A series of experiments has been conducted in a low-speed wind tunnel in which measurements were performed in a two-dimensional turbulent shear layer experiencing the mixing of both a passive and a chemically reacting species. The low-temperature air in the jet's primary flow was seeded with dilute concentrations of N2O4 so that the dissociation reaction N2 + N2O4 [harr ] 2NO2 + N2 occurred in a near-equilibrium manner within the mixing layer owing to the turbulent mixing properties and the imposed temperature gradient. Mean and fluctuating values of velocity, temperature and NO2 concentration were measured up to axial distances of 25 in. for jet velocities of 23 and 50ft/s (Rex [les ] 7 × 105) and for three primary temperatures (252, 273 and 305°K). Velocity and temperature measurements were performed with hot-wire probes, whereas a fibre optics light sensor probe was used to measure NO2 concentrations. Local correlations between species and other fluid properties were obtained by positioning a hot-wire sensor within the light gap of the fibre optics probe and simultaneously recording output signals from both probes. A relatively complete set of turbulent statistics was measured for the non-reacting shear layer, including such results as temperature/species correlations, probability densities, filtered and unfiltered moving-frame velocities, skewness and flatness factors, spectra, velocity and temperature integral scales, intermittency factors for velocity, temperature and passive species, and conventional intensities. Some typical results from the investigation are as follows: the turbulent Schmidt and Lewis numbers were 0·5 and 1·0 respectively; the correlation between passive NO2 concentration and temperature was approximately 0·95; dramatic changes consistent with equilibrium chemistry occurred in NO2 concentration profiles with chemical reaction; velocity, temperature and concentration spectra were comparable over a 2½-decade range in wavenumber (k−2); spectra, probability densities, time-trace data and smoke-seeded shear-layer photographs indicate that, for axial locations x = x0 [ges ] 18·5 in. and for speeds u1 [ges ] 23ft/s, undisturbed edge fluid rarely penetrates completely across the mixing region. Although not specifically addressed during the current study, measured results herein suggest that the turbulent motion for the present shear layer is characterized more by random and/or three-dimensionality effects than by large-scale two-dimensional coherent structures, as has been observed recently in other shear-layer investigations.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022112077000536

Turbulent mixing of passive and chemically reacting species in a low-speed shear layer

A method of optimizing performance of a wind turbine electric generator (WTG) comprises the steps of measuring the performance of a wind turbine electric generator, defining an area on a blade of the WTG, placing stall flags within said defined area, monitoring the behavior of the stall flags when the WTG is operating, determining a stall line based upon the stall flags during operation, installing vortex generators on the blade adjacent to and upwind of said stall line, monitoring the behavior of said stall flags during operation with vortex generators installed on all blades, and measuring the performance of the WTG to detect improved performance. If there is little or no improvement, repeating the steps on a second WTG using different placement within the defined area for the vortex generators.

Method for determining optimum vortex generator placement for maximum efficiency on a retrofitted wind turbine generator of unknown aerodynamic design

In order to investigate and analyse vibrations of any object, light from a laser is split with part being emitted to an object and part being mixed with the light reflected from the object to create an interference signal. That interference signal is investigated to derive therefrom a signal representing the vibrations of the object If there is bulk movement of the object, the effect of that bulk movement may impose a popular shift on the reflected light. To eliminate this from the investigation of the vibrations of the object, an estimate of frequency corresponding to the effect of the bulk movement is derived from the signal, and that used to defuse a signal of reduced bandwidth encouraging the frequency due to the bulk movement and also the frequencies of vibration Thus, the vibrations can then be derived and investigated from analysis of that signal of reduced bandwidth.

Method of investigating vibrations and an apparatus therefor

: The mean flow field of the axisymmetric turbulent wake shed by a very slender body at Mach 3 has been mapped with the aid of the pitot and static pressure probes and the hot-wire anemometer The experimental geometry was chosen so that no inviscid wake existed, and the measurements were carried out to about 100 diameters downstream of the base The axial variation of the velocity and temperature defects appears to obey classical decay laws following a relaxation distance of at least 40 diameters from the transition region By contrast, the radial profiles of these properties relax quickly to a self- preserving form; both the temperature and the velocity radial variations fit single-parameter Gaussian distributions quite well The proper radial similarity variable is the radius divided by the transverse wake scale; equally good agreement obtains for a Howarth-Dorodnitzyn-transformed radius, although this issue is still unsettled because of the low Mach number used The turbulent Reynolds and Prandtl numbers computed indirectly from the data agree well with similar results from low-speed turbulent flows

Mean-flow measurements in an axisymmetric compressible turbulent wake.

The present invention relates generally to the utilization of laser interferometry for performing detection of buried structures such as underground natural gas pipeline. More specifically, the invention relates to the use of a laser interferometer system for detecting leaks and similar defects, such as corrosion, in buried pipelines, pressurized containers or other metallic structures, based upon the sensing of subnanometer earth surface displacements produced by elastic waves which are emanated from the leak or defect and propagate in the surrounding earth medium.

Laser interferometry detection method/apparatus for buried structure

Methods and apparatus are disclosed for measuring and monitoring vibrational or similar motion in mechanical elements. Retroreflectors on the elements are illuminated with monochromatic light, preferably a laser, and the reflected beams form an interference pattern. Shifts in the interference fringes correspond to motion which changes the relative length of the paths of reflected light and these shifts are counted or analyzed to monitor such motion. Both micro and macro motion can be monitored.

Motion detection and measurement

The effects of temperature fluctuations in a hypersonic turbulent wake on a chemical reaction with a strong temperature dependence are analyzed to determine the appropriate turbulence parameters for several different turbulent wake models. The chemical reaction selected for its temperature sensitivity is the atomic-oxygen chemiluminescent recombination. This radiation has been measured behind nonablating spheres in air in the General Motors Ballistic Range by Reis. The wake turbulence models are: a) random inviscid convection (so-called "marble cake"), b) homogeneous mixing, c) partial dissipation or bimodal model, d) mixinglag models, and e) gaussian mean-temperature profile with superimposed fluctuations. The data are interpreted in terms of each model. It is shown that models a, b, and d are inconsistent with the data. The radiation is interpreted in terms of the unmixed volume fraction of the partial dissipation model to obtain the rms turbulent temperature and mass density fluctuations and the turbulent dissipation function, which is then applied to predict the rms fluctuations of electron density. It is found that the resulting predictions are consistent with other measurements. The dissipation function indicates that the mixing-lag length is equal to about 20 wake radii. The model involving the Gaussian mean-temperature profile and fluctuations is consistent with the data for a thermal half width equal to slightly less than ha]f the mean turbulent front wake radius, with the temperature fluctuation ratio on the axis between 0.3 and 0.5. This is consistent with the measured mean-temperature profiles and temperature fluctuations, but the results are very sensitive to the mean temperature in the wake.

Wake-temperature turbulent fluctuation decay rates deduced from O sub 2 radiation.

Methods and apparatus are disclosed for studying motion of an object or element, to determine not only quantities of motion but also direction of motion. A laser beam or the like is circularly polarized and directed to two or more retroreflectors and then to a detector. Beams of different frequencies are established and determination of relative direction of motion of the retroreflectors is made from the increase or decrease of frequency of beats of one beam against the other. In one embodiment, left and right circularly polarized light is reflected, and one of the beams is frequency-shifted. The light, being circularly polarized, is insensitive to rotational orientation of the test object, while maintaining directional and motion information.

Method of monitoring motion

A method to measure the frequency and amplitude of vibration in a rotating element is presented. Using optical interferometric techniques, the flexure and torsion of a gas turbine compressor blade is shown to be measurable over the entire 360 deg of rotation. Vibrations are shown to be measurable independent of blade rotation speed; the effects of misalignment in system are shown to be small. Angular deflections from 0.5 to 500 mrad were measured in the test system.

Morton Camac

Papers

Motion detection and measurement

Wake-temperature turbulent fluctuation decay rates deduced from O sub 2 radiation.

Method of monitoring motion

An optical technique for measuring vibratory motion in rotating machinery