A gas-turbine-driven pump system was designed and tested. Pump systems are generally driven by an electric motor, but a gas turbine is occasionally used as the power source for high power and performance; for example, the turbopump of a liquid rocket propulsion system. For research on turbopumps, a gas generator, turbine, and pump are developed. After each component is developed, the performance should be confirmed with a link test. In the case of a turbopump, an axial turbine is applied to generate huge torque, but a radial inflow turbine was used in this research. A radial inflow turbine can be obtained easily and mass-produced. System analysis was conducted using a link test with all components at once. The turbine generated shaft power under steady operation of the gas generator, and the pump performance was measured using a stepped closing valve at the pump exit. Turbine heat loss was considered and a slip factor was applied to the impeller design to modify performance. This research shows the feasibility of developing a pump system operated by a radial inflow turbine and its application to a small turbopump for a hybrid rocket propulsion system and an air-independent system.

View full abstract

For spacecraft to rendezvous in a halo orbit around Earth Moon Lagrange Point 2 with an amplitude of several ten-thousand kilometers, we propose selecting a chaser's rendezvous trajectory from two different types, depending on the phase difference to the target. In the first trajectory, the chaser approaches the target from behind along the orbit, similarly to a rendezvous in a low Earth orbit. The second trajectory utilizes the homoclinic intersection of invariant manifolds of the halo orbit extended toward the Moon, where the chaser's trajectory is controlled so that it first departs from the halo orbit along an unstable manifold, is connected to a stable manifold through the intersection, and then returns to the halo orbit. We showed that this detour can adjust the time of arrival to the halo orbit with low fuel usage and the total delta-v for the rendezvous can be significantly reduced in comparison to the first trajectory if the initial phase difference is large. The strategy employed can significantly increase the flexibility of the flight plan, increase the launch window of the visiting vehicle to the target and enhance the tolerance against failure compared to the application of a traditional phasing method.

View full abstract

The paper proposes a new autopilot design for agile missiles flying at a high angle of attack (AoA). A maneuver strategy applicable to 90° AoA flight for agile turning is described prior to the missile modeling. Accounting for the disturbance rejection, the extended state observer (ESO) technique is employed for online estimation of the system uncertainties due to the aerodynamic unpredictability at high AoA regimes. Under the circumstances, linearization with dynamic compensation and non-singular terminal sliding mode control are applied to achieve controllability during 90° AoA flight. Numerical simulation results demonstrate the effectiveness and robustness of the proposed scheme. Additionally, the chattering caused by unmodeled dynamics is obviously mitigated with the action of the ESO.

View full abstract

Three-dimensional numerical simulations were conducted to understand the effects of low Reynolds numbers on the performance of a transonic axial compressor. For the reference case, the computational results showed good agreement with the experimental data in total pressure ratio and exit flow. With decreasing Reynolds number, the mass flow rate and total pressure ratio of the axial compressor decreased by 4% and 1%, respectively, in comparison to the reference case. This study found that large viscosity significantly affects the location and intensity of the passage shock, which moves toward the leading-edge at low Reynolds numbers. Additionally, these results successively revealed changes in internal flow pattern such as pressure distribution on the blade surface, tip leakage flow and separation. An attempt has been made to explain the dependence of the performance and the total pressure loss on the Reynolds number in a one-stage transonic axial compressor. In addition, it was confirmed that there is a critical Reynolds number around 250,000 in axial compressors, below which total pressure loss increases rapidly.

View full abstract

Future space programs will require an agile relative position and attitude control technology for spacecraft. Rendezvous and docking, capture of inoperative spacecraft and formation flight in orbit are the typical scenarios. One of the key technologies is designing the tracking controllers that can control the six degrees-of-freedom (d.o.f.) of spacecraft under the influence of physical parameter uncertainties and external disturbances. To achieve agility, the controller design must be formulated as nonlinear control problems where translational and rotational motions are dynamically coupled with each other. This paper proposes a tracking controller, proportional-integral-derivative (PID)-type H_∞ adaptive state feedback controller, that can attenuate disturbances. The proposed controller has positive definite gain matrices whose conditions to be satisfied are given by linear matrix inequalities. The properties of the proposed controller were evaluated through numerical studies and compared with those of existing controllers.

View full abstract

This paper presents the unsteady numerical simulation and analysis of the slipstream generated by distributed propellers on a solar-powered UAV using the CFD method based on structured/unstructured hybrid grids. Sliding mesh technology and a transition model are used for the numerical simulation of a NACA propeller and an Eppler 387 airfoil, the results of which are well compatible with the experimental data, proving the calculation method to be highly credible and accurate. Numerical simulations are run for configurations with the propeller in front of and behind the wing, and comparative analyses are conducted with a pure propeller and pure wing. The results suggest the existence of mutual disturbance between the propeller and the wing, as the propeller, either in front of or behind the wing, causes an increase in cyclical fluctuation of the wing’s lift, drag and nose-down moment. The wing, in return, gives rise to an increase in fluctuation of the propeller's pulling force, absorbing power and efficiency, with propeller oscillation being triggered by the discontinuity of the flow field. The configuration with the propeller posed behind the wing is proven to be of smaller disturbance to the whole system.

View full abstract

The effectiveness of a “staged aftbody” proposed by Toyoda et al. (AIAA J., Vol. 52, 2014, pp. 2899–2901) was further investigated using an aeroballistic range with a free-flight Mach number of 1.7. Near-field pressure signatures were obtained from a pressure transducer that was flush-mounted on a flat plate. From these signatures, far-field pressure signatures were obtained by the waveform parameter method. It was demonstrated that a flight model whose length-to-diameter ratio was even as high as 21 exhibited considerable elongation of the overall tail-boom pressure signature duration, thereby effectively mitigating the tail boom.

View full abstract