Due to the rapid depletion of conventional energy resources like fossil fuels and their harmful effects on the environment, there is an urgent need to seek alternative and sustainable energy sources. Wind energy is considered as one of the efficient source of energy which can be converted to useful form of energy like electrical energy. Though the field of wind engineering has developed in the recent era there is still scope for improvement in the effective utilization of energy. Energy efficiency in wind turbine is largely determined by the aerodynamics of the turbine blades and the characteristics of the turbulent fluid flow. The objective of this paper is to have a review on the improvement of Horizontal Axis Wind Turbine (HAWT) blade design by incorporating biomimetics into blades. Biomimetics is the field of science in which we adapt designs from nature to solve modern problems. The morphology of the wing-like flipper of the humpback whale (Megaptera novaeangliae) has potential for aerodynamic applications. Instead of straight leading edges like that of conventional hydrofoils, the humpback whale flipper has a number of sinusoidal rounded bumps, called tubercles arranged periodically along the leading edge. The presence of tubercles modifies the flow over the blade surface, creating vortices between the tubercles. These vortices interact with the flow over the tubercle and accelerate that flow, helping to maintain a partially attached boundary layer. This aerodynamic effect can delay stall to higher angles of attack, increase lift and reduce drag compared to the post-stall condition of conventional airfoils. The modified airfoil is characterized by a superior lift/drag ratio (L/D ratio) due to greater boundary layer attachment from vortices energizing the boundary layer.
In this paper, we aim to delay the onset of stall phenomenon of the blades by applying leading edge modifications to the turbine blade. In nature, the control over the phenomenon of stall is observed in case of Humpback Whales. For these marine creatures, their flippers are having certain projections called tubercles which help it delay flow separation while performing tight underwater maneuvers while preying .These tubercles acts like a passive vortex generator at the tip of blade [2]. So we selected an optimum design from literatures to study their effects when applied to wind turbine blade airfoils. A widely used wind turbine airfoil developed by Delft University in Netherlands was chosen for this project. CFD analysis was used to evaluate and compare the aerodynamic characteristics like lift and drag coefficients of the tubercle modified and the baseline airfoil. The aerodynamic characteristics were analyzed at various angles of attack (AOA) of the airfoil and the study was mainly focused at the performance on the stall angles of the airfoil. After the numerical analysis of the tubercle modified wind turbine airfoil, it was found that the coefficient of lift was increased and coefficient of drag was reduced in the stalling angles effectively delaying the stall. Also it was observed that the tubercle modification does not have any detrimental effects on the aerodynamic performance in the pre-stall regions.
In the present study computational tests were carried out to get an understanding of the flow field in a pure mixedcompression hypersonic inlet at a free stream Mach number of 7 and an altitude of 35km. Structured meshes have been used for depicting the motion of fluid inside the inlet. First, a grid has been selected after conducting a grid study. Two dimensional simulations were carried out with standard sst k-ω model using FLUENT. Computational results are compared with the available data. The results obtained from the computational tests revealed several important flow field details at hypersonic speeds. The basic shock structure inside the inlet was obtained. The boundary layer formed inner side of the engine had an adverse pressure gradient on the top ramp. Due to this the boundary layer thickens and the static pressure starts to decrease whose effect leads till the trailing edge of inlet. By providing small wedge shaped Micro-Vortex Generator (MVG) where the shockboundary layer occurs we can smooth the boundary layer formed inside the inlet. Thus there will be more efficient compression than the actual case. The results obtained in the present series of tests, could help the hypersonic inlet design optimization at offdesign condition
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