  We present an unstable periodic orbit in large eddy simulation of an
incompressible fluid in a periodic box subject to a constant body force. The
width of the inertial range of spatial scales, on which this simulation models
high-Reynolds-number turbulence, is about three quarters of a decade, and a
significant $-5/3$ scaling range is observed. We identify events of intense
energy transfer across spatial scales and relate them to vortical dynamics.
