https://doi.org/10.1007/s00348-012-1306-4