Takashi Nagumo

Streamwise and Spanwise Flow Structures Over Backward Facing Step in Low Reynolds Number

A study on the low Reynolds number flow such as the flow in or around the micro device is strongly required along with the development of the micro manufacturing technology. The low Reynolds number flow over a backward facing step is selected as one of the representative examples of the vortex dominant flows in the present study, because the mixing promotion is expected by an oscillatory motion of the vortex in the separating and reattaching shear layer over the step. It is important to clarify the flow fields in small channel or around the small device by flow visualization, since minimum disturbance in the measurement is achieved due to non-intrusive method. The objective of the present study is to clarify the flow behavior in the cross section in the spanwise, transverse and streamwise direction by the flow visualization using a high speed video camera. The Reynolds number based on the step height and the bulk velocity is set at 380 to 960. The visualization results in the cross section in the spanwise direction show that the separating shear layer from the step edge introduces a series of the primary vortices which have a rotation axis around the spanwise direction, and the main stream has a regularly whipping, wavy motion caused by the vortices moving toward the downstream direction along the upper and lower walls. The observation in the cross section in the transverse direction indicates that a scale of the vortex length in the streamwise direction is almost constant, but the primary vortex shows a periodic change in the spanwise direction, as the Reynolds number increases.Copyright

Computation of Rotor/Stator Interaction With Hydrogen-Fuelled Combustion

For the next-generation aircraft, a new propulsion system using hydrogen fuel has been proposed. In the present system, hydrogen fuel injected from a stator surface combusts in the turbine passages, accordingly, the conventional combustor can be cut out. The advantage of this system is that we can design a lighter and smaller engine with low emission. We have demonstrated the realizability of this system by using the cycle analysis and the numerical simulations. Through the previous studies, it was confirmed that the rotor/stator interaction has to be investigated, because the hydrogen combustion phenomena within the stator passage is so complex, and thus it would highly affect the rotor performance. In this paper, we focus on the rotor/stator interaction for the detailed investigation of realizability of this system. The 2- and 3-dimensional numerical simulations are performed for a single stage turbine with hydrogen-fuelled combustion. In the 2-dimensional study, the effects of the injection position and injection rate on the flow structure, the static temperature over the blades, and the blade performance are investigated. Furthermore, 3-dimensional numerical simulation is performed. The general aspect of 3-dimensional flow field is demonstrated, and the effect of hydrogen combustion on the components of turbine, for example hub, tip and blade, are investigated.Copyright

A Flow Study of Pulsed Jet Cross-Flow Interaction by Micro Particle Image Velocimetry

Recent development of micro devices is remarkable as in the examples of Micro-TAS, Lab-on-a-chip or ultra micro gas turbine. In order to make the micro devices smaller and more effective, an appropriate use of a micro scale jet as an actuator can be a key technology. Aiming at the development of a measurement system of the micro flow control devices in the future micro aerodynamics, we have established a system to measure a continuous jet, a pulsed jet and a synthetic jet for the flow control in the low Reynolds number air flow with a micro length scale. The two-dimensional flow field around the micro jet using micro particle image velocimetry (PIV) was measured. The jet was injected through the device using an acoustic speaker. It was observed that a saddle point existed at the certain phase where the velocity is 0 at the boundary of the jet blowing and suction phase for the synthetic jet into a still air. It was found that the pulsed jet and the synthetic jet are more effective in the fluid mixing in the low Reynolds number flow than the continuous jet. The dead water region was observed downstream of the jet in case of the jet injection into cross flow. It was recognized that the synthetic jet at the certain oscillation frequency generated a vortex pair near the jet hole.Copyright

An Evaluation of Auxiliary Part Configuration in the Micro Flow Sensor by Using Micro PIV

The paper describes the configuration effects of the auxiliary parts on the flow behavior around the microfluidic device. Recent development of the devices in MEMS is noticeable. The devices are manufactured in more complicated configuration and arrangement with the auxiliary part for the requirement of higher performance. An evaluation of the flow field around the microfluidic device is strongly required in MEMS design. The aim of the paper is to clarify the effect of the auxiliary part arrangement on the flow field around the micro flow sensor which has both the sensing element and the auxiliary parts such as the pins, pillars and electric bonding wires. The flow around the sensor is measured by using the Micro Particle Image Velocimetry (PIV) system. We investigate four types of the micro flow sensor with different configuration and arrangement of the pin, the bonding wires and the pillars. The result shows that the effect of the supporting pillars is negligible.Copyright