NDLI: Large-Eddy Simulation of Unsteady Surface Pressure Over a LP Turbine Blade Due to Interactions of Passing Wakes and Inflexional Boundary Layer

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Sarkar, S. Peter, R. Voke
Copyright Year	2005
Abstract	The unsteady pressure over the suction surface of a modern low-pressure (LP) turbine blade subjected to periodically passing wakes from a moving bar wake generator is described. The results presented are a part of detailed Large-Eddy Simulation (LES) following earlier experiments over the T106 profile for a Reynolds number of 1.6×105 (based on the chord and exit velocity) and the cascade pitch to chord ratio of 0.8. The present LES uses coupled simulations of cylinder for wake, providing four-dimensional inflow conditions for successor simulations of wake interactions with the blade. The three-dimensional, time-dependent, incompressible Navier-Stokes equations in fully covariant form are solved with 2.4×106 grid points for the cascade and 3.05×106 grid points for the cylinder using a symmetry-preserving finite difference scheme of second-order spatial and temporal accuracy. A separation bubble on the suction surface of the blade was found to form under the steady state condition. Pressure fluctuations of large amplitude appear on the suction surface as the wake passes over the separation region. Enhanced receptivity of perturbations associated with the inflexional velocity profile is the cause of instability and coherent vortices appear over the rear half of the suction surface by the rollup of shear layer via Kelvin-Helmholtz (K-H) mechanism. Once these vortices are formed, the steady-flow separation changes remarkably. These coherent structures embedded in the boundary amplify before breakdown while traveling downstream with a convective speed of about 37 percent of the local free-stream speed. The vortices play an important role in the generation of turbulence and thus to decide the transitional length, which becomes time-dependent. The source of the pressure fluctuations on the rear part of the suction surface is also identified as the formation of these coherent structures. When compared with experiments, it reveals that LES is worth pursuing as an understanding of the eddy motions and interactions is of vital importance for the problem.
Sponsorship	International Gas Turbine Institute
Starting Page	1435
Ending Page	1446
Page Count	12
File Format	PDF
ISBN	0791847306
DOI	10.1115/GT2005-68867
e-ISBN	0791837548
Volume Number	Volume 6: Turbo Expo 2005, Parts A and B
Conference Proceedings	ASME Turbo Expo 2005: Power for Land, Sea, and Air
Language	English
Publisher Date	2005-06-06
Publisher Place	Reno, Nevada, USA
Access Restriction	Subscribed
Subject Keyword	Suction Navier-stokes equations Blades Cascades (fluid dynamics) Separation (technology) Bubbles Large eddy simulation Chords (trusses) Eddies (fluid dynamics) Wakes Engineering simulation Cylinders Turbulence Turbine blades Reynolds number Generators Pressure Flow (dynamics) Steady state Simulation Vortices Fluctuations (physics) Inflow Shear (mechanics) Boundary layers
Content Type	Text
Resource Type	Article

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