The Hayabusa spacecraft (MUSES-C) carries a small capsule for bringing asteroid samples back to the earth. The initial spin rate of the reentry capsule together with the flight path angle of the reentry trajectory is a key parameter for the aerodynamic motion during the reentry flight. The initial spin rate is given by the spin-release mechanism attached between the capsule and the mother spacecraft, and the flight path angle can be modified by adjusting the earth approach orbit. To determine the desired values of both parameters, the attitude motion during atmospheric flight must be clarified, and angles of attack at the maximum dynamic pressure and the parachute deployment must be assessed. In previous studies, to characterize the aerodynamic effects of the reentry capsule, several wind-tunnel tests were conducted using the ISAS high-speed flow test facilities. In addition to the ground test data, the aerodynamic properties in hypersonic flows were analyzed numerically. Moreover, these data were made more accurate using the results of balloon drop tests. This paper summarized the aerodynamic properties of the reentry capsule and simulates the attitude motion of the full-configuration capsule during atmospheric flight in three dimensions with six degrees of freedom. The results show the best conditions for the initial spin rates and flight path angles of the reentry trajectory.
To enhance laser-propulsion thrust performance, a unique Laser-driven In-Tube Accelerator (LITA) has been developed. This paper numerically analyzes the impulse generation mechanisms in LITA. For this purpose, a LITA performance experiment was conducted in atmospheric air with a projectile installed on a ballistic pendulum to calibrate the numerical approximations. We conducted experimental flow visualization by framing shadowgraph and computational fluid dynamics solving the axi-symmetric Euler equation applied to an ideal gas. The results show that a laser-driven blast wave is generated by a spherical hot gas core where the supplied laser energy is absorbed first. The effect of confinement by the tube or shroud wall is confirmed. The impulse production is established not only from the interaction between the incident blast wave and projectile, but also from the following repetitive pressure waves. Assuming that about 30% of the input laser energy is absorbed by the working air, both the impulse and peak pressure agrees quantitatively between the experiment and numerical simulation.
The study presents a computational method for unsteady flows around moving multiple objects using overset unstructured grid method. To capture unsteady flow characteristics, the dual time-stepping method coupled with the LU-SGS implicit scheme is applied to the time integration. Two or more moving boundaries can be treated easily by the overset unstructured grid method. In this study, Chimera-hole cutting is performed automatically along with movement of the objects. For validation, the numerical results for inviscid and viscous flow and the experimental results are compared using the lift coefficient and pressure coefficient distribution of a pitching NACA0012 airfoil. Both results show the tendency of the experimental data, confirming the validity of this method. Furthermore, the flow around several objects is examined and the generality of the overset grid method is verified. Two demonstrations of the unsteady computation flapping airfoil, and a section of a vertical-axis wind turbine with three rotors are also described.
Three-dimensional reactive full Navier-Stokes simulations of hydrogen/oxygen flow in a nozzle with area ratio of 140 are evaluated using a detailed chemical kinetics reaction model. The flows over each overlapped grid are computed using a unified zonal method technique. The flow field computed by the present CFD code shows good agreement with the flow field computed by the TDK code except the position of the weak compression wave focusing on the nozzle axis. Isp profiles of the subscale nozzle computed by the CFD code assuming a laminar condition agree well with the experiment and those calculated by the TDK code. The measured heat flux distributions at higher nozzle expansion ratios also agree well with the laminar CFD results. The inconsistency of the prediction of turbulent boundary layer loss between TDK and CFD leads to some difference in Isp. The effect of grid resolution on Isp turned out to be small in the present conditions.
A 3D computation was conducted to investigate the role of hub-corner-separation on the rotating stall in a low-speed axial compressor. It is generally known that tip leakage flow plays an important role in stall inception. However, not much attention has been paid to the role of hub-corner-separation on the rotating stall although it is a common flow feature in an axial compressor operating near the stall point. During our time-accurate unsteady simulation, we suspected that hub-corner-separation might be a trigger for the rotating stall. After an asymmetric disturbance is initiated at hub-corner-separation, this disturbance is transferred to the tip leakage flows and grows to become an attached stall cell, which adheres to the blade passage and rotates at the same speed as the rotor. When the attached stall cell reaches a critical size, it moves along the blade row and becomes the rotating stall. The rotating speed of the stall cell decreases to 79% of the rotor so the stall cell rotates in the opposite direction to the rotor in the rotating frame.
The L2 Civilian (L2C) signal transmitted by the GPS Block IIR-M satellite is the first of the new generation of signals available for public users. The second and third satellites (SVN52/PRN31 and SVN58/PRN12) were launched successfully in 2006. This work focuses on development of a GPS L2C software receiver and on evaluation of ionospheric delay estimation using observations from L1C/A and L2C tracking. We developed a software GPS receiver to measure L1C/A and L2C observations, and compared ionospheric delay of the developed receiver and conventional receiver. Several tests were conducted to evaluate performance of the L2C signal using actual data. Two advantages of the L2C signal were confirmed through the tests. First, the C⁄N0 for the L2C code is higher than that of the L2P(Y). The L2C signal can be used for vertical and horizontal measurement along with L1C/A as dual-frequency application becomes available over wider area and for longer each day. Second, is that the direct tracking for the L2C signal allows the ionopheric delay to be estimated as accurately as the proprietary tracking for L2P(Y).
Iwama et al. invented the I-burner to investigate acoustic combustion instability in solid-propellant rockets (Proceedings of ICT Conference, 1994, pp. 26-1–26-14). Longitudinal pressure oscillations were induced in the combustion chamber of a thick-walled rocket by combustion of a stepped-perforation grain (I-burner). These oscillations were studied here experimentally. Two I-burners with an internal diameter of 80 mm and a length of 1208 mm or 2240 mm were made. The grain had stepped perforations (20 and 42 mm in diameter and 657 and 160 mm in length, respectively). Longitudinal pressure oscillations always occur in two stages when an HTPB (hydroxyl-terminated polybutadiene)/AP (ammonium perchlorate)/aluminum-powder propellant burns (54 tests; the highest average pressure in the combustion chamber was 9.5–29 MPa), but no oscillations occur when an HTPB/AP propellant burns (29 tests). The pressure oscillations are essentially linear, but dissipation adds a nonlinear nature to them. In the first stage, the amplitudes are small and the first wave group predominates. In the next stage, the amplitudes are large and many wave groups are present. The change in the grain form accompanying the combustion affects the pressure oscillations.
We studied the optimum flapping wing motions of a dragonfly (Anax parthenope julius) from hovering to cruising flight at various speeds, using a 3D Navier-Stokes code coupled with an optimization algorithm. The minimum necessary power curve and optimum flapping wing motions for the various flight velocities were determined using the optimization algorithm. The minimum power curve shows the typical U-shape. The optimum flapping wing motions were evaluated by comparison with experimental data. Examining the flow patterns showed that the large-scale flow separation around the wings is suppressed at these optimum conditions, except for very low flight speeds including hovering.