between "Boussinesq's Hypothesis" and ..

Abstract:

Propellants are materials having high energy content which can undergo combustion and sustain it in the absence of an ambient oxidizer. Propellants are used in space propulsion systems, guns, automobile air bags and ejection seats of airplanes where generation of high pressure within a very short time is necessary. To make sure that the above mentioned devices are well designed, it is essential to select an appropriate propellant for the particular application under consideration. In addition, it is also essential that the burning characteristics of the selected propellant are understood properly. For example, if a solid propellant is used in a rocket booster, thorough information must be available of its burn rate and specific impulse for the specified operating conditions. The combustion phenomena of a propellant are complex and involve different processes including, among others, decomposition, oxidation, phase conversion, species diffusion, etc. Most of the propellants used in practical applications contain two or more ingredients. Research presented in this seminar is directed towards enhancing the knowledge of combustion behavior of the widely used RDX propellant and that of the high-nitrogen compounds which can be potentially used as propellant additives. These compounds are triaminoguanidinium azotetrazolate (TAGzT) and guanidinium5-aminotetrazole (GA). In first part of this research a detailed model of steady-state combustion of a pseudo-propellant containing cyclotrimethylene trinitramine (RDX) and triaminoguanidinium azotetrazolate (TAGzT) is presented. To improve the predictive capability of such models, it is essential to understand the liquid-phase decomposition chemistry of propellants and their additives. Hence in the second part, the decomposition of liquid-phase RDX was studied using FTIR spectroscopy. Finally in the third part, a detailed reaction mechanism of the decomposition of the high-nitrogen compound guanidinium 5-amino tetrazolate (GA) in the liquid phase is formulated. This compound is chosen because it has a simpler molecular structure as compared to TAGzT.

ANSYS FLUENT 12.0 Theory Guide - 4.2.3 Boussinesq …

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The Boussinesq approximation - IITK

The pressure losses across multiple interactive and individual in-duct fittings are compared (see ). In , the pressure losses across interactive fittings for Cases 7–15 are directly measured in the tests. In order to evaluate the effect of the fittings' interaction on the total pressure loss, for each case, the pressure losses across every individual fitting are summed for comparison. Taking Case 8 as an example, the pressure losses across its individual fittings are summed from Case 1 and Case 2. Based on the summations of individual pressure loss, the percentage decreases in pressure losses across multiple fittings are calculated. It can be seen that the pressure losses across multiple interactive fittings are lower than those across multiple individual fittings, and the percentage decrease is dependent on the configuration and combination of the fittings. This finding is supported by the previous study on two bends by Rahmeyer []. Again, this demonstrates that the calculation of pressure losses across multiple closely mounted fittings via summing those across individual fittings is inaccurate. This method overpredicts the total pressure loss, which may consequently result in energy waste owing to the selection of larger fans. In such a condition, exploring an accurate, reliable, and high-efficiency predictive method, such as a validated CFD model, is crucially important.

employs the Boussinesq hypothesis) ..

This article reports on heat transfer measurements made on a rotating test rig representing the internal disc-cone cavity of a gas turbine high-pressure (H.P.) compressor stack. Tests were carried out for a range of flow rates and rotational speeds at engine representative nondimensional conditions. The rig also had a central drive shaft, which could rotate in the same direction as the discs, contrarotate relative to the discs, or remain static. Measurements of heat transfer were obtained from a conduction solution method using measured surface temperatures as boundary conditions. Results from the outer surface of the cone are in reasonable agreement with theoretical predictions for the heat transfer from a free cone in turbulent flow. The heat transfer measurements from the inner surface of the cone reveal two regimes of heat transfer: one governed by rotation, the other by action of the throughflow. In the rotationally dominated regime, the heat transfer from the inner surface of the cone is higher for a co-rotating shaft than for either a static or contra-rotating shaft. In the throughflow-dominated regime the heat transfer shows little consistent dependence on the direction of shaft rotation. Tests carried out at different values of surface-to-fluid temperature difference add support to the hypothesis that in the rotationally dominated regime the heat transfer occurs through a process of free convection, where the buoyancy force is induced by rotation. The heat transfer from the disc is significantly lower than that from the inner surface of the cone and more or less insensitive to the sense of shaft rotation. The disc average Nusselt numbers show similar behavior to those from the inner surface of the cone and suggest that the disc heat transfer too is governed either by rotationally induced buoyancy or by the axial throughflow.

Indeed, there are well-known deficiencies of the widely used eddy viscosity turbulence models based on the applied Boussinesq hypothesis.
The Boussinesq hypothesis is used in the Spalart-Allmaras model, the - models, and the - models

is resolved through the hypothesis of Boussinesq: (3) ..

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Boussinesq hypothesis • Many turbulence models are based upon the Boussinesq hypothesis

Boussinesq eddy viscosity hypothesis

He argued that a phenomenon is explained when we can see that it is the logical consequence of a law of nature. He championed a hypothetico-deductive account of confirmation, similar to the way we characterize making a scientific argument in this website. Karl Popper (1924-1994) #151; Argued that falsifiability is both the hallmark of scientific theories and the proper methodology for scientists to employ. He believed that scientists should always regard their theories with a skeptical eye, seeking every opportunity to try to falsify them. Thomas Kuhn (1922-1996) #151; Historian and philosopher who argued that the picture of science developed by logical empiricists such as Popper didn't resemble the history of science. Kuhn famously distinguished between normal science, where scientists solve puzzles within a particular framework or paradigm, and revolutionary science, when the paradigm gets overturned. Paul Feyerabend (1924-1994) #151; A rebel within the philosophy of science.

(Boussinesq’s hypothesis), thus the fluid flow characteristics are affected by the buoyancy force

Boussinesq Approximation - ResearchGate

Advances in the development and application of computational fluid dynamics (CFD) to gas turbine internal air systems are discussed in this paper. It is shown that the combination of parallel computation, using powerful PC clusters, with relatively robust and flexible CFD solvers is now having considerable impact in industry. At the same time research studies demonstrate that capability continues to expand. Examples are given of 3D, steady and unsteady industrial applications, with discussions of computing times on PC clusters using both ethernet and myrinet network connections. Integration of CFD into the design process is also considered. Research studies, centring on model validation and methods improvement are also illustrated and discussed, with inclusion of very recent work using a 32 processor cluster with fast myrinet networking.