Phase Doppler Anemometry System Research Articles

Effect of air preheating temperature on the dynamic behaviour of a swirled spray flame

The effects of the air inlet temperature on the dynamic behaviour of a spray flame are reported for different air flow rates. Dodecane droplets are generated through a pressurised nozzle and introduced in the combustion chamber fed with air via two co-rotating swirlers. The flow rate of dodecane is kept constant (1.24gs-1) while the air flow rate is changed from 28gs-1 to 35gs-1 and its temperature from 70°C to 220°C. Microphones are used to record the different dynamics observed while a camera and a Phase Doppler Anemometry system allow to monitor the flame and the fuel spray.For low flow rates (between 28gs-1 and 32gs-1, leading to an overall equivalence ratio ranging between 0.6 and 0.7), the pressure fluctuations start by increasing with an increase of the temperature until, for a given temperature, the pressure fluctuations suddenly drop. This threshold temperature depends on the air flow rate. When displaying the pressure fluctuation level as a function of the bulk velocity (taking both air flow rate and temperature into account), the curves collapse into a similar shape. The instability frequency monotonically increases with the bulk velocity. For high flow rates (between 32gs-1 and 35gs-1, leading to overall equivalence ratio ranging between 0.5 and 0.6), a hysteresis phenomenon is found. Pressure fluctuations are relatively high for constantly decreasing temperature conditions and have almost similar levels as those obtained for lower flow rates. When constantly increasing the temperature, the levels are much lower, showing a bi-stable behaviour for the pressure fluctuations at a given operating point. A simple analysis based on the acoustic energy balance equation allows to qualitatively retrieve the behaviour of the pressure fluctuations amplitude and frequency for the low flow rate cases.

Model development for flash boiling spray and validations with isooctane, hexane, ethanol and their binary mixtures

The main objective of this study is to develop a comprehensive model for spray atomization under the consideration of flash boiling, which includes nucleation, bubble growth, and droplet breakup. Although flash boiling has been previously studied, there is still no well-established analytical and numerical model of their mechanisms, or general guidelines on the implementation of this atomization strategy. In this study, detailed formulations are elaborated for the unified spray atomization model under both non-flash and flash boiling conditions. Next, the model was implemented into CFD software and 3-D simulations were performed for model validations. Two fuel blends are tested: ethanol-isooctane blends and hexane-isooctane blends. Simulation results were compared with the experimental measurements conducted using two methodologies, DBI (Diffuse Backlight Imaging) system for spray images captured by a high-speed camera, and a PDA (Phase Doppler Anemometry) system for droplet size measurement during the spray injection process. It was found that the current flash boiling model can accurately capture the spray characteristics under different environment conditions, such as the spray plume interactions and liquid penetration. The averaged Sauter mean diameter (SMD) calculations match the measurement sufficiently well. The spray structures for both single- and multi-component fuels during the injection process are well represented by current model.

Experimental and numerical investigation of cross-sectional structures of liquid jets in supersonic crossflow

The cross-sectional distributions of liquid jets in Mach 2.85 air crossflow were investigated experimentally and numerically. The Phase Doppler Anemometry system was adopted to obtain the droplet diameter and two velocity components. The experimental results show that the cross-sectional plane presents Omega shape. The Sauter Mean Diameter is 40 μm in the central region of the cross-sectional plane, and decreases from center to periphery. An increase in Sauter Mean Diameter is observed in the lateral boundary near the nozzle because of flow characteristics near the liquid column. The final Sauter Mean Diameter is 15 μm when the secondary atomization finished. The averaged traverse velocity peasants a stripe shape distribution and the high velocity value appears at the top and bottom region of the cross-sectional plane. Numerical results show three counter-rotating vortex pairs. The wall counter-rotating vortex pairs influence droplets motion and transport droplets. Smaller droplets with lower momentum flow into the vortex of the gas flow. Larger droplets with higher momentum flow along the wall toward lateral sides, resulting the spray foot structure of Omega shape. The nozzle diameter has effects on the cross-sectional distribution. With the nozzle diameter increasing, the cross-sectional plane becomes a Quasi-Omega shape but the non-dimensionalized height and width remain unchanged. A smaller nozzle diameter decreases the streamwise velocity near the wall and increases the negative traverse velocity, which leads to a larger spray foot.

Experimental study of spray characteristics of liquid jets in supersonic crossflow

The spray characteristics of a water jet in Mach 2.85 air crossflow were investigated experimentally using a Phase Doppler Anemometry system. The droplet diameter and velocity of liquid jets with various nozzle diameters were measured and analyzed. Experiments with liquid jets positioned ahead of a cavity were performed to investigate the effects of the cavity on the spray characteristics. It was found that the Sauter Mean Diameter distribution presented a C shape, and the streamwise velocity component presented a mirrored C shape. The Sauter Mean Diameter increased downstream in the upper layer of the liquid jet spray, and this is because large droplets are more prone than small droplets to move from the lower layer to the upper layer of the liquid jet, resulting in a larger Sauter Mean Diameter downstream. A smaller nozzle resulted in an earlier secondary atomization and the final Sauter Mean Diameter had a lower value. A comparison between liquid jets from a plane wall and those positioned ahead of a cavity found an increase in Sauter Mean Diameter near the shear layer of the cavity and a decrease in the streamwise velocity. This mixing process caused an oblique airflow at the outlet of the cavity and changed the distribution of droplets.

Effect of aviation fuel temperature on refractive index in droplet size measurement using phase Doppler anemometry

To accurately measure droplet size using a phase Doppler anemometry (PDA) system, many variables, such as the physical properties of the fuel and optical parameters of the PDA system, should be known, particularly the refractive index of liquid droplets, which is often underestimated. In this study, the effect of a refractive index change on droplet size measurements according to the fuel temperature was experimentally investigated in detail. Light, commercial aviation fuels were used as the working fluids, and a conventional PDA system (DANTEC Co.) was used as the droplet size measuring device. It was confirmed that the change in the refractive index with fuel temperature has a great influence on droplet size measurement. Through extensive experimental investigations, a method for calculating the refractive index according to the fuel temperature change is proposed here.

Comparison of different configurations of Phase Doppler Analyser

A phase Doppler anemometry (PDA) technique is widely used in experimental fluid mechanics to measure size and velocity of particles in the fluid flow. Even though this method is common in experimental fluid mechanics, there are only few techniques that might serve for the purpose of the evaluation of the PDA system. To examine results of the PDA visualizations techniques are usually used. However, this approach suffers from several aspects. Mainly, it is difficult to determine the exact position of the measurement volume of PDA system. Then it is complicated to determine which particles are passing through the measuring volume. Another way how to examine performance of the PDA system is to use two PDA systems simultaneously. By using one laser for both systems we can avoid previously mentioned aspects. In our experiments, we use fiber based PDA system and classical PDA system both made by Dantec Dynamics. The aim of this paper is to compare results from various configurations and highlight crucial parameters that influence measurements.

Emissions From a Gas Turbine Sector Rig Operated With Synthetic Aviation and Biodiesel Fuel

Differences in exhaust emissions, smoke production, exhaust pattern factor, deposit buildup, and fuel nozzle spray characteristics for various blends of conventional commercial jet fuel (Jet A-1) with synthetic and biodiesel formulations were investigated. Three synthetic fuel formulations and four fatty acid methyl esters (FAMEs) were evaluated as such. The synthetic fuels were tested in both neat (100%) and 50% by volume blends with Jet A-1, while the FAME fuels were blended in 2% and 20% proportions. The combustion chamber sector rig, which houses a Rolls Royce T-56-A-15 combustion section, was utilized for emissions, deposits, and exhaust pattern factor evaluation. A combustion chamber exhaust plane traversing thermocouple rake was employed to generate two-dimensional temperature maps during operation. Following combustion testing, several combustion system components, including the combustion chamber, fuel nozzle, and igniter plug, were analyzed for relative levels of deposit buildup. A phase Doppler anemometry system was employed to determine differences in droplet size distributions, while an optical spray pattern analyzer was used to compare the spray pattern for the various fuel blends as they emerged from the T-56 nozzle.

Experimental Investigation of Droplet Dynamics and Spray Atomization inside Thermostatic Expansion Valves

Experimental investigation on spray atomization and droplet dynamics inside a thermostatic expansion valve (TEV) was conducted. A needle and an orifice were copied from a commercial TEV and machined to be mounted inside a chamber with optical access so that the flow inside the TEV is simulated and visualized at the same time. The break-up and atomization of the refrigerant were documented near the downstream of the orifice under different feed conditions on micro-second scale. A Phase Doppler Anemometry (PDA) system was used later to measure the size of atomized refrigerant droplets. It is found that spray impingement is inevitable and crucial to the atomization. Under steady-state operation, liquid film was seen formed on the needle plate and caused droplets splashed from plate, which will further have an effect on the droplets size. The before impact and after impact droplets were characterized by PDA system and for studying the impingement. In addition, the impact of the needle geometry inside the valve on refrigerant atomization has also been investigated. * Corresponding author: Chia-fon F. Lee

Investigation of Electrostatic Properties of Pharmaceutical Powders Using Phase Doppler Anemometry

Electrostatic properties of formulation component materials and blends play an important role in dry powder inhalation (DPI) products. Valid measurement of charge distribution will therefore lead to better control of powder behavior in DPI manufacturing processes. Ultrafine powders are known to have bipolar charge, have nonspherical shapes, and tend to be highly cohesive. Real-time noninvasive techniques need to be developed to obtain a precise and accurate measurement of electrically charged powders, as they aerosolize from a DPI product. How this measure relates to materials behavior throughout the various steps of a manufacturing process, e.g., from drug micronization and blending with lactose to filling dose units, also needs to be addressed. A novel noninvasive technique, which employs the phase Doppler anemometry (PDA) system for simultaneous measurement of size and charge of pharmaceutical powders, is currently being considered. Previous research demonstrated the advantages of this technique in measuring the bipolar charge distribution on a population of liquid aerosols. These findings led to significant improvements in understanding the performance of inhaler formulations, manufacturing processes, and development of new devices for inhaled drug delivery. This paper presents an investigation of electrostatic properties of lactose materials (typically used as a DPI excipient) using the PDA system. PDA calibration was checked using dry polystyrene microspheres, followed by an investigation of different grades of lactose. The PDA technique was used to track the motion of charged particles in the presence of an electric field. The magnitude, as well as the polarity of the particle charge, can be obtained by solving the equation of particle motion combined with the simultaneous measurement of its size and velocity. Results show the capability of the technique to allow real-time charge distribution and size measurement in the control of dry powder attributes that are critical to a better understanding of the manufacturing design space.

The Particle In-Flight Characteristics in Plasma Spraying Process Measured by Phase Doppler Anemometry (PDA)

Detailed measurements of particle in-flight characteristics have been carried out using a PDA system for benchmarking as well as to provide further information to aid the development of simulation models. The parameters studied included four conditions of primary gas flow rate and carrier gas flow rate. The particle velocities, diameters, and the corresponding volume flux at different locations were obtained. Due to the one port particle injection arrangement, it was noted that particles in general sprayed with an angle η deviated from the nozzle axis Z n , to the opposite side of the powder feeder port. The particles would also deviate from the spraying cone axis with a divergence angle (φ). The deviation and divergence angles were examined under different plasma spraying conditions. The measurement data rates at different cross-sectional planes were also obtained so as to compare the results derived from the volume flux measurement and the actual coating on a substrate at the equivalent standoff distance. It was found that the spraying area obtained from the measurement-data-rate increased with downstream distance and a linear relationship between spraying area and distance was also established. Comparing the integrated results, it was noted that the spraying areas derived from the measurement data rate were close to the actual spraying areas obtained from the coordinate measurement machine (CMM) results.

Near Nozzle PIV Measurements and Droplets Size Pattern of a GDI Swirled Spray(Spray Technologies, Atomization)

The aim of the present work is to analyze the effect of the injection pressure on the flow pattern and droplets size in a gasoline hollow-cone spray generated by a swirled injector, applying Particle Image Velocimetry (PIV) and Phase Doppler Anemometry (PDA). Experiments were carried out in the range of injection pressures between 6 and 10 Mpa using a common rail injection system, a commercial swirled type injector with a nozzle diameter of 0.50 mm and a cone angle of 67°. The investigation was carried out injecting the fuel in a chamber at ambient temperature and pressure. A 2-D imaging technique was used to follow the global evolution of the spray as function of the injection time in order to estimate the jet development, the morphology of the spray, and the instantaneous velocity field of fuel droplets. PIV images were captured, firstly, aligning the light sheet to the vertical axis of the spray; then, experiments were also taken with the light sheet placed through the cross section of the spray in order to explore the structure and velocity field, at different distances from the nozzle. A PDA system was used to acquire, simultaneously, the droplets velocity as well the droplets size. The system, equipped with an argon-ion laser, was set in forward scattering mode at an off-axis of 30°. Measurements were performed at the same operative conditions as for the visualization ones, choosing different distances from the nozzle. Droplets velocity and size data set provided a minimum of 40,000 in-cycle resolved valid data that were analyzed using the ensemble averaging technique. Results provided detailed information on the spatial velocity distribution and size of droplets close to the nozzle region. Ensemble averaged velocity field of fuel droplets obtained on the vertical plane through the injector axis showed high velocity values up to 100 m/s in the early stage of injection, whereas during the transition to completely developed main spray, droplets travel at lower velocities. The velocity field obtained on the cross section of the spray, at locations close to the nozzle (5 and 10 mm) and in the early stage of injection (up to 0.6 ms), showed a symmetric radial velocity field around the spray axis. Size measurements performed near the nozzle showed a D_<10> profile constant along the stationary period of injection and not affected by the injection pressure. Results also gave a global increasing trend of the temporally averaged mean diameter along the spray axis.

Simultaneous measurement of particle size and electrostatic charge distribution in DC electric field using phase doppler anemometry

The proposed noninvasive method of measurement of the charge level on a population of particles employs the phase Doppler anemometry (PDA) technique in conjunction with a high-resolution computer-controlled traversing system. The PDA system was used to track the motion of charged particles in the presence of a DC electric field. By solving the equation of particle motion in a viscous medium combined with the simultaneous measurement of its size and velocity, the magnitude as well as the polarity of the particle charge can be obtained. In order to detect particles with high electrical mobility and to cover the wide range of electrostatic charges the probe volume was moved mapping the velocity of the particles within the space between the parallel-plate electrodes. The preliminary experimental tests were carried out on dioctyl-phthalate aerosol droplets produced by nebulizing isopropanolic solutions using a Medic-Aid Sidestream nebulizer. The narrow size distribution, in the range from 0.5 to 3 /spl mu/m, was achieved using this method of aerosolization. The experimental results show that inherent electrostatic charge on dioctyl-phthalate droplets ranged from -250 to 250 electrons with an average charge-to-mass ratio of 0.24 /spl mu/C/g. After charging the aerosol using corona source the average charge-to-mass ratio increased to 20 /spl mu/C/g. The results demonstrate the capability of the technique to allow real-time determination of particle size and charge with a high-particle-count rate on the order of several thousands particles per second.

Eliminating high-order scattering effects in optical microbubble sizing.

Measurements of bubble size and velocity in multiphase flows are important in much research and many industrial applications. It has been found that high-order refractions have great impact on microbubble sizing by use of phase-Doppler anemometry (PDA). The problem has been investigated, and a model of phase-size correlation, which also takes high-order refractions into consideration, is introduced to improve the accuracy of bubble sizing. Hence the model relaxes the assumption of a single-scattering mechanism in a conventional PDA system. The results of simulation based on this new model are compared with those based on a single-scattering-mechanism approach or a first-order approach. An optimization method for accurately sizing air bubbles in water has been suggested.

Measurement of phase interaction in dispersed gas/particle two-phase flow

For simultaneous measurement of size and velocity distributions of continuous and dispersed phases in a two-phase flow a method is proposed and applied to increase the sensitivity of a phase-Doppler-anemometry (PDA) system. Design considerations are presented to increase the detectable size range of the PDA system to approximately 1:200 (in diameter) for simultaneous detection of tracers and particles. For this the optical properties for light scattering of the particles are properly adjusted to the measurement problem by using homogeneously coloured particles and a special signal processing procedure, which is developed to guarantee reliable signal processing of the tracer signals even with poor signal-to-noise ratios (SNR). The application of the experimental configuration is described by simultaneous measurements of gas and particle velocity and velocity fluctuation profiles in a two-phase jet arrangement with a particle diameter range from 1 (tracers) up to 160 μm (particles). In this two-phase flow at high Stokes numbers ( St≫1) different turbulence structure modification effects are identified. The height of influence of these effects depends on the local position in the jet. Near the nozzle exit high gas velocity gradients exist and therefore high turbulence production in the shear layer of the jet is observed. Here the turbulence structure in the jet mainly depends on lateral turbulence transport. Due to a changed turbulence structure with reduced intensity of large eddies, this lateral transport in the two-phase jet is decreased in comparison to the single-phase jet in this area. In the area at greater nozzle distances where the jet is nearly developed, the velocity gradient in the shear layer is lower and due to this lateral turbulence transport effects become less important. Here axial turbulence transport along the jet dominates and turbulence intensity reduction is higher.

High accuracy optical particle sizing in phase-Doppler anemometry

A novel structure for phase-Doppler anemometry (PDA) is proposed in order to eliminate the measurement-volume effect (MVE). This new PDA system consists of four receiving detectors in an optimized optical orientation. The method for the determination of the optimized optical orientation angle is introduced. In this method the vector sum of refractive and reflective rays is taken into consideration in describing a dual-mechanism-scattering model caused by a nonuniformly illuminated PDA measurement volume. The constraint of the single-mechanism-scattering model in the conventional PDA is removed. As a result the error caused by MVE, which consists of a Gaussian beam defect and a slit effect, can be eliminated. Analytical and experimental studies were conducted to investigate the accuracy of particle sizing using this new system. Both the experimental results and the simulation based on the generalized Lorenz-Mie theory show that the new method can provide a high-accuracy PDA system free of the MVE.

Method of phase-Doppler anemometry free from the measurement-volume effect

A novel method is developed to improve the accuracy of particle sizing in laser phase-Doppler anemometry (PDA). In this method the vector sum of refractive and reflective rays is taken into consideration in describing a dual-mechanism-scattering model caused by a nonuniformly illuminated PDA measurement volume. The constraint of the single-mechanism-scattering model in the conventional PDA is removed. As a result the error caused by the measurement-volume effect, which consists of a Gaussian-beam defect and a slit effect, can be eliminated. This new method can be easily implemented with minimal modification of the conventional PDA system. The results of simulation based on the generalized Lorenz-Mie theory show that the new method can provide a PDA system free from the measurement-volume effect.

Simultaneous measurement of continuous and dispersed phase in a two phase jet flow

In the present paper, a method is proposed and applied in order to increase the size range sensitivity of a Phase-Doppler-Anemometry (PDA) system, allowing simultaneous measurement of size and velocity distributions of continuous and dispersed phases in gaseous, dispersed two phase flow. Discrimination between the two phases is here directly achieved from the detected phase difference. Design considerations are presented to increase the size range sensitivity of the PDA system to approximately 1:200. Therefore, the optical properties for light scattering of the particles are properly adjusted to the measurement problem by colouring the particles homogeneously. The application of the system is described by measurements of velocity profiles in a zone close to the nozzle of a two phase jet with a tracer to particle diameter range of 1 to 160 μm.

Standard PDA for measuring the size of inhomogeneous droplets

A method to obtain the diameter of inhomogeneous droplets by using phase-Doppler anemometry (PDA) is described. Inhomogeneities included in a fluid droplet disturb light scattered by the droplet. Consequently the phase difference measured between two Doppler bursts deviates from the value calculated by geometrical optics theory for a droplet of diameter d. Because evaluation of the measured phase differences is based on a linear relationship between phase difference and particle diameter the accuracy of PDA is deteriorated. The difference between the real and the measured diameters of such droplets can be characterized by convolution with a Gaussian probability function. For monodisperse droplets and for a given type of inhomogeneity the standard deviation of the Gaussian function increases linearly with increasing mass concentration of these inhomogeneity. Applying infrared laser-PDA (IR-PDA) with a wavelength of 1312 nm, the measuring range to investigate droplets of, for instance, water-latex suspensions containing 450 nm polystyrene spheres can be extended to suspensions with six times the measurable concentration standard PDA using a He-Ne laser at nm. The relative improvement obtained by applying IR-PDA (in comparison with a standard PDA system equipped with a 632.8 nm laser) can be estimated by the decrease of the extinction efficiency of the inclusions with laser wavelength. The linear relation between extinction E and standard deviation can be used by a blind deconvolution algorithm. Starting from the measured diameter distribution of the inhomogeneous droplets the real diameter distribution and the standard deviation of each size class of the particles can be calculated by the algorithm. From this standard deviation it is possible to determine the extinction E and the mass concentration of the inhomogeneities.

A Flow Visualization Study of Spore Release Using a Wind Tunnel-Mounted Laser Light Sheet.

A phase Doppler anemometry system in combination with a laser light sheet was used in a low-speed recirculating wind tunnel to examine the flow field around an individual leaf. Turbulence similar to that encountered near the surface of the earth in a neutral stability boundary layer was generated using a grid at the upwind end of the wind tunnel test section. Individual healthy and diseased plant leaves were introduced into the tunnel with the leaf tip pointing downwind. The Mie-scattered radiation from the spores departing the diseased leaf was captured on videotape. Image processing software was used to enhance the visual quality of the individual frames from the videotape and to make spore velocity calculations. Three main vortex regions around the leaf were identified. The importance of these regions to the separation of the spores from the leaf surface and their subsequent downwind movement was analyzed.

Simultaneous measurement of continuous and dispersed phase in a two phase jet flow

In the present paper, a method is proposed and applied in order to increase the size range sensitivity of a Phase–Doppler–Anemometry (PDA) system, allowing simultaneous measurement of size and velocity distributions of continuous and dispersed phases in gaseous, dispersed two phase flow. Discrimination between the two phases is directly achieved here from the detected phase difference. Design considerations are presented to increase the size range sensitivity of the PDA system to ∼1:200. Therefore, the optical properties for light scattering of the particles are properly adjusted to the measurement problem by colouring the particles homogeneously. The application of the system is described by measurements of velocity profiles in a zone close to the nozzle of a two phase jet with a tracer to particle diameter range of 1–160μm.