TY - GEN
T1 - Acoustic waves emanating from transitional structures in a compressible boundary-layer for high-speed train
AU - Watanabe, Daisuke
AU - Takami, Hajime
AU - Maekawa, Hiroshi
AU - Kikuchi, Katsuhiro
AU - Iida, Masanobu
AU - Suzuki, Hiroki
PY - 2006
Y1 - 2006
N2 - Spatial direct numerical simulations are used to study the formation and development of three-dimensional structures and the resultant sound emission mechanism in a compressible boundary layer, for a high-speed train model, where the free stream velocity of 500Km/h, corresponding Mach number is 0.41. The Reynolds number at the inlet based on the displacement thickness is 1640, which meets the boundary layer of model measurements undergoing transition. In the present work, to overcome the difficulties of the spectral method or pade-type compact schemes for compressible free-shear flows at high Reynolds numbers, the spectral-like finite difference high-order upwind-biased compact schemes (Deng, Maekawa & Shen 1995) [1] are employed. A 4th order Runge-Kutta scheme is used for time advancement. Boundary conditions based on characteristic analysis for the Navier-Stokes equations (Poinsot & Lele 1992) [2] are used so that acoustic waves are not reflected back into the domain. Random disturbances/T-S waves of compressible isotropic turbulence are superimposed on the laminar profile at the inlet plane of the boundary layer computational box. The magnitude of random disturbance is 3% of the free stream velocity. Rapid growth of oblique modes due to second instability of the laminar boundary layer with the amplified T-S waves produces peak-valley splitting structures downstream and later hairpin vortices (hairpin packet) on a low speed streak are observed. Simulation results show that the further complex development of the hairpin vortices lead to vortex interactions of the deformed hairpin vortices, which is responsible to sound generation in the transitional compressible boundary layer. The development of the peak-valley splitting structures is similar to the incompressible boundary layer measurements by Kachanov et al. (1984) [3]. Further comparisons of sound pressure levels between the numerical results and experimental data obtained by a moving model facility for high-speed 500km/h train will be made.
AB - Spatial direct numerical simulations are used to study the formation and development of three-dimensional structures and the resultant sound emission mechanism in a compressible boundary layer, for a high-speed train model, where the free stream velocity of 500Km/h, corresponding Mach number is 0.41. The Reynolds number at the inlet based on the displacement thickness is 1640, which meets the boundary layer of model measurements undergoing transition. In the present work, to overcome the difficulties of the spectral method or pade-type compact schemes for compressible free-shear flows at high Reynolds numbers, the spectral-like finite difference high-order upwind-biased compact schemes (Deng, Maekawa & Shen 1995) [1] are employed. A 4th order Runge-Kutta scheme is used for time advancement. Boundary conditions based on characteristic analysis for the Navier-Stokes equations (Poinsot & Lele 1992) [2] are used so that acoustic waves are not reflected back into the domain. Random disturbances/T-S waves of compressible isotropic turbulence are superimposed on the laminar profile at the inlet plane of the boundary layer computational box. The magnitude of random disturbance is 3% of the free stream velocity. Rapid growth of oblique modes due to second instability of the laminar boundary layer with the amplified T-S waves produces peak-valley splitting structures downstream and later hairpin vortices (hairpin packet) on a low speed streak are observed. Simulation results show that the further complex development of the hairpin vortices lead to vortex interactions of the deformed hairpin vortices, which is responsible to sound generation in the transitional compressible boundary layer. The development of the peak-valley splitting structures is similar to the incompressible boundary layer measurements by Kachanov et al. (1984) [3]. Further comparisons of sound pressure levels between the numerical results and experimental data obtained by a moving model facility for high-speed 500km/h train will be made.
UR - http://www.scopus.com/inward/record.url?scp=84883431821&partnerID=8YFLogxK
M3 - 会議への寄与
AN - SCOPUS:84883431821
SN - 9781627481502
T3 - 13th International Congress on Sound and Vibration 2006, ICSV 2006
SP - 1668
EP - 1675
BT - 13th International Congress on Sound and Vibration 2006, ICSV 2006
T2 - 13th International Congress on Sound and Vibration 2006, ICSV 2006
Y2 - 2 July 2006 through 6 July 2006
ER -