Global Skin Friction Diagnostics: The Glof Technique and Measurements of Complex Separated Flows
Date of Award
Doctor of Philosophy
Mechanical and Aeronautical Engineering
Dr. Tianshu Liu
Dr. Parviz Merati
Dr. Javier Martin Montefort-Sanchez
Dr. Phuriwat Anusonti-Inthra
skin friction, global measurement, oil film, surface temperature, mass transfer
This work describes the application of the global luminescent oil film skin friction meter to quantitative global skin friction diagnostics of complex separated flows. The development of this technique is based on the relationship between the oil film thickness and luminescent intensity of a luminescent oil film. The projected thin oil film equation is given to relate the normalized luminescent intensity with skin friction. The variational formulation with a smoothness constraint on skin friction is proposed to obtain a snap shot solution from two consecutive images for a relative skin friction field. A complete skin friction field is reconstructed through superposition of a sequence of snap shot solutions.
A refinement is implemented for this technique focused on data reduction simplification and robustness, luminescent oil formulation, UV excitation and oil film application. This is complemented by a systematic study with emphasis on parametric analysis of data reduction variables such as spatial resolution, time step, Lagrange multiplier, image file format and image filtering.
A number of separated flows were also investigated – a low aspect ratio NACA0012 rectangular wing at different angles of attack, wing-body junction flow and delta wings at different angles of attack, yaw and roll. Detailed analysis of the complex skin friction topology of each test case was carried out along with topological constraint analysis using the Poincare-Bendixson index formula. The conservation law given by the Poincare-Bendixson index formula for the number of isolated singular points and boundary switch points in a region enclosed by a penetrable boundary is utilized as a general approach in analyzing the topological features of the skin friction fields.
A systematic approach was developed to map skin friction vectors from the two dimensional image plane to a three dimensional model surface in the object space. Combined surface pressure and global skin friction measurements were also conducted for junction flows and the Ahmed body to provide a unique perspective of studying these separated flows. Finally, the feasibility of heat transfer and mass transfer approaches for global skin friction diagnostics were also investigated.
Woodiga, Sudesh A., "Global Skin Friction Diagnostics: The Glof Technique and Measurements of Complex Separated Flows" (2013). Dissertations. 173.