Harunori Nagata

Bio: Harunori Nagata is an academic researcher from Hokkaido University. The author has contributed to research in topics: Rocket & Combustion. The author has an hindex of 11, co-authored 141 publications receiving 618 citations. Previous affiliations of Harunori Nagata include Nikon.

Fuel Regression Characteristics of a Novel Axial-Injection End-Burning Hybrid Rocket

Abstract: The regression characteristics of axial-injection end-burning hybrid rocket were experimentally investigated using a laboratory-scale motor. The axial-injection end-burning type fuel grains were ma...

Verification Firings of End-Burning Type Hybrid Rockets

Abstract: The authors have previously proposed the concept of end-burning-type hybrid rockets, which would use cylindrical fuel grains consisting of an array of many small ports running in the axial directio...

A Flux Splitting Scheme with High-Resolution and Robustness for Discontinuities(Proceedings of the 12th NAL Symposium on Aircraft Computational Aerodynamics)

Abstract: A flux splitting scheme is proposed for the general nonequilibrium flow equations with an aim at removing numerical dissipation of Van-Leer-type flux-vector splittings on a contact discontinuity. The scheme obtained is also recognized as an improved Advection Upwind Splitting Method (AUSM) where a slight numerical overshoot immediately behind the shock is eliminated. The proposed scheme has favorable properties: high-resolution for contact discontinuities; conservation of enthalpy for steady flows; numerical efficiency; applicability to chemically reacting flows. In fact, for a single contact discontinuity, even if it is moving, this scheme gives the numerical flux of the exact solution of the Riemann problem. Various numerical experiments including that of a thermo-chemical nonequilibrium flow were performed, which indicate no oscillation and robustness of the scheme for shock/expansion waves. A cure for carbuncle phenomenon is discussed as well.

Approaches to Low Fuel Regression Rate in Hybrid Rocket Engines

Abstract: Hybrid rocket engines are promising propulsion systems which present appealing features such as safety, low cost, and environmental friendliness. On the other hand, certain issues hamper the development hoped for. The present paper discusses approaches addressing improvements to one of the most important among these issues: low fuel regression rate. To highlight the consequence of such an issue and to better understand the concepts proposed, fundamentals are summarized. Two approaches are presented (multiport grain and high mixture ratio) which aim at reducing negative effects without enhancing regression rate. Furthermore, fuel material changes and nonconventional geometries of grain and/or injector are presented as methods to increase fuel regression rate. Although most of these approaches are still at the laboratory or concept scale, many of them are promising.

A physical approach to the radiation damage mechanisms induced by X‐rays in X‐ray microscopy and related techniques

Abstract: A physical approach is used to analyse the various mechanisms induced by the absorption of X-ray photons of energies in the 0.2–20 keV range. At the atomic scale, besides the (Auger and photo) electron transport in the bulk or the ejection into the surrounding media, special attention is devoted to the specific consequences of the initial Auger decay mechanism. At the macroscopic scale, the decisive role of the poor electronic conductivity of the radiation-sensitive materials is outlined and it is shown that the damaging effects occur in irradiated insulators because the lack of conduction electrons prevents the initial charge of the excited atoms being quickly restored. Correlating irradiation conditions and physical properties of the specimen, various expressions are proposed for the first time to quantify these effects. Some are neither dose- nor dose-rate-dependent and the influence of the surrounding medium is also considered. The fundamental mechanisms investigated here hold for a wide variety of specimens or components investigated in X-ray microscopy. Their consequences can be easily transposed to other techniques using transmitted X-rays.