There have been several advancements in the aerospace industry in areas of design such as aerodynamics, designs, controls and propulsion; all aimed at one common goal i.e. increasing efficiency-range and scope of operation with lesser fuel consumption. Several methods of flow control have been tried. Some were successful, some failed and many were termed as impractical. The low Reynolds number regime of 10 4-10 5 is a very interesting range. Flow physics in this range are quite different than those of higher Reynolds number range. Mid and high altitude UAV's, MAV's, sailplanes, jet engine fan blades, inboard helicopter rotor blades and wind turbine rotors are some of the aerodynamic applications that fall in this range. The current study deals with using dynamic roughness as a means of flow control over a NACA 0012 airfoil at low Reynolds numbers. Dynamic 3-D surface roughness elements on an airfoil placed near the leading edge aim at increasing the efficiency by suppressing the effects of leading edge separation like leading edge stall by delaying or totally eliminating flow separation. A numerical study of the above method has been carried out by means of a Large Eddy Simulation, a mathematical model for turbulence in Computational Fluid Dynamics, owing to the highly unsteady nature of the flow. A user defined function has been developed for the 3-D dynamic roughness element motion. Results from simulations have been compared to those from experimental PIV data. Large eddy simulations have relatively well captured the leading edge stall. For the clean cases, i.e. with the DR not actuated, the LES was able to reproduce experimental results in a reasonable fashion. However DR simulation results show that it fails to reattach the flow and suppress flow separation compared to experiments. Several novel techniques of grid design and hump creation are introduced through this study. iii "The desire to fly is an idea handed down to us by our ancestors who, in their grueling travels across trackless lands in prehistoric times, looked enviously on the birds soaring freely through space, at full speed, above all obstacles, on the infinite highway of the air."
Investigation of Rope Formation in Gas-Solid Flows using Flow Visualization and CFD Simulations Venkata Subba Sai Satish Guda Coal is still one of the widely-used resources for power generation all over the world. Most of the relevant industries use pulverized coal as fuel which is delivered to the furnace by pneumatic conveying. Extensive use of coal has resulted in severe environmental problems due to emissions such as Carbon dioxide, Nitrogen and Sulphur compounds among others. It is postulated that if combustion efficiency is improved, this will lead to significant reduction in pollutant emissions. Combustion efficiency of pulverized coal power plants is influenced strongly by particle size distribution. Most industries use Cyclone Separators (or Classifiers) to separate the larger particles from the smaller ones as part of pre-combustion processes. The sizing and scaling of these classifiers are mostly based on empirical formulations. Detailed 3D numerical studies of these classifiers have not been successful in prediction of experimental observations, hence as such cannot be used as reliable tools for scale up studies. The main reason for this anomaly is believed to be failure of the models in capturing the dynamics of particle behavior in bends and ducts where particles form rope like structures with dense particle clusters. It is then imperative that more study is needed into the understanding of rope or cluster formation in gas-solid flows. My heartfelt thanks and salutations to my grandfather Dr. K. Sivananda Murthy garu for directing me, guiding me and making me achieve my PhD goal. He has always provided solutions to all the problems in such a manner that the problem never existed or reappeared later. Without him, this goal of PhD would have always remained a dream. Of course there is no question of him not being there for me. This degree is dedicated to him.
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