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In the current study, simulations of hydrodynamic characteristics of a propeller under different geometrical and physical characteristics are conducted by the computational fluid dynamic (CFD). Then, by designing appropriate artificial neural networks (ANNs), the hydrodynamic performance and cavitation volume of propellers are predicted under intended conditions. For this accomplishment, finite volume-based Navier-Stokes equations associated with incompressible large eddy simulation turbulence model are used. In order to verify the computational procedure, mesh sensitivity analysis and validation study are conducted and appropriate accuracy is observed. In the CFD simulations, propeller thrust, torque and cavitation volume are computed under different pitch ratio (P/D), rake angle (RA) and skew angle (SA), advance velocity ratio (J) and cavitation number (σ). By the CFD results, a significant increase in propeller thrust and torque is observable by enhancement of P/D and positive value of RA. Moreover, maximum mean square errors of ANNs output in the prediction of propeller thrust, torque and cavitation volume achieved are 0.000111, 7.4206E−5 and 0.000667, respectively. Also, related to ANNs' weights and bias, four set of equations are proposed to predict the performance and cavitation volume of propellers.

In the present paper, the energy gradient method is implemented to study the instability of 2-D laminar backward-facing step (BFS) flow under different Reynolds numbers and expansion ratios. For this purpose, six different Reynolds numbers (50 ≤ Re ≤ 1000) and two various expansion ratios of 1.9423 and 3 are considered. We compared our results of the present study with existing experimental and numerical data and good agreement is achieved. To study of fluid flow instability, we evaluated the distributions of velocity, vorticity and energy gradient function K. The results of our study show that as the expansion ratio decreases the flow becomes more stable. We also found that the origin of instability in the entire flow field is located on the separated shear layer nearby the step edge. In addition, we approved that the inflection point on the profile of velocity corresponds to the maximum of vorticity resulted to the instability.

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