Mechanical Engineering - Research Publications
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemA wall-wake model for the turbulence structure of boundary layers. Part 1. Extension of the attached eddy hypothesis(Cambridge University Press, 1995)The attached eddy hypothesis developed for zero pressure gradient boundary layers and for pipe flow is extended here to boundary layers with arbitary streamwise pressure gradients, both favourable and adverse. It is found that in order to obtain the correct quantitative results for all components of the Reynolds stresses, two basiv types of eddy structure geometries are required. The first type, called type-A, is interpreted to give a 'wall structure' and the second, referred to as type-B, gives a 'wake structure'. This is an 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. This is done by using the momentum equation and certain convolution integrals developed here based on the attached eddy hypothesis. The theory is developed using data from equilibrium and quasi-equilibrium flows. In Part 2 the authors' non-equilibrium data are used.
-
ItemSome predictions of the attached eddy model for a high Reynolds number boundary layer(Royal Society Publishing, 2007-01)Many flows of practical interest occur at high Reynolds number, at which the flow inmost of the boundary layer is turbulent, showing apparently random fluctuations invelocity across a wide range of scales. The range of scales over which these fluctuationsoccur increases with the Reynolds number and hence high Reynolds number flows aredifficult to compute or predict. In this paper, we discuss the structure of these flows anddescribe a physical model, based on the attached eddy hypothesis, which makespredictions for the statistical properties of these flows and their variation with Reynoldsnumber. The predictions are shown to compare well with the results from recentexperiments in a new purpose-built high Reynolds number facility. The model is alsoshown to provide a clear physical explanation for the trends in the data. The limits ofapplicability of the model are also discussed.
-
ItemNew evolution equations for turbulent boundary layers in arbitrary pressure gradients(Indian Academy of Sciences, 1998)A new approach to the classical closure problem for turbulent boundary layers is presented. This involves using the well-known mean-flow 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 non-equilibrium 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.
-
ItemTurbulence intensity similarity laws for turbulent boundary layers(SPRINGER, 2004-01-01)