Showing papers in "Experiments in Fluids in 1984"
TL;DR: In this article, the authors used the laser-induced fluorescence technique to detect the steady swirling flow produced in a closed cylindrical container completely full of fluid (a glycerine/water mixture for the experiments reported here).
Abstract: Observations made using the laser-induced fluorescence technique are presented of the steady swirling flow produced in a closed cylindrical container completely full of fluid (a glycerine/water mixture for the experiments reported here) by rotating one endwall. The flow behaviour is determined by two parameters: the height-to-radius ratioH/R and a rotation Reynolds number ΩR
2/ν. In an earlier study, Vogel (1968) defined the stability limit in the (H/R, Ω R2/ν) plane within which a vortex breakdown bubble occurred on the axis of symmetry. The results of Vogel's investigation are confirmed and extended by the present work. In particular, it is found that asH/R is increased two further stability limits can be determined within which two and ultimately three breakdown bubbles occur in succession. It is also found that there is a Reynolds number boundary above which the flow is oscillatory and at even higher Reynolds number the flow becomes turbulent. Until well into the unsteady-flow domain, the flow shows negligible departure from axisymmetry.
454 citations
TL;DR: In this article, the influence of wall proximity on hot-wire readings was eliminated by using a highly insulating wall material and using a single hotwire boundary layer probe to obtain the longitudinal velocity informatemperature-wake sensor for the cross flow flow information.
Abstract: Hot-wire anemometer measurements, using two types of probes, are reported for wall boundary layer flows with particular attention being given to the near-wall region and to measurements at high Reynolds numbers up to Rϕ≈ 15,000. To obtain accurate near-wall measurements, the influence of wall proximity on hot-wire readings was eliminated by using a highly insulating wall material. Measurements were carried out with a single hot-wire boundary layer probe to obtain the longitudinal velocity informatemperature-wake sensor for the cross flow tion and a hot-wire, information.
83 citations
TL;DR: In this paper, the behavior of longitudinal Taylor-Gortler-like vortices was studied in a three-dimensional lid-driven cavity flow to study the behaviour of longitudinal torsion.
Abstract: Experiments were conducted in a three-dimensional lid-driven cavity flow to study the behavior of longitudinal Taylor-Gortler-like vortices. Flow visualization was accomplished by use of a rheoscopic liquid and of liquid crystals, together with laser-light and white-light sheets, respectively. Photographs of the lighted planes in the flow confirmed the existence of the vortices for a wide range of Reynolds numbers and for stable, neutrally-buoyant and buoyant global flow conditions. As usual the flow visualization revealed flow patterns not deducible by in situ measurements; the liquid crystal photographs give both flow pathlines and temperature distribution on any lighted plane.
78 citations
TL;DR: Mesures d'ecoulement moyen et de turbulence dans une couche limite se developpant d'abord sur une paroi plane puis sur a paroi convexe as mentioned in this paper.
Abstract: Mesures d'ecoulement moyen et de turbulence dans une couche limite se developpant d'abord sur une paroi plane puis sur une paroi convexe dont le rayon de courbure est d'environ 100 fois l'epaisseur de la couche limite. Les donnees incluent les profils des quatre composantes non nulles du tenseur des contraintes de Reynolds et trois triple produits de vitesse obtenus en 5 points differents de l'ecoulement. La courbure reduit les intensites turbulentes, la contrainte de cisaillement et le frottement surperficiel d'environ 10% par rapport a la paroi plane
59 citations
TL;DR: In this article, a method for calibrating seven-hole probes to measure local total and static pressures and relative flow angles of up to 70 degrees in subsonic compressible flows is presented.
Abstract: This paper illustrates a method for calibrating seven-hole probes to measure local total and static pressures and relative flow angles of up to 70 degrees in subsonic compressible flows. The method of Latin Squares was used to statistically sample a large and otherwise unmanageable data set, thereby reducing to a minimum the number of data points required to construct a polynomial curve fit to the data. Calibration produces three-variable third order polynomials which permit all of the desired flow properties to be found explicitly from probe measured pressures. This method determines the flow angles to within 2 degrees and Mach number to within 0.04 with 95 percent certainty.
47 citations
TL;DR: In this paper, single point turbulence measurements made in the boundary layer on a mildly curved heated convex wall show that the turbulence heat fluxes and Stanton number are more sensitive to a change in wall curvature than the Reynolds stresses and skinfriction coefficient, and that downstream, as the flow adjusts to new curved conditions, the St/cf ratio of Reynolds analogy is appreciably lower than in plane wall flow for the same conditions.
Abstract: Extensive single point turbulence measurements made in the boundary layer on a mildly curved heated convex wall show that the turbulence heat fluxes and Stanton number are more sensitive to a change in wall curvature than the Reynolds stresses and skinfriction coefficient, and that downstream, as the flow adjusts to new curved conditions, the St/c
f ratio of Reynolds analogy is appreciably lower than in plane wall flow for the same conditions. Details of the turbulence structure in unheated flow have been documented in an earlier paper; temperature field measurements now described comprise mean temperature distributions, the streamwise variation of wall heat flux, profiles of the temperature variance, transverse and streamwise heat fluxes, and triple correlations. Turbulent diffusion of heat flux is drastically reduced even by mild curvature; changes in the heat fluxes are of the same order as changes in the shear stress, that is, an order of magnitude greater than the ratio of boundary layer thickness to wall radius of curvature. The data include plane flow measurements taken in a developed boundary layer upstream of a change in wall curvature.
45 citations
TL;DR: In this article, a variable angle calibration technique for hot wire and hot film X-probes incorporating a new method of interpolation is described along with measurements in a fully developed turbulent channel flow.
Abstract: A variable angle calibration technique for hot wire and hot film X-probes incorporating a new method of interpolation is described here along with measurements in a fully developed turbulent channel flow. Results based on the new method of calibration include the mean velocity profile, Reynolds stress, and probability density distributions for fluctuating velocity components u and υ and for the flow angle. Also skewness and flatness factors for u and υ are given. Measurement data were also evaluated using the conventional method. A comparison of both techniques shows that the new method does not yield appreciable differences in statistical flow analyses but is more accurate in measuring rare flow events associated with large flow angles. An extended version of the new method of calibration allowing three dimensional measurements in turbulent flow will be discussed.
41 citations
TL;DR: The tracer method was used to visualize the three-dimensional structure of turbulent open-channel flow as discussed by the authors, where a horizontal cross-section of the flow was illuminated by light passing through a thin slit and successive pictures of flow patterns were taken.
Abstract: The tracer method was used to visualize the three-dimensional structure of turbulent open-channel flow A horizontal cross-section of the flow was illuminated by light passing through a thin slit The illuminated cross-section was shifted upward, and at the time, successive pictures of flow patterns were taken The picture-taking system was then shifted in downstream direction to follow the flow structures The pictures obtained were processed by computer Various kinds of physical properties of the flow were quantitatively evaluated and displayed as graphical outputs These results contribute to the elucidation of the three-dimensional structure of turbulent open-channel flows
37 citations
TL;DR: In this article, a flying hot-wire arrangement was developed for the measurement of the velocity characteristics of the flow around airfoils, and particularly in regions where negative values of instantaneous velocity occur.
Abstract: A flying hot-wire arrangement has been developed for the measurement of the velocity characteristics of the flow around airfoils, and particularly in regions where negative values of instantaneous velocity occur. The mechanism and signal processing system are described and appraised by comparing stationary and flying wire measurements obtained in the trailing edge region of a flap at an angle of attack which leads to upper-surface separation.
35 citations
Abstract: Results are reported from an extensive series of experiments on boundary layers in which the location of pressure gradient and transition onset could be varied almost independently, by judicious use of tunnel wall liners and transition-fixing devices. The experiments show that the transition zone is sensitive to the pressure gradient especially near onset, and can be significantly asymmetric; no universal similarity appears valid in general. Observed intermittency distributions cannot be explained on the basis of the hypothesis, often made, that the spot propagates at speeds proportional to the local free-stream velocity but is otherwise unaffected by the pressure gradient.
34 citations
TL;DR: In this paper, the results of extensive experimental studies of the structure of three-dimensional flow in a region of interaction of asymmetrically developing incompressible turbulent boundary layers by a longitudinal flow around corner configurations are presented.
Abstract: The results of extensive experimental studies of the structure of three-dimensional flow in a region of interaction of asymmetrically developing incompressible turbulent boundary layers by a longitudinal flow around corner configurations are presented. The character of the originating secondary flows is analysed depending on the degree of the flow asymmetry and on the geometry of the leading edge corner. The mechanisms of origin, subsequent development and transformation of secondary flows along the length of a model are discussed. In particular, it is shown that a one-vortex scheme of the flow gradually transforms into a two-vortical one with increasing distance from the leading edge corner.
TL;DR: In this article, two-dimensional boundary layer profiles of heated and rotating circular cylinders in crossflow were investigated for subcritical freestream-Reynolds numbers, and the location of separation points was determined as a function of the velocity ratio, whereby a strong influence of wall temperature was revealed.
Abstract: Two-dimensional boundary layer profiles of heated and rotating circular cylinders in crossflow were investigated for subcritical freestream-Reynolds-numbersRe = 34 · 104 andRe = 48 · 104 The peripheral speed of the cylinder surface corresponds to velocity ratios 0 ≦ ξ ≦ 2(α, circular/freestream-velocity) Special attention was focused on the location of separation points, which was determined as a function of the velocity ratio a whereby a strong influence of wall temperature was revealed
TL;DR: In this paper, two optical methods, light absorption and LDA, are applied to measure the concentration and velocity profiles of droplet suspensions flowing through a tube, and the results can be qualitatively compared with the theory of Chan and Leal.
Abstract: Two optical methods, light absorption and LDA, are applied to measure the concentration and velocity profiles of droplet suspensions flowing through a tube. The droplet concentration is non-uniform and has two maxima, one near the tube wall and one on the tube axis. The measured velocity profiles are blunted, but a central plug-flow region is not observed. The concentration of droplets on the tube axis and the degree of velocity profile blunting depend on relative viscosity. These results can be qualitatively compared with the theory of Chan and Leal.
TL;DR: In this article, a methode utilisant des cristaux liquides thermographiques is decrit for obtenir des mesures de temperature de surface quantitatives sur des maquettes en tunnel hydrodynamique.
Abstract: On decrit une methode utilisant des cristaux liquides thermographiques pour obtenir des mesures de temperature de surface quantitatives sur des maquettes en tunnel hydrodynamique
TL;DR: In this article, a methode basee sur l'interferometrie holographique and dedoublement du front d'onde is proposed, and application a mesrure du profil de gouttelettes de liquide en equilibre dans l'air sur des supports de verre plats and horizontaux.
Abstract: On developpe une methode basee sur l'interferometrie holographique et a dedoublement du front d'onde; application a la mesrure du profil de gouttelettes de liquide en equilibre dans l'air sur des supports de verre plats et horizontaux
TL;DR: The authors describe a liquide birefringent permettant une bonne visualisation des ecoulements and reproduisant exactement le comportement non newtonien du sang humain.
Abstract: Description d'un liquide birefringent permettant une bonne visualisation des ecoulements et reproduisant exactement le comportement non newtonien du sang humain
TL;DR: In this paper, the effects of relatively strong shock waves propagating through a mixture of an aqueous glycerol solution and small helium or argon bubbles are investigated experimentally.
Abstract: Relatively strong shock waves propagating through a mixture of an aqueous glycerol solution and small helium or argon bubbles are investigated experimentally. Shock strength and void fraction are varied in the experiments. Results regarding shock speed and other aspects are presented and discussed in connection with previous studies. Good agreement with isothermal theory is found.
TL;DR: In this article, the response of a rectangular basin along a straight, perfectly reflecting coastline, subject to monochromatic waves coming either normally or obliquely from the sea, was investigated theoretically and experimentally.
Abstract: The response of a rectangular basin along a straight, perfectly reflecting coastline, subject to monochromatic waves coming either normally or obliquely from the sea, was investigated theoretically and experimentally.
TL;DR: In this article, the authors used a laser-Doppler anemometer to measure velocities in a fluid with a larger variation in its refractive index perpendicular to the laser beams.
Abstract: The use of a laser-Doppler anemometer to measure velocities in a fluid with a larger variation in its refractive index perpendicular to the laser beams may introduce appreciable errors. This situation is commonly encountered in convective heat transfer studies. The beams are refracted as they pass through the fluid and the distance of the intersection of the beams, control volume, from the surface may be significantly different than the distance of the beams from the surface when they entered the fluid. If the flow is unsteady or turbulent, the relative movement of the beams may be such that the size and location of the control volume is constantly changing causing appreciable errors.
TL;DR: In this paper, a laser doppler anemometer (LDA) was used to measure local dispersion coefficients of particles in turbulent flow and a second estimate for the diffusivity was obtained from mean square dispersion measurements.
Abstract: A laser doppler anemometer (LDA) was used to measure local dispersion coefficients of particles in turbulent flow. The experimental set-up is described along with the data acquisition equipment and processing procedures. Results for 5 μ particles dispersing from a point source in pipe flow are shown. A second estimate for the diffusivity was obtained from mean square dispersion measurements.
TL;DR: In this article, a feasibility study has been conducted on the use of laser-Raman spectroscopy as a remote temperature sensing technique for liquids, using a 2-W argon ion laser and two 0.25m monochromators in tandem.
Abstract: A feasibility study has been conducted on the use of laser-Raman spectroscopy as a remote temperature sensing technique for liquids. Empirical relations between the temperature and parameters describing Raman band intensities were determined over a temperature range of 15 to 65 °C in carbon tetrachloride, benzene, ethylene glycol, aqueous sodium nitrate (5 M), and water. Using a 2-W argon ion laser and two 0.25-m monochromators in tandem, it was possible to measure temperatures in water to within 2 °C and, in ethylene glycol, to within 4 °C.
TL;DR: In this article, the authors reported measurements of axial and radial velocities obtained with laser-Doppler anemometry in the transitional region of a round jet and the predominant frequencies of the coherent structures detected in the non-artificially excited jet correspond to Strouhal numbers, around 033 and 055 and an interpretation of these observations is made.
Abstract: The present paper reports measurements of axial and radial velocities obtained with laser-Doppler anemometry in the transitional region of a round jet The predominant frequencies of the coherent structures detected in the non-artificially excited jet, correspond to Strouhal numbers, around 033 and 055 and an interpretation of these observations is made The use of external excitation can modify some characteristics of the jets disturbing the balance between the different flow structures, namely those corresponding to the two values of St The jet diameter was 300 mm and the velocities ranged from near zero up to 15 m/s, corresponding to Reynolds number of 287 × 104
TL;DR: In this article, it is shown that any such correlation can be recast with no loss of generality in the explicit form Δu/u¯¯¯¯m = f (y u¯¯¯¯m/υ), which is more convenient for use.
Abstract: Correlations for corrections to hot-wire data for the effects of wall proximity within the viscous sublayer are usually presented in the form Δu/u
τ = F (y u
τ/υ). The application of such correlations requires a prior knowledge of the wall shear stress; alternatively, the correlation must be used in an iterative fashion. It is shown in the present note that any such correlation may be recast with no loss of generality in the explicit form Δu/u
m = f (y u
m/υ), which is more convenient for use.
TL;DR: In this article, the Gaudet and Johnson's logarithmic drag coefficient relationship for zero pressure gradient is valid over a wide range of pressure gradients over six different free stream pressure gradient flows.
Abstract: Different methods for measuring the drag of small two-dimensional surface irregularities are considered. The pressure distribution technique is employed to measure the drag of small backward-facing steps in six different free stream pressure gradient flows. Results obtained show that Gaudet and Johnson's logarithmic drag coefficient relationship for zero pressure gradient is valid over a wide range of pressure gradients.
TL;DR: In this paper, the authors describe a new sonic anemometer arrangement with improved pulse transit time detection, which can also be used to obtain accurate measurements of the wind velocity component along the line of the sonic array.
Abstract: Recent developments in sonic anemometers have enabled us to obtain accurate measurements of the wind velocity component along the line of the sonic array. Measurements of vorticity can also be obtained by using multiple sensing elements of the sonic anemometer and the procedures are described here. In the early vorticity measurements of Mitsuta (1966b), zero point drifts limited the accuracy of vorticity measurements and this paper describes a new sonic anemometer arrangement with improved pulse transit time detection.
TL;DR: In this article, a method for rapidly measuring and visualizing the extent of separated flow suitable for a wind tunnel environment is described, where a continuously swinging total pressure probe is used to detect the presence of highly complicated three-dimensional separated regions for a typical general aviation twin-engine aircraft.
Abstract: A method is described for rapidly measuring and visualizing the extent of separated flow suitable for a wind tunnel environment. The method utilizes a continuously swinging total pressure probe. This technique permits acquiring and presenting graphical records of separated regions in a fraction of the time required by other methods. Typical results indicate the presence of highly complicated three-dimensional separated regions for a typical general aviation twin-engine aircraft at post-stall conditions.
TL;DR: In this paper, an experimental technique for the diagnosis of rarefied ionized gases was developed, where the source of the ionized gas is formed by the region behind the reflected shock in a shock tube from which it is expanded through a nozzle.
Abstract: An experimental technique for the diagnosis of rarefied ionized gases has been developed. The source of the ionized gas is formed by the region behind the reflected shock in a shock tube from which it is expanded through a nozzle. This flow is sampled by an adjustable skimmer forming a molecular beam. The velocity of the electrons on the centerline of the beam is analyzed in a magnetic field and registered by an electron multiplier. By sweeping the intensity of the field during the test time the whole range of the velocity distribution is scanned. The geometric dimensions of nozzle and skimmer together with the characteristic of the analyzer allow to neglect the divergence of the flow in the evaluation of the distribution. Comparisons of evaluated electron temperatures show good agreement with a theoretically predicted temperature decay in an expansion flow.
TL;DR: In this paper, a vorticity meter of the vane type has been used for direct and quantitative measurements of vertical flows and a vane calibration procedure is carried out by using measurements deduced from a preliminary cross-wires survey of the flow-field generated in the wake of a half wing set at incidence in the wind tunnel.
Abstract: A vorticity meter of the vane-type has been used in this study for direct and quantitative measurements of vertical flows The vane calibration procedure is carried out by using measurements deduced from a preliminary cross-wires survey of the flow-field generated in the wake of a half wing set at incidence in the wind tunnel Emphasis is placed on the resulting calibration law which relates the vane rotational speed to the fluid angular velocity Specially it is shown that this calibration law can be obtained as a linear expression by taking into account the minimum threshold rotational speed necessary for vane rotation When comparing vorticity distributions obtained through the vortical wing wake by the indirect cross-wires technique, good agreements are found with the corresponding vorticity distributions as deduced from the so calibrated vorticity meter
TL;DR: In this article, the transition between the motion of a subsurface buoyant jet and a supersurface SUJET has been studied and the transition region is sharp and characterized by an intermediate regime where both a wall-hugging flow and the more standard outlet flow are present.
Abstract: The transition between the motion of a subsurface buoyant jet and a supersurface buoyant jet has been studied. Measurements indicate that the transition region is sharp and characterized by an intermediate regime where both a wall-hugging flow and the more standard outlet flow are present. The point of transition was found to exhibit significant hysteresis depending on whether the receiving pool height was increasing or decreasing with time. Measurements of the temperature field downstream show that the effects of the different regimes on the density stratification can persist for long distances.