FLUID MECHANICS AND AERODYNAMICS JOURNAL
Year:2017 | Volume:6 | Issue:1 (19) |Papers Count:6

Main difference between planning vessels, conventional displacement, and semi-displacement marine vessels is in their utilization hydrodynamic loads in addition to buoyancy force. The hydrodynamic pressure field on the bottom surface of planning vessels decreases the vessel draught and the thereafter their resistance. The resistance reduction introduces achieving higher speeds. One of the methods for improving hydrodynamic efficiency of planning vessels is utilization of transverse steps under their bottoms. Selecting their locations and heights has high sensitivity to loading conditions, speed, and center of gravity of the vessel. If proper design does not occur, it maybe followed by un-favorite effects. In this research, the flow field over the bottom of two stepped high speed planning vessels at different lading conditions were obtained, using CFD. VOF method was used for capturing the interface between water and air. Simulation was performed for one-step and two-step planning vessels of Cigar. For validating of the simulations, a grid-independency study and some comparisons with experiments are carried out. The emphasis of this study was on identification of the sensitivity of loading conditions on air-breathing of the transverse steps. The results show that the sensitivity is much higher than the traditional non-stepped planning vessels.

In this study, mixed convection of a water-Al2O3 nanofluid was numerically investigated in an open square cavity. All cavity walls were insulated and a solid body heat source was placed at the center of the cavity. The nanofluid enters the cavity with uniform velocity and temperature and leaves it as a fully developed flow. The governing equations were discretized using finite volume method and using Patankar’s SIMPLE algorithm. The effects of relevant parameters, such as Reynolds and Richardson numbers, length ratio (The ratio of the heat source length to the length of the cavity), the source thermal conductivity, and solid volume fraction of the nanoparticles were examined, both from flow field and the heat transfer rate considerations. The results show that the average Nusselt number increases with increase in Reynolds and Richardson numbers. A change in length ratio changes the flow and temperature fields. In addition, Increase of heat source thermal conductivity increases the average Nusselt number. The results also show that thermal performance of cavity is enhanced by increasing solid volume fraction of the nanoparticles.

In this article, a comprehensive procedure is proposed to calculate the stability derivatives of a NACA0012 airfoil by means of wind tunnel test and computational fluid dynamics (CFD). To accomplish maneuverability study and dynamic analysis of the flight vehicle, these derivatives were obtained finding the body aerodynamic responses to some specified time variant motions. Here, on the basis of linearized equations of motion, in which the aerodynamic coefficients appear explicitly, two distinct oscillating maneuvers were considered: plunging and fish-like oscillating motion. To obtain the aerodynamic responses of the moving airfoil, a CFD method based on Reynolds Averaged Navier–Stokes (RANS) equations was used with dynamic mesh technique to simulate the specified maneuvers. The computational results were then validated comparing the wind tunnel tests data of the plunging maneuver. Afterwards, the aerodynamic coefficients were calculated using the resulting loads. Finally, the effects of oscillating motion parameters variations on these coefficients are investigated, which shows that dimensionless coefficients are dependent on the oscillations amplitude and frequency. However, they are independent of the Strouhal number in the studied range.

In this work, the problem of designing a hypersonic vehicle with high lift-drag ratio in hypersonic rarefied regimes is investigated. At high altitudes, the assumption of continuity employed in the Navier Stocks equations is no longer true and is not possible to simulate the problem with conventional CFD routines. The Direct Simulation of Monte Carlo (DSMC) which is a particle-based method was employed to simulate the hypersonic rarefied regimes of hypersonic vehicles. In the first step, based on momentum theory, a simple definition for increasing aerodynamic efficiency was provided. According to this definition, a two-dimensional body under considerations of hypersonic-rarefied flow regimes was analyzed using the DSMC code of DS2V. According to the facts obtained from this analysis, we considered a typical three-dimensional body, and developed the configurations of high aerodynamic efficiencies. The simulations were conducted in three-dimensional space by the DSMC program of DS3V showed that the above-mentioned definition is applicable to three-dimensional geometries. Finally, based on authenticated definitions, we exemplified a three-dimensional body, which is capable to produce high aerodynamic efficiencies in hypersonic regimes at high altitudes.

In this paper, a numerical study of a 2-D combined convection-radiation heat transfer in a horizontal rectangular duct with two sudden contractions is presented. Contractions in duct are created by two inclined forward facing steps. To simulate the incline surfaces of the FFS, the blocked- off method was employed for both fluid mechanic and radiation problems. The fluid was treated as a gray, absorbing, emitting and scattering medium. To solve the governing equations, the 2-D Cartesian coordinate system was used. These equations were solved numerically, using the CFD techniques and SIMPLE algorithm. For computation of radiative term in energy equation, the radiative transfer equation (RTE) was solved numerically by discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution. The effects of optical thickness, radiation-conduction parameter and albedo coefficient on heat transfer behavior of the system were carried out. Comparison of numerical results with available credential data shows good consistency.

This paper presents molecular dynamics modeling for calculating viscosity of nanofluids containing copper nanoparticles. In the first case, the copper nanoparticles were located as a spherical region in water-based fluid module SPC. System under specified boundary conditions, and writing code by LAMMPS software, and nanofluid ratios of 3.2, 4.4, 6.9 and 9.1 percented by Brownian motion of atoms, was carried out. three popular potential function, Lennard-Jones, Coulomb, and embedded atom method were used. Between equilibrium molecule dynamic, and non- equilibrium molecule dynamic, (EMD) and Green-kubo formula were used to calculate viscosity. The results show that by increasing the amount of voloume fraction, viscosity increases. nanofluids in addition to other factors, such as volume fraction of particles in Brownian motion and clustering phenomenon, each in turn causes changes in viscosity. The simulation results were compared with other's works and found that the obtained results are remarkably accurate.