We use the commercial computational fluid dynamics code Fluent to simulate the flow around a sphere in several different flow regimes; steady-state laminar flow at a Reynolds number (Re) of 100, time-dependent laminar flow at Re = 300, and turbulent flow at Re = 10 to the 4th and Re = 10 to the 6th. These simulations provide a test of the ability of the code to accurately reproduce typical flow structures observed in generic bluff body flows, such as those experienced by submarines and Unmanned Underwater Vehicles (UUVs). The simulations are compared both with experimental results and computations from other computer codes and it is found that Fluent is able to accurately simulate the fluid behaviour in each of the above flow regimes.
The use of Computational Fluid Dynamics (CFD) codes to simulate the flow around geometrically complicated shapes such as aeroplanes, cars and ships has become standard engineering practice in the last few years. The computer code Fluent is a commercial CFD code which is used routinely by members of the Hydrodynamics Group within DSTO's Maritime Platforms Division (MPD) to simulate flows relevant to underwater vehicle design and surface ship wakes. In this report we test the ability of the code to accurately simulate the flow around a sphere over a large range of Reynolds numbers (Re). This is a stringent test of the code as it involves a number of very different flow regimes, varying from laminar steady-state flow near Re = 100 to time-dependent turbulent flow at Re = 10 to the 6th. These simulations are also intended to provide a benchmark comparison for the finite difference CFD code Vortel, currently under development at Naval Underwater Warfare Center, Newport, Rhode Island in collaboration with researchers at MPD. Vortel is based on the Lagrangian Vorticity method and offers advantages over commercial CFD codes for the simulation of flow around multiple bodies in relative motion. It has already been used to simulate unmanned undersea vehicle docking manoeuvres, as well as unsteady bow thruster hydrodynamics and the unsteady separated flow fields past an oscillating airfoil. Four different flow regimes are studied in detail: steady-state laminar flow at Re = 100, time-dependent laminar flow at Re = 300, turbulent flow with laminar boundary layers at Re = 10 to the 4th and turbulent flow with turbulent boundary layers at Re = 10 to the 6th. The simulated flows were found to be in excellent agreement with both experimental results, where available, and with the results obtained by other authors using different simulation codes. The simulations described in this report illustrate the capability of the Fluent code to accurately reproduce typical flow structures observed on this generic bluff body flow for both time independent/time-dependent and laminar/turbulent flow regimes.
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