METU NCC>>SEMINAR

SEMINAR ANNOUNCEMENT

Measurement Techniques in Applied Mechanics

by

Dr. F. Gökhan Ergin

Monday, 26 October, 2009

Time: 13.30

Place: Cultural and Convention Center, Amfi 2

Abstract:

Boundary layer stability and transition remains to be an important topic in fluid mechanics. Roughness effects on boundary layers have been studied experimentally to provide qualitative results or empirical transition relations, but these works do not address theoretical models that consider the streamwise disturbance evolution in the boundary layer. One such theory – transient growth – suggests that 3D disturbances, the ones that are generated by roughness elements, undergo algebraic growth followed by exponential decay. In the first part of this talk a brief overview of boundary layer theory and the Blasius flow geometry is presented. Steady and unsteady hotwire measurements of roughnes-induced velocity disturbances confirm the validity of the transient growth theory and provide quantitative information for direct numerical simulations and receptivity calculations. While the steady flow reveal the existance of a horseshoe vortex system, the unsteady fluctuations exhibit how certain frequencies bring about transition thru a turbulence cascade in the power spectrum.

Although constant temperature anemometry is well suited for high-bandwidth turbulence measurements, alternative optical techniques are available for flow diagnostics with the recent advances in the laser and detector technology. Measurements of velocity, temperature, particle size and species concentration are presented in the second part. Popular methods include Particle Image Velocimetry (PIV), Laser Induced Fluorescense (LIF), Interferometric Particle Imaging (IPI), Laser Induced Incandescense (LII) and Rayleigh Thermometry. Application examples of combined measurements will be presented with an emphasis on combustion diagnostics.

Short Biography:

• BSc: 2000, Middle East Technical University, Department of Mechanical Engineering, Ankara, Turkey.
• PhD: 2005, Case Western Reserve University, Department of Mechanical and Aerospace Engineering, Cleveland, OH, USA.
• 2005-present: Regional Export Manager, Dantec Dynamics A/S, Copenhagen, Denmark.