A numerical investigation is performed on the three discrete models (δ type, step type, and linear type) for lifting airfoils. Types of downwash investigated are that of flat plate (w=1) as well as those of wavy plates (w=cos mθ). Collocation method is used to determine the strength of vortex distributions. The following results are obtaind: a) A number E is appropriately defined as a measure of lift distribution errors. b) For accuracy, the δ type is best which is followed by the linear type and then by the step type. c) The control point locations should be at the 75% point for the δ type, 85-95% point for the step type, and 60-90% point for the linear type. d) The locations of error-estimation should be at the 25% point for the δ type, 50% point for the Step type, and 0% (=100%) point for the linear type. e) The error E versus number of panels N are plotted on log-log graphs. through which we can predict the number of panels necessary for a speciled accuracy. Also linearity of this log-log graphs serves as an indication how the method is superior. f) For error concentration to the both edge panels, the δ type is most predominant over the other types.
Based on the conformal transformation, a method for calculating the pressure distribution, the lift and the moment of a two-dimensional symmetrical airfoil executing unsteady motion in ideal fluid. The vortex sheet shed from the trailing edge is represented as the row of discretized vortices carried along with the fluid particles, assuming, for simplicity, that the amplitude of motion is very small and so the wake vortices lie on the real axis of the physical plane This method was applied to the symmetrical Joukowski airfoils with the thickness ratios of 6% to 30% and NACA 0012 airfoil, executing simple harmonic oscillation. The results show that the airfoil thickness effect tends to increase the amplitudes and the phase lags of the predicted aerodynamic forces.
Axisymmetric and double helix types of vortex breakdown in a straight circular pipe are observed by the flow visualization with kerosene mist. The type and position of the breakdowns are Studied by varying the Reynolds number and the circulation number. Vortex breakdown is so sensitive to the external disturbance that the use of measuring method With no disturbance to the flow is required. In this connection, we make use of the laserdoppler velocimeter with injecting kerosene mist as a tracer. Distributions of axial and circumferential velocity components along the radius are measured at various axial stations for two cases of the axisymmetric type. The velocity along the axis, flow patters, the axial variation of the vortex core, and so on are also obtained. From the results described above, the structure of axisymmetric breakdown, especially, the outline of the flow reversal region is clarified to some degree.
Different from usual architectures, aircraft has a very long and slender room which is exposed to many varied levels of external noises, including internal noise sources. In such a case the interior noise is widely distributed even in the same room. Research for quantity of soundproof material to be necessary and the efficient way to put it on the walls in aircraft design necessitates practical and reliable method to estimate the interior noise level of aircraft. An approximate estimation scheme is proposed in this report. This method was applied to two practical examples and the result was satisfactorily well within 5 dB in comparison with test results.