Split Stream Flow Past a Blunt Trailing Edge with Application to Combustion Instabilities

In shear coaxial injectors, commonly used for cryogenic liquid rocket engines, propellants traveling at different velocities are separated by the inner jet post before they come into contact with each other, mix, and combust. Knowing how the fluids mix and how susceptible they are to hydrodynamic instabilities is paramount for a successful liquid rocket engine. In this study, the wake behind a blunt trailing edge of a long plate, similar to an unwrapped coaxial injector, was studied in a water tunnel. Two fluid streams of different velocities were introduced on opposite sides of the plate. PIV was used to visualize and determine the influence of the velocity ratio of the split stream on the wake behavior. Measurements of the vortex shedding frequency were taken at various velocity ratios and compared with well characterized cases with a uniform free stream. Operating conditions ranged from Reynolds number 6,000 to 22,000 and velocity ratios 0.30 to 1.00

Constant-frequency time cells in the vortex-shedding from a square cylinder in accelerating flows

An extensive experimental campaign has been carried out in a multiple-fan wind tunnel to study the effects of flow acceleration on a sectional model of a sharp-edged square cylinder. Different levels of positive and negative acceleration are reproduced, which are compatible with those induced by full-scale thunderstorm outflows. Various initial and final conditions are also explored and, in all conditions, multiple test repeats are carried out in order to obtain satisfactory ensemble averages. Particular attention is devoted to the acquisition of signals associated with vortex-shedding, for which tailored time-frequency analyses, based on the continuous wavelet and Hilbert transforms, are introduced. Sensitivity analyses are carried out on a selection of the relevant pa-rameters that better allow the tracing of the temporal variation of the shedding frequency. Time intervals in which the shedding frequency is constant, separated by discontinuities, are found during the transients. The number and extent of such constant-frequency time cells and discontinuities seem to be connected with the flow acceleration, but are not strictly repetitive. For higher levels of acceleration the ensemble mean of the Strouhal number is found to be comparable with or moderately lower than the steady-flow value corresponding to the instantaneous velocity

Split Stream Flow Past a Blunt Trailing Edge with Application to Combustion Instabilities

In shear coaxial injectors, commonly used for cryogenic liquid rocket engines, propellants traveling at different velocities are separated by the inner jet post before they come into contact with each other, mix, and combust. Knowing how the fluids mix and how susceptible they are to hydrodynamic instabilities is paramount for a successful liquid rocket engine. In this study, the wake behind a blunt trailing edge of a long plate, similar to an unwrapped coaxial injector, was studied in a water tunnel. Two fluid streams of different velocities were introduced on opposite sides of the plate. PIV was used to visualize and determine the influence of the velocity ratio of the split stream on the wake behavior. Measurements of the vortex shedding frequency were taken at various velocity ratios and compared with well characterized cases with a uniform free stream. Operating conditions ranged from Reynolds number 6,000 to 22,000 and velocity ratios 0.30 to 1.00

Young workers’ access to and awareness of occupational safety and health services: age-differences and possible drivers in a large survey of employees in Italy

Young workers are in particular need of occupational safety and health (OSH) services, but it is unclear whether they have the necessary access to such services. We compared young with older workers in terms of the access to and awareness of OSH services, and examined if differences in employment conditions accounted for age-differences. We used survey data from Italy (INSuLA 1, 2014), with a sample of 8000 employed men and women aged 19 to 65 years, including 732 young workers aged under 30 years. Six questions measured access to services, and five questions assessed awareness of different OSH issues. Several employment conditions were included. Analyses revealed that young workers had less access and a lower awareness of OSH issues compared with older workers. For instance, odds ratios (OR) suggest that young workers had a 1.44 times higher likelihood [95%—confidence interval 1.21–1.70] of having no access to an occupational physician, and were more likely (2.22 [1.39–3.38]) to be unaware of legal OSH frameworks. Adjustment for selected employment conditions (company size, temporary contract) substantially reduced OR’s, indicating that these conditions contribute to differences between older and younger workers. We conclude that OSH management should pay particular attention to young workers in general and, to young workers in precarious employment, and working in small companies in particular

Assessment of DNA Damage and Telomerase Activity in Exfoliated Urinary Cells as Sensitive and Noninvasive Biomarkers for Early Diagnosis of Bladder Cancer in Ex-Workers of a Rubber Tyres Industry

The aim of the present study was to identify sensitive and noninvasive biomarkers of early carcinogenic effect at target organ to use in biomonitoring studies of workers at risk for previous occupational exposure to potential carcinogens. Standard urine cytology (Papanicolaou staining test), comet assay, and quantitative telomerase repeat amplification protocol (TRAP) assay were performed in 159 ex-rubber workers employed in tyres production and 97 unexposed subjects. In TRAP positive cases, a second level analysis using FISH (Urovysion) was done. Cystoscopy results were available for 11 individuals whose 6 FISH/TRAP/comet positive showed in 3 cases a dysplastic condition confirmed by biopsy, 1 comet positive resulted in infiltrating UBC to the biopsy and with hyperplasia and slight dysplasia to the urinary cytology, 1 comet positive resulted in papillary superficial UBC to the biopsy, 1 FISH/TRAP positive showed a normal condition, and 2 TRAP positive showed in one case a phlogosis condition. The results evidenced good concordance of TRAP, comet, and FISH assays as early biomarkers of procarcinogenic effect confirmed by the dysplastic condition and UBC found by cystoscopy-biopsy analysis. The analysis of these markers in urine cells could be potentially more accurate than conventional cytology in monitoring workers exposed to mixture of bladder potential carcinogens

IMPAcT-RLS2: Indagine nazionale sulla salute e la sicurezza sul lavoro: il ruolo dei Rappresentanti dei Lavoratori per la Sicurezza

L’Indagine IMPAcT-RLS2 si inserisce nel più ampio programma di ricerca INSuLa2, la cui prima edizione, condotta nel 2014 e rivolta a tutti gli attori della prevenzione, ha approfondito aspetti della tutela della salute e sicurezza sul lavoro (SSL) secondo il punto di vista delle varie figure intervistate. La survey indirizzata ai Rappresentanti dei lavoratori per la sicurezza (RLS), focalizzata inizialmente su tre contesti regionali, è stata implementata grazie all’indagine IMPAcT-RLS, realizzata nel 2016, che ha coinvolto un campione di circa 2.100 soggetti, rappresentativo a livello nazionale, per dimensione aziendale e settore di attività economica. L’indagine ha evidenziato l’importanza di disporre di informazioni sempre più approfondite sul ruolo dei RLS e di monitorarne l’andamento nel tempo. Il presente studio ribadisce l’importanza di istituire rilevazioni periodiche e replicabili, finalizzate ad aumentare le conoscenze e la consapevolezza sui sistemi di prevenzione e promuovere interventi sempre più mirati per il miglioramento della tutela della SSL.The IMPAcT-RLS2 survey is part of a larger context of INSuLa2 research program; its first edition was conducted in 2014 and targeted to all prevention professionals, investigating occupational health and safety (OSH) protection issues perceived by the various professionals’ point of view. The survey addressed to Health and Safety Representatives (HS reps.), focused on three regional contexts, was further implemented in 2016 through the IMPAcT-RLS survey, which involved a sample representative at national level, by company size and economic activity sector consisting of about 2,100 subjects. The survey highlighted the importance of having ever more in-depth information on the role of HS reps. and monitoring their evolution over time. This study arises from the need to create periodic and replicable surveys, aimed at increasing knowledge and awareness of prevention systems and promoting increasingly targeted interventions for improving the protection of OS

Aeroelastic Flight Data Analysis with the Hilbert-Huang Algorithm

This paper investigates the utility of the Hilbert-Huang transform for the analysis of aeroelastic flight data. It is well known that the classical Hilbert transform can be used for time-frequency analysis of functions or signals. Unfortunately, the Hilbert transform can only be effectively applied to an extremely small class of signals, namely those that are characterized by a single frequency component at any instant in time. The recently-developed Hilbert-Huang algorithm addresses the limitations of the classical Hilbert transform through a process known as empirical mode decomposition. Using this approach, the data is filtered into a series of intrinsic mode functions, each of which admits a well-behaved Hilbert transform. In this manner, the Hilbert-Huang algorithm affords time-frequency analysis of a large class of signals. This powerful tool has been applied in the analysis of scientific data, structural system identification, mechanical system fault detection, and even image processing. The purpose of this paper is to demonstrate the potential applications of the Hilbert-Huang algorithm for the analysis of aeroelastic systems, with improvements such as localized/online processing. Applications for correlations between system input and output, and amongst output sensors, are discussed to characterize the time-varying amplitude and frequency correlations present in the various components of multiple data channels. Online stability analyses and modal identification are also presented. Examples are given using aeroelastic test data from the F/A-18 Active Aeroelastic Wing aircraft, an Aerostructures Test Wing, and pitch-plunge simulation

LES-based Study of the Roughness Effects on the Wake of a Circular Cylinder from Subcritical to Transcritical Reynolds Numbers

This paper investigates the effects of surface roughness on the flow past a circular cylinder at subcritical to transcritical Reynolds numbers. Large eddy simulations of the flow for sand grain roughness of size k/D = 0.02 are performed (D is the cylinder diameter). Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased momentum deficit, especially at transcritical Reynolds numbers. Even at subcritical Reynolds numbers, boundary layer instabilities are triggered in the roughness sublayer and eventually lead to the transition to turbulence. The early separation at transcritical Reynolds numbers leads to a wake topology similar to that of the subcritical regime, resulting in an increased drag coefficient and lower Strouhal number. Turbulent statistics in the wake are also affected by roughness; the Reynolds stresses are larger due to the increased turbulent kinetic energy production in the boundary layer and separated shear layers close to the cylinder shoulders.We acknowledge “Red Española de Surpercomputación” (RES) for awarding us access to the MareNostrum III machine based in Barcelona, Spain (Ref. FI-2015-2-0026 and FI-2015-3-0011). We also acknowledge PRACE for awarding us access to Fermi and Marconi Supercomputers at Cineca, Italy (Ref. 2015133120). Oriol Lehmkuhl acknowledges a PDJ 2014 Grant by AGAUR (Generalitat de Catalunya). Ugo Piomelli acknowledges the support of the Natural Sciences and Engineering Research Council (NSERC) of Canada under the Discovery Grant Programme (Grant No. RGPIN-2016-04391). Ricard Borrell acknowledges a Juan de la Cierva postdoctoral grant (IJCI-2014-21034). Ivette Rodriguez, Oriol Lehmkuhl, Ricard Borrell and Assensi Oliva acknowledge Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ref. ENE2014-60577-R).Peer ReviewedPostprint (author's final draft