Modeling Complex Turbulent Flows


Book Description

Turbulence modeling both addresses a fundamental problem in physics, 'the last great unsolved problem of classical physics,' and has far-reaching importance in the solution of difficult practical problems from aeronautical engineering to dynamic meteorology. However, the growth of supercom puter facilities has recently caused an apparent shift in the focus of tur bulence research from modeling to direct numerical simulation (DNS) and large eddy simulation (LES). This shift in emphasis comes at a time when claims are being made in the world around us that scientific analysis itself will shortly be transformed or replaced by a more powerful 'paradigm' based on massive computations and sophisticated visualization. Although this viewpoint has not lacked ar ticulate and influential advocates, these claims can at best only be judged premature. After all, as one computational researcher lamented, 'the com puter only does what I tell it to do, and not what I want it to do. ' In turbulence research, the initial speculation that computational meth ods would replace not only model-based computations but even experimen tal measurements, have not come close to fulfillment. It is becoming clear that computational methods and model development are equal partners in turbulence research: DNS and LES remain valuable tools for suggesting and validating models, while turbulence models continue to be the preferred tool for practical computations. We believed that a symposium which would reaffirm the practical and scientific importance of turbulence modeling was both necessary and timely.










The Finding Guide to AIAA Meeting Papers


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Near-wall Measurements of a Three-dimensional Turbulent Boundary Layer


Book Description

In order to improve predictions of flow behavior in numerous applications there is a great need to understand the physics of three-dimensional turbulent boundary layers, dominated by near-wall behavior. To that end, an experiment was performed to measure near-wall velocity and Reynolds stress profiles in a pressure-driven three-dimensional turbulent boundary layer. The flow was achieved by placing a 30 deg wedge in a straight duct in a wind tunnel, with-additional pressure gradient control above the test surface. An initially two-dimensional boundary layer (Re approx. equal 4000) was exposed to a strong spanwise pressure gradient. At the furthest downstream measurement locations there was also a fairly strong favorable pressure gradient. Measurements were made using a specially-designed near-wall laser Doppler anemometer (LDA), in addition to conventional methods. The LDA used short focal length optics, a mirror probe suspended in the flow, and side-scatter collection to achieve a nearly spherical measuring volume approximately 35 microns in diameter. Good agreement with previous two-dimensional boundary layer data was achieved. The three-dimensional turbulent boundary layer data presented include mean velocity measurements and Reynolds stresses, all extending well below y(+) = 10, at several profile locations. Terms of the Reynolds stress transport equations are calculated at two profile locations. The mean flow is nearly collateral at the wall. Turbulent kinetic energy is mildly suppressed in the near-wall region and the shear stress components are strongly affected by three-dimensionality. As a result, the ratio of shear stress to turbulent kinetic energy is suppressed throughout most of the boundary layer. The angles of stress and strain are misaligned, except very near the wall (around y(+) = 10) where the angles nearly coincide with the mean flow angle.




Advances in Turbulence


Book Description

This book presents selected papers from the 12th edition of the Spring School of Transition and Turbulence which took place in 2020. The papers cover applications on a number of industrial processes, such as the automotive, aeronautics, chemicals, oil and gas, food, nanotechnology, and others. The readers find out research and applied works on the topics of aerodynamics, computational fluid dynamics, instrumentation and experiments, multi-phase flows, and theoretical and analytical modeling.




Turbulence in Open Channel Flows


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A review of open channel turbulence, focusing especially on certain features stemming from the presence of the free surface and the bed of a river. Part one presents the statistical theory of turbulence; Part two addresses the coherent structures in open-channel flows and boundary layers.










Physics Briefs


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