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Experimental analysis of the freestream length scale and turbulence intensity impact on bypass transition in boundary layer on a ﬂat plate

Grzelak J., Wierciński Z.

Transactions of the Institute of Fluid-Flow Machinery

2018

nr 139

23--44

An experimental investigation of the turbulent ﬂow over a ﬂat plate in a subsonic wind tunnel was carried out. The enhanced level of turbulence was generated by ﬁve wicker grids with square meshes, and diﬀerent parameters (diameter of the grid rod 0.3–3 mm and the grid mesh size 1–30 mm). The velocity of the ﬂow was measured by means of a 1D hot-wire probe, suitable for measurements in a boundary layer. The aim of the investigation was to explore the turbulence length scale in the ﬂow behind grids and to study its inﬂuence on the onset of laminar-turbulent bypass transition in a boundary layer on a ﬂat plate. To assess the isotropy of turbulence, the skewness and kurtosis factors of the ﬂow velocity distribution were determined. Several longitudinal scales of turbulence were determined and compared (integral, dissipation, Taylor microscale, and Kolmogorov scale) for diﬀerent grids and diﬀerent velocities of the mean ﬂow 4, 6, 10, 15, and 20 m/s.

An overview of Millionschikov's quasi-normality hypothesis applied to turbulence

Mamaloukas C., Mazumdar H. P.

International Journal of Applied Mechanics and Engineering

2014

Vol. 19, no. 1

123--132

In this paper, we examine the zero-fourth cumulant approximation that was applied to fluctuating velocity components of homogeneous and isotropic turbulence by M.D. Millionschikov. Since the publication of the remarkable paper of Millionschikov, many authors have applied this hypothesis to solve the closure problem of turbulence. We discuss here various studies by the other authors on the developments of this hypothesis and their applications to the incompressible velocity temperature, hydrodynamic and magnetohydrodynamic fluctuating pressure fields and the general magnetohydrodynamic turbulence field. Lastly, we discuss broadly the computational difficulties that arise in turbulence problems and their possible refinements. We include also some enlightments of the process of future work that could be undertaken in this field of research.

Two-points statistics of kinematic velocity models in isotropic turbulence

Wacławczyk M., Pozorski J.

Turbulence : international journal

2002

Vol. 8-9

99-112

Kinematic models for 2D and 3D velocity fields of homogeneous isotropic turbulence are considered. Numerical simulation is performed to obtain a number of independent realisations of the field and some two-point statistics are computed and discussed. The statistics include the velocity correlations and the spectral energy density.