H H Bruun

A dual optical probe for volume fraction, drop velocity and drop size measurements in liquid-liquid two-phase flow

This paper describes the development and application of a dual optical probe for local volume fraction, drop velocity and drop size measurements in a kerosene-water liquid-liquid two-phase flow. A sampling tube procedure and interface tests were used to calibrate the leading optical sensor and both optical sensors for measurements of the local volume fraction and drop velocity as described in this paper. Measurements were carried out in a large-scale vertical two-phase facility mainly at the pipe centre-line to demonstrate the advantages of using optical fibres with normal cut ends in a kerosene-water two-phase flow. Finally the applicability of this probe for measurements in gas-liquid two-phase flows and gas-kerosene-water three-phase flows has also been demonstrated.

A computer-based hot-film technique for two-phase flow measurements

This paper describes the development of a novel computer-based hot-film anemometer measurement technique for the investigation of the local structure of two-phase flows. The technique enables the total signal to be separated into the parts corresponding to bubbles and continuous phase, from which the local volume fraction can be evaluated. Evaluation procedures are also presented for analysing the remainder of the signal corresponding to the turbulent continuous phase after eliminating the bubble signals. Methods are described and discussed for the evaluation of the longitudinal mean velocity, normal stress, autocorrelation and energy spectrum. Finally typical results for a vertical up-flow of a bubbly kerosene/water mixture are presented.

Calibration and analysis of X hot-wire probe signals

The authors deal with the use of X hot-wire probes for measurements of two velocity components. Using the effective velocity concept, four different analytical expressions for the yaw response of the hot wire signals have been considered. Using a set of reference calibration data the curve-fit accuracy of the four methods are first investigated. Then the related sum and difference signal analysis methods are compared and finally the velocity component errors caused by uncertainty in the value of the mean yaw angle are established.

Velocity component measurements by X hot-wire anemometry

The authors are concerned with the interpretation of the instantaneous signals from an X hot-wire probe used for velocity component measurements. A detailed calibration study was carried out to identify the correct velocity and yaw response of a typical plated X hot-wire probe. The calibration data identified an accurate calibration relationship for the X hot-wire probe, and enabled the development of a related look-up inversion method. This provided a reference for the assessment of the accuracy of common signal analysis methods. Using a step-by-step approach, the errors caused by the assumptions of constant values for the offset and exponent in a power law relationship were first identified. Then, the errors relating to the introduction of the concept of an effective velocity Veff and analysis in terms of Veff2 were determined and finally the errors in the sum and difference method based on Veff. The authors demonstrate that these errors cannot be neglected, even at low turbulence intensity, if accurate flow measurements are required.

Evaluation of a flying X hot-wire probe system

The authors present an evaluation of a flying X hot-wire probe system based on the four-bar mechanism proposed by Thompson and Whitelaw in 1984. An in situ calibration procedure and new hot-wire signal analysis procedure based on a modified sum and difference method are presented. Validation tests in still air and uniform flow demonstrate the accuracy of the proposed analysis procedure.

The calibration of and measurements with cylindrical hot-film probes in water flows

This paper describes an integrated experimental procedure for obtaining accurate measurements with both single normal (SN) and X hot-film probes in water flows. The first part of the paper describes techniques developed to overcome the common problems of temperature variations and contamination in a recirculating test facility, leading to long-term calibration stability. The second part of the paper describes the development of fast, reliable and accurate computer-based calibration methods for both SN and X probes. The final section of the paper describes comparative measurements between an SN and an X probe in vertical upward water pipe flow, demonstrating the validity of the methods developed.

Optical development in the foetal bovine lens

The refractive index variations along the optic axes of nine foetal bovine lenses were measured using an optic fibre reflectometer. The device measures refractive index directly, using the principle of Fresnel reflectance. These results show that lenses with a wet weight >0.7 g (corresponding to 4.5 months gestational age), have a refractive index profile which approximates a parabolic shape, akin to that found in post-natal and adult bovine lenses. In lenses of wet weight below 0.7 g, the refractive index distributions show irregularities. These findings suggest that the refractive index profile in the bovine lens starts to form into a parabolic distribution, as seen in adult lenses, about half-way through gestation. The trigger for this formation is not known.

Water flow studies using split-film anemometry

This paper describes an integrated experimental procedure for obtaining accurate measurements with split-film (SF) probe anemometry in water flows. The paper describes the development of a fast, reliable and accurate calibration and signal analysis technique. Comparative measurements between the SF probe, single normal (SN) and hot-film probes demonstrate the validity of the method developed.

Two-phase flow

The simultaneous flow of two phases or two immiscible liquids within common boundaries. Two-phase fl…

Experimental Investigation of Turbulent Flow With Separation Over a NACA 4412 Airfoil at Angle of Attack 20 Degree

This paper presents the measured mean flow and Reynolds stresses results, obtained on the center-line plane of the airfoil, covering the boundary layers over the upper surface, the potential flow region and the wake downstream of the trailing edge, at αa = 20°. The flying X-hot-wire probe was used to measure mean velocity and turbulence structure over the airfoil. An improved understanding of the physical characteristics of separation on the airfoil sections and in the region of the trailing edge is of direct value for the improvement of high lift wings for aircraft. From the study of the separation flow at angle of attack αa = 20°, the following can be concluded: A stable separation bubble has developed near the trailing edge of the airfoil, covering around 0.6c of the airfoil surface. Also it is found that values of the Reynolds normal and shear stresses move away from the surface with downstream distance, showing turbulence diffusion to be more evident in this flow. In the wake region, relatively large values of Reynolds stresses occurred, which were related to the vertical oscillations in the upper wake.Copyright