Journal of Aerospace Science and Technology
Volume:3 Issue: 1, Spring 2006

An extensive experimental study is conducted to examine effects of different winglet-shapes and orientations on the vortex behind a wing, static surface pressure over the wing, and wing wake of a swept wing at various angles of attack. Four types of winglets, spiroid (forward and aft), blended, and winggrid are used in this investigation. Wing static surface pressure measurements are obtained for both chordwise and spanwise, as well as the wake profiles at various angles of attack using the aforementioned winglets. The data are compared with those of the wing without winglet, bare wing. The results show that addition of winglets change the flowfield over and around the wing significantly. Furthermore, it is found that certain winglet configurations improve both the wake and the wing pressure distribution. The total pressure in the wake of the model varies drastically when the wing is equipped with winglets. Keywords: Winglets, Pressure Distribution, Induced Drag, Spiroid Winglet, Turbulator.

The present study is devoted to an approximate modeling for numerical simulation of flows past oscillating airfoils. In this study, it is shown that the harmonic oscillating objects can be studied by simple numerical codes that are not able to solve moving grids. Instead of using moving grid for the simulation of flowfield around an oscillating airfoil, this unsteady flow is solved on a fixed grid having oscillated its free stream velocity vector on the boundaries. It is shown that, with a time shift, resulting airfoil forces have a good agreement with moving grid results. This time shift, which is not noted by others, is the time that takes for the flow to move from upstream boundary and pass the airfoil completely. Resulting - ellipse diameter using this approximate modeling, is only a little bigger than the experimental results. This modeling is applicable in simple codes that are not able to model moving grids.

In this paper application of a simulation algorithm for dynamic and nonlinear analysis of a specific liquid propellant engine is presented. The mathematical model of the engine includes a set of nonlinear algebraic equations which is coupled with a set of time varying differential equations. In contrast to the existing liquid propellant simulation algorithms, the presented work does not depend on the method of modeling. The simulation algorithm is composed of six primary steps. Comparison of the nominal values obtained from simulation with actual designed values is presented. Typical simulation outputs of primary engine variables are also given. The results of this study are used in the initial and conceptual design stages in order to advance to the other design stages.

The contribution of this paper to the space transportation system field is to select promising Reusable Launch Vehicle (RLV) concepts by using a formal evaluation procedure. The vehicle system is divided into design features. Every design feature can have alternative characteristics. All combinations of design features and characteristics are compared pairwise with each other. The innovation and novelty of this evaluation procedure is to assess these characteristics with respect to relative importance for a feasible vehicle concept as seen from technical, economic and political aspects. This valuation process leads to a ranked list of design features for suborbital and orbital applications. The result is a theoretical optimized suborbital and orbital vehicle each. The method of pairwise comparison allows to determine not only ranking but also assessing the relative weight of each feature compared to others.

Turbulent flow over wall-mounted cube in a channel was investigated numerically using Large Eddy Simulation. The Selective Structure Function model was used to determine eddy viscosity that appeared in the subgrid scale stress terms in momentum equations. Studies were carried out for the flows with Reynolds number ranging from 1000 to 40000. To evaluate the computational results, data was compared with experimental results at Re=40000, showing a good correspondence. In this study the effect of Reynolds numbers on flow characteristics such as time-averaged streamlines, turbulent intensity and Reynolds stresses were investigated. Results of computations show that the flow with higher Reynolds number has a shorter reattachment length and by increasing the Reynolds number, the number of horseshoe vortex in the upstream decreases. The vortex structures were similar in the upstream of the cube for time-averaged and instantaneous flow field. While on the downstream, the vortex structure does not show any similarity and had complex flow field structure. Reynolds stress was became stronger at the sides of the cube where the horseshoe vortexes were built and it''s become more significant at the higher Reynolds number.