This paper presents some additional numerical results to our previous papers, concerning about a new computation method for unsteady subsonic lifting surfaces, BIS (Box-in-Strip). It consists of two parts. The one is comparisons between BIS and PCKFM (Piecewise Continuous Kernel-Function Method), which seems to be appreciated as an excellent method in USA. The other is comparisons between BIS and analytical solutions for circular and/or elliptic planform wings in steady incompressible flow. As a result, it is found that PCKFM yields fairly close results to BIS in the case of the rectangular wing with AR=10 and that correlation between BIS and analytical solutions is much more excellent than VLM. Thus we confirmed again the superiority of BIS over VLM.
Flow patterns on a rotary wing with low aspect ratio of 3.3 are experimentally investigated in the Göttingen type low speed wind tunnel. Single rotation propeller blade with radius of 0.3m is used as the model wing for the flow visualization. The flow phenomena on the blade are visualized by means of oil flow, tuft, mini-tuft and china clay methods, and recorded by the simultaneous photographs. The experimental results clearly show that the mini-tuft method is more suitable to visualize the flow on the rotary wing.
Reduced-order controllers for active flutter suppression of a two-dimensional airfoil are studied using two design approaches. One is based on the Generalized Hessenberg Representation (GHR) in the time domain, and the other called the Nyquist frequency approximation (NFA) is a method in the frequency domain. In the NFA method, the reduced-order controllers are designed so that the stability margin of the Nyquist plot may be increased over a specific frequency range. To illustrate and to make a comparison between the two methods, numerical simulations are carried out using a thirteenth-order controlled plant. It is to be noted that the GHR method can yield quasi-optimal controllers in the sense of minimizing quadratic performance indices. The designed controllers, however, do not have enough stability margin, and the order reduction resulting from full state controllers may not be satisfactory. On the other hand, reduced-order controllers in the NFA method can be designed with increased stability margin at the expense of the performance index. For all simulation cases the NFA method yields second-order controllers with better stability margin than those by the GHR method. Thus, the NFA method gives us one of the effective methods for synthesizing robust reduced-order controllers.