Date of Award

2007

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Kiran Bhaganagar

Second Committee Member

Mohen Shahinpoor

Third Committee Member

R.C. Hill

Abstract

Turbulent flow over rough surfaces is a complex problem and many fundamental issues remain unanswered. Surface-roughness cannot be ignored in real-life of the practical applications of the turbulent flow, including biomedical, naval applications, environmental flows and turbo machinery flows. Although rough-wall turbulent boundary layer is characterized by random flow behavior, there are organized and highly energetic structures lying beneath this chaos which are called coherent structures. Fundamental issues in the turbulent boundary analysis over rough surfaces are (a) nature of the interaction between the inner and outer layer regions of the flow, (b) measure of the depth of the roughness sublayer, (c) modification of the coherent structures due to surface-roughness. The objective of the present thesis is to address some of the fundamental questions related to surface-roughness. For this purpose, a snapshot Proper Orthogonal Decomposition (POD) is used to investigate rough-wall turbulent boundary layer in a " channel geometry. A code is developed for the snapshot POD method based on a two point correlation tensor of the flow field. 1-D POD in the wall-normal y direction, 2-D POD in the y - z and in x - y planes has been performed on the 3-D velocity database obtained from direct numerical simulations (DNS) for a channel flow at Rer = 180. 1-D POD analysis has revealed that convergence of the POD for the rough-wall is slower compared to the smooth-wall, which is attributed to the increase in range of length scales due to surface-roughness. For the egg-carton roughness elements, the depth of a i roughness sublayer \^2ode) for POD mode n decays with increasing mode number in an exponential manner.

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