ALBERT

Notes: The density field of underexpanded supersonic free jets issuing from a choked circular nozzle was measured using a Rayleigh scattering-based technique. This reliable and nonintrusive technique is particularly suitable for high-speed flows and is fundamentally superior to the intrusive probes and particle-based techniques such as laser Doppler velocimetry. A continuous wave laser and photon counting electronics were employed for time and phase-averaged density measurements. The use of dust-free air for the entrained flow allowed measurements in the shear layer region. The free jets were produced in the plenum to ambient pressure ratio range of 1.88–5.75, which corresponded to a fully expanded Mach number range of 0.99≤Mj≤1.8. A comparative study of schlieren photographs and time-averaged density data provided insight into the shock-cell structures. The radial profiles obtained at various axial stations covering a downstream distance of 10 jet diameters show the development of the jet shear layer and the decay of the shock–cells. The supersonic free jets produced screech sound. A phase-averaged photon counting technique, using the screech tone as the trigger source, was used to measure the unsteady density variation. The phase-averaged density data show the evolution of the large-scale turbulent vortices that are found to be modulated periodically along the flow direction. A comparison with previously obtained data showing near-field pressure fluctuation and convective speed of the organized vortices reveals many interesting dynamics. All quantities show regular spatial modulation. The locations of local maxima in density fluctuations are found to coincide with the high convective speed and the antinode points in the near-field pressure fluctuation. Interestingly, the periodicity of modulation is found to be somewhat different from the shock spacing. Instead it shows that the standing wave system, known to exist in the near-field pressure fluctuation, extends into the jet shear layer. The standing wave is formed between the downstream moving Kelvin–Helmholtz instability waves and the upstream propagating part of sound waves. A detailed field measurement of the unsteady density fluctuation was conducted for the Mj=1.19 and 1.42 jets for which the near-field pressure fluctuation data were obtained previously. The phase-matched, combined plots of the density fluctuation present inside the jet flow, and the pressure fluctuation present just outside the jet boundary provide a charming insight into the shock–vortex interaction leading to the sound wave generation. © 1999 American Institute of Physics.

Notes: Instabilities present in a swirling jet in the Reynolds number range from 20 000 to 60 000 and a nominal swirl number of 0.5 were studied experimentally, using smoke visualization, hot-wire anemometry and acoustic excitation. Flow visualization photographs of the natural jet show vortex breakdown at the core and rolling up of the shear layer around the jet into weak, irregular, large-scale organized structures. When forced by acoustic excitation these structures became energetic and periodic. Axisymmetric and helical instability waves in the Strouhal number range 0.75 to 1.5 were excited and their evolution along the axial direction were measured from velocity spectra and ensemble averaged measurements. Compared to a nonswirling jet, the overall growth of the instability waves is considerably smaller, and vortex pairing is suppressed in a swirling jet. However, the overall spread and mass entrainment rates are higher in the latter. Measurements of the mean velocity components and turbulence fluctuations show that the vortex breakdown affects the axial velocity distribution and rapidly replaces the potential core with a large amount of turbulence. Upon interacting with the vortex breakdown, the shear layer along the jet periphery loses its organized structure and, in general, "random turbulence'' follows.

Notes: Scattering of coherent light as it propagates parallel to a shock wave, formed in front of a bluff cylindrical body placed in a supersonic stream, is studied experimentally and numerically. Two incident optical fields are considered. First, a large diameter collimated beam is allowed to pass through the shock containing flow. The light intensity distribution in the resultant shadowgraph image, measured by a low light CCD camera, shows well-defined fringes upstream and downstream of the shadow cast by the shock. In the second situation, a narrow laser beam is brought to a grazing incidence on the shock and the scattered light, which appears as a diverging sheet from the point of interaction, is visualized and measured on a screen placed normal to the laser path. Experiments are conducted on shocks formed at various free-stream Mach numbers, M, and total pressures, P0. It is found that the widths of the shock shadows in a shadowgraph image become independent of M and P0 when plotted against the jump in the refractive index, Δn, created across the shock. The total scattered light measured from the narrow laser beam and shock interaction also follows the same trend. In the numerical part of the study, the shock is assumed to be a "phase object,'' which introduces phase difference between the upstream and downstream propagating parts of the light disturbances. For a given shape and Δn of the bow shock the phase and amplitude modulations are first calculated by ray tracing. The wave front is then propagated to the screen using the Fresnel diffraction equation. The calculated intensity distribution, for both of the incident optical fields, shows good agreement with the experimental data. © 1995 American Institute of Physics.

Notes: Summary Influence of thyroid hormones on splenic activities and the role of the spleen during pregnancy were not known. The present study revealed that increased enzyme activities of spleen are associated with pregnancy, and hypothyroidism during gestation led to decreased activities, indicating that the thyroid gland influences them.

Notes: Abstract A number of samples from the pre-burning zone of a wet-process cement rotary kiln were examined by combined DTA/TG and XRD for estimation of spurrite (2Ca2SiO4·CaCO3). It was found that decarbonation temperatures of spurrite range from 1130 to 1190 K and they are 45 to 75 K higher than that of calcite occurring in the same sample. In the TG curves calcite and spurrite can be easily distinguished and accordingly both can be estimated from the same TG scan. Combined DTA/TG, supplemented by XRD, is a very effective method for qualitative and quantitative estimation of spurrite in cement rotary kiln materials.

Notes: Summary The problem on boundary layer flow of an visco-elastic fluid around a harmonically oscillating right circular cylinder has been discussed in this paper. The equations for the velocity field have been solved by using the successive approximation method. It is observed that in the immediate neighbourhood of the wall of the cylinder the stream lines are closed loops, but beyond this layer they are not so.

Notes: Abstract The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid〉acrylic acid〉fumaric acid〉maleic acid. A plausible mechanism is discussed.