https://nova.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:34227 λ). For example, in the region below about 0.2δ (δ is the boundary layer thickness) where Re_λ varies significantly, S and F strongly vary with Re_λ and can be multivalued at a given Re_λ. In the outer region, between 0.3δ and 0.6δ, S, F, and Re_λ remain approximately constant. The channel flow direct numerical simulation data for S and F exhibit a similar behavior. These results point to the ambiguity that can arise when assessing the Re_λ dependence of S and F in wall shear flows. In particular, the multivaluedness of S and F can lead to erroneous conclusions if y/δ is known only poorly, as is the case for the atmospheric shear layer (ASL). If the laboratory turbulent boundary layer is considered an adequate surrogate to the neutral ASL, then the behavior of S and F in the ASL is expected to be similar to that reported here.]]> Wed 20 Feb 2019 15:55:38 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:47127 U ¯ . It is shown that, in the MSU, the large-scale structures become approximately two-dimensional at h+=1020. In this case, the streamwise velocity fluctuation u is energized, whereas the spanwise velocity fluctuation w is weakened significantly. Indeed, there is a reduced energy redistribution arising from the impaired global nature of the pressure, which is linked to the reduced linear–nonlinear interaction in the Poisson equation (i.e. the rapid pressure). The logarithmic dependence of $\stackrel{¯<!--\; ¯\; -->}{ww}$ is also more evident due to the reduced large-scale spanwise meandering. On the other hand, the spanwise organization of the large-scale u structures is essentially identical for the MSU and large streamwise domain (LSD). One discernible difference, relative to the LSD, is that the large-scale structures in the MSU are more energized in the outer region due to a reduced turbulent diffusion. In this region, there is a tight coupling between neighbouring structures, which yields antisymmetric pairs (with respect to centreline) of large-scale structures with a spanwise spacing of approximately 3h; this is intrinsically identical with the outer energetic mode in the optimal transient growth of perturbations.]]> Wed 14 Dec 2022 14:17:29 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:4415 Wed 11 Apr 2018 14:33:14 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:39624 Re) and localised wall suction applied through a porous strip on a fully rough wall turbulent boundary layer (TBL) is investigated using hot-wire anemometry. The measurements show that the response of the TBL to suction is modulated by the ratio U_s/U_τ, where U_s and U_τ are the suction and friction velocities, respectively. For example the suction impact on the mean velocity and the turbulence intensity profiles, which is felt across the boundary layer, decreases as U_s/U_τ decreases. Interestingly, the velocity spectra contour maps reveal that suction reduces the energy at all scales of motion across the boundary layer. Further, measurements of the velocity skewness indicate that the TBL undergoes a structural change when the ratio U_s/U_τ is relatively important. However, the measurements also reveal that TBL does not show a relaminarisation behaviour as it can be observed in a smooth wall TBL with similar localised wall suction. This lack of relaminarisation is due to the development of a growing internal boundary layer which evolves on a rough surface within the existing TBL.]]> Thu 16 Jun 2022 11:25:11 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:51678 Thu 14 Sep 2023 11:40:07 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:50736 Thu 03 Aug 2023 16:26:36 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:30615 Pr of 0.71. A logarithmic dependence on the Kármán number h⁺ is established for the integrated mean scalar in the range h⁺ ≽400 where the mean part of the total scalar dissipation exhibits near constancy, whilst the integral of the turbulent scalar dissipation rate ̅ϵ_θ increases logarithmically with h⁺. This logarithmic dependence is similar to that established in a previous paper (Abe & Antonia, J. Fluid Mech., vol. 798, 2016, pp. 140–164) for the bulk mean velocity. However, the slope (2.18) for the integrated mean scalar is smaller than that (2.54) for the bulk mean velocity. The ratio of these two slopes is 0.85, which can be identified with the value of the turbulent Prandtl number in the overlap region. It is shown that the logarithmic h⁺ increase of the integrated mean scalar is intrinsically associated with the overlap region of ̅ϵ_θ, established for h⁺ (≽400). The resulting heat transfer law also holds at a smaller h⁺ (≽200) than that derived by assuming a log law for the mean temperature.]]> Sat 24 Mar 2018 07:39:00 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:29610 b = 2:54 ln(h⁺)+ 2:41 (U_b is the bulk mean velocity). This latter relationship is established on the basis of energy balances for both the mean and turbulent kinetic energy. When h⁺ is smaller than 300, viscosity affects the integrals of both the mean and turbulent energy dissipation rates significantly due to the lack of distinct separation between inner and outer regions. The logarithmic h⁺ dependence of U⁺_b is clarified through the scaling behaviour of the turbulent energy dissipation rate ε̅ in different parts of the flow. The overlap between inner and outer regions is readily established in the region 30/h⁺ ≼ y/h ≼ 0:2 for h⁺ ≽ 300. At large h⁺ (≽5000) when the finite Reynolds number effect disappears, the magnitude of [could not be replicated] approaches 2.54 near the lower bound of the overlap region. This value is identical between the channel, pipe and boundary layer as a result of similarity in the constant stress region. As h⁺ becomes large, the overlap region tends to contribute exclusively to the 2.54 ln(h⁺) dependence of the integrated turbulent energy dissipation rate. The present logarithmic h⁺ dependence of U⁺_b is essentially linked to the overlap region, even at small h⁺.]]> Sat 24 Mar 2018 07:32:05 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:24369 e), 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∗ 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∝x.]]> Sat 24 Mar 2018 07:16:18 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:48246 Sat 11 Mar 2023 12:51:32 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:36517 Mon 25 May 2020 14:14:48 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:45502 Fri 28 Oct 2022 16:07:26 AEDT ]]>