In case of designing a horizontal-axis wind turbine rotor, especially for the purpose of high efficiency of energy conversion, it should be examined how the blade geometry be optimized and how the blade pitch angle be controlled for a specified geometry. In this paper, applying the momentum theory with PRANDTL's tip correction, an optimal aerodynamic design method for a wind turbine rotor at a given tip speed ratio is presented and the effects of section lift-to-drag ratio, activity factor and number of blades are investigated. A quasi-optimization method for a linear taper blade is also proposed from a practical view point. Additional considerations are made with respect to the pitch control at the off-design range for large wind turbines. Two typical pitch control schemes of maximum and constant power modes are studied, which correspond to the control modes in the range over and below the rated wind speed, respectively. As a result, it is pointed out that a blade stall and a turbulent wake state may become the operational obstacles especially for high efficiency rotors.
It is the purpose of this Part 2 of the paper to examine the two devices for improvement proposed in Part 1 numerically. We call these two devices Method 1 and Method 2. Downwash angle is calculated of a steady rectangular wing assuming a simple loading. It is shown that Method 1 makes it possible to greatly reduce the computing time in cases of oscillating wings, and that remarkable improvement in convergence with respect to the number of spanwise integration points is obtained by Method 2.
This paper reports the results of a wind tunnel experiment conducted to investigate the property of aeroelastic galloping and the pressure distribution of a two-dimensional flat plate set normal to a uniform flow with a wake splitter plate attached to it. Measurements show that (1) the instability of galloping starts and develops rapidly as the streamwise depth of the splitter plate exceeds a certain value, and (2) at around this singular depth, the pressure at the trailing edge of the splitter plate reaches a minimum. The correlation between the onset of galloping and the pressure variation, mentioned above, is similar to that observed for rectangular, or D-shaped cross-sectional cylinders.
Nonsteady load distributions are investigated on a thin airfoil having oscillating flap, when there is a narrow hinge gap, in an invicid incompressible flow. The angle of attack is assumed to be zero in front of the hinge gap. First the problem is attacked numerically through the POSSIO's integral equation to compare it with the analytical method. The logarithmic singularity in the kernel function is treated with special care. Second the method of matched asymptotic expansion is used to analyze the problem. This brings simple closed expressions. Comparisons of results of the two methods show excellent agreement each other, when the gap width to chord ratio is less than 0.1, say. In appendix, a simplified method is presented where no inner solution needs to be considered; it is useful for gap/chord ratio less than 0.01.
The aim of the present paper is to clarify the mechanism of dynamic buckling through analyzing the behavior of cylindrical shells under axial step loading. An energy approach is used to derive the critical value of the dynamic buckling load. The physical meaning of this bound is clarified and illustrated through numerical integration of the equations of motion and comparison of the results.
From the point of view of designing an actual shock-in-rotor type rotor according to the radial equilibrium consideration, a few problems on the blade passage and its thickness are mainly investigated in connection with the flows at the inlet, before and behind normal shock, and at the outlet. Cases having the uniform inlet flow with no swirl component and the reasonable value of relative Mach number are treated in this report. The results show the possibility of designing a blade for practical use, whose supersonic portion can satisfy the starting condition for a supersonic diffuser at every radial station, if the turning angles are appropriately taken along the radius. But the blade has a tendency to take a subsonic portion having an adverse turning or the flow acceleration in relation to the magnitude of the energy addition in the rotor blade.