  The development of NekRS, a GPU-oriented thermal-fluids simulation code based
on the spectral element method (SEM) is described. For performance portability,
the code is based on the open concurrent compute abstraction and leverages
scalable developments in the SEM code Nek5000 and in libParanumal, which is a
library of high-performance kernels for high-order discretizations and
PDE-based miniapps. Critical performance sections of the Navier-Stokes time
advancement are addressed. Performance results on several platforms are
presented, including scaling to 27,648 V100s on OLCF Summit, for calculations
of up to 60B gridpoints.
