Sharif Digital Repository

In the last decade, harvesting energy from renewable phenomena in nature has attracted the attention of many researchers and turned it into a hot research focus. Wind flow around the world is an endless, repeatable and available source of energy. Therefore, harvesting wind energy disrupts the damaging cycle of fossil fuels to nature and fades over time. Therefore, in order to convert the mechanical green energy in the wind into electricity, mechanisms based on aeroelastic instabilities have attracted the attention of researchers. In this research, it is intended to design and build a test platform that is a suitable platform for research and testing on the aeroelastic instability of... 

In this research, aeroelastic model of an elastic flapping wing has been derived in order to be integrated with the flight dynamic model. The model developed in this research well describes the coupled and nonlinear behavior of the passive torsional deformations of the wing during flapping motion. Based on this obtained equations, a precise propulsion model proper for flapping wing vehicles has been introduced. The effect of geometric and mechanical properties of the wing is being accounted. In order to validation of the analytical model several FMAVs as well as an instrumented test stand for online measurements of forces, flapping angle and power consumption have been designed and built... 

Thrust vector control as a method toward increasing of the aircrafts’ maneuverability and expanding the flight envelope into poor aerodynamic conditions, is considered a major field of academic and industrial appeal. Older methods based upon an approach of utilizing a mechanical instrument, impose quite a large amount of cost onto the design, prototyping and operation of the aircraft, even though they lead to improve in maneuverability. Having taken these setbacks into account, to simplify the manufacturing process and to reduce the thrust losses due to mechanical control of the thrust vector, the direction of research was set toward realizing and employing the flow control procedures. In... 

In the present study, the effect of the diffuser inlet-to-nozzle exit area ratio (A_d/A_e ) on the gradual starting performance of a second throat exhaust diffuser has been investigated experimentally. Experiments have been carried out with four conical nozzles with different expansion ratios and considering two approaches of gradual increase and gradual decrease of nozzle chamber pressure by a high-pressure air tank. Investigations show that at high area ratios before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as A_d/A_e... 

Depending on the geometry and nozzle pressure, increasing the ratio of the diffuser inlet area to the nozzle outlet area can lead to instability in the high-altitude simulator vacuum chamber startup process. This instability results in the formation of harmonic pressure oscillations throughout the diffuser and the vacuum chamber. In this study, a scaled down second throat diffuser with compressed air has been utilized. The performance of the diffuser has been investigated using four conical nozzles with different expansion ratios to simulate instability at area ratios of 1.27, 1.91, 4.1, and 7.81 with rapid nozzle pressure rise. Experiments were conducted by measuring wall pressures along...