Underbody diffusers are used widely in race car applications because they can significantly improve the cornering capacity of the vehicle through the generation of a downforce. They are also likely to have a wider role in reducing the drag in road vehicles as it becomes increasingly important to reduce emissions of carbon dioxide. This paper reports on a wind tunnel investigation, using a simplified bluff body model, into the effect of splitting a simple plane diffuser into multiple channels. Tests are reported for a range of diffuser geometries suitable for road and race car applications. The results for the lift, the drag, and the incremental changes to the lift-to-drag ratio are reported and discussed in terms of the underbody pressures. While broadly similar trends to the single-channel plane diffuser are seen in the multiplechannel diffuser configurations, it was found that the effect of increasing the number of channels depended on the flow regimes present in the plane diffuser. At angles just above the plane diffuser optimum, where the flow is partially separated, the multiple-channel configurations give large improvements in the downforce with minimal increase in the drag, significantly extending the performance envelope. The pressure maps indicate that the gains occur through improved diffuser pumping and pressure recovery in both the inner and the outer channels. An investigation into the performance of plane and multiple-channel diffusers has been carried out using force and pressure measurements. Ten diffuser angles and eight ride heights were investigated. The plane diffuser showed similar trends in the lift and drag to published data. The optimum angle for the downforce lies between 13 deg and 16 deg. Above 16 deg the downforce levels are reduced with a corresponding increase in the drag. The centre-line pressure distributions indicate that, above 13 deg, local separation occurs at the diffuser inlet and that, at 25 deg and above, the diffuser is stalled although it continues to generate a downforce through the mechanism of upsweep. The multiple-channel diffusers showed similar trends in the lift and drag to the plane diffuser and, for angles of 13 deg and above, the multiplechannel configurations show an improved downforce, with the percentage gains increasing with increasing diffuser angle. For the midrange angles (16 deg - 19 deg) where the degree of separation is small, the multiplechannel configurations show large improvements in the downforce with minimal increase in the drag. In this range the total downforce is increased by 13 per cent compared with the optimum plane diffuser, significantly extending the performance envelope. The pressure maps indicate that the gains occur through improved diffuser pumping and pressure recovery in both the inner channel and the outer channel. Above 19 deg, large improvements in performance are observed compared with the plane configuration, particularly for three- and four-channel setups; however, the levels of downforce produced remain relatively low. The pressure data indicate that the gains arise from improved pressure recovery in the outer channels.
Experimental study of multiple-channel automotive underbody diffusers
Experimentelle Untersuchung des Fahrzeugunterboden-Mehrkanaldiffusors
2010
15 Seiten, 14 Bilder, 14 Quellen
Article (Journal)
English
Anwendung im Fahrzeugbau , Formelrennwagen , Unterboden , experimentelle Untersuchung , Luftwiderstand , Fahrzeugaerodynamik , Karosserieluftführung , Seitenstabilität , Stromlinienverkleidung , Strömungsdiffusor , Windkanal , Windkanalprüfung , Fahrverhalten , Auftrieb , Anpressdruck , Kraftstoffverbrauch , Luftdruckmessung
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