Research Papers: Fundamental Issues and Canonical Flows

Influence of Freestream Turbulence Intensity on Bypass Transition Parameters in a Boundary Layer

[+] Author and Article Information
Joanna Grzelak

Institute of Fluid-Flow Machinery,
ul. Fiszera 14,
Gdansk 80-231, Poland
e-mail: jj@imp.gda.pl

Zygmunt Wierciński

Institute of Fluid-Flow Machinery,
ul. Fiszera 14,
Gdansk 80-231, Poland
e-mail: zw@imp.gda.pl

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 2, 2015; final manuscript received November 19, 2016; published online March 14, 2017. Assoc. Editor: D. Keith Walters.

J. Fluids Eng 139(5), 051201 (Mar 14, 2017) (7 pages) Paper No: FE-15-1792; doi: 10.1115/1.4035632 History: Received November 02, 2015; Revised November 19, 2016

An experimental investigation was carried out to study the turbulent flow behind passive grids in a subsonic wind tunnel. The enhanced level of turbulence was generated by five wicker metal grids with square meshes and different parameters (diameter of the grid rod d = 0.3 to 3 mm and the grid mesh size M = 1 to 30 mm). The velocity of the flow was measured by means of a one-dimensional hot-wire probe. For this purpose, skewness, kurtosis, and transverse variation of the velocity fluctuations were determined, obtaining knowledge of the degree of turbulence isotropy and homogeneity in the flow behind grids of variable geometry, for different incoming velocities U = 4, 6, 10, 15, 20 m/s. Approximately, the isotropic and homogeneous turbulence was obtained for x/M > 30. Next, several correlations for turbulence degeneration law were tested. Finally, as the main goal of the study, impact of turbulence intensity on bypass laminar–turbulent transition parameters (transition inception, shape parameter, and the length of the transition region) on a flat plate was investigated. Parameter ITum was created as an integral taken from the leading edge of the plate to the transition inception, divided by the distance from the leading edge to the transition inception, expressing in this way the averaged value of turbulence intensity.

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Fig. 1

Test section of wind tunnel: (a) flat plate (1), grid (2) at the distance Ls from the leading edge, (b) shape of the leading edge, and (c) cross section of the measurement chamber. All dimensions are in millimeters.

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Fig. 2

Skewness (a) and kurtosis (b) for grids G1–G5 and different flow velocities

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Fig. 3

Transverse variation for grids G2, G5 at different distances from the grid

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Fig. 4

Decay power law for grids G1–G5; (a) formula (5), (b) formula (6), and (c) formula (7)

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Fig. 9

Local skin friction coefficients Cf (a), and relative boundary layer thickness δ/x (b) as a function of Rex for grids G1–G4, U = 10 m/s and Ls = 450 mm; solid and dashed lines represent the Blasius [35] laminar and turbulent solutions, respectively

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Fig. 8

The length of transition ( Re end** −  Ret**) raised to the power α for grids G1–G4

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Fig. 7

Shape parameter α as a function of ITum (a); Re ** for γ = 0.632 (characteristic length) and γ = 0.95 (transition end) as a function of ITum (b), for grids G1–G4

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Fig. 6

Ret** at the onset of transition as a function of the intensity at the leading edge, for different grids, flow velocities, and grid distances, compared with Mayle (--- • ---), Hourmouziadis (····), and Abu–Ghannam and Shaw (--)

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Fig. 5

Ret** at the onset of transition as a function of averaged turbulence intensity, for different grids, flow velocities, and grid distances




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