Koichi Shibamoto

Active Control of Flow Field Structure in a Transitional Flat Plate Boundary Layer

The aim of this study is to develop a method to control twodimensional Tollmien-Schlichting wave (T-S wave) and oblique wave at the early stage of transition of a flat-plate boundary layer. Small and thin piezo-ceramic (PZT) actuators are used as the control device. In this study, twelve actuators are attached in line in the spanwise direction on the flat-plate surface and wired independently from each other. These actuators are used to generate a wave with the same amplitude and opposite sign of the incoming wave in order to cancel it. From the experimental results, it is found that the cancellation of the velocity fluctuation is successful while the sweep angle of target wave is small. However, as the sweep angle becomes larger, the canceling effect becomes insufficient in some spanwise locations even when the phases and the amplitudes of the controlling signals are fine-tuned. It is also shown that the difficulty in the fine-tuning is due to the deformation of the velocity fluctuation pattern introduced by each actuator.

Low-acoustic attenuation and high-mechanical strength silicone rubber lens doped with ZnO nanopowder for medical ultrasonic array probe

Effects of zinc oxide (ZnO) nanopowder dopant, on the acoustical and physical properties of silicone (Q) rubber have been investigated, in order to develop a low-acoustic attenuation, low sound velocity, and high-mechanical properties lens material for medical array probes. The ZnO-doped Q rubbers showed acoustic impedance (Z) = 1.29 to 1.46 times 106 kg middot m-2s-1, acoustic attenuation = 0.54 to 0.74 dB. mm-1 M.Hz-1, and attenuation figure of merits (FOM) (attenuation times sound velocity) = 471 to 621 at 37degC. The attenuation FOM values for the Q rubber lens material are the lowest attenuation ever reported. The performance of 7.5 MHz linear array probe using the ZnO-doped Q rubber lens showed an increase of 3.5 dB in sensitivity compared to that of conventional Q rubber lens doped with SiO2 powder. In addition, the material showed a high tear strength and a large elongation. The excellent mechanical properties of the ZnO-doped-Q rubber lens enable higher performance during longer operation in diagnosis compared with conventional Q rubber lens for medical array probe application.

609 Numerical Study of Active Control of Oblique Waves in a transitional boundary layer

The aim of this paper is to actively control oblique waves in a transitional boundary layer using piezo-ceramic actuators. Each actuator attached on the flat plate surface is thin enough to keep the boundary layer in the laminar state. The actuators introduce velocity fluctuation into the flow field by moving their edge for about several tens of t -meters. The results show that these actuators are capable of generating two-dimensional T-S wave, a pair of oblique waves crossing each other and a one-sided oblique wave. The capability of the actuator to generate a pair of oblique waves upstream and then weakening it downstream was successfully demonstrated using two rows of actuators.