@article { author = {Behrouzi, Parviz}, title = {LDA Experimental Data of Three-Poster Jet Impingement System}, journal = {Journal of Aerospace Science and Technology}, volume = {1}, number = {1}, pages = {1-8}, year = {2004}, publisher = {Iranian Aerospace Society}, issn = {1735-2134}, eissn = {2345-3648}, doi = {}, abstract = {During its near-ground hovering phase a Short Take-Off and Vertical Landing (STOVL) aircraft creates a complex three-dimensional flow field between jet streams, the airframe surface and the ground. A proper understanding and numerical prediction of this flow is important in the design of such aircraft. In this paper an experimental facility, used to gather validation data suitable for testing Computational Fluid Dynamics (CFD) model predictions of multi-jet ground impingement flows, is described. Water is used as the working medium and Laser Doppler Anemometry (LDA) measurements of three-poster impinging jet flow fields are reported. Emphasis is placed on the presentation of the mean and rms velocity contours in the fountain formation region between the jets. The effect of jet imbalance and splay-angle were studied. An overview were provided to guide users through the data and highlight several important flow features which have already emerged from the data and which are considered of importance to CFD model validation.}, keywords = {}, url = {https://jast.ias.ir/article_51477.html}, eprint = {https://jast.ias.ir/article_51477_257e07537654c0c4a22c86c5ced8da9c.pdf} } @article { author = {Suntivarakorn, Prapat and Matsuuchi, Kazuo}, title = {Numerical Investigation of Vortex Interaction in Pipe Flow}, journal = {Journal of Aerospace Science and Technology}, volume = {1}, number = {1}, pages = {9-15}, year = {2004}, publisher = {Iranian Aerospace Society}, issn = {1735-2134}, eissn = {2345-3648}, doi = {}, abstract = {To discover the nonlinear characteristics of pipe flow, we simulated the flow as a sum of many vortex rings. As a first step, we investigated the nonlinear interaction among a maximum of three vortex rings. The pipe wall was replaced by many bound vortices. A free vortex ring moves right or left according to the radius, and that of a particular radius keeps the initial position. The energy of a free vortex ring, except when it is close to a wall, coincides with that without boundaries. Two vortex rings of equal radii always show a repeated overtaking process. In the case of three vortex rings, they show a wide variety of behavior. For certain combinations of radii and the axial spaces among them, the motion, which seems to be very complex, is limited on a curved surface in three-dimensional space whose axes correspond to the three radii. It was found that this simplicity comes from the momentum conservation law, and also that its direction depends on the energy contribution calculated from free vortex rings. Our results elucidate the nonlinear behavior among many vortices.}, keywords = {}, url = {https://jast.ias.ir/article_51478.html}, eprint = {https://jast.ias.ir/article_51478_ad1b56423f8a19f3d3f94777de9c708f.pdf} } @article { author = {Ahmadi, Goodarz}, title = {Overview of Direct Numerical Simulation of Particle Entrainment in Turbulent Flows}, journal = {Journal of Aerospace Science and Technology}, volume = {1}, number = {1}, pages = {17-22}, year = {2004}, publisher = {Iranian Aerospace Society}, issn = {1735-2134}, eissn = {2345-3648}, doi = {}, abstract = {An overview of removal and re-entrainment of particles in turbulent flows is presented. The procedure for the direct numerical simulation (DNS) of the Navier-Stokes equation via a pseudospectral method for simulating the instantaneous fluid velocity field is described. Particle removal mechanisms in turbulent flows in a duct are examined and effects of the near-wall coherent eddies on the particle detachment and removal are discussed. The particle equation of motion, including the hydrodynamic drag and lift, as well as the Brownian and gravitational forces, are used in the analysis. The simulation results show that large size particles move away roughly perpendicular to the wall due to the action of the shear lift force. Small particles, however, follow the upward flows formed by the near wall eddies in the low speed streak regions. Thus, turbulent near wall eddies play an important role in small particle resuspension, while the lift force is an important factor for re-entrainment of large particles. The results also suggest that small particles primarily move away from the wall in the low speed streaks, while larger particles are mostly removed in the high-speed streaks.}, keywords = {}, url = {https://jast.ias.ir/article_51479.html}, eprint = {https://jast.ias.ir/article_51479_3930d749143428560c5f2323b197804e.pdf} } @article { author = {Daneshjou, Kamran and Alasty, Aria and Rezaei, Shahram}, title = {Orbital Perturbation Effect on LEO Satellite Trajectory}, journal = {Journal of Aerospace Science and Technology}, volume = {1}, number = {1}, pages = {23-29}, year = {2004}, publisher = {Iranian Aerospace Society}, issn = {1735-2134}, eissn = {2345-3648}, doi = {}, abstract = {A satellite, in its orbit, is affected by perturbing forces, such as atmospheric drag, solar radiation pressure, Earth oblateness, and gravity of the celestial masses (other than the Earth). In this paper, the effects of these forces on the trajectories of different types of LEO satellites and a sample satellite (Z-SAT) are discussed. A few analyses are done on these orbits and the relevant results are categorized as substantial logics of perturbation influences on Keplerian parameters of the orbits. The Variation of Parameters Method is used for analyses.}, keywords = {}, url = {https://jast.ias.ir/article_51480.html}, eprint = {https://jast.ias.ir/article_51480_ddb8430a3fa2da3637d4f4811009e146.pdf} } @article { author = {Atashbaz, G.}, title = {Experimental Investigation of Asymmetry of Vortex Flow Over Single Delta Wings}, journal = {Journal of Aerospace Science and Technology}, volume = {1}, number = {1}, pages = {31-39}, year = {2004}, publisher = {Iranian Aerospace Society}, issn = {1735-2134}, eissn = {2345-3648}, doi = {}, abstract = {It is generally believed that, on slender delta wings, there is a critical state at which strong asymmetric vortices are found along the leading edge on the lee-side of the delta wing. These asymmetric vortices can lead to high lateral forces even when slender delta wing is at the zero angle of yaw. Some experimental studies reported recently, cast considerable doubt as to the validity of the above explanations. A wind tunnel investigation was, therefore, performed to study afresh this phenomenon. The flow over four sharp edged delta wings with aspect to a ratio ranging of 0.56 to 1.46 was investigated using flow visualization with laser light sheet and some surface pressure as well as hot wire measurement. The tests were conducted for angles of attack ranging from 0 to 30 deg and at a free-stream velocity of 30m/s corresponding to a Reynolds number of $4.8 times10^{5}$ based on the center line chord of the wing. The results obtained suggest the absence of asymmetry in the vortex core position in the flow.}, keywords = {}, url = {https://jast.ias.ir/article_51481.html}, eprint = {https://jast.ias.ir/article_51481_ef27031f26360f9630e517cd222d13e4.pdf} }