Direct numerical simulation of fractal-generated turbulence

Abstract

We simulate fractal-generated turbulence (Hurst and Vassilicos 2007 Phys. Fluids 19 035103)) by means of a direct numerical simulation and address its fundamental characteristics. We examine whether the fractal-generated turbulence in the upstream region has a nature similar to that of a wake. We propose an equation for predicting peak values of the velocity fluctuation intensity and devise a method for formulating the functional form of the quantity of interest by focusing on the time scale of decaying turbulence, and we examine those forms for the turbulent kinetic energy and rms of pressure fluctuation through this method. By using the method, both of these functional forms are found to be power-law functions in the downstream region, even though these profiles follow exponential functions around these peaks. In addition, decay exponents of these quantities are estimated. The integral length scales of velocity fluctuations for transverse as well as streamwise directions are essentially constant in the downstream direction. Decaying turbulence having both these characteristics conflicts with decaying turbulence described by the theory predicting exponential decay. We discuss a factor causing the difference by focusing on the functional form of the transfer function of homogeneous, isotropic turbulence.