**Commenced**in January 2007

**Frequency:**Monthly

**Edition:**International

**Paper Count:**32131

##### DNS of a Laminar Separation Bubble

**Authors:**
N. K. Singh,
S. Sarkar

**Abstract:**

Direct numerical simulation (DNS) is used to study the evolution of a boundary layer that was laminar initially followed by separation and then reattachment owing to generation of turbulence. This creates a closed region of recirculation, known as the laminar-separation bubble. The present simulation emulates the flow environment encountered in a modern LP turbine blade, where a laminar separation bubble may occur on the suction surface. The unsteady, incompressible three-dimensional (3-D) Navier-Stokes (NS) equations have been solved over a flat plate in the Cartesian coordinates. The adverse pressure gradient, which causes the flow to separate, is created by a boundary condition. The separated shear layer undergoes transition through appearance of ╬ø vortices, stretching of these create longitudinal streaks. Breakdown of the streaks into small and irregular structures makes the flow turbulent downstream.

**Keywords:**
Adverse pressure gradient,
direct numerical simulation,
laminar separation bubble.

**Digital Object Identifier (DOI):**
doi.org/10.5281/zenodo.1077223

**References:**

[1] Horton, H.P., 1968, "Laminar Separation in Two and Three-dimensional Incompressible Flow", PhD Dissertation, University of London.

[2] Jones, B. M., 1934, "Stalling", J. Roy. Aero. Soc., 38, pp. 753-770.

[3] Gault., D. E., 1957, "A Correlation of Low-speed Airfoil Section Stalling Characteristics with Reynolds Number and Airfoil Geometry", NACA TN 3963.

[4] Gaster, M., 1968, "Growth of Disturbances in Both Space and Time", Phys. Fluids, 11, pp.723-727.

[5] Briley, W.R., 1971, "Numerical Study of Laminar Separation Bubbles Using the Navier-Stokes Equations", J.Fluid Mech., 47, Part 4, pp. 713- 736.

[6] Pauley, L. L., Moin, P., and Reynolds, W. C., 1990, "The Structure of Two-dimensional Separation", J. Fluid Mech., 220, pp.397-412.

[7] Ripley M. D., and. Pauley, L. L, 1993, "The Unsteady Structure of Twodimensional Steady Laminar Separation", Phys. Fluids, A, 5(12).

[8] Alam. M., and Sandham, N. D., 2000, "Direct Numerical Simulation of -Short- Laminar Separation Bubbles with Turbulent Reattachment", J. Fluid Mech, 403, pp.223-250.

[9] Sarkar, S., and Voke, P., 2005a, "Large Eddy Simulation of Unsteady Surface Pressure Over a LP Turbine Blade due to Interactions of Passing Waves and Inflexional Boundary Layer", Proceedings of GT 2005 ASME Turbo Expo 2005.

[10] Spalart P.R., and Strelets, M.K.,1997, "Direct and Reynolds-averaged Numerical Simulation of a Transitional Separation Bubble", 11th symp. on Turbulent shear Flows, Grenoble , France.