Characteristics of transitional multicomponent gaseous and drop-laden mixing layers from direct numerical simulation: Composition effects

Transitional states are obtained by exercising a model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer at larger Reynolds numbers, Re, than in a previous study. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete dynamic and thermodynamic coupling between phases is included. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass, is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of their PDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices, resulting into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions, and the effects of the initial mass loading and initial free-stream gas temperature are explored. For reference, simulations are also performed for gaseous multicomponent mixing layers for which the effect of Re is investigated in the direct-numerical-simulation–accessible regime. The results encompass examination of the global layer characteristics, flow visualizations, and homogeneous-plane statistics at transition. Comparisons are performed with previous pretransitional MC-liquid simulations and with transitional single-component (SC) liquid-drop-laden mixing layer studies. Contrasting to pretransitional MC flows, the vorticity and drop organization depend on the initial gas temperature, this being due to drop/turbulence coupling. The vapor-composition mean molar mass and standard deviation distributions strongly correlate with the initial liquid-composition PDF. Unlike in pretransitional situations, regions of large composition standard deviation no longer necessarily coincide with those of large mean molar mass. The rotational and composition characteristics are all liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The classical energy cascade is found to be of similar strength, but the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation for MC flows. The kinetic energy and dissipation are liquid-specific and the variation among liquids is amplified with increasing free-stream gas temperature. The gas composition, of which the first four moments are calculated, is shown to be close to, but distinct from, a SGPDF. Eulerian and Lagrangian statistics of gas-phase quantities show that the different observation framework may affect the perception of the flow

An Analysis of the Impacts of the Illinois Board of Higher Education\u27 s Admission Requirements on Selected High Schools in East Central Illinois

The Illinois Board of Higher Education in 1985 instituted mandatory subject admission requirements for all state universities beginning in the year 1990. Subsequent legislative action by the Illinois General Assembly has moved these requirements back to 1993. This field experience investigated the possible impacts of these requirements on rural schools of under 500 students in east central Illinois. A cover letter explaining the purpose of the study and a two page questionnaire were mailed to twenty- one schools. Sixteen schools in the counties of Vermillion, Ford, Iroquois, Kankakee, and Will responded and were the focus of the study. Enrollment patterns in college preparatory classes and vocational classes before and after the implementation of the 1990 IBHE requirements were analyzed. The study also determined changes implemented by schools since the inception of the 1990 IBHE requirements in the areas of curriculum additions and deletions, staff additions and deletions, scheduling and graduation requirements. The study identified methods of maintaining a flexible curriculum to meet the needs of all students. Results of the study indicated that in the majority of the schools surveyed a significant amount of growth has taken place, since the enactment of the 1990 IBHE requirements, in the number of college-preparatory courses offered and in the enrollment of students in upper level mathematics and science courses. There has also been a larger number of students enrolled in social studies and foreign language classes in the schools surveyed since the enactment of the 1990 admission requirements. The study also determined that during this same period of time the majority of the schools surveyed experienced significant enrollment declines in vocational subjects, and the majority of courses dropped from curriculums of these schools have been vocational subjects. The greatest decreases in enrollments of the schools surveyed in this study have been in the vocational areas of industrial arts and home economics. Twenty-five percent of the schools surveyed have cut staff within the last three years with most of the programs eliminated being in the vocational areas. The majority of the schools surveyed have instituted some type of scheduling change since the enactment of the 1990 IBHE requirements that has allowed students to enroll in additional academic subjects during the school day. The study determined that over two-thirds of the schools surveyed have increased graduation requirements since the enactment of the 1990 IBHE requirements. Finally, the study determined that among those schools surveyed the most common method of maintaining curricular offerings is to alternate course offerings on an every-other year basis, especially in the upper level science and vocational subject areas

An Analysis of the Impacts of the Illinois Board of Higher Education\u27 s Admission Requirements on Selected High Schools in East Central Illinois

The Illinois Board of Higher Education in 1985 instituted mandatory subject admission requirements for all state universities beginning in the year 1990. Subsequent legislative action by the Illinois General Assembly has moved these requirements back to 1993. This field experience investigated the possible impacts of these requirements on rural schools of under 500 students in east central Illinois. A cover letter explaining the purpose of the study and a two page questionnaire were mailed to twenty- one schools. Sixteen schools in the counties of Vermillion, Ford, Iroquois, Kankakee, and Will responded and were the focus of the study. Enrollment patterns in college preparatory classes and vocational classes before and after the implementation of the 1990 IBHE requirements were analyzed. The study also determined changes implemented by schools since the inception of the 1990 IBHE requirements in the areas of curriculum additions and deletions, staff additions and deletions, scheduling and graduation requirements. The study identified methods of maintaining a flexible curriculum to meet the needs of all students. Results of the study indicated that in the majority of the schools surveyed a significant amount of growth has taken place, since the enactment of the 1990 IBHE requirements, in the number of college-preparatory courses offered and in the enrollment of students in upper level mathematics and science courses. There has also been a larger number of students enrolled in social studies and foreign language classes in the schools surveyed since the enactment of the 1990 admission requirements. The study also determined that during this same period of time the majority of the schools surveyed experienced significant enrollment declines in vocational subjects, and the majority of courses dropped from curriculums of these schools have been vocational subjects. The greatest decreases in enrollments of the schools surveyed in this study have been in the vocational areas of industrial arts and home economics. Twenty-five percent of the schools surveyed have cut staff within the last three years with most of the programs eliminated being in the vocational areas. The majority of the schools surveyed have instituted some type of scheduling change since the enactment of the 1990 IBHE requirements that has allowed students to enroll in additional academic subjects during the school day. The study determined that over two-thirds of the schools surveyed have increased graduation requirements since the enactment of the 1990 IBHE requirements. Finally, the study determined that among those schools surveyed the most common method of maintaining curricular offerings is to alternate course offerings on an every-other year basis, especially in the upper level science and vocational subject areas

Modelling of subgrid-scale phenomena in supercritical transitional mixing layers: an a priori study

A database of transitional direct numerical simulation (DNS) realizations of a supercritical mixing layer is analysed for understanding small-scale behaviour and examining subgrid-scale (SGS) models duplicating that behaviour. Initially, the mixing layer contains a single chemical species in each of the two streams, and a perturbation promotes roll-up and a double pairing of the four spanwise vortices initially present. The database encompasses three combinations of chemical species, several perturbation wavelengths and amplitudes, and several initial Reynolds numbers specifically chosen for the sole purpose of achieving transition. The DNS equations are the Navier-Stokes, total energy and species equations coupled to a real-gas equation of state; the fluxes of species and heat include the Soret and Dufour effects. The large-eddy simulation (LES) equations are derived from the DNS ones through filtering. Compared to the DNS equations, two types of additional terms are identified in the LES equations: SGS fluxes and other terms for which either assumptions or models are necessary. The magnitude of all terms in the LES conservation equations is analysed on the DNS database, with special attention to terms that could possibly be neglected. It is shown that in contrast to atmospheric-pressure gaseous flows, there are two new terms that must be modelled: one in each of the momentum and the energy equations. These new terms can be thought to result from the filtering of the nonlinear equation of state, and are associated with regions of high density-gradient magnitude both found in DNS and observed experimentally in fully turbulent high-pressure flows. A model is derived for the momentum-equation additional term that performs well at small filter size but deteriorates as the filter size increases, highlighting the necessity of ensuring appropriate grid resolution in LES. Modelling approaches for the energy-equation additional term are proposed, all of which may be too computationally intensive in LES. Several SGS flux models are tested on an a priori basis. The Smagorinsky (SM) model has a poor correlation with the data, while the gradient (GR) and scale-similarity (SS) models have high correlations. Calibrated model coefficients for the GR and SS models yield good agreement with the SGS fluxes, although statistically, the coefficients are not valid over all realizations. The GR model is also tested for the variances entering the calculation of the new terms in the momentum and energy equations; high correlations are obtained, although the calibrated coefficients are not statistically significant over the entire database at fixed filter size. As a manifestation of the small-scale supercritical mixing peculiarities, both scalar-dissipation visualizations and the scalar-dissipation probability density functions (PDF) are examined. The PDF is shown to exhibit minor peaks, with particular significance for those at larger scalar dissipation values than the mean, thus significantly departing from the Gaussian behaviour

The actual impedance of non-reflecting boundary conditions : implications for the computation of resonators

Non-reflecting boundary conditions are essential elements in the computation of many compressible flows: such simulations are very sensitive to the treatment of acoustic waves at boundaries. Non-reflecting conditions allow acoustic waves to propagate through boundaries with zero or small levels of reflection into the domain. However, perfectly non-reflecting conditions must be avoided because they can lead to ill-posed problems for the mean flow. Various methods have been proposed to construct boundary conditions which can be sufficiently non-reflecting for the acoustic field while still making the mean-flow problem well posed. This paper analyses a widely-used technique for non-reflecting outlets (Rudy and Strikwerda, Poinsot and Lele). It shows that the correction introduced by these authors can lead to large reflection levels and non-physical resonant behaviors. A simple scaling is proposed to evaluate the relaxation coefficient used in theses methods for a non-reflecting outlet. The proposed scaling is tested for simple cases (ducts) both theoretically and numerically

(+)-Chlorido[(1,2,3,4-η;P 2′)-2′- diphenylphosphanyl-2-diphenylphosphoryl-1,1′-binaphthyl]rhodium(I) methanol monosolvate

In the title complex, [RhCl(C 44H 32OP 2)]·CH 3OH, the Rh I ion is coordinated by a naphthyl group of a partially oxidized 2,2′-bis-(diphenylphosphanyl)-1, 1′-binaphthyl (BINAP) ligand in a 4 mode, one P atom of the diphenylphosphanyl group and one Cl atom. The P=O group does not interact with the Rh I ion but accepts an O - H⋯O hydrogen bond from the methanol solvent molecule

Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach

An extension to the classical FPV model is developed for transcritical real-fluid combustion simulations in the context of finite volume, fully compressible, explicit solvers. A double-flux model is developed for transcritical flows to eliminate the spurious pressure oscillations. A hybrid scheme with entropy-stable flux correction is formulated to robustly represent large density ratios. The thermodynamics for ideal-gas values is modeled by a linearized specific heat ratio model. Parameters needed for the cubic EoS are pre-tabulated for the evaluation of departure functions and a quadratic expression is used to recover the attraction parameter. The novelty of the proposed approach lies in the ability to account for pressure and temperature variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases are performed to demonstrate the capability of the proposed approach in multidimensional simulations. The proposed combustion model and numerical schemes are directly applicable for LES simulations of real applications under transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T

Modeling and Real-Time Simulation of a Vascularized Liver Tissue

International audienceIn Europe only, about 100,000 deaths per year are related to cirrhosis or liver cancer. While surgery remains the option that offers the foremost success rate against such pathologies, several limitations still hinder its widespread development. Among the limiting factors is the lack of accurate planning systems, which has been a motivation for several recent works, aiming at better resection planning and training systems, relying on pre-operative imaging, anatomical and biomechanical modelling. While the vascular network in the liver plays a key role in defining the operative strategy, its influence at a biomechanical level has not been taken into account. In the paper we propose a real-time model of vascularized organs such as the liver. The model takes into account separate constitutive laws for the parenchyma and vessels, and defines a coupling mechanism between these two entities. In the evaluation section, we present results of in vitro porcine liver experiments that indicate a significant influence of vascular structures on the mechanical behaviour of tissue. We confirm the val- ues obtained in the experiments by computer simulation using standard FEM. Finally, we show that the conventional modelling approach can be efficiently approximated with the proposed composite model capable of real-time calculations

Is Venice an ideal habitat for Legionella pneumophila?

Introduction. Legionella bacterium manifests itself in Legion- naire?s disease and Pontiac fever, it is mainly found and trans- mitted by aerosol produced in cooling towers, water distribution plants and medical equipment, and it affects mainly elder persons in poor health. Methods. The population of Venice Local Health Unit was divided in two areas of study and the incidence of legionellosis in residents of Venice historical centre (Distretto Sanitario 1) and in residents of the mainland and coastal areas (Distretti Sanitari 2, 3, 4) was calculated. The cases were those notified to the Public Health Unit by law, and the population of residents was that of the eligible for health care in the archives of the Local Health Unit. Only cases of legionellosis in residents who had not travelled in the 10 days previous of the onset of disease, and not related to nosocomial clusters were considered. The standardized incidence ratio was then calculated and confidence interval were defined by Poisson distribution. Results. Given the population of the two areas, 59801 in Distretto Sanitario 1 and 237555 in Distretti 2, 3, 4, the raw incidence of disease is respectively 87 per 100000 and 20 per 100000 in time 2002-2010. The standardized incidence ratio for the population of Distretto Sanitario 1 vs the remaining population is 4.3. Discussion. The difference in risk of getting the disease in this two residential areas geographically very close, is probably related to the different buildings? characteristics, old and difficult to main- tain in Venice historical centre

Numerical Benchmark for High-Reynolds-Number Supercritical Flows with Large Density Gradients

Because of the extreme complexity of physical phenomena at high pressure, only limited data are available for solver validation at device-relevant conditions such as liquid rocket engines, gas turbines, or diesel engines. In the present study, a two-dimensional direct numerical simulation is used to establish a benchmark for supercritical flow at a high Reynolds number and high-density ratio at conditions typically encountered in liquid rocket engines. Emphasis has been placed on maintaining the flow characteristics of actual systems with simple boundary conditions, grid spacing, and geometry. Results from two different state-of-the-art codes, with markedly different numerical formalisms, are compared using this benchmark. The strong similarity between the two numerical predictions lends confidence to the physical accuracy of the results. The established database can be used for solver benchmarking and model development at conditions relevant to many propulsion and power systems