Influence of diesel fuel viscosity on cavitating throttle flow simulations at erosive operation conditions

This work investigates the effect of liquid fuel viscosity, as specific by the European Committee for Standardization 2009 (European Norm) for all automotive fuels, on the predicted cavitating flow in micro-orifice flows. The wide range of viscosities allowed, leads to a significant variation of orifice nominal Reynolds numbers for the same pressure drop across the orifice. This in turn, is found to affect flow detachment, formation of large-scale vortices and micro-scale turbulence. A pressure-based compressible solver is used on the filtered Navier-Stokes equations using the multi-fluid approach; separate velocity fields are solved for each phase that share a common pressure. The rates of evaporation and condensation are evaluated with a simplified model based on the Rayleigh-Plesset equation; the Coherent Structure Model is adopted for the sub-grid scales modeling in the momentum conservation equation. The test case simulated is a well reported benchmark throttled flow channel geometry, referred to as ’I-channel’; this has allowed for easy optical access for which flow visualization and LIF measurements allowed for validation of the developed methodology. Despite its simplicity, the Ichannel geometry is found to reproduce the most characteristic flow features prevailing in high-speed flows realized in cavitating fuel injectors. Following, the effect of liquid viscosity on integral mass flow, velocity profiles, vapor cavities distribution and pressure peaks indicating locations prone to cavitation erosion are reported

Impact of cavitation erosion on nozzle flow characteristics and liquid fuel atomization

Modern Diesel engines with high injection pressures can suffer from cavitation erosion phenomena. Signs of cavitation erosion in automotive components can manifest in high pressure liquid systems components (e.g. injectors, valves and pumps), as well as in the narrow fluid regions next to the cylinder liners on both the water cooling jacket side and the ring assembly side. Special attention must also be given during the design of marine propellers and water turbines, since the performances and the lifespan of these components mainly depends by the appearance of cavitation and, potentially, erosion.Cavitation erosion alters metal devices by changing their geometry from the original design, with consequences on the overall system performances. Since the lifetime of the components can be significantly shortened due to cavitation erosion, numerical and experimental investigations are usually carried out during the design process to evaluate the risk of incurring in cavitation erosion. It is then of crucial importance for the industry to have access to validated numerical models for the prediction of cavitation erosion within the softwares used for the evaluation of new designs. The scope of this work is then to develop a state–of–the–art numerical framework for the prediction of cavitation erosion in a commercially available software. For this reason, liquid compressibility models are implemented in the software with both, analytical formulations and tabular data, commonly used by the industry. The solver capability to correctly resolve pressure wave velocities is proven with simple 1D test cases, comparing the simulation results against analytical solutions. A novel scientific contribution is made by applying the multifluid model to cavitating flows, thus allowing to model slip velocity between the liquid and the vapor phase. The developed numerical framework for the simulation of cavitating flows at erosive conditions is validated against experimental results of simplified geometries and the obtained results about the effect of viscosity variability of commercial diesel showed the importance of fluid properties for the investigation of cavitation erosion. For the first time, pressure peaks related to the collapse of vapor clouds are recorded due to end of injection events and the effect of actual erosion patterns is investigated in terms of internal injector flow and spray. All the developed methods are implemented in a software commercialized by AVL GmbH,therefore of immediate use to engineers for industrial applications

Extraocular muscle sampled volume in Graves' orbitopathy using 3-T fast spin-echo MRI with iterative decomposition of water and fat sequences

Abstract Background: Current magnetic resonance imaging (MRI) techniques for measuring extraocular muscle (EOM) volume enlargement are not ideally suited for routine follow-up of Graves’ ophthalmopathy (GO) because the difficulty of segmenting the muscles at the tendon insertion complicates and lengthens the study protocol. Purpose: To measure the EOM sampled volume (SV) and assess its correlation with proptosis. Material and Methods: A total of 37 patients with newly diagnosed GO underwent 3-T MRI scanning with iterative decomposition of water and fat (IDEAL) sequences with and without contrast enhancement. In each patient, the three largest contiguous coronal cross-sectional areas (CSA) on the EOM slices were segmented using a polygon selection tool and then summed to compute the EOM-SV. Proptosis was evaluated with the Hertel index (HI). The relationships between the HI value and EOM-SV and between HI and EOM-CSA were compared and assessed with Pearson’s correlation coefficient and the univariate regression coefficient. Inter-observer and intra-observer variability were calculated. Results: HI showed a stronger correlation with EOM-SV (P<0.001; r¼0.712, r2¼0.507) than with EOM-CSA (P<0.001; r¼0.645 and r2¼0.329). The intraclass correlation coefficient indicated that the inter-observer agreement was high (0.998). The standard deviation between repeated measurements was 1.9–5.3%. Conclusion: IDEAL sequences allow for the measurement EOM-SV both on non-contrast and contrast-enhanced scans. EOM-SV predicts proptosis more accurately than does EOM-CSA. The measurement of EOM-SV is practical and reproducible. EOM-SV changes of 3.5–8.3% can be assumed to reflect true volume changes

Approaching Skyscape Archaeology: A Note on Method and Fieldwork for the Case Study of Pompeii

The urban layout of Pompeii presents several orientations, possibly due to an uneven bare ground plateau. However, its main east-west axes have the same orientation of Herculaneum ones, suggesting that not only geomorphological constrains acted as topographical factors. Starting from a hypothesis by Nissen (1906), the method of skyscape archaeology was applied to Pompeii urban grid and temples, testing digital models with fieldwork measurements. The results show that the main east-west axes aligned with the rising summer solstice sun above the local horizon. Furthermore, the Doric Temple was oriented with the sunset on the same time of the year, suggesting an intentional design

Multiconsensus control of homogeneous LTI hybrid systems under time-driven jumps

In this paper, we consider a network of homogeneous LTI hybrid dynamics under time-driven aperiodic jumps and exchanging information over a fixed communication graph. Based on the notion of almost equitable partitions, we explicitly characterize the clusters induced by the network over the nodes and, consequently, the corresponding multi-consensus trajectories. Then, we design a decentralized control ensuring convergence of all agents to the corresponding multi-consensus trajectory. Simulations over an academic example illustrate the results

Genetic and morphological studies of Trichosirocalus species introduced to North America, Australia and New Zealand for the biological control of thistles

Trichosirocalus horridus sensu lato has been used as a biological control agent of several invasive thistles (Carduus spp., Cirsium spp. and Onopordum spp.) since 1974. It has been recognized as a single species until 2002, when it was split into three species based on morphological characters: T. horridus, Trichosirocalus briesei and Trichosirocalus mortadelo, each purported to have different host plants. Because of this taxonomic change, uncertainty exists as to which species were released in various countries; furthermore, there appears to be some exceptions to the purported host plants of some of these species. To resolve these questions, we conducted an integrative taxonomic study of the T. horridus species complex using molecular genetic and morphological analyses of specimens from three continents. Both mitochondrial cytochrome c oxidase subunit I and nuclear elongation factor 1α markers clearly indicate that there are only two distinct species, T. horridus and T. briesei. Molecular evidence, morphological analysis and host plant associations support the synonymy of T. horridus (Panzer, 1801) and T. mortadelo Alonso-Zarazaga & Sánchez-Ruiz, 2002. We determine that T. horridus has been established in Canada, USA, New Zealand and Australia and that T. briesei is established in Australia. The former species was collected from Carduus, Cirsium and Onopordum spp. in the field, whereas the latter appears to be specific to Onopordum

Non-Financial Resources to Enhance Companies’ Profitability: A Stakeholder Perspective

Purpose This study aims to investigate the impact of stakeholders’ nonfinancial resources (NFRs) on companies’ profitability, filling a significant gap in the literature regarding the role of NFRs in value creation. Design/methodology/approach Data from 76 organizations from 2017 to 2019 were collected and analyzed. Four primary NFRs and their key value drivers were identified, representing core elements that support different dimensions of a company’s performance. Statistical tests examined the relationship between stakeholders’ NFRs and financial performance measures. Findings When analyzed collectively and individually, the results reveal a significant positive influence of stakeholders’ NFRs on a firm’s profitability. Higher importance assigned to NFRs correlates with a higher return on sales. Originality/value This study contributes to the literature by empirically bridging the gap between stakeholder theory and the resource-based view, addressing the intersection of these perspectives. It also provides novel insights into how stakeholders’ NFRs impact profitability, offering valuable implications for research and managerial practice. It suggests that managers should integrate nonfinancial measures of NFRs within their performance measurement system to manage better and sustain companies’ value-creation process

Exploring the Entrepreneurial Jungle: Unicorns, Gazelles, Zebras, and Other Venture Species

This paper proposes pioneering the exploration of new entrepreneurial species as a novel and essential research avenue within the entrepreneurship domain. By likening entrepreneurial ventures to diverse species inhabiting a jungle, the study ventures into unexplored territories of entrepreneurial taxonomy. It advocates delving into distinct classifications such as unicorns, zebras, and gazelles, offering a fresh perspective on their impact on economies and societies. The research argues for the relevance of these unique ventures, emphasizing their significant influence on entrepreneurial thought and challenging traditional theories. By shedding light on uncharted species and their inter-relationships, the paper opens promising avenues for future research, contributing to the evolving landscape of entrepreneurship studies

Large Eddy Simulation of the internal injector flow during pilot injection

The aim of this work is to simulate the internal flow of a Diesel injector during an entire pilot injection event. In common rail systems a small quantity of fuel can be injected before the main injection is started. This increases the temperature in the combustion chamber and improves the combustion, leading to higher engine efficiency and reduced emissions. The internal nozzle flow during this short event is highly dynamic and vapor cavities may appear at the end of the injection. In order to study the flow characteristics, a numerical methodology based on the Eulerian multi-fluid approach is adopted. The filtered Navier-Stokes equations are discretized with the finite volume method and then solved with an implicit pressure-based solver. The flow field is modelled considering single pressure and velocity fields. The Coherent Structure Model is used to derive the eddy viscosity applied to the Large Eddy Simulation approach. The liquid evaporation rate is evaluated with a cavitation model based on the Rayleigh-Plesset equation for a single bubble. Even though thermodynamic equilibrium is not satisfied a priori, the main parameter is adjusted in order to limit the thermodynamic states to be in a range close to the equilibrium conditions. The liquid compressibility is modelled with a linear correlation between pressure and density variations. The needle longitudinal movement obtained from the experiments is applied to the simulation. The adopted geometry is the Spray A case defined by the Engine Combustion Network. It is an asymmetric single hole Diesel injector that has been extensively studied in the past both experimentally and numerically. The injection pressure is 1,500 [bar] and the ambient pressure is 60 [bar] with a fuel temperature of 363 K inside the injector. Pure n-dodecane is used as fluid in order to have a precise specification of the physical properties. Although both experiments and simulations showed no cavitation for completely open needle at fixed position, recent studies demonstrated that phase-change of the liquid can appear during the needle closing phase. Cavitation erosion prone locations are then evaluated by recording the maximum intensity of pressure on the surface