  A new computational framework for the simulation of turbulent flow through
complex objects and along irregular boundaries is presented. This is motivated
by the application of metal foams in compact heat-transfer devices, or as
catalyst substrates in process-engineering. The flow-consequences of such
complicated objects are incorporated by adding explicit multiscale forcing to
the Navier-Stokes equations. The forcing represents the simultaneous agitation
of a wide spectrum of length-scales when flow passes through the complex
object. It is found that a considerable modulation of the traditional energy
cascading can be introduced with a specific forcing strategy. In spectral
space, forcing yields strongly localized deviations from the common Kolmogorov
scaling law, directly associated with the explicitly forced scales. In
addition, the accumulated effect of forcing induces a significant non-local
alteration of the kinetic energy including the spectrum for the large scales.
Consequently, a manipulation of turbulent flow can be achieved over an extended
range, well beyond the directly forced scales. The turbulent mixing of a
passive scalar field is also investigated, in order to quantify the
physical-space modifications of transport processes in multiscale forced
turbulence. The surface-area and wrinkling of level-sets of the scalar field
are monitored as measures of the influence of explicit forcing on the local and
global mixing efficiency.
