# University of Minnesota

Aerospace Engineering and Mechanics

**Fall 1999 Seminar Series**

*Rotating Turbulence Forced Randomly at Small Scales*

*Abstract*

### Rotating turbulence is important in engineering and geophysical
applications, and presents a challenge for turbulence modeling. We study the
problem of rotating turbulence forced randomly at small scales by using direct
numerical simulations in a triply periodic box. The implications of several new
results will be discussed. First, weak small-scale forcing leads to the
transfer of energy to scales larger than the forcing scale. This is in contrast
to non-rotating 3D turbulence in which energy is transferred only to scales
smaller than the forcing scale. Second, the large-scales motions are
predominantly 2D, in the plane perpendicular to the rotation axis, in spite of
the decoupling of these 2D motions at lowest order in weak turbulence theory.
Third, the energy spectrum of the large-scale motions varies inversely with the
cube of the wavelength, consistent with heuristic arguments based on
dimensional analysis using the rotation rate as the only relevant parameter.
Thus the transfer of energy to 2D large scales in forced, rotating 3D
turbulence is distinctly different from a 2D inverse cascade characterized by
an energy spectrum inversely proportional to the 5/3 power of the wavelength.

### Friday, October 1, 1999

209 Akerman
Hall

2:30-3:30 p.m.

### Refreshments served after the seminar in
227 Akerman Hall.

Disability accomodations provided upon request.

Contact Kristal Belisle, Senior
Secretary, 625-8000.