ORCID Profile
0000-0001-6304-1289
Current Organisation
University of Newcastle Australia
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Publisher: Informa UK Limited
Date: 21-02-2023
Publisher: Springer Science and Business Media LLC
Date: 12-2018
Publisher: Cambridge University Press (CUP)
Date: 15-03-2017
DOI: 10.1017/JFM.2017.110
Publisher: Springer Science and Business Media LLC
Date: 06-2015
Publisher: Springer Science and Business Media LLC
Date: 15-02-2019
Publisher: Springer Berlin Heidelberg
Date: 18-12-2016
Publisher: Elsevier BV
Date: 10-2015
Publisher: Springer Science and Business Media LLC
Date: 22-01-2021
Publisher: Cambridge University Press (CUP)
Date: 18-08-2015
DOI: 10.1017/JFM.2015.428
Abstract: Hot-wire measurements are carried out in grid-generated turbulence at moderate to low Taylor microscale Reynolds number $Re_{{\\it\\lambda}}$ to assess the appropriateness of the commonly used power-law decay for the mean turbulent kinetic energy (e.g. $k\\sim x^{n}$ , with $n\\leqslant -1$ ). It is found that in the region outside the initial and final periods of decay, which we designate a transition region, a power law with a constant exponent $n$ cannot describe adequately the decay of turbulence from its initial to final stages. One is forced to use a family of power laws of the form $x^{n_{i}}$ , where $n_{i}$ is a different constant over a portion $i$ of the decay time during the decay period. Accordingly, it is currently not possible to determine whether any grid-generated turbulence reported in the literature decays according to Saffman or Batchelor because the reported data fall in the transition period where $n$ differs from its initial and final values. It is suggested that a power law of the form $k\\sim x^{n_{init}+m(x)}$ , where $m(x)$ is a continuous function of $x$ , could be used to describe the decay from the initial period to the final stage. The present results, which corroborate the numerical simulations of decaying homogeneous isotropic turbulence of Orlandi & Antonia ( J. Turbul. , vol. 5, 2004, doi: 10.1088/1468-5248/5/1/009 ) and Meldi & Sagaut ( J. Turbul. , vol. 14, 2013, pp. 24–53), show that the values of $n$ reported in the literature, and which fall in the transition region, have been mistakenly assigned to the initial stage of decay.
Publisher: Cambridge University Press (CUP)
Date: 22-12-2016
DOI: 10.1017/JFM.2015.665
Abstract: A self-preservation (SP) analysis is carried out for a zero pressure gradient (ZPG) rough-wall turbulent boundary layer with a view to establishing the requirements of complete SP (i.e. SP across the entire layer) and determining if these are achievable. The analysis shows that SP is achievable in certain rough-wall boundary layers (irrespectively of the Reynolds number $Re$ ), when the mean viscous stress is zero or negligible compared to the form drag across the entire boundary layer. In this case, the velocity scale $u^{\\ast }$ must be constant, the length scale $l$ should vary linearly with the streamwise distance $x$ and the roughness height $k$ must be proportional to $l$ . Although this result is consistent with that of Rotta ( Prog. Aeronaut. Sci. , vol. 2 (1), 1962, pp. 1–95), it is derived in a more rigorous manner than the method employed by Rotta. Further, it is noted that complete SP is not possible in a smooth-wall ZPG turbulent boundary layer. The SP conditions are tested against published experimental data on both a smooth wall (Kulandaivelu, 2012, PhD thesis, The University of Melbourne) and a rough wall, where the roughness height increases linearly with $x$ (Kameda et al. , J. Fluid Sci. Technol. , vol. 3 (1), 2008, pp. 31–42). Complete SP in a ZPG rough-wall turbulent boundary layer seems indeed possible when $k\\propto x$ .
Publisher: AIP Publishing
Date: 09-2021
DOI: 10.1063/5.0061739
Abstract: Hot-wire measurements are carried out in a decaying turbulence downstream of a grid made up of two juxtaposed perforated plates with different mesh sizes but same solidity. The two perforated plates generate two interacting (quasi–) homogeneous and isotropic decaying turbulent flows with distinct turbulence intensities and integral length scales. The interaction between these two flows leads to the development of a shearless turbulent mixing layer (STML). The main focus is on the decay of the turbulence centerline of the STML. Along the downstream distance x, the Taylor microscale Reynolds number, Reλ, remains constant, the streamwise velocity variance behaves like x−1, and the Taylor microscale (λ) varies as x1/2. This indicates that the turbulence on the centerline of the STML decays in a perfectly self-preserving manner at all scales of motion. This is further supported by the very good collapse of the velocity spectra, second-, and third-order velocity structure functions.
Publisher: American Physical Society (APS)
Date: 12-12-2022
No related grants have been discovered for MD KAMRUZZAMAN.