Gregory Elliott

High Reynolds number compressible free shear layers were studied experimentally to explore the effects of compressibility on the turbulence field. Previous preliminary results reported by the authors showed that the level and the lateral extent of turbulence fluctuations are reduced as the compressibility, which is characterized by a convective Mach number, is increased. The two convective Mach numbers used in the previous study were relatively close, Mc=0.51 and 0.64, and as a result the conclusions were not concrete. The present results with Mc=0.86 strongly support the earlier results, showing even higher reductions in the level and the lateral extent of Reynolds stresses. The higher-order moments of turbulence fluctuations such as skewness and flatness are reported, which show that the intermittency resulting from the excursion of large-scale structures into the free streams at the edge of shear layers was significantly reduced (both in the level and the extent) because of increased Mc. In the developing region of shear layers, development of mean flow and turbulence fluctuation profiles are reported that have similar trends seen in incompressible shear layers.

A high Reynolds number two-dimensional constant pressure compressible shear layer was formed at the trailing edge of an 0.5 mm-thick splitter plate. Convective Mach numbers of 0.51 and 0.64 were investigated using a two-component coincident LDV for the measurements. For the lower convective Mach number case, the nondimensionalized shear-layer and vorticity thickness growth rates were over 20 percent higher and the momentum thickness growth rate was over 30 percent higher than those of the higher convective Mach number case. The results seen to indicate that both small scale and large scale mixing are reduced with increasing convective Mach number.

An experimental investigation was conducted to examine the effect of a pulsed Nd:YAG laser energy addition on the shock structures and surface pressure in a Mach 3.45 flow past a sphere. Two configurations were considered: 1) a sphere in a uniform freestream and 2) an Edney IV interaction generated by impingement of an oblique shock on the bow shock of the sphere

Experiments were conducted to quantify the temperature and electron number density of a laser spark formed in air. The laser spark was created by focusing a 180-mJ beam from the second harmonic (wavelength of 532 nm) of a pulsed Nd:YAG laser with a 100-mm focal length lens. For early times, between 50 ns and 1 μs, images of the spark emission have been obtained to characterize the geometry. Also the temperature and electron number density were measured from the emission spectra between 490 and 520 nm where 46 N II lines are observed. The methodology of fitting the experimental data to the modeled spectra to deduce the temperature and electron number density is described. For the initial temporal range, the temperature peaks at approximately 50,000 K and decays over the first 1 μs. The electron number density peaks at approximately 10 19 cm -3 , decaying only slightly slower than t -1 . For the longer temporal evolution, from 20 to 1000 μs, planar temperature measurements were achieved using filtered Rayleigh scattering. The peak temperature starts at approximately 4100 K at 20 μs and decays to 580 K by 1 ms. The planar temperature images show a center jet propagating in the opposite direction as the initiating laser beam, which induces a vortex ring (or torus) propagating in the direction of the beam. The evolution of the position and radius of the torus structure is described and fit with a power law utilized by previous investigators. The temperature of the plasma created by laser-induced optical breakdown appears to fit quite well using a triple exponential over the four orders of magnitude of temporal range where measurements were conducted.

Abstract Increasingly mechanical engineering departments are beginning to incorporate remotely operated laboratories into their laboratory curriculums. Yet very few studies exist detailing the extent to which this new medium for laboratory delivery fulfills the educational goals of traditional in‐person laboratories. This paper describes a comparison of educational outcomes between in‐person and remotely operated laboratories in the mechanical engineering curriculum. The study carried out in the 2001 Fall semester was performed using a remotely operated and an in‐person jet thrust laboratory. The laboratories illustrate the fundamentals of compressible fluid mechanics as part of an undergraduate mechanical engineering curriculum. The results from this study indicated no significant difference in the educational outcomes between students who performed the in‐person or the remote experiment.