Mach 10 Bow-Shock Unsteadiness Modeled by Linear Combination of Two Mechanisms.

This paper presents mechanisms to explain, as well as mathematics to model, time-averaged spatially resolved amplitude observations of number density and number density unsteadiness in a Mach 10 flow as it transitions from the freestream, through a bow-shock wave, and into the gas cap created by a blunt-body model. The primary driver for bow-shock unsteadiness is freestream unsteadiness or "tunnel noise." Primary unsteadiness is bow-shock oscillation. It scales spatially with the number density first derivative and is modeled using a sech2(z) term. Secondary weaker unsteadiness begins as freestream unsteadiness and increases linearly in direct proportion to the gas number density across the bow shock and into the gas cap. This is the well-known amplification of the freestream turbulent kinetic energy mechanism and is modeled using a tanh(z) term. Total unsteadiness [fit using tanh(z) term + sech2(z) term] is expressed as the number density standard deviation and modeled as a linear combination of these two independent, simultaneous, and nonlinear unsteadiness mechanisms. Relationships between mechanism coefficients and various flowfield and wind-tunnel parameters are discussed. For example, bow-shock and gas cap oscillation amplitudes are linearly correlated with stagnation pressure and, by deduction, freestream unsteadiness.

Pressure measurement in supersonic air flow by differential absorptive laser-induced thermal acoustics.

Nonintrusive, off-body flow barometry in Mach 2 airflow has been demonstrated in a large-scale supersonic wind tunnel using seedless laser-induced thermal acoustics (LITA). The static pressure of the gas flow is determined with a novel differential absorption measurement of the ultrasonic sound produced by the LITA pump process. Simultaneously, the streamwise velocity and static gas temperature of the same spatially resolved sample volume were measured with this nonresonant time-averaged LITA technique. Mach number, temperature, and pressure have 0.2%, 0.4%, and 4% rms agreement, respectively, in comparison with known free-stream conditions.

Common-path heterodyne laser-induced thermal acoustics for seedless laser velocimetry.

We demonstrate the use of a novel technique for the detection of heterodyne laser-induced thermal acoustic signals that allows the construction of a highly stable seedless laser velocimeter. A common-path configuration is combined with quadrature detection to provide flow direction, to greatly improve robustness to misalignment and vibration, and to give reliable velocity measurement at low-flow velocities. Comparison with Pitot tube measurements in the free stream of a wind tunnel shows root-mean-square errors of 0.67 m/s over the 0-55-m/s velocity range.

Simultaneous velocimetry and thermometry of air by use of nonresonant heterodyned laser-induced thermal acoustics.

Nonresonant laser-induced thermal acoustics is used with heterodyne detection to measure temperature (285-295 K) and a single component of velocity (20-150 m/s) in an atmospheric pressure, subsonic, unseeded air jet. Good agreement is found with Pitot-tube measurements of velocity (0.2% at 150 m/s and 2% at 20 m/s) and the isentropic expansion model for temperature (0.3%).

Optical measurement of the speed of sound in air over the temperature range 300-650 K.

Using laser-induced thermal acoustics (LITA), the speed of sound in room air (1 atm) is measured over the temperature range 300-650 K. Since the LITA apparatus maintains a fixed sound wavelength as temperature is varied, this temperature range simultaneously corresponds to a sound frequency range of 10-15 MHz. The data are compared to a published model and typically agree within 0.1%-0.4% at each of 21 temperatures.

Nonresonant referenced laser-induced thermal acoustics thermometry in air.

We report a detailed investigation of nonresonant laser-induced thermal acoustics (LITA) for the single-shot measurement of the speed of sound (v(S)) in an oven containing room air. A model for the speed of sound that includes important acoustic relaxation effects is used to convert the speed of sound into temperature. A reference LITA channel is used to reduce uncertainties in v(S). Comparing thermocouple temperatures with temperatures deduced from our v(S) measurements and model, we find the mean temperature difference from 300 to 650 K to be 1% (+/-2sigma). The advantages of using a reference LITA channel are discussed.

Planar Rayleigh scattering results in helium-air mixing experiments in a Mach-6 wind tunnel.

Planar Rayleigh scattering measurements with an argon-fluoride excimer laser are performed to investigate helium mixing into air at supersonic speeds. The capability of the Rayleigh scattering technique for flow visualization of a turbulent environment is demonstrated in a large-scale, Mach-6 facility. The detection limit obtained with the present setup indicates that planar, quantitative measurements of density can be made over a large cross-sectional area (5 cm x 10 cm) of the flow field in the absence of clusters.

Histological study of furcation perforations treated with tricalcium phosphate, hydroxylapatite, amalgam, and Life.

One-hundred twenty experimental furcation perforations were created in the mandibular and maxillary premolars and molars of six rhesus monkeys. Tricalcium phosphate, hydroxylapatite, amalgam, and Life were used to repair the furcation perforations. The animals were sacrificed at the intervals of 2, 4, and 6 months after the experiment. Histological evaluation revealed lack of complete healing of furcation perforations repaired with any materials. Epithelium was present in the furcation perforations in both experimental and positive control groups. No hard tissue formation was observed in this study. Inflammation in the furcation area may be due to inadequate sealing ability of the repair materials.

Postnatal and antenatal laboratory diagnosis of glutaric aciduria II in a South African family.

Glutaric aciduria type II (GA II) was proved in a neonate who presented shortly after birth with respiratory distress, metabolic acidosis, non-ketotic hypoglycaemia and a sweaty-feet-like odour. The diagnosis was based on elevated levels of glutaric and other acids in the urine and on studies on cultured skin fibroblasts where defective metabolism of fatty acids of varying chain length was demonstrated. Antenatal diagnosis was performed on a subsequent pregnancy in this family where an abnormal amniotic fluid organic acid profile together with defective fatty acid oxidation in cultured amnion cells was indicative of GA II in the fetus. This is the first report of this genetic disorder in a South African family and it should be considered in suspected organic acidaemia in the neonatal period.

Evaluation of aortic valve endocarditis by two-dimensional echocardiography.

Fourteen patients with aortic valve endocarditis were evaluated. Twelve patients had vegetations detected by two-dimensional echocardiography and two were diagnosed anatomically. M-mode echocardiography was positive in eight patients. Two-dimensional echocardiography was superior to M-mode in determining size, shape, and mobility of vegetations. The following three morphologic types of vegetative lesions were seen on two-dimensional echocardiogram: globular polypoid masses (seven); irregular, elongated lesions with chaotic movement (four); and a cord-like structure (one). Serial two-dimensional echocardiograms performed after completion of antibiotic therapy in seven patients revealed no change in appearance in five and complete disappearance in two patients. Among the 12 patients with vegetations visualized on the two-dimensional echocardiogram, seven responded to medical therapy, four required aortic valve replacement, and one patient died. One of the patients who initially responded to medical therapy eventually required aortic valve replacement following a second episode of aortic endocarditis. In those patients with negative two-dimensional echocardiograms, the vegetations were 3 mm in diameter or less at surgery or autopsy. Vegetations that were visualized on two-dimensional echocardiography were found to be at least 5 mm in diameter at the time of operation. Two-dimensional echocardiography is a valuable noninvasive tool in the evaluation of patients with aortic valve endocarditis.