 Mechanical Engineering  Research Publications
Mechanical Engineering  Research Publications
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ItemSimilarity law for the streamwise turbulence intensity in zeropressuregradient turbulent boundary layersMarusic, I. ; Uddin, A. K. M. ; Perry, A. E. ( 1997)A similarity relationship is proposed to describe the streamwise broadbandturbulence intensity in a zeropressuregradient boundary layer. The formulation is applicable to the entire region of the flow beyond the viscous buffer zone and is based on the attached eddy hypothesis, the Reynoldsnumbersimilarity hypothesis and the assumed existence of Kolmogorov eddies with a universal inertial subrange. Experimental data of the authors and those from various published works covering a large Reynolds number range are investigated in light of this formulation.

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.

ItemNew evolution equations for turbulent boundary layers in arbitrary pressure gradientsPerry, A. E. ; Marusic, I. ; Jones, M. B. ( 1997)A new approach at looking at the classic closure problem for turbulent boundary layers is presented. This involves using the well known meanflow scaling laws such as Prandtl's law of the wall and Coles' law of the wake together with the mean momentum integral and differential equations. The important parameters governing the flow in the general nonequilibrium case are identified and are used to formulate the closure hypothesis. Once the mean flow field has been determined, relevant turbulence quantities can be computed using a coherent structure eddy model based on the attached eddy hypothesis.

ItemOn the validity of Taylor's hypothesis in wall turbulenceUddin, A. K. Mesbah ; Perry, A. E. ; MARUSIC, IVAN ( 1997)The validity of Taylor’s hypothesis of frozen turbulence has been the issue of much debate, especially when applied to flows with strong shear and high turbulence intensities. In the past, Taylor’s hypothesis was used by various researchers for the quantitative interpretation of the structure angle of the eddies on the basis of doublevelocity correlations (eg. Alving et al. [1]) or velocitywall pressure or velocitywall shear stress correlations (e.g. Brown & Thomas [2] , Rajagopalan & Antonia [6]. In light of the ambiguity associated with Taylor’s hypothesis, naturally, there are resultant uncertainties in terms of the measured structure angle. Subsequently there is a need to investigate how do these uncertainties effect the structure angle measurements and as well as to examine the validity of Taylor’s hypothesis when applied to twopoint doublevelocity correlation measurements in an anisotropic shear flow.

ItemNew evolution equations for turbulent boundary layers in arbitrary pressure gradientsPerry, A. E. ; Marusic, I. ; Jones, M. B. (Indian Academy of Sciences, 1998)A new approach to the classical closure problem for turbulent boundary layers is presented. This involves using the wellknown 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. Initially, closure is done here empirically from the data but the framework is most suitable for applying the attached eddy hypothesis in future work. How this might be done is indicated here.