Research Papers: Flows in Complex Systems

Drag Reduction on the 25-deg Ahmed Model Using Fluidic Oscillators

[+] Author and Article Information
Matthew Metka

Aerospace Research Center,
The Ohio State University,
2300 West Case Road,
Columbus, OH 43235
e-mail: metka.4@osu.edu

James W. Gregory

Aerospace Research Center,
The Ohio State University,
2300 West Case Road,
Columbus, OH 43235
e-mail: gregory.234@osu.edu

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received July 28, 2014; final manuscript received January 7, 2015; published online February 9, 2015. Assoc. Editor: Feng Liu.

J. Fluids Eng 137(5), 051108 (May 01, 2015) (8 pages) Paper No: FE-14-1410; doi: 10.1115/1.4029535 History: Received July 28, 2014; Revised January 07, 2015; Online February 09, 2015

Transportation of goods and people involves moving objects through air, which leads to a force opposing motion. This drag force can account for more than 60% of power consumed by a ground vehicle, such as a car or truck, at highway speeds. This paper studies drag reduction on the 25-deg Ahmed generic vehicle model with quasi-steady blowing at the roof–slant interface using a spanwise array of fluidic oscillators. A fluidic oscillator is a simple device that converts a steady pressure input into a spatially oscillating jet. Drag reduction near 7% was attributed to separation control on the rear slant surface. Particle image velocimetry (PIV) and pressure taps were used to characterize the flow structure changes behind the model. Oil flow visualization was used to understand the mechanism behind oscillator effectiveness. An energy analysis suggests that this method may be viable from a flow energy perspective.

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Fig. 1

Drag characteristics (a) and flow structures (b) for the Ahmed model. Adapted from Ref. [8].

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Fig. 2

Instantaneous and time averaged jet pattern from a single fluidic oscillator

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Fig. 3

Dimensions of the Ahmed model used in this study

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Fig. 4

Actuator implementation. The angle of the sweeping jets relative to the freestream velocity is shown in (a), with the sweeping plane oriented out of the page. The array configuration is shown in (b) along with a representation of the jet action.

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Fig. 5

Actuator array constructed from laser-cut acrylic

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Fig. 6

Relationship between momentum coefficient and measured mass flow rate

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Fig. 7

Drag coefficient characteristics with the oscillator thrust component included (a) and with the thrust component removed (b)

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Fig. 8

Slant surface PIV at various actuation rates

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Fig. 9

Instantaneous vector field over the rear slant with swirling strength criterion for baseline and active control

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Fig. 10

Surface pressure data on projected rear surface (a), and percentage change relative to baseline model at the slant (b) and base (c) regions

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Fig. 11

PIV of near wake region downstream of the model base

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Fig. 12

Oil flow visualization on the slant surface (a) and close to the actuator outlet (b) at Cμ = 3.3%

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Fig. 13

Power analysis for determining net energy benefit




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