Mechanical Engineering - Research Publications
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ItemA wall-wake model for the turbulence structure of boundary layers. Part 2. Further experimental support(Cambridge University Press, 1995)In Part 1 an extension of the attached eddy hypothesis was developed and applied to equilibrium pressure gradient turbulent boundary layers. In this paper the formulation is applied to data measured by the authors from non-equilibrium layers and agreement with the extended theory is encouraging. Also power spectra of the Reynolds stresses as developed from the extended theory compare favourably with experiment. The experimental data include a check of cone-angle effects by using a flying hot wire.
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ItemThe effect of aspect ratio and divergence on the turbulence structure of boundary layers( 2007)The effect of the aspect ratio of a turbulent boundary layer on the mean flow, broadband turbulence intensities and Reynolds shear stress has been studied. The aspect ratio (AR) is defined as the boundary layer thickness divided by the boundary layer width, i.e. the effective wind tunnel width. Measurements have been taken in a nominally zero pressure gradient layer at a single station for three different aspect ratio settings, AR=1/4, AR=1/7, and AR=1/13. The measurements show that the turbulent quantities were unaffected when the aspect ratio was increased from AR=1/13 to AR=1/7. However at AR=1/4 there appears to be a slight increase in the broadband turbulence intensities and Reynolds shear stress.
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ItemObservations on high Reynolds number turbulent boundary layer measurements(The University of Sydney, 2004)
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ItemSpanwise periodicity and the existence of very large scale coherence in turbulent boundary layers(Begellhouse, 2005-12-01)
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ItemDominant spanwise Fourier modes, and the existence of very large scale coherence in turbulent boundary layers( 2004)Multiple plane stereo PIV results and data from a rake often hot-wire probes are used to investigate the largest scalestructures in a zero-pressure-gradient turbulent boundary layer.Instantaneous vector fields from stereo PIV in spanwise-streamwiseplanes reveal long low- and high-speed regions,with a length that often exceeds the viewing window (> 2d).Also evident is a remarkable degree of spanwise organisation,that manifests as a persistent spanwise stripiness in the u componentof the PIV vector field. Almost all trace of such spanwiseorganisation is lost in the mean statistics, presumably dueto the multitude of scales naturally present in wall-bounded turbulence.This can be overcome by ‘de-jittering’ the instantaneousvector fields. By sorting the data according to dominantspanwise fourier modes, and then applying simple statisticaltools to the sorted subsets, we are able to extract a clear viewof spanwise organisation. Results are confirmed in the variousPIV data-sets. Since the PIV fails to adequately capture the fullstreamwise extent of the low-speed regions, a rake of hot-wireprobes is also employed to capture a continuous view of thespanwise coherence. It is found that the low-speed regions arein fact extremely persistent in the streamwise direction, oftenexceeding 20 d in length. The fact that these long features meanderappreciably in the spanwise direction will limit the overallstreamwise length-scale as witnessed by a single probe or singlepoint statistic. For instance, premultiplied one-dimensionalspectra of the streamwise velocity (kxFuu) at this z/d show apeak contribution for characteristic lengthscales of 5-7d.
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ItemThe bottleneck 2-connected k-Steiner network problem for k=2(Elsevier Science, 2012)