Mechanical Engineering - Research Publications
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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)
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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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ItemThree dimensional structure characterization and visualization in a turbulent boundary layer(CIMNE - International Center for Numical Methods in Engineering, 2004)
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ItemA study of the Reynolds-shear-stress spectra in zero- pressure-gradient boundary layers( 1989)Measurements of Reynolds-shear-stress spectra in smooth-wall zero-pressure-gradient turbulent boundary layers are presented for four different Karman numbers. The results are plotted using various scaling variables and found to collapse with 'inner-flow' scaling for a modest range of mid-range wavenumbers, the extent of collapse increasing for higher Karman numbers. The results are discussed in light of the attached eddy hypothesis of Townsend (1976)as extended by Perry and Chong (1982). A computation of the cross-power spectra, based upon the same theory, is also presented.
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ItemAn experimental and computational study on the orientation of attached eddies in turbulent boundary layers( 1992)The flow visualisation results of various researchers suggest that the attached eddies align themselves with the direction of the principal rate of mean strain. The principal rate of mean strain is influenced by pressure gradient. With the knowledge of this dependence and using the wall turbulence model proposed by Perry & Chong (1982) and later modified by Perry et al. (1986, 1991) it may be possible to predict the characteristics of a turbulent boundary layer flow subjected to any arbitrary pressure gradient.This work investigates quantitatively the orientation of attached eddies in a turbulent boundary layer. This is achieved by maximising the two point correlation coefficient between the signals obtained from two normal hot-wires having a streamwise offset and a predetermined normal to the wall spacing between them. The experimental results will also be compared with some computational results based on the attached eddy hypothesis.
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ItemCone angles and Reynolds stresses in an adverse pressure gradient boundary layer( 1992)A comparison of the Reynolds stresses measured with a stationary and flying hot-wire is made for flow in a turbulent boundary layer on a smooth wall with streamwise pressure gradient. A cone angle is defined, based on the p.d.f. of velocity vector angles for 90o X-wire. From these measurements it is possible to evaluate the conditions under which a stationary X-wire will give erroneous estimates of the Reynolds stresses in fields of strong turbulence intensities. The response of the Reynolds stresses to the application of an adverse pressure gradient is discussed.
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ItemA comparative study of the spectra of turbulent jets and boundary layers at high wavenumbers( 1994)This paper describes measurements of spectra taken in a coflowing jet and in a boundary layer with zero streamwise pressure gradient. The spectra are compared to examine universality of the small scales and to examine the scaling laws of Kolmogorov. Comparisons are also used to examine differences in the distribution of the Reynolds shear-stress spectra in wavenumber space between the two flows and these experimental observations are explained in terms of models for the turbulence structure which have been developed by the authors for each of these flows.
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ItemSimilarity predictions based on the attached eddy hypothesis in turbulent boundary layers( 1995)The paper presents a similarity formulation for the streamwise component of the fluctuating velocity u1 in a turbulent boundary layer based on the attached eddy model of wall turbulence being developed at the University of Melbourne by Perry and co-workers. The consequences of this formulation for increasing Reynolds numbers is tested against recent high Reynolds number data. The model is based on the assumption that there exist eddies of different length scales in a turbulent boundary layer and the probability density function (p.d.f.) of the eddy length scale distribution follows an inverse power law for eddies in the turbulent wall region. Such a distribution is necessary to obtain a log-law of the mean velocity: the spectral scaling laws provide indirect evidence for this. In this paper the results from a template matching technique will be presented which gives further support for the proposition of an inverse power law p.d.f. of attached eddy length scales.
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ItemSimilarity laws and attached eddy shapes in turbulent boundary layers( 1995)This paper presents a similarity formulation for the streamwise component of the fluctuating velocity u1 in a turbulent boundary layer based on the attached eddy model of wall turbulence being developed at the University of Melbourne by Perry and co-workers. The consequences of this formulation for increasing Reynolds numbers is tested against recent high Reynolds number data. The model is based on the assumption that there exist eddies of different length scales in a turbulent boundary layer and the probability density function (p.d.f.) of the eddy length scale distribution follows a -1 power law for eddies in the turbulent wall region. Such a distribution is necessary to obtain the log-law of the mean velocity: the spectral scaling laws provide indirect evidence of this. In this paper the results from a template matching technique will be presented which gives further support for the proposition of a -1 power law p.d.f. of attached eddy length scales.Using space time correlation coefficients further details can be obtained regarding eddy shape. The simple II-shaped representative eddy needs to be modified to give reasonable correlation coefficients.