Direct Numerical Simulation (DNS) of turbulence requires many CPU days and Gigabytes of memory.These requirements limit most DNS to using supercomputers, available at supercomputer centres.With the rapid development and low cost of PCs, PC clusters are evaluated as a viable low-cost option for scientific computing.Both low-end and high-end PC clusters, ranging from 2 to 128 processors, are compared to a range of existing supercomputers, such as the IBM SP nodes, Silicon Graphics Origin 2000, Fujitsu AP3000 and Cray T3E.The comparison concentrates on CPU and communication performance.At the kernel level, BLAS libraries are used for CPU performance evaluation.Regarding communication, the free implementations of MPICH and LAM are used on fast-ethernet-based systems and compared to myrinet-based and supercomputer networks.At the application level, serial and parallel simulations are performed on state of the art DNS, such as turbulent wake flows in stationary and moving computational domains.