Research Papers: Flows in Complex Systems

Vehicles Drag Reduction With Control of Critical Reynolds Number

[+] Author and Article Information
E. L. Amromin

Mechmath LLC,
Prior Lake, MN 55372

Contributed by the Fluids Engineering Division of ASME for publication in the Journal of Fluids Engineering. Manuscript received November 8, 2012; final manuscript received June 10, 2013; published online August 6, 2013. Assoc. Editor: Mark F. Tachie.

J. Fluids Eng 135(10), 101105 (Aug 06, 2013) (7 pages) Paper No: FE-12-1565; doi: 10.1115/1.4024803 History: Received November 08, 2012; Revised June 10, 2013

Various vehicles have been designed as short blunt bodies. Drag coefficients of these bodies are high because adverse pressure gradients cause boundary layer separation from their surfaces, but a reduction of the size of separation zone allows for a substantial reduction of the body drag. It can be done via displacement of their boundary layer separation far downstream. In this study, such displacement was achieved with a combination of passive and active flow control. First, the whole body side surface includes two constant pressure surfaces of selected lengths and the surface of a high adverse pressure gradient in the middle of them. Second, the boundary layer suction maintained on this middle surface prevents separation there. The concept feasibility is manifested for very short axisymmetric bodies (of length to width ratios from 1.02 till 1.25). For moderate Reynolds numbers (from 3,000,000 to 10,000,000) and at the optimum suction intensity, the total drag coefficient of the designed bodies is about tenfold lower than the drag of spheroids of the same slenderness. The 3D design problem is also considered.

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Fig. 1

Measured effect of Reynolds number on the drag of spheres and circular cylinders

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Fig. 2

Meridian section of a short axisymmetric body with the boundary layer control by suction

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Fig. 3

Flow scheme with boundaries iteratively changed by solving of boundary-value problem in Eqs. (1)–(3)

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Fig. 4

Body meridian sections for Q** = 0 (solid line) and Q** = 0.02 (dashed line)

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Fig. 5

Effect of R1 on body shape at A = 1.05 and Q** = const

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Fig. 6

Meridian sections of designed bodies with various angles of conical parts

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Fig. 7

Computed (lines) and measured (symbols) velocities around an axisymmetric body L/B = 6

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Fig. 8

Computed (line) and measured [5] (rhombs) drag coefficient for axisymmetric ellipsoids

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Fig. 9

Pressure along meridian sections of two designed bodies with CD = 0.038 and 0.036 at Re = 107

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Fig. 10

Computed effects of Re and suction on CD of body with A = 0.65 in comparison with measured [5] effect of Re on CD of circular cylinder

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Fig. 11

Effects of Re and Q** on friction in turbulent boundary layer of the body A = 0.65; solid thick line for Q** goes only up to the boundary layer separation at 2x/B ≈ 1.73

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Fig. 12

Middle cross sections of Sc behind ellipsoids of various axis ratios (shown at curves) for σ = 1.03

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Fig. 13

Cross sections of a 3D short body with the aspect ratio 0.8 of its fixed cross section

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Fig. 14

Cross sections of a 3D short body with the aspect ratio 1.1 of its fixed cross section

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Fig. 15

Cross sections of a body with a bow-ellipsoid of y to z axis ratio 5 and cylindrical central part




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