Sharif Digital Repository

The unsteady phenomena occur in rotors of helicopters, wind turbines and compressors. Investigation of the unsteady flow is a very important test, since it can affect and restrict the performance of rotors of helicopters and wind turbine's blades when operating at high angles of attack. Dynamic tests, such as pitching and plunging oscillations are one of the best methods for studying these phenomena due to the complexity of the unsteady flows. In analyzing the results of dynamic tests one must consider the interference effects of wind tunnel walls. Different investigations show that in dynamic tests, the interference effects of flow field around the model, wind tunnel walls and support of... 

Wake aerodynamic of plunging airfoils have received less attention than the other unsteady phenomena. An experimental investigation was carried out to study the unsteady characteristics of flow field behind a model of a plunging airfoil in various conditions. The model has 0.25cm chord and is the 16m section of a 660kW wind turbine blade. All tests were conducted in the subsonic closed circuit wind tunnel in Iran. Invariable parameters were plunging amplitude, mean angle of attack and plunging frequency. The Wakes of plunging airfoil can be characterized as drag-producing, neutral, or thrust-producing .Our preliminary results show that the structure of vortex in the wake for the plunging... 

An experimental investigation of unsteady boundary layer over a wind turbine blade conducted in a subsonic wind tunnel. The experiment performed at different positions along the airfoil chord. Model was oscillated with amplitude of ±5 cm. Reynolds number, based on airfoil chord, ranged 3˟105 upto 6.5˟105 and the reduced frequency ranged from 0.0055 to 0.0981. Velocity profile measured with a total pressure rake. The data were reduced via a low-pass filter. Increasing the reduced frequency, the velocity profile increases the level on turbulence fluctuation and becomes more attached to the surface.

 

Prediction of the location of transition point is important for wind turbine applications. The laminar/turbulent properties of the flow field have an important influence on the skin friction and separation location that affect both lift and drag characteristics of the blade significantly. In this study, a series of experiments were conducted on a section of a 660 kW wind turbine blade in subsonic flow. Boundary layer transition point was measured using multiple hot-film sensors. Hot-film data were analyzed in both time and frequency domains. The experiments involved static and dynamic tests where the airfoil motion was of plunging type oscillation. The effects of several parameters such as... 

A ten percent thick supercritical airfoil, having special previllage rather than conventional airfoils tested in a low speed wind tunnel to measure pressure distribution over the airfoil in steady and unsteady flow. Present thesis is set out to discuss effects of reduced frequency and mean angle of attack on pressure distribution during plunging motion in low-subsonic flow. Investigation of experimental data from frequency domain aspect is very challenging area in experimental aerodynamics. Therefore, the concepts of frequency domain analysis is pointed out. The analysis of experiment data is devidind in two different part, that is, steady and unsteady flow. Flow separation over the airfoil... 

Laminar-to-turbulent transition is very important concept in fluid dynamics due to its significant role on skin friction drag and heat transfer. It is more important in the fluid-based systems such as wind turbines. Employing computational fluid dynamics is still not efficient on prediction of flow transition, especially in complex problems such as oscillating airfoils. In one hand, flow transition models are not still suitable for general engineering flows such as oscillating airfoils. On other hand, due to the lack of experimental data, the existing flow solvers have not proven in the accurate simulation of the flow field simulation for complex problems such as oscillating airfoils. This...