Ki-Wahn Ryu

Optimal Aerodynamic Design and Performance Analysis for Pitch-Controlled HAWT

Optimal aerodynamic design for the pitch-controlled horizontal axis wind turbine and its aerodynamic performance for various pitch angles are performed numerically by using the blade element momentum theory. The numerical calculation includes effects such as Prandtl‘s tip loss, airfoil distribution, and wake rotation. Six different airfoils are distributed along the blade span, and the special airfoil i.e. airfoil of 40% thickness ratio is adopted at the hub side to have structural integrity. The nonlinear chord obtained from the optimal design procedure is linearized to decrease the weight and to increase the productivity with very little change of the aerodynamic performance. From the comparisons of the power, thrust, and torque coefficients with corresponding values of different pitch angles, the aerodynamic performance shows delicate changes for just 3o increase or decrease of the pitch angle. For precisive pitch control, it requires the pitch control algorithm and its drive mechanism below 3o increment of pitch angle. The maximum torque is generated when the speed ratio is smaller than the designed one.

Thickness and Loading Noise from Helicopter Rotor at various Pitch Angles

Noises from the helicopter rotor model are calculated numerically at various pitch angles. The aerodynamic data are calculated by using prescribed wake model and unsteady panel method. The distribution of aerodynamic loads on the blade surface are obtained from 0o to 9o pitch angles with equiangular increments of 1.5o. Although thickness noise is not related to the change of pitch angles, loading noise level increases about 3~4dBA every 1.5o increment of pitch angle. The additive noise level shows sufficient value to perceive the loudness. From the result of directivity pattern the sound level at the lower region of the blade disc plane is higher than that of the upper region.

A Study on the Wind Turbine Blade Optimization and Pitch Control Using the Hybrid Genetic Algorithm

This paper introduced a new hybrid genetic algorithm, verified its performance, and applied it to the optimization of blade design and pitch control for 30kW pitch-controlled variable-speed horizontal-axis wind turbine system to determine the optimum blade chord and twist distributions that maximize the energy production for a given Weibull wind distribution and the optimum blade pitch angles that maintain constant power output.

Aerodynamic Performance for Horizontal Axis Wind Turbine Model using Subsonic Wind Tunnel

Wind turbine experiment was carried out for the horizontal axis wind turbine with the aerodynamically optimized blade. From the comparison of aerodynamic performance between upwind and downwind type wind turbine rotor, the measured torque fluctuation of the latter is larger than that of the former. This phenomenon is owing to the interaction of wake generated from support column and blades. The wind turbine model satisfies the design condition in that the measured result of the power coefficient at zero pitch angle shows maximum peak at the designed tip speed ratio, λ

Comparison of Discrete Noise with Broadband Noise from Small-scaled UH-1H Rotor

The thickness, loading, and broadband noise generated from the trailing edge of the UH-1H main rotor are numerically compared each other. The Kocureck and Tangler`s prescribed wake model is adopted to represent the wake geometry during the hovering motion. Three tip Mach numbers of

Numerical Calculation of the Far Field Acoustic Pressure from the Unsteady Motion of the Three-dimensional Vortex Filament

Far field acoustic pressure from the evolution and interaction of three-dimensional vortex filament is calculated numerically. A vortex ring is a typical example of the three-dimensional vortex filament. An elliptic vortex ring emits a strong sound signal due to significant distortion and stretching of the vortec filament. The far field acoustic pressure is linearly dependent on the third time derivatives of the vortex positions. A numerical scheme of high resolution is employed to describe in detail the elliptic vortex ring motions which ar highly nonlinear. Descretized vortex filaments are interpolated by using a parametric blending function to remove a possible numerical instability. The distorted vortex filament, owing to the self-induced and the induced velocity from the other vortex segments, is redistributed at each time step. The accuracy and efficiency of the scheme are validated by comparisons with the analytic solution of circular vortex ring interaction.

Sound generation due to a spinning vortex pair near the flat and curved wall

A numerical study of a two-dimensional acoustic field is carried out for a spinning vortex pair located near a wall to investigate the effect of the wall from the spinning quadrupole source in unsteady vortical flows. Based on the unsteady hydrodynamic information from the known incompressible flow field, the perturbed compressible acoustic terms derived from the Euler equations are calculated. Non-reflecting boundary conditions on the free field and the solid boundary conditions are developed for a generalized curvilinear coordinates system to investigate the effect of a curved wall. It is concluded that the sound generated by the quadrupole sources of unsteady vortical flows in the presence of a flat wall or a circular cylinder can be calculated by using the source terms of hydrodynamic flow fluctuations in both near and far acoustic fields simultaneously.

Numerical Simulation of Evolutions of a Vortex Ring and Its Interactions with a Rigid Sphere

Evolution of an elliptic vortex ring and vortex ring interaction with a rigid sphere are simulated numerically for kinematic motion and sound propagation. The flow field is regarded as three dimensional inviscid and incompressible. The vorticity is assumed as concentrated inside the finite core of vortex filaments. The vortex filament, described by parabolic blending curve functions, is used to effectively solve the Biot-Savart equation. An elliptic vortex ring emits a strong sound signal due to significant distortion and stretching of the vortex filament. Interaction between a vortex ring and a rigid sphere using the integration scheme are calculated with several initial positions. The evolution mechanism for an circular vortex ring interaction with a rigid sphere is predicted. The circular vortex ring is distorted after interaction with a sphere, and it has a similar kinematic motion like the elliptic vortex ring. The force variations around the sphere during the interaction are also calculated by using the unsteady Bernoulli equation. The unsteady pressure term, obtained using the potential based panel method, contributes significantly both the unsteady lift and drag force during interaction.