 Mechanical Engineering  Research Publications
Mechanical Engineering  Research Publications
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ItemA study of the Reynoldsshearstress spectra in zero pressuregradient boundary layersMarusic, I. ; Li, J. D. ; Perry, A. E. ( 1989)Measurements of Reynoldsshearstress spectra in smoothwall zeropressuregradient turbulent boundary layers are presented for four different Karman numbers. The results are plotted using various scaling variables and found to collapse with 'innerflow' scaling for a modest range of midrange 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 crosspower spectra, based upon the same theory, is also presented.

ItemAn experimental and computational study on the orientation of attached eddies in turbulent boundary layersPerry, A. E. ; Uddin, A. K. M. ; Marusic, I. ( 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 hotwires 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.

ItemCone angles and Reynolds stresses in an adverse pressure gradient boundary layerMarusic, I. ; Perry, A. E. ( 1992)A comparison of the Reynolds stresses measured with a stationary and flying hotwire 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 Xwire. From these measurements it is possible to evaluate the conditions under which a stationary Xwire 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.

ItemA comparative study of the spectra of turbulent jets and boundary layers at high wavenumbersMarusic, I. ; Nickels, T. B. ; Perry, A. E. ( 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 shearstress 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.

ItemSimilarity predictions based on the attached eddy hypothesis in turbulent boundary layersUddin, A. K. M. ; Perry, A. E. ; Marusic, I. ( 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 coworkers. 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 loglaw 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.

ItemSimilarity laws and attached eddy shapes in turbulent boundary layersPerry, A. E. ; Uddin, A. K. M. ; Marusic, I. ( 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 coworkers. 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 loglaw 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 IIshaped representative eddy needs to be modified to give reasonable correlation coefficients.

ItemA wallwake model for turbulent boundary layers with pressure gradientsMarusic, I. ; Perry, A. E. ( 1995)The attached eddy hypothesis is considered here for boundary layers with arbitrary streamwise pressure gradients. It is found that in order to obtain the correct quantitative results for all components of the Reynolds stresses, two basic types of eddy structure geometries are required. The first type, called typeA, is interpreted to give a "wall structure" and the second referred to as typeB gives a "wake structure". This is in analogy with the conventional mean velocity formulation of Coles where the velocity is decomposed into a law of the wall and a law of the wake. If the above mean velocity formulation is accepted then in principle, once the eddy geometries are fixed for the two eddy types, all Reynolds stresses and associated spectra contributed from the attached eddies can be computed without any further empirical constants.

ItemApplication of the wavelet transform in turbulenceUddin, A. K. M. ; Perry, A. E. ; Marusic, I. ( 1997)Traditionally, Fourier transforms have been used to elicit the scalebased behaviour of the turbulent motion and one speaks synonymously of its wavenumber components with scales (large scales are associated with small wavenumbers and viceversa). Although, this approach is theoretically correct, many workers have questioned its appropriateness on the grounds that a Fourier mode represents a wave like disturbance which is global in the physical domain, whereas an eddy is a disturbance with finite spatial extent. Consequently, a more appropriate scheme should involve a local decomposition of the velocity field which is more reminiscent of eddy like phenomena. In this paper we have explored the feasibility of the wavelet transform as an analyzing tool in deducing the turbulence spectrum.

ItemApplication of the attached eddy hypothesis for the evolution of turbulent boundary layersMarusic, I. ; Perry, A. E. ( 1997)The wallwake attached eddy model of Perry & Marusic [1] is incorporated in a new approach to the classic closure problem for turbulent boundary layers recently proposed by Perry, Marusic & Jones [2]. This involves using the well known meanflow scaling laws such as Prandtl's law of the wall and the law of the wake of Coles together with the mean continuity and the mean momentum differential and integral equations. The important parameters governing the flow in the general nonequilibrium case are identified and are used for establishing a framework for closure.

ItemEvidence of the 1law in a high Reynolds number turbulent boundary layerNickels, T. B. ; Hafez, S. ; Marusic, I. ; Chong, M. S. ( 2004)Dimensional analysis leads to a prediction of a 1powerlawfor the streamwise velocity spectrum in a turbulent boundarylayer. This law can be derived from overlap arguments or fromphysical arguments based on the attached eddy hypothesis ofTownsend (1976). Some recent experiments have questionedthe existence of this powerlaw region in wallbounded ows.In this paper experimental spectra are presented which supportthe existence of the 1law in a high Reynolds number boundarylayer, measured in the large boundary layer facility in theWalterBasset laboratory at the University of Melbourne. The paperpresents the experimental results and discusses the theoreticaland experimental issues involved in examining the existence ofthe 1law and reasons why it has proved so elusive.