Mechanical Engineering - Research Publications

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Author: Hutchins, Nicholas × Start date: 2020 × End date: 2021 × Type: Conference Paper ×

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    Heat Transfer Coefficient Estimation for Turbulent Boundary Layers
    Wang, S ; Xia, Y ; Abu Rowin, W ; Marusic, I ; Sandberg, R ; Chung, D ; Hutchins, N ; Tanimoto, K ; Oda, T (The University of Queensland, 2020-12-11)
    Convective heat transfer in rough wall-bounded turbulent flows is prevalent in many engineering applications, such as in gas turbines and heat exchangers. At present, engineers lack the design tools to accurately predict the convective heat transfer in the presence of non-smooth boundaries. Accordingly, a new turbulent boundary layer facility has been commissioned, where the temperature of an interchangeable test surface can be precisely controlled, and conductive heat losses are minimized. Using this facility, we can estimate the heat transfer coefficient (Stanton number, St), through measurement of the power supplied to the electrical heaters and also from measurements of the thermal and momentum boundary layers evolving over this surface. These methods have been initially investigated over a shorter smooth prototype heated surface and compared with existing St prediction models. Preliminary results suggest that we can accurately estimate St in this facility.
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    An investigation of cold-wire spatial resolution using a DNS database
    Xia, Y ; Rowin, W ; Jelly, T ; Chung, D ; Marusic, I ; Hutchins, N (The University of Queensland, 2020-12-11)
    The effect of spatial resolution of cold-wire anemometry on both the variance and energy spectrum of temperature fluctuations is analyzed through the use of a numerical database. Temperature fluctuation snapshots from a direct numerical simulation (DNS) of a heated smooth-wall turbulent channel flow are spatially averaged in the spanwise direction to simulate the wire filtering. The results show that the wire length does not affect the mean temperature while it significantly attenuates the variance of temperature fluctuations, particularly in the vicinity of the wall. As the filter length grows, the peaks of the one- and two-dimensional energy spectrograms are further attenuated. Limited attenuation is seen when the filter length is smaller than 30 wall units in the vicinity of the wall, whereas a complete suppression of the near-wall energetic peak is observed when the filter length exceeds 100 wall units.
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    The Effects of Anisotropic Surface Roughness on Turbulent Boundary-Layer Flow
    Ramani, A ; Nugroho, B ; Busse, A ; Monty, JP ; Hutchins, N ; Jelly, TO (The University of Queensland, 2020-01-01)
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    Turbulent flow over spanwise-varying roughness in a minimal streamwise channel
    Xie, MX ; Chung, D ; Hutchins, N (IOP Publishing, 2020-06-10)
    All rights reserved. We report direct numerical simulations in a minimal streamwise domain of turbulent channel flow over spanwise-alternating patches of rough and smooth walls. Despite the minimal streamwise domain overpredicting streamwise-velocity fluctuations and inhibiting the meandering of long turbulent structures, it captures the rotational behaviour of mean secondary flows also observed in other studies with spanwise-varying roughness. To extend the study of spanwise-varying roughness, we prescribe a lateral velocity to the wall roughness to mimic flow over oblique patches of roughness. Far from the wall, long-lived turbulent structures are convected in the direction of the moving roughness, but their speeds are only weakly perturbed from a preferential value of around 40% of the friction velocity. The turbulence-driven secondary flows laterally convect at comparable speeds, but depend on the roughness patch width.