Effects of open area ratio and boundary layer thickness upon the flow around a permeable wall cube set on a flat wall, on which a turbulent boundary layer is developing, have been investigated experimentally. The permeable wall cube consists of six perforated plates whose open area ratio is determined by the number of the plate holes. Eachcube model has different open area ratios β of 0, 0.114, 0.256, 0.349 and 0.456. The height ratio h/δ. which indicates the ratio of cube height h to boundary layer thickness δ, is changed in two cases of 2.86 and 0.72. The critical open area ratio when there is a separation bubble behind the present perforated wall cube becomes larger relative to the lattice member cube, and therefore the permeability of fluid in the present perforated wall cube may be smaller than in the lattice member cube. The minimum pressure on the ground wall in the separation bubble behind the cube rises with increasing β and with decreasing h/δ, and the position which takes the minimum pressure moves downstream away from the cube with increase of both β and h/δ. The drag coefficient of the present perforated wall cube tends to decrease roughly with increasing β, but shows a significant change beyond about β=0.256 in the case of h/δ=2.86 and beyond about β=0.349 in the case of h/δ=0.72.
Unstart phenomena due to compound choking of airframe-integrated scramjet engine inlets were investigated numerically. The compound choking is a phenomenon caused by interaction between the main flow and the boundary layer flow ingested into engines. The numerical analysis was performed by using a one-dimensional two-stream-tube model and a quasi-three dimensional MacCormack differential model. The two-stream-tube model allowed to predict the choking condition at the throat from the given inlet conditions of stream tubes. The results of both analyses coincide qualitatively, and it is shown that the boundary layer flow spreads and pushes out the main flow in engine inlets, and that engines designed assuming a uniform inlet flow can be made unstart easily because of the existence of a low flow speed region like a boundary layer. When side walls of engines sweep backward, the transition from start to unstart is rather continuous and the inlet performance at unstart conditions is not so badly deteriorated as the performance of inlets without sweep.
In the previous report (ref. 2), we showed characteristics of compound choking in scramjet engines caused by ingestion of forebody thick boundary layers. In this report, we investigated how thermal choking is influenced by the amount of heat and the position of heating in a combustion chamber, and how compound choking is related to thermal choking. We used the same analytical models as ones in the previous report, namely, 1-D stream tube-model and quasi 3-D MacCormack model. As a result, it is found that the inlet can be thermally choked quite easily in the presence of boundary layers, and that the choked flow condition satisfies the same characteristics of compound choking as the case of a shear flow without heating. It is also found that the transition to unstart conditions can be delayed by expanding the region of heat addition towards the rear portion of the engine. For heating the transition to unstart in inlets without sweep accompanies hysteresis significantly, while the ones with sweep experience little hysteresis.
This paper treates a 3-axis stabilized satellite which has a momentum wheel on pitch axis and a reaction wheel on each axis of roll and yaw. At first, gyroscopic motion is described based on angular momentum vectors. Then, three stabilizing methods of both nutation and precession modes are described. They are an ordinary PID, a new spatial (roll/yaw) phase compensation, and a simple form of the former. All methods include dynamical characters of the reaction wheels and utilize inter-axis cross-coupling feedback. Analyses of linearized models are performed using approximate eigenvalue and root locus method. Finally, several numerical examples are shown.
Approach paths of an aircraft under the influence of the other aircraft are solved numerically in the horizontal plane. The problem of approach paths of two aircraft is formulated in terms of the optimal control problem. And then, the relative distance is limited as the state valuables constraint and each bank angle is limited as the control valuable constraint. Numerical results which we have obtained in this way explain fairly well the behavior of actual aircraft. It is also shown how the approach paths should depend upon performance functions, inequality constraints, and boundary conditions.
One of the most critical stages of operation for an externally insulated cryogenic wind tunnel is the cooldown stage. The NDA cryogenic wind tunnel is such a tunnel, and has suffered from the rather inefficient cryogenic operation due to its poor cooldown characteristics. To correct this defect, the original total pressure control system and the cooldown preocedure were modified. The test results with the new ones showed that the modified system and preocedure save substantial amount of liquid nitrogen and time for the cooldown.