Inflow/outflow boundary conditions and global dynamics of spatial mixing layers
Abstract
The numerical simulation of incompressible spatiallydeveloping shear flows poses a special challenge to computational fluid dynamicists. The NavierStokes equations are elliptic and boundary equations need to be specified at the inflow and outflow boundaries in order to compute the fluid properties within the region of interest. It is, however, difficult to choose inflow and outflow conditions corresponding to a given experimental situation. Furthermore the effects that changes in the boundary conditions or in the size of the computational domain may induce on the global dynamics of the flow are presently unknown. These issues are examined in light of recent developments in hydrodynamic stability theory. The particular flow considered is the spatial mixing layer but it was expected that similar phenomena were bound to occur in other cases such as channel flow, the boundary layer, etc. A short summary of local/global and absolute/convective instability concepts is given. The results of numerical simulations are presented which strongly suggest that global resonances may be triggered in domains of finite streamwise extent although the evolution of the perturbation vorticity field is everywhere locally convective. A relationship between finite domains and pressure sources which might help in devising a scheme to eliminate these difficulties is discussed.
 Publication:

Studying Turbulence Using Numerical Simulation Databases, 2
 Pub Date:
 December 1988
 Bibcode:
 1988stun.proc...19B
 Keywords:

 Boundary Conditions;
 Boundary Layer Flow;
 Digital Simulation;
 Incompressible Flow;
 Mixing Layers (Fluids);
 Shear Flow;
 Turbulent Flow;
 Computational Fluid Dynamics;
 Flow Stability;
 Perturbation Theory;
 Spatial Marching;
 Vorticity;
 Fluid Mechanics and Heat Transfer