The numerical calculation code by using the Fourier-Chebyshev spectral collocation method was developed to solve the three-dimensional Euler equations at the hypersonic flow regime. The governing equations are transformed to the generalized coordinates in order to treat the arbitrary shape body. That is, the coordinates can be arbitrarily placed around the body. As examples, a sphere and the forward part of the shuttle-like body were calculated at M∞=4 and 8. The present results show good agreement with other numerical and analytical results and experiments in spite of small number of grid points.
Characteristics of a combustion-driven CO2 Gasdynamic Laser (CO2 GDL), which should be a radiation heating simulator for re-entry of a planetary probe and AOTV, are experimentally and theoretically obtained. In the present GDL system carbon dioxide CO2 produced in the combustion process of liquid benzene C6H6 with gaseous oxygen CO2 is used as lasing media associated with the energy-pumping gaseous nitrogen N2. The influence of gas components on the small-signal gain is investigated using four expansion ratios of 5, 7.5, 10 and 15, which have common throat height 1.0mm. The experimental results show that the small-signal gain increases as the nozzle expansion ratio increases and that the maximum gain obtained is 0.2m-1 at the expansion ratio of 10 and 15. Comparison is made between the experimental and theoretical results based on the Anderson model, and fairly reasonable agreement is obtained. The theoretical results show that the small-signal gain decreases when combustion pressure increases and the maximum small-signal gain is obtained by optimum composition of combustion pressure and expansion ratio which are able to be produced in several GDL system.
Fluctuations of wall pressure and heat transfer rate have been measured in the regions of interaction between oblique incident shock waves and turbulent boundary layers. Experiments were made at a nominal Mach number of 4, and Reynolds number of 1.26×107 based on the distance from the leading edge of the flat plate, and under cold wall condition. When boundary layer is unseparated, fluctuations of wall pressure and heat transfer rate get strong near the impingement point of the incident shock wave, and no intermittency is observed. When boundary layer is separated, significant fluctuations of wall pressure and heat transfer rate are observed throughout the interaction region, particularly near the separation point and near the reattachment point. Near the separation point, remarkable intermittency is observed in the fluctuations of wall pressure and heat transfer rate.
An inverse problem of optimal linear quadratic regulators (LQR) is examined for single-input systems, and the selection of the weighting matrices which achieves a specified pole location is discussed in this paper. In particular, the Kessler polynomial is used as a desirable pole location, and the weighting matrices are derived in an analytical form. Although this pole specification results in the use of some negative weights in the performance index, the existence and uniqueness of the solution are guaranteed by Molinari's theorem. At the sacrifice of the circle condition, it is shown that some of deficiencies of the LQR controllers are avoided and several characteristics which classical controllers provide, but which modern methods cannot so far, are retained. An application to roll autopilot systems for missiles is given to illustrate and substantiate the proposed method as well as to make a comparison with the conventional LQR.
Recently, large-scale, high-power railguns have been vigorously developed in order to investigate material behavior at high-pressures and to simulate meteorites impacts in space. On the other hand, when we intend to apply the railgun acceleration technique to more industrial fields (such as, for instance, new type of machining and impact testing of materials), miniaturization of the railgun system will be one of the courses to take. In this situation, high-power supply unit is not always required. Keeping these in mind, we consider a mini-railgun of 10cm length, which is driven by 2mF capacitor bank charged at 400V. In this note the influence of cross-sectional shape of the rail and initial position of the projectile (complete conductor) on the acceleration characteristics are examined theoretically. It is found that the cross-sectional shape of rail has appreciable influence on the acceleration and, for a given rail length, range of proper initial position of the projectile exists.