In altitude test facility (ATF) operation, the requirements to control humidity to generate defined icing conditions are gaining more and more importance. In this context, the ability to predict humidity and condensation becomes a fundamental part of ATF control. For this purpose, classical nucleation theory has been applied in combination with in situ measurements to derive a model suitable to predict the onset of condensation during very low temperature ATF operation. The model parameters have been acquired inside the ATF of the University of Stuttgart downstream of its air coolers. This makes the application or assumption of generalized atmospheric aerosol data unnecessary. Polydisperse nano aerosol distributions were measured and statistically evaluated, showing that a constant distribution of nano aerosol particle size can be assumed. The composition of the ingested nanoparticles was analyzed and Arizona test dust was chosen as a valid substitute material for the application in the prediction model leading to a conservative prediction. The approach has been successfully verified using optical measurements during ATF testing. Its prediction accuracy fulfills the requirements of ATF control for a variety of icing conditions in component and engine altitude testing.

In order to understand the reasons for the apparent benefits of using a flow-blurring (FB) atomizer in a combustion system, it is necessary to first examine fundamental spray characteristics under nonreacting conditions. Previous work on FB atomizers, however, has mostly involved only water and a relatively narrow range of parameters. In this study, a phase Doppler anemometry (PDA) instrument was used to characterize FB atomizer sprays and determine the effects of varying surface tension and viscosity of the liquid. Operating at room pressure and temperature (i.e., a “cold spray”), droplet sizes and velocities were measured for water, a water/surfactant mixture (lower surface tension), a water/glycerol mixture (higher viscosity), and glycerol (much higher viscosity). For all of the tested fluids, with the exception of pure glycerol, the FB atomizer produced small droplets (below 50 μm) whose size did not vary significantly in the radial or axial direction, particularly above a characteristic distance from the atomizer exit. Results show that the spray is essentially unaffected by a 4.5× decrease in surface tension or a 7× increase in viscosity, and that Sauter mean diameter (SMD) only increased by approximately a factor of three when substituting glycerol (750× higher viscosity) for water. The results suggest that the FB atomizer can effectively atomize a wide range of liquids, making it a useful fuel-flexible atomizer for combustion applications.

Thin-film flows encountered in engineering systems such as aero-engine bearing chambers often exhibit capillary waves and occur within a moderate to high Weber number range. Although the depth-averaged simulation of these thin-film flows is computationally efficient relative to traditional volume-of-fluid (VOF) methods, numerical challenges remain particularly for solutions involving capillary waves and in the higher Weber number, low surface tension range. A depth-averaged approximation of the Navier–Stokes equations has been used to explore the effect of surface tension, grid resolution, and inertia on thin-film rimming solution accuracy and numerical stability. In shock and pooling solutions where capillary ripples are present, solution stability, and accuracy are shown to be highly sensitive to surface tension. The common practice in analytical studies of enforcing unphysical low Weber number stability constraints is shown to stabilize the solution by artificially damping capillary oscillations. This approach, however, although providing stable solutions is shown to adversely affect solution accuracy. An alternative grid resolution-based stability criterion is demonstrated and used to obtain numerically stable shock and pooling solutions without recourse to unphysical surface tension values. This allows for the accurate simulation of thin-film flows with capillary waves within the constrained parameter space corresponding to physical material and flow properties. Results obtained using the proposed formulation and solution strategy show good agreement with available experimental data from literature for low Re coating flows and moderate to high Re falling wavy film flows.

Late fuel during closing of the valve of a fuel injector and fuel films stuck on the wall around the nozzle outlets are sources of particulate matters (PM). In this study, we focused on the effects of the valve motions on the late fuel and the fuel films stuck on the walls around the nozzle outlets. We previously developed a particle/grid hybrid method: fuel flows within the flow paths of fuel injectors were simulated by a front capturing method, and liquid-column breakup at the nozzle outlets was mainly simulated by a particle method. The velocity at the inlet boundary of a fuel injector was controlled in order to affect the valve motions on the late-fuel behavior. The simulated late fuel broke up with surface tension around the time of zero-stroke position of the valve, then liquid columns and coarse droplets formed after the bounds of the valve, and finally only coarse droplets were left. We found that the late fuel was generated by low-speed fuel-flows through the nozzles during the bounds of the valve. The effect of the bounds of the valve on the fuel films stuck on the wall around the nozzle outlets was also studied with a simulation that removed the bounds of the valve. The volume of the fuel films stuck on the wall of the nozzle outlets decreased without the bounds of the valve.

For boiling water reactors (BWR) and steam generators, the water level is a safety-relevant process variable. The most commonly applied measuring method is based on the calculation of the liquid level from geodetic pressure differences to a reference column of defined height and density. However, transition processes occurring under operational and accident conditions may lead to dynamic changes in the reference level and, therefore, to fluctuations in the differential pressure signal. This paper presents experiments and numerical simulations on the steady-state and transient behavior of gas/liquid phase boundaries in “zero chamber level vessels” (ZCLV). In these slightly inclined miniature tubes, the constant reference level is provided by surface tension forces and the capillary effect, respectively. To investigate the basic topology of gas/liquid interfaces under simplified conditions (environmental parameters, no heat transfer), a test facility with optical access was developed. The construction allows for variations of the inner tube diameter, inclination angle, and liquid mass flow rate, respectively. By this means, experiments on phase boundaries were carried out for ethanol/air and water/air. The results provide information about the impact of geometry parameters and their interactions on the interface topology. In addition, the dynamic draining of excess liquid mass at the free end of the tube and at artificial weld seams, which is supposed to be the reason for temperature fluctuations observed in ZCLV during power operation of BWR, was experimentally analyzed. The measurements represent the basis for an experimental validation and optimizations of the numerical flow code ANSYS CFX 12.0. In the next step, water/vapor phase boundaries at 286 °C and 70 bars will be investigated by applying X-ray radiography to a scale model. The results will be discussed in context with the hydrostatic level measurement in BWR.

A new meshless Lagrangian particle code has been developed to tackle the challenging numerical modeling of primary atomization. In doing so the correct treatment and representation of the interfacial physics are crucial prerequisites. Grid based codes using interface tracking or interface capturing techniques, such as the volume of fluid or level set method, exhibit difficulties regarding mass conservation, curvature capturing and interface diffusion. The objective of this work is to overcome these shortcomings of common state-of-the-art grid based approaches. Our multidimensional meshless particle code is based on the smoothed particle hydrodynamics (SPH) method. Various test cases have been conducted, by which the capability of accurately capturing the physics of single and multiphase flows is verified and the future potential of this approach is demonstrated. Compressible as well as incompresssible fluids can be modeled. Surface tension effects are taken into account by two different models. Solid walls as well as periodic boundary conditions offer a broad variety of numerically modeling technical applications. In a first step, single phase calculations of shear driven liquid flows have been carried out. Furthermore, the disintegration of a gravity driven liquid jet emerging from a generic nozzle has been investigated in free surface simulations. The typical formation of a meniscus due to surface tension is observed. Spray formation is qualitatively in good agreement compared to experiments. Finally, the results of a two-phase simulation with a fluid density ratio of 1000, which is similar to a fuel-air fluid system as in airblast atomizers, are presented. The surface minimization and pressure jump across the droplet interface due to surface tension can be predicted accurately. The test cases conducted so far demonstrate the accuracy of the existing code and underline the promising potential of this new method for successfully predicting primary atomization.

This paper presents numerical simulation results of the primary atomization of a turbulent liquid jet injected into a gaseous crossflow. Simulations are performed using the balanced force refined level set grid method. The phase interface during the initial breakup phase is tracked by a level set method on a separate refined grid. A balanced force finite volume algorithm together with an interface projected curvature evaluation is used to ensure the stable and accurate treatment of surface tension forces even on small scales. Broken off, small scale nearly spherical drops are transferred into a Lagrangian point particle description allowing for full two-way coupling and continued secondary atomization. The numerical method is applied to the simulation of the primary atomization region of a turbulent liquid jet ( q = 6.6 , We = 330 , Re = 14 , 000 ) injected into a gaseous crossflow ( Re = 570 , 000 ) , analyzed experimentally by Brown and McDonell ( 2006, “Near Field Behavior of a Liquid Jet in a Crossflow,” ILASS Americas, 19th Annual Conference on Liquid Atomization and Spray Systems ). The simulations take the actual geometry of the injector into account. Grid converged simulation results of the jet penetration agree well with experimentally obtained correlations. Both column/bag breakup and shear/ligament breakup modes can be observed on the liquid jet. A grid refinement study shows that on the finest employed grids (flow solver 64 points per injector diameter, level set solver 128 points per injector diameter), grid converged drop sizes are achieved for drops as small as one-hundredth the size of the injector diameter.

This paper deals with characteristics of surface vortex in a cylindrical vessel. One of the characteristics is a gas core length, which is important to estimate the onset condition of the gas entrainment but influenced easily by the experimental condition. In the experiment using water, the effects of the water temperature, water level, and the surface tension on the gas core length were investigated. The onset condition of the gas entrainment is sometimes estimated by using the Burgers vortex model but the real flow in the vessel is different from the model. The velocity fields were measured by particle image velocimetry (PIV) and the velocity gradient of the downward flow was discussed. The proper flow conditions for the Burgers vortex model are a high water level and a high flow rate.

Recent increases in fuel costs, concerns for global warming, and limited supplies of fossil fuels have prompted wide spread research on renewable liquid biofuels produced domestically from agricultural feedstock. In this study, two types of biodiesels and vegetable oil (VO) are investigated as potential fuels for gas turbines to generate power. Biodiesels produced from VO and animal fat were considered in this study. The problems of high viscosity and poor volatility of VO (soybean oil) were addressed by using diesel-VO blends with up to 30% VO by volume. Gas chromatography/mass spectrometry, thermogravimetric analysis, and density, kinematic viscosity, surface tension, and water content measurements were used to characterize the fuel properties. The combustion performance of different fuels was compared experimentally in an atmospheric pressure burner with an air-assist injector and swirling primary air around it. For different fuels, the effect of the atomizing airflow rate on Sauter mean diameter was determined from a correlation for air-assist atomizers. Profiles of nitric oxides ( NO x ) and carbon monoxide (CO) emissions were obtained for different atomizing airflow rates, while the total airflow rate was kept constant. The results show that despite the compositional differences, the physical properties and emissions of the two biodiesel fuels are similar. Diesel-VO fuel blends resulted in slightly higher CO emissions compared with diesel, while the NO x emissions correlated well with the flame temperature. The results show that the CO and NO x emissions are determined mainly by fuel atomization and fuel/air mixing processes, and that the fuel composition effects are of secondary importance for fuels and operating conditions of the present study.

In this study, void drift phenomena, which are one of three components of the intersubchannel fluid transfer, have been investigated experimentally and analytically. In the experiments, data on flow and void redistributions were obtained for hydraulically nonequilibrium flows in a multiple channel consisting of two subchannels simplifying a triangle tight lattice rod bundle. In order to know the effects of the reduced surface tension on the void drift, water and water with a surfactant were used as test liquids. In addition, data on the void diffusion coefficient, D ̃ , needed in a void drift model, have been obtained from the redistribution data. In the analysis, the flow and the void redistributions were predicted by a subchannel analysis code based on a one-dimensional two-fluid model. From a comparison between the experiment and the code prediction, the present analysis code was found to be valid against the present data if newly developed constitutive equations of wall and interfacial friction were incorporated in to the model to account for the reduced surface tension effects.

This work addresses primary atomization modeling, multidimensional spray prediction, and flow characteristics of compound nozzle gasoline injectors. Compound nozzles are designed to improve the gasoline spray quality by increasing turbulence at the injector exit. Under the typical operating conditions of 270-1015 kPa, spray atomization in the compound nozzle gasoline injectors is mainly due to primary atomization where the flow turbulence and the surface tension are the dominant factors. A primary atomization model has been developed to predict the mean droplet size far downstream by taking into account the effect of turbulent intensity at the injector exit. Two multidimensional spray codes, KIVA-2 and STAR-CD, originally developed for high-pressure diesel injection, are employed for the lower-pressure gasoline injection. A separate CFD analysis was performed on the complex internal flows of the compound nozzles to obtain the initial and boundary conditions for the spray codes. The TAB breakup model used in KIVA-2 adequately facilitates the atomization process in the gasoline injection.

The breakup of a liquid sheet is of fundamental interest in the atomization of liquid fuels. The present study explores the breakup of a two-dimensional liquid sheet in the presence of co-flow air with emphasis on the extent to which liquid properties affect breakup. Three liquids, selected with varying values of viscosity and surface tension, are introduced through a twin-fluid, two-dimensional nozzle. A pulsed laser imaging system is used to determine the sheet structure at breakup, the distance and time to breakup, and the character of the ligaments and droplets formed. Experiments are conducted at two liquid flow rates with five flow rates of co-flowing air. Liquid properties affect the residence time required to initiate sheet breakup, and alter the time and length scales in the breakup mechanism.

The physical properties of the fuel, such as density, viscosity, surface tension, and bulk modulus of elasticity, affect many aspects of the diesel injection process. The effects of these fuel properties on the fuel pressure in the high-pressure line, rate of injection, leakage, spray penetration, and droplet size distribution were determined experimentally. The mechanism of spray development was investigated by injecting the fuel into a high-pressure chamber. A pulsed Malvern drop-size analyzer, based on Fraunhofer diffraction, was utilized to determine droplet size ranges for various fuels.

Fuel atomization with prefilming airblast nozzles has been investigated. The present analysis is directed toward a detailed investigation of the atomization processes and the clarification of the fundamental phenomena. Two-dimensional models were utilized. High-speed films, showing the deterioration of the liquid film close to the atomizing edge, reveal the dynamics of the liquid’s deterioration and show the motion of the film during the drop formation. The liquid separation is shown to be a periodic process with the drop formation caused by momentum transfer. The frequency spectrum of the liquid separation is determined by means of an optical technique. It is seen that the main frequencies depend only on the air velocity. They are always lower than the corresponding wave frequencies. The droplet size measurements obtained by a light scattering technique emphasize the dominant role of the air velocity at the atomizing edge. A decrease in the surface tension provides an improvement in atomization quality. Other parameters such as liquid flow rate, liquid viscosity, gap height, and length of the prefilming surface within the nozzle were found not to affect directly the droplet size distribution produced, if the air velocity in each of the two ducts of the nozzle is kept constant. The pressure drop of the air, however, rises. It is shown that the droplet size distribution can be easily determined, if the arithmetic mean value of the air velocity in both ducts is known, e.g., from a calculation of the internal flow. Due to the high liquid mass flow rates of airblast nozzles, the wavy film is partly atomized within the nozzle before the liquid separates at the atomizing edge. The measurements show that the portion of the liquid mass flow atomized remains relatively small and that the droplet sizes are equivalent to those produced at the atomizing edge.

Published correlations for the Sauter Mean Diameter (SMD) of sprays produced by pressure atomizing injectors have generally taken the form, SMD = Aω˙ B ΔP C . The system of units and the fuel properties are reflected by the coefficient A . The exponent of the flow rate term (B) has been found to be approximately 0.20. There has been less agreement relative to the appropriate value of the pressure drop exponent ( C ). Simmons [1] reported the value of the pressure drop exponent to be 0.354, and this value has been widely used. This paper presents recently acquired experimental data that reveal that for We greater than 10.0 a different atomization process occurs, i.e., “shear-type” breakup, which results in much finer atomization than predicted by previously reported correlations. To accurately represent the high We data, a significantly different SMD correlation form is required and is reported in this paper. The effects of large variations in the nozzle size, fuel density, viscosity, surface tension, and fuel temperature have been included in the derivation of the correlations.

A systematic investigation was made of the differences in atomizing performance between water and kerosene fuel for six simplex fuel nozzles of small flow capacity. A large number of tests was run using two methods of spray analysis, to determine the effect of nozzle liquid pressure drop (ΔP F ) on Sauter Mean Diameter (SMD). It was found that there is a clearly-defined relationship dependent on both the relative values of surface tension and also on a Weber Number calculated for conditions in the liquid film at the nozzle discharge orifice. It is concluded that large errors in estimating SMD for modeling programs are possible if results observed with water are assumed to be representative of behavior with kerosene fuel.

The Eighth International Conference on the Properties of Steam has adopted a new skeleton table and formulation for viscosity. The formulation is valid from the triple point to 1100 K (∼2000 R) and pressures to 100 MPa (∼15,000 psia). Comparisons are made between the calculated and the skeletal table values, and also between the new values and those in the 1967 ASME Steam Tables. A set of figures and tables in both English and SI units are presented to replace those in the Steam Tables. Sources for computer programs are given.

A series of tests has been carried out on a specially designed airblast atomizer in which the liquid is first spread into a thin sheet and then subjected on both sides to the atomizing action of high velocity air. The primary aim of the invesitgation was to examine the influence on mean drop size of liquid viscosity, surface tension and density. The liquids employed represented a range of values of surface tension from 26 to 73 dynes/cm, while viscosity and density were varied between 1.3 and 124 centipoise and 0.8 and 1.8 gm / cm 3 , respectively. Atomizing air velocities covered the range of practical interest to the designers of continuous combustion systems and varied between 60 and 125 m/sec. Analysis of the experimental data showed that they could be described to a reasonable order of accuracy by the following empirical expression: SMD = 521 V a − 1 · σ 0.5 · ρ 0.75 ( 1 + W l W a ) + 0.037 η 0.85 ( σ ρ ) 1.2 ( 1 + W l W a ) 2