Applied Scientific Research

In this paper experimental results are given concerning stationary heat and mass transfer in the laminar boundary layer of a vertical cylinder placed in still air. The combined effect is considered as well as the two separate effects. Measurements are carried out on heat transfer and evaporation of water. Results are in close agreement with the classical free convection boundary layer theory for a vertical flat plate, if only a small cylinder correction is applied.

Experimental evidence is presented to support Brinkman's modification of Darcy's law for fluid flow through porous media. The results of the measurements performed are in close accordance with the prediction from theory.

It is shown that breakdown of insulating or dielectric material may be caused either by polarizable particles or permanent dipoles. Induced dipoles as well as permanent dipoles may gather at a place of maximum stress and form a bridge. Bridges consisting of permanent dipoles may cause the gap between the valence energy band and the conduction energy band to be filled by impurity or imperfection levels. The low ionization potentials of electrons attached to permanent dipoles may facilitate breakdown. An attempt is made to reconcile Crowe's results with ours.

This paper carefully investigates the precise role of internal damping on the whirling motion of an elastic shaft. Damping is introduced through a measured stress-strain law. The equations of motion are studied on an analog computer. It is shown that material damping tends to destabilize the motion.

Turbulent flow over variably-shaped rough walls, characterized by either a regular or a random arrangement of axisymmetric roughness elements in an open channel flow configuration, is investigated computationally within a VLES (Very Large Eddy Simulation) framework by utilizing a volumetric forcing-based roughness model. The prime objective of the present work is to assess the roughness model’s capability to predict mean velocities and turbulent intensities in conjunction with this recently formulated hybrid LES/RANS (Reynolds-Averaged Navier-Stokes) model. The friction velocity-based Reynolds number is in the range Reτ = 460 − 500. A non-dimensional drag function accounting for the shape of the roughness elements is introduced and evaluated based on the results of complementary direct numerical simulations (DNS). The dynamics of the residual motion of the presently adopted VLES methodology is described by an appropriately modified elliptic-relaxation-based ζ − f ( $\zeta =\overline {v^{2}}/k$ ) RANS model.

Motivated by the sizable increase of available computing resources, large-eddy simulation of complex turbulent flow is becoming increasingly popular. The underlying filtering operation of this approach enables to represent only large-scale motions. However, the small-scale fluctuations and their effects on the resolved flow field require additional modeling. As a consequence, the assumptions made in the closure formulations become potential sources of incertitude that can impact the quantities of interest. The objective of this work is to introduce a framework for the systematic estimation of structural uncertainty in large-eddy simulation closures. In particular, the methodology proposed is independent of the initial model form, computationally efficient, and suitable to general flow solvers. The approach is based on introducing controlled perturbations to the turbulent stress tensor in terms of magnitude, shape and orientation, such that propagation of their effects can be assessed. The framework is rigorously described, and physically plausible bounds for the perturbations are proposed. As a means to test its performance, a comprehensive set of numerical experiments are reported for which physical interpretation of the deviations in the quantities of interest are discussed.

Chúng tôi mô tả các bài trình bày tại hội nghị/ hội thảo quốc tế về sự Trộn lẫn trong Các dòng địa vật lý diễn ra tại Vilanova i la Geltru, gần Barcelona từ ngày 20 đến 22 tháng 3 năm 1997. Có hơn 100 người tham dự từ 20 quốc gia với 66 bài thuyết trình bằng miệng và poster, bao gồm các khía cạnh thực nghiệm và lý thuyết về các chất lỏng quay và phân lớp cũng như các quan sát thực địa. Các chủ đề chính được thảo luận tại hội thảo bao gồm các dòng phân lớp, các dòng phân lớp quay, sóng trọng lực, sự không ổn định và sự trộn lẫn, đối lưu, thí nghiệm và mô phỏng số trong các dòng địa vật lý và sự trộn lẫn hỗn loạn. Các bài báo được tóm tắt trong báo cáo này, cung cấp cái nhìn tổng quát về các nghiên cứu hiện tại trong lĩnh vực trộn lẫn hỗn loạn địa vật lý.

Relations have been derived for the frictional resistance of finite discs and cones rotating in Ostwald-de Waele (power-law) type non-Newtonian fluids. The obtained equations can be formulated as dimensionless relations between the dimensionless moment coefficient and the generalized Reynolds number; the flow-behaviour index n enters the equations as a parameter. The relations derived for cones contain the apex angle 2α0 as an additional parameter in the form of A=sin α0. The validity of the theoretically derived relations has been verified by measurements of the torque of discs and cones for a number of pseudoplastic power-law fluids.