@MISC{Davidson10inletfluctuating, author = {Lars Davidson}, title = {Inlet fluctuating boundary conditions for 3D Hill Flow}, year = {2010} }

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Abstract

Synthetic inlet fluctuations are created using the method described in [1, 2]. The provided Matlab code does Item 1 and 2 below. The code includes the following steps. 1. Isotropic, homogeneous turbulence is first created on a mesh (Nj = 80, Nk = 128 cells) at the inlet plane which has 8 % stretching from the two walls. This is denoted the η grid. This means that the fluctuations in the first 11 cells on the CFD grid (denoted the y grid, see Item 3 below) vary linearly between 0 and the value at the first η cell. In the spanwise direction the grid spacing of the CFD grid is used. The kinematic viscosity is 1/130 000. • 600 modes are used N = 600 (see Eq. 3 in [1]). The number of modes is high because min(∆η) is small which means that the CPU time for generating the fluctuations for the 5000 files is not negligible large (half an hour on a single core of a standard PC). Since we generate the fluctuations once and store them on disk, the required CPU time is of no concern. However, if this procedure were to be used at run time, we could maybe let ∆η ≡ ∆z so that N = 32; this reduces the required CPU time by one order of magnitude.