Exploring laminar-to-turbulent transition in hypersonic boundary layers using planar laser induced fluorescence (PLIF)
Wednesday, February 2, 2PM
Paul M. Danehy
Laminar to turbulent transition is a critical design and operational consideration on hypersonic vehicles. Transitional and turbulent hypersonic boundary layers can have 5x higher heating levels than laminar boundary layers. In the past, extensive surface heating data has been obtained to quantify transitional boundary layers, for example for NASAâ€™s Space Shuttle Program. However to better understand the physics of the transition process, detailed flowfield data are needed. Some flowfield data have been acquired, for example using hotwire and pressure probes. These probes can be delicate, can perturb the flow and usually provide single-point measurements. Schlieren flow visualization has provided valuable imagery of transitional boundary layer flows, but this method is path-averaged which complicates identification of the flowfield structures. We have developed and applied the nitric oxide planar laser induced fluorescence (NO PLIF) imaging technique to study transition in hypersonic boundary layers. NO PLIF is a non-intrusive, laser-based spectroscopic method. We have used NO PLIF for planar and 3D flow visualizations at repetition rates up to 1 MHz in a Mach 10 wind tunnel. We have also measured quantitative velocity profiles in laminar and transitional hypersonic boundary layers passing over discrete roughness attached to a flat plate. Various shaped discrete protuberances have been investigated, including cylinder, triangles, and a smooth bump identical in shape to the protuberance attached to the windward surface of the Space Shuttle Orbiter in recent flights. Some of the data obtained with the NO PLIF method have been compared with computational predictions of the flow.
Biography: Paul Danehy received a BS in Mechanical Engineering from the University of New Hampshire in 1989 and MS and PhD degrees in Mechanical Engineering from Stanford University in 1991 and 1995 respectively. Between 1995 and 2000 he worked in the Physics Department at the Australian National University in Canberra, Australia, first as a post-doc and then as a faculty member. In 2000, he moved to the NASA Langley Research Center in Hampton, Virginia. He currently works in the Advanced Sensing and Optical Measurement Branch where he leads a research group studying hypersonic flows using planar laser-induced fluorescence (PLIF).
Host: N. Clemens