ISSN:0030-3909    

DOI:10.1080/713820139

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The problems of biased velocity statistics in laser anemometry in turbulent flows, whereby the higher velocities are sampled more frequently than the lower ones, is now well accepted and understood. This paper deals with the additional and previously unquantified bias which occurs when two fluids with different particle concentrations undergo turbulent mixing. A simplified one-dimensional analysis of this effect is presented and applied to a typical turbulent mixing flow, where it is shown that large errors in turbulence intensity and moderate errors in mean velocity are possible. Methods of avoiding or minimizing these errors are discussed.

ISSN:0030-3909    

DOI:10.1080/713820143

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Photon correlation spectroscopy has been used to study a monodisperse polystyrene latex during swelling by styrene monomer. Experimental results are presented which show that the latex became less stable and aggregated. A theory was developed to describe the results in terms of a static structure factor S(K) expressed as a sum of interference form factors between particles constituting the aggregates. By making the approximation that interference between nearest neighbours was the dominant term, it was possible to describe the state of aggregation of a system in terms of a mean coordination number. Where sufficient experimental data was available the theory was used to determine approximate values for both the swollen particle diameter and the degree of aggregation.

ISSN:0030-3909    

DOI:10.1080/713820144

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Laser Doppler anemometry has been applied to the study of particle velocity in an electrostatic precipitator. With the precipitator switched off the air flow velocity and turbulence levels are obtained. When the precipitator is operating the particles are charged and migrate towards the earthed walls of the duct. Migration velocities of the order of 0·2 m s-1are measured.

ISSN:0030-3909    

DOI:10.1080/713820134

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

In this contribution we investigate the applicability of photon correlation techniques as a clinical tool for the evaluation of motility parameters of undiluted human sperm. Measurements on semen samples, selected visually for ‘good’ motility, yielded reproducible estimates of the fraction motile spermatozoa and the mean speed of the motile cells.

ISSN:0030-3909    

DOI:10.1080/713820141

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A stochastic model (‘conveyer belt’ model) is applied to analyse the correlation function of the recurrance rate of events in turbulent flow. The modification owing to single-clipping in a digital correlator also is investigated. The results are applied to experiments in vortex flow and to the fluctuating intensity behind random phase screens under coherent illumination. Experimental setups for recurrence rate processing with photon detection are described. Furthermore, the use of CCD arrays for the spatial analysis of extended flow field maps is exemplified. The caustic lines behind random phase screens observed by Jakeman, Pusey and co-workers are found to form Poisson line systems. They can serve as virtual ‘particles’ in variants of laser anemometry. The probability after-effect function can be analysed by the theoretical model, and good agreement with experimental results is found, particularly for a single-clip level of zero.

ISSN:0030-3909    

DOI:10.1080/713820136

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The cross-beam rate correlation method allows one to determine eulerian velocity correlation functions with an improved signal-to-noise ratio, if a phase locked loop type LDA tracker is inserted into the system. Quantization noise due to scaling can be greatly reduced by a digital subtractor in situations of high rates of background pulses as they commonly occur in PLL rate correlation.

ISSN:0030-3909    

DOI:10.1080/713820137

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Laser transit anemometry (LTA) systems find many practical applications where the statistical variability noise produced by wall flare light limits signal detection. Under these conditions, non-linear threshold-detection and pulse-centre-estimation, along with cross-correlation processing, is superior to either photon correlation or to classical pulse pair timing. We have developed a photon-limited pulse-centre estimation discriminator and demonstrated the efficiency of this with cross-correlation processing in recent unseeded back-scatter wind tunnel tests with the new SDL LTA system. This paper introduces ideas concerning cross-correlation of non-linearly discriminated LTA signals, some effects of correlator parameters on the measurement of turbulence, and supportive experimental results from steady transonic flow.

ISSN:0030-3909    

DOI:10.1080/713820133

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Mechanical Engineering Laboratory of GEC Power Engineering Ltd. has developed a dual focus laser anemometer primarily for the measurement of flow velocities and directions in turbomachinery components. Typically, the anemometer is required to measure supersonic velocities in hostile environments with access to the point of measurement so restricted that a backscatter optical arrangement must be used. The GEC anemometer is an integrated optical unit which is mounted on a motorized traverse table thereby providing the opportunity for remote operation of the whole unit. Signals from the photomultipliers are processed in a Malvern correlator which is interfaced with a HP 9825A desk-top computer for on-line data reduction. In fact, the operation of the whole system is centred on this computer which is also used to control the motorized traverse movements. The policy within GEC is that experimental work should be directed towards the validation of design assumptions and the improvement of theoretical prediction techniques. To this end the anemometry equipment has recently been employed in the measurement of flow conditions through a cascade of turbine guide blades with supersonic exit velocities. The blades under test represented typical turbine sections and in this application the cascade was fed from a compressed air supply which exhausted from the cascade to atmosphere. The anemometer measurements were all made at the mid-span plane of the cascade where the flow conditions were two-dimensional, a series of traverses being conducted to evaluate flow conditions within and downstream of the blade passages. These measurements also permitted a detailed investigation of shock waves and blade wakes, features which had been previously located from Schlieren photographs. A programme of theoretical predictions of the flow through the cascade was subsequently undertaken using a two-dimensional time-marching method. The comparison between these predictions and the test data revealed serious errors in the flow predictions near the blade trailing edges, the errors being attributed to difficulties in accurately modelling the blade trailing edge geometry in the computer program. These problems are being attended to during the course of program development, which has clearly benefited from the availability of accurate experimental data.

ISSN:0030-3909    

DOI:10.1080/713820142

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Effective models for fitting a whole range of photon-correlation data are described. They incorporate the maximum number of degrees of freedom which may be used without the fit becoming unstable due to ill-conditioning and lead to a computer program which is extremely fast and may readily be implemented on a minicomputer. The results of some preliminary calculations on laser anemometry and macromolecular polydispersity are presented.

ISSN:0030-3909    

DOI:10.1080/713820140

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor