Scattered light streaming birefringence in colloidal solutions

Summary The light scattered from particles or molecules in a fluid flow is often used to perform local measurements in a three-dimensional flow field. The scattered light technique has been adopted by McAfee and Pih to the field of streaming birefringence. Their empirical relationship between the observed optical pattern and the state of the flow is extended here to describe more general flow situations. The new set of equations which includes all possible shear and dilatation terms is tested with a number of experiments in the flow of a colloidal solution. The range of validity of these equations is restricted to low-Reynolds number flows.With 14 figures     

综述:面向工程应用的激光干涉动态测量

进入21世纪之后,激光干涉作为一种成熟的非接触式动态测量技术,开始逐步应用于不同的工业领域.激光干涉动态测量技术主要分成两类:一类是基于高速相机的干涉测量技术,而另一类则是基于单像素光电探测器的干涉测量技术.这两类技术都有其局限性:基于高速相机的技术受限于相机时间轴上的采样率;而基于光电探测器的技术则在空间域上只能进行...     

Experimental study of the induced flow birefringence of a suspension of rigid particles at the transition from Couette flow to Taylor vortex flow

The flow birefringence induced in solutions of rigid particles is studied experimentally in the region of the axisymmetrical Taylor vortex flow which arises once the velocity gradient G in the annular gap of a conventional Couette cell reaches a critical value G _c .The measurements are performed for several values of G > G _c and for 10 radial observation points in the annular gap. Solutions of two types of rigid particles are investigated: the first is a suspension of flattened clay particles like bentonite, while the second contains rod-like particles of tobacco mosaic virus (TMV). The variations of the birefringence intensity n and of the extinction angle measured in the domain of the axisymmetrical flow show a different behavior according to the shape of the particle in solution. This fact is confirmed theoretically with a good agreement for the measurements performed with solutions of flat particles.     

Analysis of regular and irregular acoustic streaming patterns in a rectangular enclosure

This study reports an experimental investigation of the non-linear phenomena of regular (classical) and irregular streaming patterns generated in an air-filled rigid-walled square channel subjected to the acoustic standing waves of different frequencies and intensities. The interaction of acoustic waves and thermoviscous fluids is responsible for these phenomena. The resonator’s walls are maintained at isothermal condition. Synchronized particle image velocimetry (PIV) technique has been used to measure the streaming velocity fields. The experimental results show that at a given excitation frequency, regular streaming flow patterns are observed up to a certain value of the excitation amplitude. As the amplitude increases beyond this limit, the regular streaming is distorted to an irregular flow structure. The regular and irregular streaming are classified in terms of streaming Reynolds number . It is found that for Re_s2<50, classical streaming flow patterns are established and then deform to irregular and complex shapes as Re_s2 exceeds 50.     

Simultaneous measurements of velocity and stress distributions in polyisobutylenes using laser-Doppler velocimetry and flow induced birefringence

An experimental device was set up for the synchronous measurement of velocities and stresses in polyisobutylenes using laser-Doppler velocimetry (LDV) and the two-colour flow-induced birefringence method (FIB). The materials investigated are three low molecular polyisobutylenes. Velocity (LDV) and stress (FIB) measurements are performed in the flow entrance region and inside a slit die with a contraction ratio of 1:10. The behaviour of the polyisobutylenes is Newtonian under the flow conditions applied. Therefore, the stresses inside the fluids can be calculated and compared to the stresses experimentally determined. A good agreement in shear and elongational flows was found between the calculated (LDV) and directly measured stresses (FIB). This result demonstrates the applicability of the experimental setup as an optical rheometer that can preferentially be used to measure elongational properties of low viscous fluids.

Simultaneous measurement of transient stress and flow birefringence in one-sided compression (biaxial extension) of a polymer melt

Summary Investigation of time dependent behaviour of a polystyrene melt is carried out with the aid of a new apparatus for biaxial extension. Use is made of the method of two impinging fluid streams guided by lubricated trumpet shaped metal walls. The flow birefringence is measured in the plane of symmetry and, at the same time, the force is measured which tends to separate the trumpets. The linear stress-optical relation turns out to be valid in this new flow geometry. An accurate value for the stress-optical coefficient can be determined from the relaxation experiments. The stress build-up as calculated from the optical measurements, is compared with the pertinent result of the theory of linear viscoelasticity. For the desired interconversion of dynamic moduli use is made of the approximation by Schwarzl and Struik. The steady state measurements are checked by the results of the non-linear model of Acierno et al.With 16 figures and 2 tables     

An improved method for the measurement of strong flow birefringence

An improved procedure is proposed to solve the problem of measuring strong birefringence on flowing samples which have a retardation larger than /2 The procedure can be applied to devices which are based on the modulation of the polarization vector with a high-speed rotating half-wave plate. It uses two optical configurations which have different responses to the retardation. By combining the information obtained from the two configurations, one can easily and accurately determine the actual retardation of the sample, irrespective of the quadrant in which the measured retardation is located, provided the sample is isotropic. This technique can also overcome the problem of large errors occurring in the vicinity of = (2m+1)/2 due to the limited sensitivity around these values of . The use of the technique is illustrated with measurements on an isotropic solution of poly(benzyl glutamate) in m-cresol, which is strongly birefringent during shear flow.     

Flow birefringence study of sharkskin and stress relaxation in polybutadiene melts

In this paper we report rheo-optical and rheological observations made through a transparent slit die attached to a capillary rheometer. We find that the flow birefringence signal oscillates periodically near the die exit when sharkskin-like extrudate distortion is present. In contrast, steady behavior is observed in the die inland region. Specifically, the flow birefringence varies at the die exit with a period identical to that measured directly from the sharkskin extrudate. We also show that the exit flow instability leading to sharkskin can be observed directly through cross-polarizers in terms of the temporal change of the retardation order. We demonstrate that the same kind of interfacial flow instability can occur at a boundary discontinuity within the die land where the upper portion of a clean die wall meets the lower portion of a polysiloxane-coated die wall. Finally, stress relaxation upon the cessation of the slit die flow of two polybutadiene melts is studied through time-dependent flow birefringence measurements. The stress relaxation is then correlated with sharkskin time scales to describe the role of relaxation in sharkskin ridge formation. Received: 8 February 1999 Accepted: 28 July 1999     

Holographic interferometric investigation of shock wave interaction with a ramp

The internal flowfield including shock reflections structure inside a 2-D half inlet model was examined by a double exposure holographic interferometry using a Q-switched pulse laser. The interferograms give detailed flow visualization pictures. The structures of regular reflection, lambda reflection and Mach reflection in the inlet channel were observed. From the analysis of fringe patterns, the quantitative distributions of flow density, pressure and Mach number of the internal flowfield have been reconstructed. The boundary layer thickening and separation in the case of lambda reflection and the Mach stem in the case of Mach reflection were clearly demonstrated in the holographic fringe patterns. The results show that the shock interacitons with the ramp and the wall introduce a complicated flow structure which could strongly affect the efficiency of the inlet.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

流体双折射方法及其应用

本文在1923—1989年的工作基础上,论述了流体双折射方法,对它的发展和原理进行了详细讨论,介绍了流体双折射方法的各种应用,尤其是在生物力学,二维三维场显示方面的应用.     

An optical interferometric system for 3-D displacement measurement

Experimental Techniques -     

Two dimensional flow quantitative visualization by the hybrid method of flow birefringence and boundary integration

Flow birefringent method and its data processing was reviewed and a new hybrid method of flow birefringence and boundary integration was introduced. The basic equations and boundary conditions suitable to the hybrid method were derived, and a comparison of the hybrid and other classical methods was given. Finally as an example, the flow in a step converging tube was analyzed by the given method. The project supported by National Natural Science Foundation of China (NSFC)     

旋转翼面尾迹的流态显示技术

本文介绍了一种可用于显示旋转弹翼面在非旋转和旋转过程中拖出的涡及其轨迹的流态显示技术。本方法在烟线技术的基础上,采用新的发烟装置,既提高了发烟的浓度,延长了发烟的时间,并不增加任何附加力矩而使发烟部件随旋转弹体一起转动,从而实现了在旋转过程中进行动态的流态显示。文中对于应用此方法得到的流态的真实性进行了分析讨论,分析表明用此方法显示的流态具有一定的真实性,可以提供定性的旋转翼面尾涡流动特性。     

A laser interferometric measurement of the temperature distribution in convective thermal transfer boundary layers

By means of a double mirror interferometry a two-dimensional temperature distribution measurement in convective thermal boundary layers is presented. When the cold air flows along a hot plate model, the interferometric fringe inside the boundary layer will bend. According to the displacement of the fringe and the relation between temperature and index of refraction, a two-dimensional temperature profile is obtained. All is accomplished by optical device with the help of micro-computer without any contact with the flow field. The project supported by the National Natural Science Foundation of China     

Utilizing phase retard integration method of flow birefringence to analyse the flow with symmetric plane

The formulas which are suitable to birefringent medium with symmetric plane are derived by means of phase retard integration. We have adopted this concept to the axisymmetric problems and deduced some useful formulas for these cases. As a practical application, the strain rate analysis of flow in a diverging or a converging vessel is illustrated at the end of this paper. The project supported by National Natural Science foundation of China     

A comparison of visualization of Stokes flow in a V-shaped and rectangular channel

A comparative study of visualization of Stokes flow induced by rotation of a circular cylinder in a V-shaped and rectangular channel was performed. The visualization was carried out using solid tracers of magnesium. Some quantitative data were deduced from visualization photographs and a comparison was made.     

Numerical evaluation of extinction angle and birefringence in various directions as a function of velocity gradient

Despite the limitations of the theory of Peterlin and Stuart it still seems to be the best theory for interpreting quantitative flow birefringence measurements performed on solutions of rigid spheroidal particles. First, we repeat the numerical evaluation of the extinction angleX and the orientation factorf _z corresponding to conventional observations realized in a Couette cell, but the values are now given with a higher degree of accuracy and the range of variation of the parameters has been extended. Furthermore, using the same theory, we extend our calculations to other directions of observation. This should contribute towards avoiding false interpretations of birefringence measurements in these directions (as has sometimes occurred). Finally, we present measurements taken along the lines of flow and along the direction of the velocity gradient, thus including the principal situations met in the various cells used in flow birefringence measurements.     

Deformation measurement of conducting polythiophene thin films by an electronic speckle pattern interferometric method

The deformation measurement of electrosynthesized polythiophene (Pth) thin films is difficult because of the small thickness and high flexibility of the specimen. An electronic speckle pattern interferometry (ESPI) method is used to measure the deformation of Pth films of thicknesses in the range of 4–65 μm. Their stres-strain curve are obtained. It is found that the mechanical properties of Pth films are sensitive to the specimen thickness. The tensile strength increases with decreasing thickness of thin film from 10 μm. The influence of the electrochemical synthesis conditions on the mechanical properties of Pth films is also discussed. Project supported by the Basic-Research Foundation of Tsinghua University (JC2000057), and the Visiting Scholar Foundation of Solid Mechanical Key Lab in Tongji University of the Ministry of Education of China. Received 10 September 2001; revision received 9 November 2001.     

Heat flux measurement over a cone in a shock tube flow

This paper is the part 2 of our previous thin film heat transfer measurements. In the first report we measured time variations of heat flux over a cylinder placed in a shock tube flow and compared experimental results with CFD results, Saito et al. (Shock Waves 14:327–333, 2004). We report a result of heat transfer measurements over an 86° apex angle cone surface impinged by a Ms = 2.38 shock wave in air with distributed thin film transfer gauges along cone surface and its comparison with results of numerical simulations. We performed double exposure holographic interferometric observation, and also from the heat transfer measurement and numerical simulation, confirmed the presence of delayed transition from regular to Mach reflection over the cone. The numerical estimation of delayed transition distance from the apex agreed very well with experimental one.      

Drag force on quasi-axisymmetric scramjets at various flight Mach numbers: theory and experiment

The net axial force on a non-fuelled quasi-axisymmetric scramjet model designed for operation at Mach 6 was measured in the T4 Stalker tube at The University of Queensland using a single-component stress wave force balance. The design used was a variant of a model that was tested previously at Mach 6. The new model was equipped with a modified thrust nozzle that was designed to improve the performance of the nozzle. Tests were performed to measure the drag force on the model for Mach 6, Mach 8 and Mach 10 shock tunnel nozzles for a range of flow conditions. The nozzle-supply enthalpy was varied from 3 to 10 MJ/kg and the nozzle-supply pressure from 35 to 45 MPa. For the test model, the drag coefficient increased with increasing nozzle-supply enthalpy. The test results are compared with a force prediction method based on simple hypersonic theories and three-dimensional CFD. The test results are in good agreement with the predictions over the wide range of conditions tested. The re-designed model has a more efficient nozzle but this comes at the expense of increased drag associated with the modifications required for the cowl. The results indicate that this type of vehicle design is not likely to be suitable for flight above Mach 8.

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