Showing papers in "Experiments in Fluids in 1983"
TL;DR: In this paper, the performance of a constant-temperature normal hotwire in a supersonic flow is critically examined and it is shown that this instrument is inherently unsuitable for measuring turbulent temperature correlations because of the highly non-linear response to temperature fluctuations, particularly at low overheat ratios.
Abstract: The performance of a constant-temperature normal hotwire in a supersonic flow is critically examined. It is shown that this instrument is inherently unsuitable for measuring turbulent temperature correlations because of the highly non-linear response to temperature fluctuations, particularly at low overheat ratios. The instrument is therefore limited to measurements of mean and fluctuating mass-flow rates. Suitable calibration procedures. as well as the limits on spatial and temporal resolution are discussed. and corrections for mean stagnation temperature changes are suggested. The instrument was used to measure the mass-flow fluctuations in a zero pressure gradient Mach 2.9 turbulent boundary layer. A comparison with the available data suggests good agreement.
161 citations
TL;DR: In this article, a flow through a straight pipe is passed through a coiled section, and two stabilizing effects come into play: the flow that is turbulent in the straight pipe becomes completely laminar in the coiled part, and the stabilization effect persists to a certain degree even after the flow downstream of the coil has been allowed to develop in a long straight section.
Abstract: When a flow through a straight pipe is passed through a coiled section, two stabilizing effects come into play. First, in a certain Reynolds number range, the flow that is turbulent in the straight pipe becomes completely laminar in the coiled section. Second, the stabilization effect of the coil persists to a certain degree even after the flow downstream of the coil has been allowed to develop in a long straight section. In this paper, we report briefly on aspects related to these two effects.
93 citations
TL;DR: In this article, the Lissaman 7769 airfoil was investigated for the effect of free stream disturbances on the lift and drag performance of the airframe, and it was found that the problems associated with obtaining accurate wind tunnel data at low chord Reynolds numbers (i.e., below 200,000) are compounded by the extreme sensitivity of the boundary layers to free stream disturbance environment.
Abstract: The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a 'turbulence screen' upstream of the test section and/or the addition of a flow restrictor downstream of the test section. For the Lissaman airfoil it was found that the problems associated with obtaining accurate wind tunnel data at low chord Reynolds numbers (i.e., below 200,000) are compounded by the extreme sensitivity of the boundary layers to the free stream disturbance environment. The effect of free stream disturbances varies with magnitude, frequency content, and source of the disturbance.
90 citations
TL;DR: In this article, a method is described for monitoring the changing thickness of a thin oil film subject to an aerodynamic shear stress using two focused laser beams, which is then simply analyzed in terms of the surface skin friction of the flow, including the effects of arbitrarily large pressure and skinfriction gradients, gravity, and time-varying oil temperature.
Abstract: A method is described for monitoring the changing thickness of a thin oil film subject to an aerodynamic shear stress using two focused laser beams. The measurement is then simply analyzed in terms of the surface skin friction of the flow. The analysis includes the effects of arbitrarily large pressure and skinfriction gradients, gravity, and time-varying oil temperature. It may also be applied to three-dimensional flows with unknown direction. Applications are presented for a variety of flows including two-dimensional flows, three-dimensional swirling flows, separated flows, supersonic high-Reynolds-number flows, and delta-wing vortical flows.
49 citations
TL;DR: In this paper, laser-doppler measurements of the three components of mean velocity and their intensities have been made in an axisymmetric swirling isothermal turbulent combustion chamber flow.
Abstract: Laser-doppler measurements of the three components of mean velocity and their intensities have been made in an axisymmetric swirling isothermal turbulent combustion chamber flow. Swirl is generated by a gas-turbine aerodynamic swirler and the flow is representative of that found in the primary zone of many practical combustors. Two configurations were studied. In the first the fuel injector was removed and a central core jet entered the chamber via the resulting circular hole in the centre of the swirler. In the second case the injector was retained but a circular baffle was located at the exit plane: this latter device being necessary to prevent an inflow — not present for combusting flow — arising at the ‘exit’ plane. The velocity data is sufficiently detailed to aid the testing and further development of methods for calculating combustion chamber flows.
46 citations
TL;DR: In this article, the longitudinal velocity fluctuation and the temperature fluctuation on the centreline of a turbulent plane jet are used to obtain second and third order longitudinal velocity, temperature and velocity-temperature structure functions.
Abstract: Measurements of the longitudinal velocity fluctuation and the temperature fluctuation on the centreline of a turbulent plane jet are used to obtain second and third order longitudinal velocity, temperature and velocity-temperature structure functions Kolmogorov's equation for velocity structure functions is satisfied only for separations that lie well within the viscous range The analogous equation, obtained by Yaglom, for the temperature field is satisfied for separations which extend up to the beginning of the inertial range The difference between the measurements and the equations is discussed in the context of local isotropy and its implications on the inertial range constants are considered
38 citations
TL;DR: In this article, the centered expansion wave of a shock tube is utilized to expand and supersaturate a condensable vapor in small concentration in an inert carrier gas, and the supersaturated state, located at the rear of the expansion wave, is preserved for a controlled period and then terminated by a recompressing shock wave.
Abstract: The centered expansion wave of a shock tube is utilized to expand and supersaturate a condensable vapor in small concentration in an inert carrier gas. The supersaturated state, located at the rear of the expansion wave, is preserved for a controlled period and then terminated by a recompressing shock wave. During the period of supersaturation, condensation nuclei are formed homogeneously. The nucleation rate is measured as a function of supersaturation by a Mie-light scattering technique. The method is tested using water and the results are compared with classical nucleation theory.
37 citations
TL;DR: Cameras and lighting techniques which allow photographs to be taken of such water jet flow details as surface waves, transition, and spray eruption, as well as the various jet instability mechanisms, are described in this paper.
Abstract: Cameras and lighting techniques which allow photographs to be taken of such water jet flow details as surface waves, transition, and spray eruption, as well as the various jet instability mechanisms, are described While originally developed for very specialized cameras, many of the techniques can be adapted to conventional cameras and other areas of research
36 citations
TL;DR: In this paper, both the laser shadowgraphic and direct photographic methods are employed to study thermal stability and flow structures in evaporating drops in all heating regimes, and it is revealed that four flow regions exist in stable and unstable type drops at low liquid-film type vaporization regime.
Abstract: The literature pertinent to various aspects of drop evaporation on a heated surface is reviewed. Both the laser shadowgraphic and direct photographic methods are employed to study thermal stability and flow structures in evaporating drops in all heating regimes. It is revealed that four flow regions exist in stable and unstable type drops at low liquid-film type vaporization regime. As the surface temperature is raised, the flow regions reduce to two. In the nucleate-boiling type vaporization regime, the interracial flow structure changes due to a reduction in the Marangoni number as well as the dielectric constant of the liquid. An evidence of bubble growth in the drops is disclosed. The micro explosion of drops is found to occur in the transition- boiling type heating range. No drop explosion takes place in the spheriodal vaporization regime except when the drop rolls on to a microscratch on the heating surface. It is concluded that the mechanisms for triggering drop explosion include the sponta- neous nucleation and growth phenomena and the destabilization of fihn boiling. heated surface in the form of small drops or large portions of liquid. Figure 1 shows a typical curve illustrating the depen- dence of the total vaporization time of a liquid drop on the temperature of the heating surface T,, (Tamura and Tanasawa, 1959). Its corresponding pool boiling curve is included in Fig. 1. When T,, is below the boiling tempera- ture of the liquid Tb, liquid drops spread into a thin layer and evaporate slowly. This range a-b is called tile liquid- film type vaporization regime in which the heat is trans- ferred from the surPace to the liquid by convection. At tile point b when T., is equal to 7"/,, nucleate boiling is observed in the spreading liquid with a vapor bubble arising in the central part of the drop. With a further increase in T,,, the number of nucleation sites increases and
36 citations
TL;DR: In this article, the authors used a moving crossed-wire probe attached to an air bearing sled to obtain phase-averaged velocity vector fields in turbulent wakes behind three-dimensional bluff bodies.
Abstract: An illustrative way of obtaining information about largescale motions of turbulent flows is to take averages on the basis of phase. This approach has been tried by several workers [e.g. Reynolds and Hussain (1972), Kovaznay et al. (1974) and Cantwell (1975)]. This paper describes the experimental technique used at the University of Melbourne to obtain phase-averaged velocity vector fields in turbulent wakes behind three-dimensional bluff bodies [Perry and Watmuff(1981)]. The technique uses a moving crossed-wire probe attached to an air bearing sled. The mechanical features and instrumentation of the apparatus are discussed and a description is given of the computer software used to phase average the data. The system has been designed to enable measurements to be taken in regions of high turbulence intensity and reversed flow.
35 citations
TL;DR: In this article, a two-stage fluidization particle generator provides magnesium oxide particles to serve as optical scattering centers for the measurement of high-temperature gas flows, and the results indicate the influence of the combustion process on turbulence.
Abstract: A laser-Doppler velocimeter is used in the measurement of high-temperature gas flows. A two-stage fluidization particle generator provides magnesium oxide particles to serve as optical scattering centers. The one-dimensional dual-beam system is frequency shifted to permit measurements of velocities up to 300 meters per second and turbulence intensities greater than 100 percent. Exiting flows from can-type gas turbine combustors and burners with pre-mixed oxy-acetylene flames are described in terms of the velocity, turbulence intensity, and temperature profiles. The results indicate the influence of the combustion process on turbulence.
TL;DR: In this paper, the mesures de contraintes de cisaillement par anemometrie Doppler a laser en particulier en fonction des angles des differentes composantes de vitesse.
Abstract: Etude des intervalles statistiques d'incertitude sur les mesures de contraintes de cisaillement par anemometrie Doppler a laser en particulier en fonction des angles des differentes composantes de vitesse. Le choix optimal depend de la quantite a mesurer
TL;DR: In this paper, a method for calibrating a five-hole probe for extending the useful measurement range up to flow angularities of 85° is described, which involves adjustment of the calibration coefficients to allow valid calibration at larger flow angles.
Abstract: A new method is described for calibrating a five-hole probe for extending the useful measurement range up to flow angularities of 85°. The calibration method involves adjustment of the calibration coefficients to allow valid calibration at larger flow angles. The extended range calibration curves for flow angularity, total and static pressures are presented. The present range is valid in pitch only when the yaw ports are nulled.
TL;DR: In this article, the authors investigated the application of LDA for measurement of two-phase flows and determined that an important aspect of such measurement is the discrimination between the signals originating from different phases in the flow.
Abstract: The results of an investigation into the application of LDA for measurement of two-phase flows are presented. It is determined that an important aspect of such measurement is the discrimination between the signals originating from different phases in the flow. It is shown that in the regions where the number density of the discrete phase is high, the error could become considerable. Existing methods of discrimination are investigated and shown to be inadequate. A novel method of signal discrimination is presented and is shown to be capable of complete removal of this error. A two-component LDA system is modified to incorporate the discriminator. Experimental data are presented in support of the method which are in good agreement with the calculated results.
TL;DR: In this paper, the effect of wall proximity on hotwire readings was studied and corrected, and the relationship between skewness and flatness of ∂u/∂t established by Van Atta and Antonia (1980) is also valid in the flows investigated here.
Abstract: Some quantities, like boundary layer parameters, turbulence intensity, and skewness and flatness of u and ∂u/∂t, were measured to specify the flow in which the effect of the wall proximity on hot-wire readings was studied and corrected. The relationship between skewness and flatness of ∂u/∂t established by Van Atta and Antonia (1980) is also valid in the flows investigated here. Experimental results show that the sublayer next to the wall exists in all flows (i.e., with different types of pressure gradients) and the velocity in this region is linear. This layer extends to a value of Y+ approximately equal to 5. Even in turbulent flow, t
w= |δŪ/ δ Y | wis valid. The characteristics of sublayer are:
The flatness of ∂u/∂t becomes very high towards the wall.
TL;DR: In this paper, the Lagrangian motion and deformation of a single hydrogen bubble time-line in time and space is reconstructed by digitally interfacing dual-view video sequences of a bubble time line with a computer-aided display system.
Abstract: A system is described which allows the recreation of the three-dimensional motion and deformation of a single hydrogen bubble time-line in time and space. By digitally interfacing dualview video sequences of a bubble time-line with a computer-aided display system, the Lagrangian motion of the bubble-line can be displayed in any viewing perspective desired. The u and v velocity history of the bubble-line can be rapidly established and displayed for any spanwise location on the recreated pattern. The application of the system to the study of turbulent boundary layer structure in the near-wall region is demonstrated.
TL;DR: In this paper, single point hot-wire measurements have been made in the developing regions of a plane and an unstably curved single-stream mixing layer, where the high-velocity potential flow was constrained by a solid surface to form a thick wall jet.
Abstract: Single-point hot-wire measurements have been made in the developing regions of a plane and an unstably curved single-stream mixing layer. In each case the high-velocity potential flow was constrained by a solid surface to form a thick wall jet. The mean flow in the plane layer had reached approximate self-similarity before the turbulent region reached the surface at a point corresponding to the maximum length Reynolds number of 106 but turbulence quantities, particularly the individual normal stresses, were still changing appreciably with downstream distance. The curved mixing layer created by a convex surface had a spreading rate 9% greater than that of the plane flow with increases of 14% in the maximum level of shear stress.
TL;DR: In this paper, the surface of a flow seeded with aluminium oxide particles is photographed with two pulsed illuminations of whitelight, and the resulting double-exposure specklegram is optically processed using a spatial filtering technique.
Abstract: The surface of a flow seeded with aluminium oxide particles is photographed with two pulsed illuminations of whitelight. When the resultant double-exposure specklegram is optically processed using a spatial filtering technique, an equivelocity pattern can be obtained. Especially, a coloured display of the pattern by the white-light reconstruction gives many useful informations about the flow state.
TL;DR: In this paper, real-time holographic interferometry is used to study free convection in cavities heated from below and bounded by Plexiglas windows, and thermal memory of the walls of the windows and the fluid layer is investigated.
Abstract: Real-time holographic interferometry is used to study free convection in cavities heated from below and bounded by Plexiglas windows Advantages and shortcomings of this visualization technique applied to such Plexiglas boxes are discussed As Plexiglas has a high temperature-dependent refractive index, temperature fields in the windows and the fluid layer are visualized These visualizations furnished proof of a pronounced thermal influence of the walls on the flow pattern based on what we call “thermal memory” of Plexiglas
TL;DR: In this article, the positions of micrometer-sized oil drops are determined in centimeter-sized fields of a low power microscope by triple flash illumination at known intervals of 10 to 500 microseconds.
Abstract: Methods of inserting and photographing tracers in an air stream are described. Successive positions of micrometer-sized oil drops are determined in centimeter-sized fields of a low power microscope by triple flash illumination at known intervals of 10 to 500 microseconds. Tracer positions read from the picture are entered into a computer and velocities calculated throughout the field. Some examples of computer displays of velocity fields are presented.
TL;DR: In this paper, a single component, computer-operated, three dimensional traversing laser Doppler velocimetry system was designed and constructed for a supersonic wind tunnel.
Abstract: A single-component, computer-operated, three dimensional traversing laser Doppler velocimetry system was designed and constructed for a supersonic wind tunnel. The model was a 10 deg compression corner, providing an example of laminar boundary layer separation. Static pressure data and color schlieren photographs were taken. The Mach number was 2.42 and the Reynolds number was 213,000. The flow was seeded with submicron sized oil droplets. The trend of decreasing upstream influence with increasing Reynolds number was confirmed. Mean velocity profiles provided experimental evidence of reversed flow. Points of separation and reattachment were consistent with those determined by schlieren and pressure scans. The flow was of the laminar type until downstream of reattachment. Individual mean velocity and turbulence profiles, as well as velocity histograms are presented.
TL;DR: In this paper, the methods and special problems associated with interferometry, shadowgraphy, velocimetry and other laser-optical techniques applied to large test areas are reviewed and discusssed.
Abstract: The methods and special problems associated with interferometry, shadowgraphy, velocimetry and other laser-optical techniques applied to large test areas are reviewed and discusssed.
TL;DR: In this article, fine-wire thermocouple measurements of temperature and temperature fluctuations in a confined, two-dimensional, premixed methane-air flame of the equivalence ratio, stabilised by a backward-facing step, with bulk flow Reynolds numbers ranging from 2800 to 13000.
Abstract: The paper presents fine-wire thermocouple measurements of temperature and temperature fluctuations in a confined, two-dimensional, premixed methane-air flame of 08 equivalence ratio, stabilised by a backward-facing step, and with bulk flow Reynolds numbers ranging from 2800 to 13000 The results indicate a narrowing of the flame front with decrease in Reynolds number The temperature fluctuation measurements were compensated for thermal inertia and the probability density functions were bimodal with the probability density at the two extremes of the temperature range increasing with fall in Reynolds number Temperature power spectra indicated that the preferred frequencies corresponded to the acoustic frequencies of the combustor system, although the influence of vortex shedding was evident at the lowest Reynolds number
TL;DR: In this article, a Fabry-Perot etalon with a Mach Zehnder interferometer (MZI) was used to deduce the index of refraction resonant dispersion curve near the center of an atomic line from the superimposed fringe system.
Abstract: A new experimental technique, namely, the combination of a Fabry-Perot etalon with a Mach Zehnder interferometer (MZI) makes it possible to deduce the index of refraction resonant dispersion curve near the center of an atomic line from the superimposed fringe system. A tunable pulsed dye laser as light source and a sodium seeded flame as test flow enabled us to verify the very large enhancement of sensitivity for refractive flow-visualization methods such as shadowgraph, schlieren and interferometry. The specific refractivity is a direct measure of the sensitivity, and that quantity increases from a non-resonant value of 4 × 10−3 m'/kg to a peak value of 189 m3/kg at the half-power points of the sodium D2-line.
TL;DR: In this paper, the authors described a circulating water channel and experimental techniques which allowed accurate measurements of the resistance of small models and the extrapolation of the results to ship hulls.
Abstract: The distributions of velocity and their fluctuations, the steady wave of free surface and the presence of air bubbles can significantly influence the extent to which useful resistance measurements can be obtained from ship models in circulating water channels This paper describes a circulating water channel and experimental techniques which allowed accurate measurements of the resistance of small models and the extrapolation of the results to ship hulls
TL;DR: In this paper, experience de visualisation montrant que l'existence d'une couche limite d'extremite n'est pas une condition necessaire a la rupture de tourbillons.
Abstract: Experience de visualisation montrant que l'existence d'une couche limite d'extremite n'est pas une condition necessaire a la rupture de tourbillons
TL;DR: In this paper, a tentative flow resistance equation containing a relative roughness term, a channel shape or aspect ratio term, and a Froude number term was produced for a rectangular channel with an alluvial bed.
Abstract: Experiments were done to develop a flow resistance equation for a rectangular channel with an alluvial bed. The purpose of the experiments was to produce a data set containing statistical bedform measurements from which an effective channel bed roughness could be derived. A tentative flow resistance equation containing a relative roughness term, a channel shape or aspect ratio term, and a Froude number term was produced.
TL;DR: In this paper, a method of deducing airborne particle size distributions from the deposition on a collector is described, which basically consists in collecting submicron-sized particles on whisker filters for subsequent electron-microscopic examination.
Abstract: A method of deducing airborne particle size distributions from the deposition on a collector is described. The method basically consists in collecting submicron-sized particles on whisker filters for subsequent electron-microscopic examination. The empirical size distributions on the collectors can be approximated by log-normal functions. Moreover, it has been found that the variation in particle distribution across a four-stage whisker filter can be interpreted on the basis of a simple model of the collection process. The effective absorption coefficient derived from this modeling is used to correct the empirical data for the effect of a selective collection characteristic.