· · · Aerospace Engineering reports

A method is given for the calculation of the noise field of a propeller. This method is slightly different from that of Garrick and Watkins. It is believed that the differences in the results indicate the order of the inaccuracy due to the approximations inherent in the two methods. The noise field of two propellers is calculated to show these differences. To estimate the influence of the diffraction around a fuselage some numerical results are given for the diffraction of a plane wave around a circular cylindrical fuselage.

In this report a method is presented to determine optimum shapes of bodies of revolution taking into account the shape dependent part of the base drag. The latter is achieved by using the Chapman assumption that the base pressure coefficient, when correlated with conditions at a suitable point near the base, depends only on the free-stream Mach number if the boundary layer is turbulent. The present method enables the determination of quantitative results, which show the known trend that the optimum bodies have their maximum cross section ahead the base area. The drag reductions obtained are the most significant for relatively slender bodies in the lower supersonic Mach number range.

A survey is given of the results obtained at the NLR with respect to the determination of optimum body-ring wing configurations at zero lift. It is shown that if reliable data are required for practical shapes the use of exact flow theories is essential. The pressure distribution on the optimum configuration considered here is such that the conclusion seems justified that no separation of the boundary layer will take place in an actual application.

This report presents a new method to find shapes that attain minimum wave drag under certain constraints. The constraints considered here are given values for the base area and the lift. The configuration is assumed to be embedded in a volume enclosed by two opposing circular Mach cones, one going through the most forward point of the configuration, the other through the rim of the base. The flow field inside this volume is entirely governed by the perturbation velocities on the Mach cone through the base. In fact, the method deals with the procedure to determine the value of these velocities. Once the velocity distribution along the Mach cone is known the flow field and thus the shape of possible configurations can be found by applying characteristic methods. Two cases are considered; in the first only the value of the base area is prescribed, while in the second also the lift is given. As an example the shape and the axis inclinations of a possible ring-wing configuration are calculated. The analysis is based on linearized supersonic flow theory. However, the method can also be adapted to non-linear flows around shapes with circular cross-sections.