Koji OKAMOTO / Associate Professor / Division of Transdisciplinary Sciences
Department of Advanced Energy / / Space System Science and Technology

Career Summary
1997: B.Eng., Faculty of Engineering, The University of Tokyo
2002: Ph.D. in Engineering from The University of Tokyo
2002: Research Fellow, The University of Tokyo
2003: Post Doctorale of DGA at l'Office National d'Etudes et de Recherches Aerospatiales (ONERA)
2004: Research Associate (Assistant Professor), The University of Tokyo
2007: Associate Professor, The University of Tokyo

Educational Activities
Graduate school:Energy Transfer in Space Applications, Energy Systems in Space
Research Activities
Propulsion Systems and Thermofluid Devices in Aerospace Engineering

1) Ultra Micro Fluid Device:
The Ultra Micro Gas Turbine (UMGT) is expected to have advantages as a compact and lightweight power generation system because of its high power and energy densities compared to solar cells, batteries, and fuel cells. The key issue with UMGT technology is how to prevent decreases in the performance and efficiency of each component. In our laboratory, we are investigating a wave rotor, a shear-force pump, and a Tesla turbine for small fluid devices. These devices are innovative compression/expansion fluid devices with working principles that are completely different from conventional turbomachinery. They compress or expand a gas by applying unsteady shock wave propagation or a fluid viscous force on the disc surface and are expected to achieve better performance when they are miniaturized. We are also investigating a wave rotor to enhance the efficiency of the conventional and widely used gas turbine and jet engine.

Wave rotor (left), Tesla turbine (right)

2) Aeroacoustics of Sub- and Super-Sonic Jets:
Recently, the restriction on jet noise for aero-engines is becoming more severe, so it is necessary to understand aero-acoustic phenomena more in detail and to devise a method to suppress noise. Also, at the launch pad for rockets, the acoustic waves generated by the interaction between the exhaust plume and the flame deflector may vibrate and damage the payload, so it is important to understand this acoustic phenomenon and to suppress its effect. In our laboratory, we are carrying out basic experiments at the UT-Kashiwa Hypersonic and High-Temperature Wind Tunnel. In the experiments, a supersonic jet is impinged on an inclined flat plate and its acoustic phenomena are investigated. We are also working on combining a microphone measurement with an optical measurement such as Schlieren visualization to obtain more information on and a better comprehension of the acoustic and flow fields.

Supersonic jet impinging on inclined flat plate

3) Turbofan Jet Engine with Heat Exchangers:
The performance of turbofan engines has been improved mostly by increasing the bypass ratio, turbine inlet temperature, and overall pressure ratio and by improving the efficiency of each component. At this point, performance improvements with these approaches have reached a very high level, so different approaches are required for further improvement. One of these approaches is to use a heat exchanger as an intercooler and a recuperator. Recently, the production of lightweight heat exchangers is becoming possible due to advancements in manufacturing technology, but it is not easy to predict how these lightweight heat exchangers will improve the engine performance because the optimum thermodynamic cycle is changed by the heat exchanger and the effect of the increase in the entire engine weight must be evaluated simultaneously. In our laboratory, an in-house numerical code has been developed to investigate the performance of intercooled turbofan engines, in which the thermodynamic-cycle calculation and engine-weight estimation are combined. Then, a genetic algorithm and proper orthogonal decomposition are applied to the calculated results in order to discuss the optimized cycle performance of the entire engine and the required heat exchanger performance for different engine classes.

Intercooled turbofan engine

1) Okamoto, K. and Araki, M., “Shock Wave Observation in Narrow Tubes for a Parametric Study on Micro Wave Rotor Design”, Journal of Thermal Science, Vol. 17, No. 2, pp134-140, 2008.
2) Okamoto, K. and Nagashima, T., “Visualization of Wave Rotor Inner Flow Dynamics”, Journal of Propulsion and Power, Vol.23, No.2, March-April, pp.292-300, 2007.
3) Okamoto, K. and Nagashima, T., “Simple Numerical Modelling for Gasdynamic Design of Wave Rotors”, Journal of Propulsion and Power, Vol.23, No.1, January-February, pp. 99-107, 2007.
4) Nagashima T., Okamoto K., Ribaud Y., “Cycles and Thermal System Integration Issues of Ultra-Micro Gas Turbines”, RTO-AVT-VKI Lecture Series 2005 "MICRO GAS TURBINES", 14-18 Mar. 2005.

Other Activities
The Japan Society for Aeronautical and Space Sciences (JSASS)
American Institute of Aeronautics and Astronautics (AIAA)
Future Plan
Our objective is to discover new possibilities and availabilities for propulsion/power generation systems in aerospace engineering by introducing innovative ideas and approaches. In addition to the present research topics, we are also exploring heat control and heat energy application in space. In these research activities, we take both numerical and experimental approaches with making good use of various experimental facilities such as the UT-Kashiwa Hypersonic and High-Temperature Wind Tunnel.

Messages to Students
To solve a problem in a research activity, we need to consider how to apply knowledge to solve the problem as well as how to acquire the knowledge. By challenging yourselves with pioneering research topics, I expect all students to obtain and hone superior creative ability.