computational fluid dynamics

The emitted sound from ships is one of the most important sources of noise in the ocean, and the propeller sound is the main component of this sound. In this study, the numerical investigation of the functional sound level of a marine propeller has been carried out based on Computational Fluid Dynamics (CFD) and Fox Williams-Hawkings (FW-H) acoustic Analogy. In this research, in order to validate the solution method, first the fluid field around the DTMB4119 propeller was simulated, and then its sound pressure level compared with experimental results. Then the new propeller is numerically investigated. The acoustic performance of this propeller is evaluated in two permanent and non-permanent modes. First, a steady-state hydrodynamic simulation was created, and then the flow field is simulated by adopting the unsteady equations of Improved Delayed Detached Eddy Simulation (IDDES). According to the propeller diameter (D=2m), this simulation was done for the scale of the model, then ITTC87 equations are used to generalize the noise results to the actual size of the propeller. The sound level of the propeller is drawn at distances of 1 and 4 meters and at angles of 30, 60, 90, 120 and 150 degree and analyzed.

Practical employment of high angular velocity-centrifugal force field in nuclear industry, especially in separation of heavy isotopes in both industrial scale fuel production and laboratory practices, is obvious. Thermo-hydraulic differential equations of such a flow field due to ultra-high swirl velocity and also high compressibility of low mass content of gas injected into the system are very complicated and closely coupled. Thus, the analytical solution of these equations necessitates making a few assumptions. In this study, the numerical solution are conducted by the CFD approach and the finite volume method is used to evaluate assumptions of the analytical solution and to survey effects of removing these assumptions on the main variables of flow field. For this purpose, among available analytical methods to solve the governing equation, the one with the least possible assumptions is employed. The most important points in the procedure of conducting this solution are studied from the basic equations to the end and on this basis the assumptions are gathered under four titles. Then, the procedure of testing these assumptions in the FLUENT software is presented, which necessitates programming. Then the results are compared and validate by the results of the analytical method. In the next step, on the basis of consecutive elimination of the four assumptions, four different modes are defined. The novel and meaningful results obtained from the comparison of these four modes is the main incentive to present this article. This investigation, in addition to prove significant capabilities of the CFD approach for simulating this complicated flow field, clearly showed the reason of the long-term tendency toward this analytical analysis, despite its basic simplifying assumptions. Especially, with regard to the axial mass velocity due to contradictory and eliminating effect of consisting parameters.