Large-scale urbulence simulation on the Navier-Stokes computer

There exists a wide range of problems in computational physics where no analytical and few experimental results exist. Of particular interest at the Navier-Stokes Supercomputer Laboratory of Princeton University is a range of problems dealing with fluid flow. Most flows of interest are complex in nature, involving non-simple boundaries and initial conditions. A typical case involves turbulent flow over arbitrary air and water vehicles. Of particular interest is the active control of these flows. To simulate such flows directly, with boundary and initial conditions directed towards active control schemes, one must numerically solve the Navier-Stokes equations of fluid motion. These equations form a set of nonlinear, coupled, partial differential equations that account for the conservation of mass, momentum and energy in continuum flow. Because of the vast amount of computer memory and associated processing speed required to tackle even simple numerical simulations, a typical general-purpose supercomputer (e.g. Cray-2) would require unreasonably large computer time to tackle most flows involving turbulence. To overcome this difficulty, a multi-purpose parallel supercomputer has been designed and is being fabricated. Called the Navier-Stokes Computer (NSC), its primary function is the direct simulation of complex flows. The NSC is comprised of a multi-dimensional array of processing nodes with local memory. At 20 MHz, each node has a 640 MFLOP parallel-pipelined reconfigurable arithmetic unit coupled to two Gbytes of local memory. Early hardware and software benchmarks indicate that a single node is roughly comparable to the measured performance of a Cray-2. An overview of the NSC architecture along with a discussion of a turbulence simulation of this architecture is presented.