Active Control of Boundary Layer Transition by Mutual Interaction of Turbulent Spots
Grant-in-Aid for Scientific Research (C)
|Allocation Type||Single-year Grants|
|Research Institution||Toyohashi University of Technology|
MAKITA Hideharu Toyohashi University of Technology, 工学部, 教授 (40135413)
|Project Period (FY)
1998 – 1999
Completed(Fiscal Year 1999)
|Budget Amount *help
¥3,800,000 (Direct Cost : ¥3,800,000)
Fiscal Year 1999 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1998 : ¥2,900,000 (Direct Cost : ¥2,900,000)
|Keywords||Boundary Layer / Transition / Turbulent Spots / Horseshoe Vortex / Turbulent Bulge / Flow Control / Multi-Hotwire Measurement / Conditional Sampling / ヘアペン渦 / 相互干渉 / 縦渦|
In order to experimentally study interaction phenomena between the internal vortices of turbulent spots in their merging process, a pair of turbulent spots was artificially development in a laminar boundary layer. Then, a synthetic transitional boundary layer was generated by inducing many turbulent spots to clarify the effects of their interaction process on the structure of the boundary layer. Analysis on the instantaneous and ensemble-averaged views of the turbulent spots measured by a 30 channel X hot-wire led us to the following conclusions.
(1) The arrow-shaped head of a turbulent spot is composed of many small-scale streaky structures elongated in the streamwise direction and arranged in the staggered style.
(2) Each adjacent streaky structure conforms counter-rotating longitudinal vortex pairs except for the ones at both wingtips of the arrowhead.
(3) The longitudinal vortex at each inside wingtip comes into contact, as the two spots begin to merge. Mutual interaction between them generates a strong upwash and give birth to a strong velocity-defect region in the upper merged region.
(4) The unstable velocity profile there enhances spanwise vortices at the top of the merged spot.
(5) The spanwise vortices constitute the heads of large-scale horseshoe vortices connecting the longitudinal vortices beneath and may grow into turbulent bulges in the downstream turbulent boundary layer.
(6) As the array of turbulent spots grows up into a turbulent boundary layer, its periodical structure survives still around the boundary layer's outer edge.
(7) The resultant turbulent boundary layer develops more rapidly in the region between two adjacent spots than along the center line of each spot.
Research Output (27results)