Simulations of bypass transition for spatially evolving disturbances
Abstract
The spatial evolution of disturbances in plane Poiseuille flow and zero pressure gradient boundary layer flow is considered. For disturbances governed by the linearized equations, potential for significant transient growth of the amplitude is demonstrated. The maximum amplification occurs for disturbances with zero or near zero frequencies. Spatial numerical simulations of the transition scenario involving a pair of oblique waves has been conducted for both flows. A fully spectral solver using a simple but efficient fringe region technique allowed the flows to be computed with high resolution into the fully turbulent domain. A modal decomposition of the simulation results indicates that nonlinear excitation of the transient growth is responsible for the rapid emergence of lowfrequency structures. Physically, this corresponds to streaky flow structures, as seen from the results of a numerical amplitude expansion. Thus, this spatial transition scenario has been found to be similar to the corresponding temporal one. In the boundary layer simulations the streaks are seen to break down from what appears to be a secondary instability.
 Publication:

In AGARD
 Pub Date:
 December 1994
 Bibcode:
 1994adle.agar.....L
 Keywords:

 Boundary Layer Flow;
 Bypasses;
 Channel Flow;
 Computational Fluid Dynamics;
 Computational Grids;
 Computerized Simulation;
 Grid Generation (Mathematics);
 Laminar Flow;
 Secondary Flow;
 Spatial Distribution;
 Transition Flow;
 Turbulence;
 Algorithms;
 Boundary Conditions;
 Cray Computers;
 Flow Stability;
 Functions (Mathematics);
 Linear Evolution Equations;
 NavierStokes Equation;
 Operators (Mathematics);
 Pressure Gradients;
 Reynolds Number;
 Spectrum Analysis;
 Fluid Mechanics and Heat Transfer