Abstract
Direct numerical simulations in periodic plane channels are used to study turbulent flow over 'patches' of roughness distributed on otherwise smooth walls. Circular patches as well as those resembling natural bio-fouling roughness are considered. Roughnesses within the patches are statistically similar and formed by random distribution of roughness elements of truncated cone shape. The two main studied parameters are the characteristic length scale of the patches and roughness area coverage ratio (CR). To provide a reference, simulations of homogeneous roughness (i.e. with 100Â % CR) are performed at different roughness element densities translated into different values of frontal solidity. Results show that when is of the order of channel half-height, the global friction coefficient of patchy roughness is scattered around that of homogeneous roughness with similar 'mean' frontal solidity. As grows, asymptotic convergence towards an equilibrium value is identified. Considering the present data, a normalised can be satisfactorily correlated by; the normalisation includes for a homogeneous roughness similar to the patch roughness at two limiting cases. This points towards the possibility to develop a universal heterogeneous roughness correlation based on a knowledge of existing homogeneous roughness correlations. Furthermore, local and global flow statistics are studied, which among others, indicate formation of secondary motions for regular patch arrangement at with implications on the outer layer similarity of global mean velocity and Reynolds stress profiles.
| Originalsprog | Engelsk |
|---|---|
| Artikelnummer | A28 |
| Tidsskrift | Journal of Fluid Mechanics |
| Vol/bind | 1006 |
| ISSN | 0022-1120 |
| DOI | |
| Status | Udgivet - mar. 2025 |