https://ogma.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17034 2¯ is reasonably well approximated on the axis of the intermediate wake of a circular cylinder. The similarity, which scales on the Taylor microscale λ and q²¯, is then used to determine s-b-s energy budgets from the data of Antonia, Zhou, and Romano [“Small-scale turbulence characteristics of two-dimensional bluff body wakes,” J. Fluid Mech.459, 67–92 (2002)] for 5 different two-dimensional wake generators. In each case, the budget is reasonably well closed, using the locally isotropic value of the mean energy dissipation rate, except near separations comparable to the wavelength of the coherent motion (CM). The influence of the initial conditions is first felt at a separation L_c¯ identified with the cross-over between the energy transfer and large scale terms of the s-b-s budget. When normalized by q²¯ and L_c , the mean energy dissipation rate is found to be independent of the Taylor microscale Reynolds number. The CM enhances the maximum value of the energy transfer, the latter exceeding that predicted from models of decaying homogeneous isotropic turbulence.]]> Wed 11 Apr 2018 15:47:49 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17050 Wed 11 Apr 2018 15:36:30 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17030 δ = U ₀δ/ν (U ₀ being the jet inlet velocity and δ the momentum thickness) that ought to be achieved for the one-point statistics to behave in a self-similar fashion is assessed. Second, the relevance of different sets of similarity variables for normalizing the energy spectra and structure functions is explored. In particular, a new set of shear similarity variables, emphasizing the range of scales influenced by the mean velocity and temperature gradient, is derived and tested. Since the Reynolds number based on the Taylor microscale increases with respect to the streamwise distance, complete self-preservation cannot be satisfied; instead, the range of scales over which spectra and structure functions comply with self-preservation depends on the particular choice of similarity variables. A similarity analysis of the two-point transport equation, which features the large scale production term, is performed and confirms this. Log-similarity, which implicitly accounts for the variation of the Reynolds number, is also proposed and appears to provide a reasonable approximation to self-preservation, at least for u and θ.]]> Wed 11 Apr 2018 14:43:41 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17032 a, ya, x and the transverse direction y (ε_{a, yhom}) and homogeneity in the transverse plane, (ε ), are assessed. All the approximations are in agreement with ε¯ when the distance downstream of the obstacle is larger than about 40 diameters. Closer to the obstacle, the agreement remains reasonable only for ε¯_a,x , ε¯_hom and ε¯_4x. The probability density functions (PDF) and joint PDFs of ε and its surrogates show that ε_4x correlates best with ε while ε_iso and ε_hom present the smallest correlation. The results indicate that ε4x is a very good surrogate for ε and can be used for correctly determining the behaviour of ε.]]> Wed 11 Apr 2018 12:08:09 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:20918 r on the phase ϕ of the CM. This tool allows the dependence of the RM to be followed as a function of the CM dynamics. Scale-by-scale energy budget equations are established on the basis of phase-averaged structure functions. They reveal that energy transfer at a scale r is sensitive to an additional forcing mechanism due to the CM. Second, these concepts are tested using hot-wire measurements in a cylinder wake, in which the CM is characterized by a well-defined periodicity. Because the interaction between large and small scales is most likely enhanced at moderate/low Reynolds numbers, and is also likely to depend on the amplitude of the CM, we choose to test our findings against experimental data at Rλ∼102 and for downstream distances in the range 10≤x/D≤40. The effects of an increasing Reynolds number are also discussed. It is shown that: (i) a simple analytical expression describes the second-order structure functions of the purely CM. The energy of the CM is not associated with any single scale; instead, its energy is distributed over a range of scales. (ii) Close to the obstacle, the influence of the CM is perceptible even at the smallest scales, the energy of which is enhanced when the coherent strain is maximum. Further downstream from the cylinder, the CM clearly affects the largest scales, but the smallest scales are not likely to depend explicitly on the CM. (iii) The isotropic formulation of the RM energy budget compares favourably with experimental results.]]> Sat 24 Mar 2018 08:06:11 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:19088 Sat 24 Mar 2018 08:05:23 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:18223 Sat 24 Mar 2018 08:04:39 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:17808 −4, where x₀ is a virtual origin, follows immediately from the variation of the mean velocity, the constancy of the local turbulent intensity and the ratio between the axial and transverse velocity variance. Second, the limit at small separations of the two-point budget equation yields an exact relation illustrating the equilibrium between the skewness of the longitudinal velocity derivative S and the destruction coefficient G of enstrophy. By comparing the latter relation with that for homogeneous isotropic decaying turbulence, it is shown that the approach towards the asymptotic state at infinite Reynolds number of S+2G/Rλ in the jet differs from that in purely decaying turbulence, although +2G/R_λ∝R⁻¹_λ in each case. This suggests that, at finite Reynolds numbers, the transport equation for ϵ¯ imposes a fundamental constraint on the balance between S and G that depends on the type of large-scale forcing and may thus differ from flow to flow. This questions the conjecture that S and G follow a universal evolution with R_λ; instead, S and G must be tested separately in each flow. The implication for the constant C_ϵ2 in the k−ϵ¯ model is also discussed.]]> Sat 24 Mar 2018 07:57:35 AEDT ]]>