John E. LaGraff

High Frequency Surface Heat Flux Imaging of Bypass Transition

A high-frequency surface heat flux imaging technique was used to investigate bypass transition induced by freestream turbulence. Fundamental experiments were carried out at the University of Oxford using high-density thin film arrays on a flat plate wind tunnel model. Bypass transition was induced by grid-generated turbulence with varying intensities of 2.3%, 4.2%, and 17% with a fixed integral length scale of approximately 12 mm. Unique high resolution temporal heat flux images are shown which detail significant differences between unsteady surface heat flux events induced by freestream turbulence and the classical Emmons-type spots which many turbomachinery transition models are based on. The temporal imaging technique presented allows study of unsteady surface heat transfer in detail, and helps elucidate the complex nature of transition in the high-disturbance environment of turbomachinery.

Measurement of turbulent spot convection rates in a transitional boundary layer

Abstract A new technique, based on the analysis of the signature of turbulent spots on the heat flux at the wall, is used to estimate the propagation rates of naturally occurring turbulent spots in a zero pressure gradient transitional boundary layer. Experiments were performed in a compression-heated transient aerodynamic facility using a flat plate with 32 thin-film heat transfer gauges along its centerline. Simultaneous wide-bandwidth heat transfer measurements at a number of streamwise locations were used to track the coherent transitional activity along the plate. The free-stream turbulence intensity was about 0.5%, and tests were performed at unit Reynolds numbers in the range 1.8 × 106−4.2 × 106 m −1 . Special data reduction techniques were used to calculate the convection velocities of the leading and trailing edges of the turbulent spots, and these results compared well with those for artificially generated spots. The intermittency distribution in the transition zone showed good agreement with the “universal” distribution of Narasimha, confirming the reliability of this technique.

An isentropic compression-heated Ludweig tube transient wind tunnel

Abstract The operating principle of a single-stroke, compression-heated, blowdown wind tunnel is described. The facility is known as a LICH tube (a term coined by the developers of the operating technique, Drs. Oldfield, Jones, and Schultz of Oxford University) because of its original description as a Ludweig tube with Isentropic Compression Heating. The facility, formerly operated as a shock tunnel, had the diaphragm station replaced with a quick-acting ball valve and a piston placed immediately downstream. Near the end of the compression process, a fast-acting gate valve opens, allowing the flow of a high-pressure, high-temperature gas into the test section nozzle. A full analysis of the wave dynamics of the pump tube compression process is presented. Preliminary experimental measurements of the facility performance are presented and compared with the theoretical predictions of pressure, temperature, run time, and flow steadiness. Due to the fundamentally different wave dynamics of a LICH tube, the run times are significantly larger than with shock tubes/tunnels.

Research and educational initiatives at the Syracuse University Center for Hypersonics

The Department of Mechanical, Aerospace, and Manufacturing Engineering and the Northeast Parallel Architectures Center of Syracuse University have been funded by NASA to establish a program to educate young engineers in the hypersonic disciplines. This goal is being achieved through a comprehensive five-year program that includes elements of undergraduate instruction, advanced graduate coursework, undergraduate research, and leading-edge hypersonics research. The research foci of the Syracuse Center for Hypersonics are three-fold; high-temperature composite materials, measurements in turbulent hypersonic flows, and the application of high-performance computing to hypersonic fluid dynamics.