The present paper describes performance evaluation of a Dimethyl Ether (DME) propellant arcjet thruster. We have proposed to apply DME to arcjet thrusters owing to its favorable characteristics for space propulsion device such as non toxicity, weak chemical reactivity and storability. Thrust measurement using a vertical-pendulum-type thrust stand showed that thrust was almost monotonously increased with mass flow rate at a given discharge current, and rose with specific power. Specific impulse was also enhanced with specific power whereas thruster efficiency was attenuated. DME propellant presented higher thrust, specific power and thruster efficiency than nitrogen propellant at a given discharge current or specific power. Thrust measurement yielded a thrust of 0.19N, a specific impulse of 330s, thruster efficiency of 0.14 at a DME flow rate of 60-mg/s with the corresponding discharge voltage, power, and specific power of 90V, 2350W, and 39MJ/kg, respectively.
This paper describes a validation study of higher order CFD code for unsteady flow characteristics around aircraft landing gear models. A CFD code ``Cflow'' has been developed. Cflow employs higher order numerical scheme and unstructured Cartesian grid system to satisfy both of capturing unsteady flow characteristics and handling complicated geometry. Wind tunnel test data from AIAA Workshop on Benchmark problems for Airframe Noise Computations--I is used in this study. Validation was conducted for simple four wheels landing gear and realistic two wheels landing gear. Comparison of steady and unsteady surface pressure, wake characteristics, and far field aero acoustic noise showed good agreement between CFD results and wind tunnel test data.
This study shows two fundamental aspects related to fracture characterization of sandwich beams for aerospace application; 1) formulation of energy release rates associated with face sheet debonding or core cracking in sandwich beams with residual thermal stresses, and 2) crack kinking analysis of foam core sandwich beams. Energy release rates are formulated using the bi-layer shear deformable beam model with consideration of residual thermal stresses. This formulation is specifically applied to double cantilever beam (DCB), end notched flexure (ENF) and mixed mode bending (MMB) tests of sandwich structures. The derived analytical results are verified by comparison with finite element analysis. Next, the present formulation is applied to the prediction of crack kinking behaviors in foam core sandwich beams. It is demonstrated that overall crack kinking behaviors in foam core sandwich beams are well predicted using the present method. Some discussions on the fracture toughness measurement considering residual thermal stresses are also provided.
The original PARSEC (PARametric SECtion) method can satisfactorily solve the optimization problems involving transonic airfoils by using a few design variables. However, it is difficult to apply this method to the design of airfoils under other conditions such as supersonic flow and low Reynolds number flow. To solve various airfoil design problems by using a few design variables and the PARSEC representation, a modified PARSEC representation is proposed. The capability of the proposed modified representation to solve unknown real-world design problems is investigated; the proposed representation is used along with multi-objective genetic algorithms to solve two types of problems. One is the design of a conventional transonic airfoil that is to be used in the Earth's atmosphere; the other is the design of an airfoil that is to be used in the Martian atmosphere. To evaluate the aerodynamic performance of the airfoils, the structured Navier-Stokes solver is used. The results indicate that better solutions can be obtained by using the proposed PARSEC modification than by using the original PARSEC representation, especially in the Martian atmosphere.