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Breakdown process of the Klebanoff mode and origin of turbulence are experimentally investigated in detail. An acoustic excitation using a 2D roughness attached on the wall are used for T-S wave generation. Piezo-ceramic actuators are used to introduce the Klebanoff mode fluctuation. It is found that another shear layer, in which the spike phenomenon takes place and the turbulence starts, exists between the Lambda structures aligned in rows. The spreading of the turbulence along the shear layer induced by the Lambda structures is newly found., JAXA Special Publication, 宇宙航空研究開発機構特別資料

The effect of beginning of roughness patch on the evolution of two-dimensional Tollmien-Schlichting waves is investigated theoretically and numerically. The wall roughness is found to destabilize the flow through the positive energy production just above the inflection point of base flow in the concave region of the roughness. For the change in wall geometry, about 14 periods are needed to attain the stability characteristic of streamwise-periodically corrugated roughness when the wavelength of the T-S wave and wall corrugation is comparable while the effect of change in average position of roughness remains further. The latter influence is also studied by considering channel with a simple expansion/contraction. It is shown that evolution of base flow towards the plane Poiseuille flow downstream of step is found to be represented by using slowly-decaying stationary eigenmodes, similar to that for the channel entrance flow. It is also found that the influence of sudden expansion/contraction to the stability of flow persists far downstream., Meeting Information: 43rd JAXA Workshops on "Investigation and Control of Boundar-Layer Transition" (October 2-3, 2008) ; 44th JAXA Workshops on "Investigation and Control of Boundar-Layer Transition" (March 26-27, 2009), 会議: 第43回（2008年10月2日-10月3日）「境界層遷移の解明と制御」研究会; 第44回（2009年3月26日-3月27日）「境界層遷移の解明と制御」研究会

In order to clarify influences of trailing vortices of a forward wing on the aerodynamics of a backward wing in formation flight, behaviors and interactions of trailing vortices are examined experimentally in two-wing configuration at a Reynolds number Re = 2.5 x 10(exp 5). Both the wings have a NACA23012 airfoil section and rectangular plan-form with aspect ratio of 5. The wings are arranged in the horizontal plane with streamwise distance of 2.5 times the airfoil chord, and the forward wing is fixed at an angle of attack 8 deg. In such an arrangement, the lift to drag ratio is found to increase by 25% the two wings are overlapped with each other by 2.5-5 % of the full span, i.e., about the diameter of wing-tip vortex. Flow visualization and PIV measurements show that interactions of wing-tip vortices of both the wings occur most intensively in these conditions., Meeting Information: 43rd JAXA Workshops on "Investigation and Control of Boundar-Layer Transition" (October 2-3, 2008) ; 44th JAXA Workshops on "Investigation and Control of Boundar-Layer Transition" (March 26-27, 2009), 会議: 第43回（2008年10月2日-10月3日）「境界層遷移の解明と制御」研究会; 第44回（2009年3月26日-3月27日）「境界層遷移の解明と制御」研究会

The instability of axisymmetric laminar wake behind a body of revolution whose cross section is a NACA0018 airfoil is studied experimentally under a natural disturbance condition. Magnetic Suspension and Balance Systems (MSBS) are used to support the axisymmetric body in order to avoid undesirable influences of mechanical supports on the disturbance development. A multi-hotwire-sensor probe is used to identify helical instability modes. The experiment is conducted mainly at a Reynolds number based on the maximum diameter Re = 1.9 × 10(exp 4). It is found that the wake is convectively unstable despite that the flow is slightly reversed near the trailing edge. Spatially-growing instability waves are found to be helical modes with azimuthal wavenumber of 1 as predicted by the linear stability theory for the axisymmetric wake. The spatial growth rate and amplitude distribution obtained experimentally agree well with those calculated from the linear stability theory., 形態: カラー図版あり, 会議: 第42回「境界層遷移の解明と制御」研究会（2008年3月31日-4月1日）