Showing papers in "Experiments in Fluids in 1989"
TL;DR: In this paper, the flow field around a circular cylinder mounted vertically on a flat bottom has been investigated experimentally and the main flow characteristic upstream of the cylinder is a system of horse-shoe vortices which are shed quasi-periodically.
Abstract: The flow field around a circular cylinder mounted vertically on a flat bottom has been investigated experimentally. This type of flow occurs in several technical applications, e.g. local scouring around bridge piers. Hydrogen bubble flow visualization was carried out for Reynolds numbers ranging from 6,600 to 65,000. The main flow characteristic upstream of the cylinder is a system of horse-shoe vortices which are shed quasi-periodically. The number of vortices depends on Reynolds number. The vortex system was found to be independent of the vortices that are shed in the wake of the cylinder. The topology of the separated flow contains several separation and attachment lines which are Reynolds number dependent. In the wake region different flow patterns exist for each constant Reynolds number.
268 citations
TL;DR: In this paper, the properties of round jets of different densities issuing into the ambient air were investigated and it was shown that these jets have two types of behaviour depending on the density ratio between the jet and the ambient fluids.
Abstract: This is a brief report on the properties of round jets of different densities issuing into the ambient air. Different densities were obtained by premixing helium and air in various proportions. We show that these jets have two types of behaviour depending on the density ratio between the jet and the ambient fluids, one characterized by very sharp peaks in the power spectral density of the velocity in the near field of the jet, and another with broadened and much less prominant spectral peaks. We examine the possibility that the first state corresponds to absolute instability, and the second to convective instability. It appears that the nature of instability can be changed from absolute to convective by very simple means reminiscent of similar possibilities in low Reynolds number wakes of circular cylinders. Flow visualization reveals that the low-density jets intermittently breakdown, and spread spectacularly, beyond a certain small axial distance.
173 citations
TL;DR: In this article, the shadowgraph method is applied to thermal convection experiments and electro-hydrodynamic convection (EHC) in nematic liquid crystals, and the method is demostrated using various examples of thermal and EHC convection.
Abstract: The shadowgraph method is applied to thermal convection experiments and electro-hydrodynamic convection (EHC) in nematic liquid crystals. In both cases convection leads to a spatially periodic field of the refractive index causing a spatially periodic intensity modulation of parallel light passing the cell. Close to the onset of convection the temperature or director field is given by linear stability analysis. Knowing these functions the determination of their amplitudes becomes possible by means of the shadowgraph method. The method is demostrated using various examples of thermal and EHC convection experiments.
112 citations
TL;DR: In this paper, the effect of sharp corners on the air flow dynamics, shown earlier in cold flow tests, was also found in the reacting flow of a flame, where sharp corners interrupted the coherent structures generated in an axisymmetric shear flow, and the combustion at the flat sections of the flame occurred in periodic, coherent large scale structures but was continuous and homogeneous in the vertices sections.
Abstract: Combustion dynamics of burners with corners were studied using Planar Laser Induced Fluorescence (PLIF) imaging. The effect of sharp corners on the air flow dynamics, shown earlier in cold flow tests, was also found in the reacting flow of a flame. The sharp corners interrupted the coherent structures generated in an axisymmetric shear flow. The combustion at the flat sections of the flame occurred in periodic, coherent large scale structures but was continuous and homogeneous in the vertices sections. The azimuthal structure of the noncircular flame changed in a pattern similar to that found in nonreacting flows. Combined regions of small- and large-scale mixing in the same flow, a unique feature of burners having sharp corners, is beneficial for combustion applications.
111 citations
TL;DR: In this article, a new method of flow tagging based on the vibrational excitation of oxygen is applied to both supersonic and high-speed subsonic air flows to generate instantaneous velocity profiles and turbulence statistics across the free shear layer.
Abstract: A new method of flow tagging based on the vibrational excitation of oxygen is applied to both supersonic and high-speed subsonic air flows to generate instantaneous velocity profiles and turbulence statistics across the free shear layer. By simultaneously tagging two lines, both transverse and streamwise velocity correlations are found. Rayleigh scattering can also be imaged, so this flow diagnostic technique has the capability of instantaneously recording density cross sections and velocity profiles.
110 citations
TL;DR: The scalar interface is defined as the surface separating the scalar-marked regions of a turbulent flow from the rest as discussed by the authors, and it is the boundary separating the two-dimensional intersections of scalar interfaces, taking as a specific example digital images of an axisymmetric jet visualized by laser induced fluorescence.
Abstract: A scalar interface is defined as the surface separating the scalar-marked regions of a turbulent flow from the rest. The problem of determining the two-dimensional intersections of scalar interfaces is examined, taking as a specific example digital images of an axisymmetric jet visualized by laser-induced fluorescence. The usefulness of gradient and Laplacian techniques for this purpose is assessed, and it is shown that setting a proper threshold on the pixel intensity works well if the signal/noise ratio is high. Two methods of determining the proper threshold are presented, and the results are discussed. As one application of the technique, the fractal dimension of the scalar interface is calculated.
103 citations
TL;DR: In this paper, an experimental study has been made on the interaction of a vortex ring with a plane solid boundary which is inclined to the axis of the ring, which revealed the formation of bi-helical vortex lines around the circumferential axis.
Abstract: An experimental study has been made on the interaction of a vortex ring with a plane solid boundary which is inclined to the axis of the ring. Dye visualizations of the ring during the interaction revealed (i) the formation of bi-helical vortex lines around the circumferential axis of the ring, and (ii) that these vortex lines were constantly being displaced along the circumferential axis on either side of the plane of symmetry and towards the region of the ring furthest away from the wall. Key factors which may be responsible for this phenomenon have been identified and are discussed in this paper.
94 citations
TL;DR: In this article, experimental measurements were carried out for upward gas-liquid slug flow in a 50.8 mm diameter pipe, where parallel conductance wires were used to distinguish the Taylor bubbles and liquid slugs and to determine translation velocities and lengths, an electrochemical probe provided the magnitude and direction of the wall shear stress and a radio-frequency local probe was used for the axial and radial distribution of voidage in the slugs.
Abstract: Experimental measurements were carried out for upward gas-liquid slug flow in a 50.8 mm diameter pipe. Parallel conductance wires were used to distinguish the Taylor bubbles and liquid slugs and to determine translation velocities and lengths, an electrochemical probe provided the magnitude and direction of the wall shear stress and a radio-frequency local probe was used for the axial and radial distribution of voidage in the liquid slugs. Data are reported over wide range of flow conditions covering slug flow and into the churn flow pattern. Comparison with the Fernandes model predictions are presented. Numerical simulation of slug flow provided information on the structure of flow in a liquid slug and, in particular, on the process of mixing behind a Taylor bubble.
89 citations
TL;DR: In this article, equal spaced and uniform droplets are produced by vibrating orifices and move away in a straight line, intersecting with an exactly equal string of droplets and collide one by one.
Abstract: Equally spaced and uniform droplets are produced by a vibrating orifice and move away in a straight line They intersect with an exactly equal string of droplets and collide one by one With stroboscopic lighting and multiple exposures, they are photographed Thus successive stages of the collision process are shown on a single photo The droplets can be made to collide with or without angular momentum by adjusting the aim of the emitting orifices The impacting speeds can be varied from 28 to 117 m/s Droplet sizes from 70 to 200 μm are employed Motions of the coalesced drop after the merging are bizarre and well-displayed The results are important for spray modeling When the streams of droplets merge at higher speeds, they may distort to the extent that the two streams of droplets merge to a single continuous sinuous stream
76 citations
TL;DR: In this article, a special shock tube process combining a reflected expansion wave with a weak shock wave is employed to transfer water vapor carried in argon into a known supersaturated state for a short period of time (0.5 ms).
Abstract: A special shock tube process combining a reflected expansion wave with a weak shock wave is analyzed and calibrated. The process is employed to transfer water vapor carried in argon into a known supersaturated state for a short period of time (0.5 ms). During that period steady state homogeneous nucleation takes place followed by condensational growth. Nucleation and growth rates are measured by a 90° Mie-light scattering technique in the temperature range 200–260 K. The results are compared with existing theoretical models.
67 citations
TL;DR: In this paper, two kinds of colliding phenomena have been observed when a liquid drop falls to a surface of the same liquid: splash and some degree of penetration and "cleavage" and the conditions for this occurrence are identified.
Abstract: Two kinds of phenomenon have been observed when a liquid drop falls to a surface of the same liquid. The first, which can nearly always be observed, involves splash and some degree of penetration and “cleavage” and the conditions for this occurrence are identified. The experimental observations are compared with previous computational results. The second kind of colliding phenomena can be observed only by chance in an ordinary falling drop experiment and appears to be random. It includes the two phenomena investigated in this paper: the floating drop and the rolling drop.
TL;DR: In this paper, the Karman vortex street is treated as a nonlinear self-excited flow oscillator with forced oscillations using a flow visualization technique, and a variety of wake structures have been identified as a function of sound frequency and sound amplitude, but independent of the Reynolds number.
Abstract: Vortex wakes of circular cylinders at low Reynolds numbers have been investigated Sound waves are superimposed on the flow in mean flow direction In this configuration the Karman vortices are shed at the sound frequency or at subharmonics of the sound frequency The Karman vortex street is treated as a nonlinear self-excited flow oscillator with forced oscillations Using a flow visualization technique a variety of wake structures has been identified as a function of sound frequency and sound amplitude, but independent of the Reynolds number The superimposed sound influences the distribution of circulation and accordingly the shedding mechanism Primary vortex and secondary vortex are shed simultaneously from one side of the cylinder The alternate vortex shedding is arranged spatially and temporally Structures along the vortex axes are revealed
TL;DR: In this paper, a new method of interpreting the signals from triple-sensor thermal anemometer probes has been developed based on fast solution for all the roots of the non-linear Jorgensen (1971) equations describing the directional response of each cylindrical sensor.
Abstract: A new method of interpreting the signals from triple-sensor thermal anemometer probes has been developed based on fast solution for all the roots of the non-linear Jorgensen (1971) equations describing the directional response of each cylindrical sensor. The sensors can be oriented at arbitrary angles to each other, but always within a range of probe geometries that keep prong interference and thermal wake interference below acceptable levels. The properties of a class of non-orthogonal symmetric tetrahedral probe geometries are studied in relation to the range of flow vector angles that can be measured, the sensitivity of the probe with respect to changes in flow angle, and the sensitivity of the computed velocity components due to angular errors associated with the construction of the probe. The solutions of Jorgensen's equations are inherently multiple-valued, but if the velocity vector is restricted to be within a cone of angles, they are unique. It is shown that measurements with non-orthogonal triple sensor signals are sensitive to angular deviations of a few degrees of the sensor angles from the nominally orthogonal probe geometry, indicating the need of a non-orthogonal algorithm. The mean, rms, Reynolds stress, and power spectrum of the velocity in fully developed turbulent pipe flow were measured using a specially designed triple sensor probe and the proposed algorithm.
TL;DR: In this paper, an eddy viscosity model derived for flow over small amplitude waves is used to estimate the divergence of a time-averaged flow over sinusoidal waves.
Abstract: Measurements of the streamwise velocity over solid sinusoidal waves with height to wavelength ratios of 2a/λ=0.05, 0.125 and with dimensionless wave numbers α+=0.00624, 0.00135 have been made. For these conditions the instantaneous flow reverses direction, but the time-averaged flow is non-separated. Many features of the flow are similar to those reported in previous papers for a time-averaged flow that is separated. Approximate agreement is obtained from an eddy viscosity model derived for flow over small amplitude waves. However, the differences are more interesting than the agreement in that they point out shortcomings of present Reynolds stress models. Comparison with other measurements in the literature shows how increasing Reynolds number decreases the size of the separated region. Measurements of pressure profiles and of drag are interpreted in terms of measured flow patterns.
TL;DR: In this paper, particle image displacement velocimetry is applied to the measurement of fluid velocities in a centrifugal pump diffuser to define the variation of radial and tangential velocity components along a pitch.
Abstract: This work presents the application of particle image displacement velocimetry to the measurement of fluid velocities in a centrifugal pump diffuser. Measurements are taken at different operating points and allow to define the variation of radial and tangential velocity components along a pitch. They are further processed to determine the relative velocity and vorticity fields. Results are also compared with laser Doppler measurements taken in the same facility.
TL;DR: In this article, an experimental investigation of the three-dimensional flow field within a water model of a can-type gas turbine combustion chamber was presented, where internal flow patterns simulated closely those expected in real combustors.
Abstract: An experimental investigation of the three-dimensional flow field within a water model of a can-type gas turbine combustion chamber is presented. Flow visualisation demonstrated that internal flow patterns simulated closely those expected in real combustors. The combustor comprised a swirl driven primary zone, annulus fed primary and dilution jets and an exit contraction nozzle. LDA measurements of the three mean velocity components and corresponding turbulence intensities were obtained to map out the flow development throughout the combustor. Besides providing information to aid understanding of the complex flow events inside combustors, the data are believed to be of sufficient quantity and quality to act as a benchmark test case for the assessment of the predictive accuracy of computational models for gas-turbine combustors.
TL;DR: In this paper, an experimental study of local velocity, fluctuation and void fraction profiles in liquid plugs of an upward vertical gas-liquid flow as well as of wall shear stress distribution both under gas slugs and in liquid plug is presented.
Abstract: Results of an experimental study of local velocity, fluctuation and void fraction profiles in liquid plugs of an upward vertical gas-liquid flow as well as of wall shear stress distribution both under gas slugs and in liquid plugs, are presented. The conditional sampling technique allowed to obtain instantaneous profiles of the above hydrodynamical quantities, which illuminated the real physical picture of the flow in a liquid plug. The toroidal vortex adjacent to the bottom of a gas slug is shown to determine significantly the development of the flow in a liquid plug. The intensity of this vortex is determined only by the relative velocity of the gas bubble with respect to the liquid.
TL;DR: In this paper, the three-dimensional, steady flow velocity components of a viscous, incompressible, Newtonian fluid in model porous media were measured using a laser Doppler anemometer.
Abstract: The three-dimensional, steady flow velocity components of a viscous, incompressible, Newtonian fluid in model porous media were measured. The model porous geometries were constructed from 3 mm glass rods. A laser Doppler anemometer was used to measure two of the velocity components and the third was calculated by integrating the continuity equation. The effects of viscous drag, inertial flow fields and eddy losses in the model were studied. The results showed that the measured flow was laminar and stable such that micromixing of the fluid was absent. Inertial flow effects were absent due to high viscous drag coefficients.
TL;DR: In this article, an autocorrelation method was used to measure the turbulence energy dissipation rate in mixers by using of laser-Doppler measurements of the velocity auto-correlation and turbulence energy.
Abstract: An approximate method of measuring the turbulence energy dissipation rate (ɛ) in mixers by use of laser-Doppler measurements of the velocity autocorrelation and turbulence energy was successful in yielding remarkably consistent values. The necessary corrections for periodic, non-dissipative velocity fluctuations were made by an autocorrelation method. Two modes of periodic fluctuation were found to be significant. Transformation of the corrected autocorrelations yielded completely normal turbulence energy spectra.
TL;DR: In this article, the piezoelectric effect of polarized plastic foils is used to register time-dependent pressure or shear loads, and some practical applications in experimental aerodynamics are outlined.
Abstract: The experimental determination of steady and unsteady surface forces is an elementary problem in experimental fluid dynamics, e.g., in experimental aerodynamics. Up to now, unsteady forces such as pressure or shear fluctuations have been detected by means of special plug-in probes (e.g., miniature pressure transducers). An alternative and attractive technique of monitoring unsteady surface forces has become possible through the development of piezoelectric foils. With this novel type of sensor, which simply can be glued onto a surface, the piezoelectric effect of polarized plastic foils is used to register time-dependent pressure or shear loads. First of all, the paper concentrates on the fundamentals of this new measuring technique. Furthermore, some practical applications in experimental aerodynamics are outlined.
TL;DR: In this article, correction schemes for finite spatial resolution and induced downwash velocity are presented which have application to the measurement of complex three-dimensional flow fields using five-hole angle-type pressure probes.
Abstract: Correction schemes for finite spatial resolution and induced downwash velocity are presented which have application to the measurement of complex three-dimensional flow fields using five-hole angle-type pressure probes. In the study, induced downwash velocity is assumed to be proportional to the transverse gradients of streamwise velocity. The present correction schemes are validated by application to flows including vortices embedded within turbulent boundary layers and flows in a curved channel with 1.27-cm width, a 40-to-1 aspect ratio, and 59.7 cm of convex surface curvature.
TL;DR: In this paper, the effects on mean flow and turbulence caused by meander of a vortex embedded in a two-dimensional boundary layer were investigated experimentally by driving a forced lateral oscillation of the vortex generator.
Abstract: The effects on mean flow and turbulence caused by meander of a vortex embedded in a two-dimensional boundary layer were investigated experimentally by driving a forced lateral oscillation of the vortex generator. Upstream, the vorticity contours without forcing were found to be round. The forced vortex generator oscillation caused a flattening of the time-averaged vorticity contours and changes in some of the Reynolds stresses. The results indicate that the unforced vortex did not meander significantly upstream, and that the effects of meander can be understood qualitatively from production of Reynolds stresses by the forced motion acting with the exiting three-dimensional velocity field. Farther downstream, the observed differences in the mean vorticity and Reynolds stresses caused by forcing were smaller, mainly because the vortex was substantially diffused at this station, resulting in smaller mean velocity gradients.
TL;DR: In this article, the authors measured the signal speed behind the reflected shocks produced by the interaction of weak shock waves with rigid inclined surfaces and found that the measured values deviated significantly from the theoretical predictions.
Abstract: The signal speed, namely the local sound speed plus the flow velocity, behind the reflected shocks produced by the interaction of weak shock waves (M
i
< 1.4) with rigid inclined surfaces has been measured for several shock strengths close to the point of transition from regular to Mach reflection. The signal speed was measured using piezo-electric transducers, and with a multiple schlieren system to photograph acoustic signals created by a spark discharge behind a small aperture in the reflecting surfaces. Both methods yielded results with equal values within experimental error. The theoretical signal speeds behind regularly reflected shocks were calculated using a non-stationary model, and these agreed with the measured results at large angles of incidence. As the angle of incidence was reduced, for the same incident shock Mach number, so as to approach the point of transition from regular to Mach reflection, the measured values of the signal speed deviated significantly from the theoretical predictions. It was found, within experimental uncertainty, that transition from regular to Mach reflection occurred at the experimentally observed sonic point, namely, when the signal speed was equal to the speed of the reflection point along the reflecting surface. This sonic condition did not coincide with the theoretical value.
TL;DR: In this article, the principles and practice of pulsed-wire anemometry are reviewed and flow velocity is deduced from the time taken for the thermal wake of a thin wire, heated by a short pulse of current, to reach a sensor wire operating as a resistance thermometer.
Abstract: The principles and practice of pulsed-wire anemometry are reviewed. Flow velocity is deduced from the time taken for the thermal wake of a thin wire, heated by a short pulse of current, to reach a sensor wire operating as a resistance thermometer. The advantage over the hot-wire anemometer is that reversed flows can be measured by adding a second sensor wire on the “upstream” side of the pulsed wire: the main advantages over the laser Doppler anemometer are cheapness and simplicity of use. The pulsed-wire anemometer can now be regarded as a cost-effective instrument for measurements in turbulent separated flows.
TL;DR: In this paper, a water channel on the starting flow around several bluff bodies with sharp edges was investigated using the hydrogen bubble technique and threefold structures of the starting vortex behind flat plates were observed.
Abstract: Experimental investigations were made in a water channel on the starting flow around several bluff bodies with sharp edges: flat plates, circular disks and hollow hemispheres. Details of the flow structures were visualized using the hydrogen bubble technique. Three-fold structures of the starting vortex behind flat plates were observed. The shedding of the vortex sheet from the edge was also studied.
TL;DR: In this paper, Schefer et al. proposed a model for non-premixed turbulent combustion and showed that the model can be used to model the boundary-layer theory of turbulent combustion.
Abstract: Long, M. B.; Fourguette, D. C.; Escoda, M. C.; Layne, C. B. 1983: Instantaneous Ramanography of a turbulent diffusion flame. Opt. Lett. 9, 244-246 Magill, P. D.; Lightman, A. J.; Orr, C. E.; Bradley, R. P.; Roquemore, W. M. 1983: Simultaneous velocity and emission measurements in a bluff-body combustor. AIAA Paper No. AIAA-831481 Magnussen, B. F.; Hjertager, B. H. 1976: On mathematical modeling of turbulent combustion with special emphasis on soot formation and combustion. 16th Symp. (Inter'l) on Combustion. Ann Arbor/MI: The Combustion Institute Masri, A. R.; Bilger, R. W.; Dibble, R. W. 1989: The local structure of turbulent non-premixed flames near extinction. Combust. Flame (in press) Namazian, M.; Kelly, J. T.; Schefer, R. W. 1985: Flow and combustion in bluff-body stabilized flames, presented at the combined Central/Western States Section. The Combustion Institute, paper No. 2-1B Peters, N. 1984a: Laminar diffusion flamelet models in nonpremixed turbulent combustion. Combust. Sci. Tech. 19, 319-339 Peters, N. 1984b: Partially premixed diffusion flamelets in nonpremixed turbulent combustion. 20th Symp. (Inter'l) on Combustion. Ann Arbor/MI: The Combustion Institute Pitts, W. M.; Kashiwagi, T. 1984: The application of laser-induced Rayleigh light scattering to the study of turbulent mixing. J. Fluid Mech. 141, 391-429 Rogg, B.; Behrendt, F.; Warnatz, J. 1986: Turbulent nonpremixed combustion in partially premixed diffusion flamelets with detailed chemistry. 21th Symp. (Inter'l) on Combustion, Ann Arbor/MI: The Combustion Institute Roquemore, W. M.; Bradley, R. P.; Stutrud, J. S.; Reeves, C. M.; Krishnamurthy, L. 1980: Preliminary evaluation of a combustor for use in modeling and diagnostics development. ASME 80GT-93 Roquemore, W. M.; Tankin, R. S.; Chiu, H. H.; Lottes, A. A. 1986: A study of a bluff-body combustor using laser sheet lighting. Exp. Fluids 4, 205-213 Samuelsen, G. S. 1984: Mechanisms of exhaust pollutants and plume formation in continuous combustion. University of California, Irvine/CA, AFOSR Report No. UCI-ARTR-84-7 Schefer, R. W.; Namazian, M.; Kelly, J. 1987: Velocity measurements in a turbulent nonpremixed bluff-body stabilized flame. Combust. Sci. Tech. 56, 101 135 Schefer, R. W.; Namazian, M.; Kelly, J. 1989: Comparison of turbulent-jet and bluff-body flame structure. Combust. Sci. Tech. (in press) Schlichting, H. 1968: Boundary-layer theory. 6th edn. New York: McGraw-Hill Starner, S. H. 1983: Joint measurements of radial velocity and scalars in a turbulent diffusion flame. Combust. Sci. Techn. 30, 145-169 Takagi, T.; Hyun-Dong S.; Ishio, A. 1980: Local laminarization in turbulent diffusion flames. Combust. Flame 37, 163-170
TL;DR: In this article, a three-axis piezoelectric load cell was used to measure the local unsteady forces induced on cylinders placed in a cross-flow and a single hot-wire was employed to traverse the wake at a fixed distance behind the cylinder so that correlations between the induced forces on the cylinder and the wake velocity could be calculated to provide insight into the character of the flow-induced unstiffy forces.
Abstract: A three-axis piezoelectric load cell was used to measure the local unsteady forces induced on cylinders placed in a cross-flow. In conjunction with this, a single hot-wire was used to traverse the wake at a fixed distance behind the cylinder so that correlations between the induced forces on the cylinder and the wake velocity could be calculated to provide insight into the character of the flow-induced unsteady forces. Experiments were carried out on both two-dimensional and finite-span cylinders at a Reynolds number of 46,000. For the two-dimensional cylinder case, substantial evidence was obtained to demonstrate that the strength of the vortex roll-up along the span was quite uniform. Consequently, the lift-velocity correlation along the span remained unchanged. On the other hand, there was a total lack of correlation between the fluctuating drag and the wake velocity, thus indicating that the drag signal was not quite periodic. In the finite-span cylinder case, the separated flow from the top edge of the cylinder was found to suppress vortex shedding along the span of the cylinder, destroyed its coherence and caused the wake flow to oscillate in the stream direction. This oscillation induced a significant fluctuating drag on the cylinder. Consequently, the fluctuating drag far exceeded the fluctuating lift and the wake velocity was found to correlate well with the drag and not with the lift. This correlation remained intact along the span of the cylinder. Finally, the rms fluctuating lift and drag forces were found to vary along the cylinder span, with the lift increasing and the drag decreasing as the base of the cylinder is approached; thus suggesting that a submerged two-dimensional region exists near the base of the cylinder.
TL;DR: In this article, the particle number density measured by a single particle counting instrument was evaluated based on either the particle mean velocity or on the particle residence time in the measuring volume, respectively.
Abstract: (1)
This work has evaluated the particle number density measured by a single particle counting instrument, based on either the particle mean velocity or on the particle residence time in the measuring volume.
TL;DR: In this paper, a movie camera with exposure times of less than 0.1 µs and framing rates from 1 to 100 µs is used to capture supersonic flow details.
Abstract: To produce movies of supersonic flows, from which meaningful
information can be extracted, is a non-trivial task. In a supersonic wind tunnel, speeds are of the order of 1,000 m/s and the scale of turbulent structures is typically of the order of millimeter. To capture the flow details, exposure times of less than 0.1 µs, and framing rates from 1 to 100 µs are desirable. While high-speed movie cameras with framing rates up to 5 million per second are commercially available, they are expensive, require an extremely-powerful light source, and are inflexible as to adjusting the exposure and the framing rate independently.
TL;DR: In this paper, a moving laser light sheet is used to display cross-sections of an air flow in a 3D plane light sheet, which allows the global 3D visualization and simultaneous display of several crosssections of air flow.
Abstract: Flow visualizations in three dimensions by means of plane light sheets are now frequently used, particularly in wind-tunnels. In this paper, we propose a further improvement to this technique using a moving laser light sheet; this method allows the global 3-D visualization and simultaneous display of several cross-sections of an air flow.