Sharif Digital Repository

Grain geometry is an important factor affecting the stability envelop of solid rocket motors. This paper presents a series of subscale tactical motor firings, clearly showing the effect of combustion chamber internal geometry on stability. Three types of grain cartridges were used in these motors: a circular perforation (CP) and two variations of a seven-pointed star. Combination of these three basic grains produced motors that have completely different internal geometries. A polyurethane-based 81% solids composite propellant was used in all tests. This marginally stable propellant has a nominal burning rate of 7.1 mm/s for the metalized formulation that contains 7% aluminum powder and 5.7... 

The equalizing wake flow into the propeller behind the ship is important from the hydrodynamic performance viewpoint. In this study, numerical simulations of the DTMB4119 propeller with two symmetric and asymmetric duct types behind the KRISO Container Ship (KCS) are performed using Computational Fluid Dynamics (CFD). In order to improve the wake equaling flow, a combined duct and stators' configurations are installed before the propeller in the stern of the ship and its hydrodynamic performance is studied using CFD. A duct with the NACA4415 section and two types of stator configurations are selected. The STAR-CCM+ software using the finite volume discretization method was used to solve the... 

Fin stabilizers are very important device for controlling the ship roll motion against the external moments due to wave. This paper presents numerical results for flow field simulation and the hydrodynamic performance of fin stabilizer attached to a ship hull with free surface effects. Combination of CFD and RANS method has been used for this study. The fin is nonrectangular NACA0015 profile section with a finite aspect ratio. The numerical results include pressure distributions and flow field around the fin which are used to calculate lift coefficients and free surface elevation as the main interest. Some results are compared with available experimental and numerical data in literature and... 

In this article, the flow field around NACA0024 airfoil with step at lower and upper surfaces is experimentally investigated. For this purpose, particle image velocimetry technique based on the instantaneous flow structures is used to investigate the flow field around the airfoil at different times. All the experimental measurements in current study are conducted at very low Reynolds number condition based on the chord of the airfoil (Re=2000) and at angles of attack at 0° and 5° where the flow around airfoils is separated. The differences between vortical structures, mean streamlines, sizes of the wake regions, and vortex shedding of the stepped airfoils compared to unmodified airfoil are...