Direct numerical simulation of turbulence compressed in a cylinder

Summary

The behaviour of initially isotropic turbulence during compression in a cylinder is investigated by means of direct numerical simulation (DNS). The flow is governed by the 3D time-dependent Navier-Stokes equations, which have been simplified assuming an adiabatic compression process in which sound waves are unimportant and density, temperature and shear viscosity are functions of time alone. A finite volume technique is used to integrate these equations in a cylindrical coordinate system which is axially compressed while the piston moves. The numerical scheme is central and essentially second-order accurate in space and time. Initial conditions with well correlated velocity and pressure fluctuations according to decaying isotropic turbulence are generated from a stochastic divergence-free velocity field which is made to satisfy a prescribed energy spectrum. Two flow cases with different evolution of the compression rate are considered in order to study its influence on the growth rate of the turbulent kinetic energy. It is found that only the compression ratio (not the rate) has an effect. Furthermore, the simulations show that turbulence cannot be sustained in zones close to the piston surface and the cylinder head.