A Characterization of Vertical Axis Wind Turbines
Vertical axis wind turbines (VAWT) have a number of advantages over the horizontal axis wind turbines (HAWT), however the performance is a little smaller, so that researches for their development should be continued for the implementation of these turbines in urban environment for electrical energy generation. This paper provides an overview of characterization of the VAWT, through a literature review, making comparisons with the HAWT and highlighting the advantages and disadvantages of this type of turbines. The paper also defines and compares the main exist types of VAWT for application in urban environment, so that aims to be a first step towards development of a VAWT research. Finally, this paper features how the aerodynamic optimization of a VAWT can be obtained, defining the experimental and the computational numerical analysis, by the relationship between them.
A Numerical Study of Thickness Effect of the Symmetric NACA 4-Digit Airfoils on Self Starting Capability of a 1kW H-Type Vertical Axis Wind Turbine
The effect of thickness of the symmetric NACA 4-digit airfoil series on self starting of a 1kW three blades H-type vertical axis wind turbine (VAWT) using computational fluid dynamic (CFD) analysis is the main objective of this study. A sliding interface technique was used to investigate two dimensional unsteady flow around VAWT model by solving the Reynolds Average Navier-Strokes equation with k-e Realizable turbulent model. A novel CFD-dynamic coupling model is proposed to solve the dynamic of VAWT. In this model, while the aerodynamic force acting on the VAWT blades is solved by CFD, the torque of the generator and the dynamic friction force at the bearing applying on the axis of VAWT are modelled vie their physical characteristics. The during time to rotate an angle of 120° of VAWT is one of the principle parameters to investigate the self starting capability. The effect of the starting azimuth angle of blade, the wind velocity and the geometry of the airfoil (NACA 0012, 0015, 0018, 0021) on self starting capability are analysed. The qualitative result show that the considered VAWT has the highest self starting capability when the starting azimuth angle of blade is in the range of [90°÷100°] and it has the lowest self starting capability when the starting azimuth angle is in the range of [45°÷60°]. By using the CFD-dynamic coupling model and by comparing the aerodynamic moment of the wind on the steady three blades to the static friction moment, the considered VAWT rotate at the starting wind velocity of 4 m/s, 3.5 m/s, 3m/s and 3 m/s for NACA 0012, 0015, 0018 and 0021 respectively. The VAWT has the lowest self starting capability with the configuration of NACA 0012 and has the highest capability with NACA 0021.
Far-field dispersal modeling for fuel-air-explosive devices
A computer model for simulating the explosive dispersal of a fuel agent in the far-field regime is described and is applied to a wide variety of initial conditions to judge their effect upon the resulting fuel/air cloud. This work was directed toward modeling the dispersal process associated with Fuel-Air-Explosives devices. The far-field dispersal regime is taken to be that time after the initial burster charge detonation in which the shock forces no longer dominate the flow field and initial canister and fuel mass breakup has occurred. The model was applied to a low vapor pressure fuel, a high vapor pressure fuel and a solid fuel. A strong dependence of the final cloud characteristics upon the initial droplet size distribution was demonstrated. The predicted fuel-air clouds were highly non-uniform in concentration. 18 refs., 86 figs., 4 tabs.