Mechanical Engineering - Research Publications
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ItemHeat Transfer Coefficient Estimation for Turbulent Boundary Layers(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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ItemAn investigation of cold-wire spatial resolution using a DNS database(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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ItemLarge-scale structures predicted by linear models of wall-bounded turbulence(IOP Publishing, 2020-06-10)The objective of this article is to determine for which scales stochastic forcing of the linearized Navier-Stokes equations, recast as the resolvent operator, is sufficient to reproduce second-order statistics in turbulent channel flow. Our focus is on the large scales at a friction Reynolds number of Reτ = 2003. We consider a molecular resolvent operator, where only the kinematic viscosity appears, and an eddy resolvent operator, where the kinematic viscosity is augmented with an eddy viscosity profile. The molecular resolvent operator is able to identify the wall-normal height where the maximum energy of a structure is located, but it fails to predict the most energetic wave speed. It also overestimates the streamwise velocity component and underestimates the spatial support of the structures in the wall-normal direction. When the eddy resolvent operator identifies the most energetic wave speed, it also predicts the correct statistics for a given spatial scale. For spatial scales where this criterion is not met, the eddy viscosity overdamps the linear response. As a result, it predicts energetic wave speeds which are too low and velocity structures which are too energetic close to the wall. We conclude that eddy viscosity works best for structures which are most energetic in the wake region while its performance deteriorates for structures that are active in the log region.
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ItemThe effects of laser-sheet misalignment on Stereo-PIV measurements in wall-bounded turbulence(Australasian Fluid Mechanics Society, 2016)
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ItemCharacteristics of the entrainment velocity in a developing wake(International Symposium on Turbulence and Shear Flow Phenomena, 2015)
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ItemNo Preview AvailableNumerical investigation of the behaviour of wall shear stress in three-dimensional pulsatile stenotic flows(Australasian Fluid Mechanics Society (AFMS), 2014)
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ItemSurface shear stress fluctuations in the atmospheric surface layer( 2006)A lightweight, high frequency response, floating element sensor was used to measure wall shear stress fluctuations in an atmospheric surface layer. The sensor uses a laser position measurement system to track the motion of the floating element. The measurements were taken as part of an internationally coordinated experimental program designed to make extensive spatial and temporal measurements of velocity, temperature and wall shear stress of the surface layer. Velocity measurements were made with both a 27m high vertical array and a 100m wide horizontal array of sonic anemometers; 18 anemometers in total were employed. Cross-correlations of shear stress and streamwise velocity fluctuations were analysed in an attempt to identify structure angles in the flow. The results were shown to compare favourably with experimental data from controlled, laboratory turbulent boundary layer measurements at three orders of magnitude lower Reynolds number.
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ItemTurbulence intensity similarity formulations for wall-bounded flows(CIMNE - International Center for Numical Methods in Engineering, 2004)
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ItemObservations on high Reynolds number turbulent boundary layer measurements(The University of Sydney, 2004)