YIP-Low-Order Representations of Irregular Surface Roughness and Their Impact on Wall Turbulence

Abstract

REPORT DOCUMENTATION PAGEThe pubic reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathenng and maintaining the data needed, and oompietjng and reviewing the collection of information Send comments regardng this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to the Department of Defense. Executive Service Directorate (0704-0188), Respondents should be aware that notwithstanding any other provision of law. no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION. REPORT DATE (DD-MM-YYYY) 28 SPONSOR/MONITORS ACRONYM(S) AFOSR SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release SUPPLEMENTARY NOTES 2010091628014. ABSTRACT This effort explored the impact of topographical scales present within irregular surface roughness on a turbulent boundary layer. Low-order representations of a surface replicated from a turbine blade damaged by deposition of foreign materials were generated using singular value decomposition to decompose the complex topography into a set of basis functions of decreasing importance to the original ("full") surface. The low-order surface models were then formed by truncating the basis functions at the first 5 and 16 modes (containing 71 % and 95% of the full surface content, respectively), so that only the largest-scale topographical features were included. Physical replications of these surfaces were rapid prototyped and particle-image velocimetry was used to measure the flow over these surfaces in the streamwise-wall-normal plane and in a streamwise^spanwise plane deep within the roughness sublayer. A 16-mode model of the full surface faithfully reproduced most of the characteristics of flow over the full surface for both developing and developed flow conditions. However, both models failed to reproduce important details of the Reynolds-shear-stress-producing events within the roughness sublayer. The final report details these observations. This effort explored the impact of various topographical scales present within irregular surface roughness on a turbulent boundary layer. Low-order representations of a surface replicated from a turbine blade damaged by deposition of foreign materials were generated using singular value decomposition to decompose the complex topography into a set of topographical basis functions of decreasing importance to the original ("full") surface. The low-order surface models were then formed by truncating the full set of basis functions at the first 5 and 16 modes (containing 71% and 95% of the full surface content, respectively), so that only the largest-scale topographical features were included in the models while the finer-scale surface details were excluded. Physical rep...