https://nova.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:39519 Wed 27 Jul 2022 13:59:34 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:50689 Wed 02 Aug 2023 11:09:25 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:38239 3 based on d and the free-stream velocity. A multi-wire probe is deployed to measure simultaneously the fluctuating temperature and its gradient vector, at nominally the same spatial point in the plane of the mean shear. It is found that the coherent streamwise and spanwise temperature derivatives are similarly distributed with respect to the spanwise vortex, exhibiting twin peaks at the temperature fronts, while the coherent lateral component is linked to the rib-like structures. The temperature variance dissipation rate is found to be statistically independent of the temperature fluctuation when the Kármán vortex is so weak (say at x/d = 40) that the large-scale temperature front resulting from the vortex entrainment ceases to be present and the coherent strain rate at the saddle region is relatively small. In addition, the most effective turbulent mixing is found to take place around the temperature front near the wake centerline, which is in contrast to the conjecture by Hussain and Hayakawa (1987).]]> Tue 17 Aug 2021 09:45:53 AEST ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:44263 u_i and ω_i (i=1,2,3 ), are simultaneously measured, along with the fluctuating temperature θ and the temperature gradient vector, at nominally the same spatial point in the plane of mean shear at x/d=10 , where x is the streamwise distance from the cylinder axis and d is the cylinder diameter. We believe this is the first time the properties of fluctuating velocity, temperature, vorticity and temperature gradient vectors have been explored simultaneously within the Kármán vortex in detail. The Reynolds number based on d and the free-stream velocity is 2.5 x 10³ . The phase-averaged distributions of θ and ui follow closely the Gaussian distribution for r/d⩽0.2 (r is the distance from the vortex centre), but not for r/d>0.2 . The collapse of the distributions of the mean-square streamwise derivative of the velocity fluctuations within the Kármán vortex implies that the velocity field within the vortex tends to be more locally isotropic than the flow field outside the vortex. A possible physical explanation is that the large and small scales of velocity and temperature fields are statistically independent of each other near the Kármán vortex centre, but interact vigorously outside the vortex, especially in the saddle region, due to the action of coherent strain rate.]]> Tue 11 Oct 2022 13:03:27 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:31548 χ/d = 10, 20 and 40, where χ is the streamwise distance from the cylinder axis and d is the cylinder diameter, with a Reynolds number of 2.5 x 10³ based on the cylinder diameter and the free-stream velocity. A probe consisting of eight hot wires (four X-wires) and four cold wires is used to measure simultaneously the three components of the fluctuating velocity and vorticity vectors, as well as the fluctuating temperature gradient vector at nominally the same point in the plane of the mean shear. It is found that the enstrophy and scalar dissipation spectra collapse approximately at all wavenumbers except around the Kármán vortex street wavenumber for χ/d ≽ 20. The spectral similarity between the streamwise velocity fluctuation u and the passive scalar θ is better than that between the velocity fluctuation vector q and θ. This is closely related to the highly organized lateral velocity fluctuation v in this flow. The present observations are fully consistent with the expectation that small scales of the velocity and temperature fields are more likely to exhibit a close relationship than scales associated with the bulk of the turbulent energy or scalar variance. The variation across the wake of the time scale ratio between scalar and velocity fields is significantly smaller than that of the turbulent Prandtl number.]]> Sat 24 Mar 2018 08:44:26 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27921 Sat 24 Mar 2018 07:36:07 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:27919 J. Fluid Mech., vol. 250, 1993, pp. 651-668) or MA, the new model provides a more detailed description of the role the rib-like structures undertake in transporting heat and momentum, and also underlines the importance of the upstream half of the spanwise vortex rollers, instead of only one quadrant of these rollers, as in the MA model, in diffusing heat out of the vortex.]]> Sat 24 Mar 2018 07:36:07 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:30078 Sat 24 Mar 2018 07:31:16 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:45528 Mon 31 Oct 2022 14:45:03 AEDT ]]> https://nova.newcastle.edu.au/vital/access/ /manager/Repository/uon:32998 Exp. Fluids, vol. 53, 2012, pp. 1005–1013) based on the universality of the dissipation range of the longitudinal velocity spectrum normalized by the Kolmogorov scales also applies in the present flow despite the strong perturbation from the Kármán vortex street and violation of local isotropy at small x/d. The appropriateness of the spectral chart method is consistent with Antonia et al.’s (Phys. Fluids, vol. 26, 2014, 45105) observation that the two major assumptions in Kolmogorov’s first similarity hypothesis, i.e. very large Taylor microscale Reynolds number and local isotropy, can be significantly relaxed. The data also indicate that vorticity spectra are more sensitive, when testing the first similarity hypothesis, than velocity spectra. They also reveal that the velocity derivatives δu/δy and δv/δx play an important role in the interaction between large and small scales in the present flow. The phase-averaged data indicate that the energy dissipation is concentrated mostly within the coherent spanwise vortex rollers, in contrast with the model of Hussain (J. Fluid Mech., vol. 173, 1986, pp. 303–356) and Hussain & Hayakawa (J. Fluid Mech., vol. 180, 1987, p. 193), who conjectured that it resides mainly in regions of strong turbulent mixing.]]> Mon 20 Aug 2018 15:42:53 AEST ]]>