ANSYS FLUENT 12.0 Theory Guide - 4.2.3 Boussinesq …
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.