Towards an Unsteady/Flamelet Progress Variable method for non-premixed turbulent combustion at supercritical pressures

Combustion devices operating at elevated pressures, such as liquid rocket engines (LRE), are usually characterized by supercritical thermodynamic conditions. Propellants injected into the combustion cham- ber experience real fluid effects on both their mixing and combustion. Transition through super-criticality implies abrupt variations in thermochemical properties which, together with chemical reactions and high turbulent levels introduce spatial and temporal scales that make these processes impractical to be simulated directly. Reynolds-Averaged Navier-Stokes (RANS) and Large Eddies Simulation (LES) equipped with suitable turbulent combustion modeling are therefore mandatory to attempt numerical simulation on real- istic length scales. In the present work, the building blocks for extending the unsteady/flamelet progress variable approach for turbulent combustion modeling to supercritical non-premixed turbulent flames are presented. Such approach requires a large number of unsteady supercritical laminar flamelet solutions at supercritical pressures, usually referred as flame structures, to be preliminarily established by solving the flamelet equations with suitable real fluid thermodynamics. Given such unsteady flame structures, flamelet libraries can then be generated for all thermochemical quantities. The explicit dependence on flamelet time is usually eliminated using mixture fraction, reaction progress parameter, and maximum scalar dissipation rate as independent flamelet parameters. Real fluid thermodynamics used for such unsteady supercritical laminar flamelet solutions, is taken into account by means of a computationally efficient cubic equation of state. In order to have a better handling of real gas mixtures, the real gas equation of state is written in a comprehensive three-parameter fashion. A priori analysis at supercritical pressures of transient flame structures is performed in order to study how solutions populate the flamelet state space which is usually characterized by the S-shape diagram representing a collection of steady solutions. High-pressure condi- tions ranging from 60 to 300 bar are chosen as representative of a methane/liquid-oxygen rocket engine operating condition

Intrinsic instability of lean hydrogen/ammonia premixed flames: Influence of Soret effect and pressure

The addition of hydrogen in ammonia/air mixtures can lead to the onset of intrinsic flame instabilities at conditions of technical relevance. The length and time scales of intrinsic instabilities can be estimated by means of linear stability analysis of planar premixed flames by evaluating the dispersion relation. In this work, we perform such linear stability analysis for hydrogen-enriched ammonia/air flames (50%H2-50%NH3 by volume) using direct numerical simulation with a detailed chemical kinetic mechanism. The impact of pressure and the inclusion of the Soret effect in the governing equations is assessed by comparing the resulting dispersion relation at atmospheric pressure and 10 atm. Our data indicate that both pressure and the Soret effects promote the onset of intrinsic instabilities. Comparisons with available numerical literature data as well as theoretical models are also discussed

Mitigation of Darrieus-Landau instability effects on turbulent premixed flames

Theoretical considerations on the competition between the most amplified modes for Darrieus-Landau (DL) hydrodynamic instability and turbulence timescales, show that, two extremal regimes can be identified: the instability-dominated and turbulence-dominated regimes. In the latter, also denoted as unified regime, both experiments and numerical simulations give evidence showing how the large scale, cusp-like structures of the flame front surface, typical of DL instability, are hindered by turbulent fluctuations. The result is that quantities such as turbulent flame propagation and front curvature statistics, which in the instability dominated regime are enhanced or modified by the overwhelming presence of hydrodynamic instability, are now mitigated and a unified regime is reached in which the characteristics of DL unstable and stable flame configurations become indistinguishable. In this work we analyze the concealing effects of increasing level of turbulence over the hydrodynamic Darrieus-Landau instability, and we show that, although some global indices such as the skewness of the curvature p.d.f. suggest that a unified regime is reached, others show the persistence of residual differences: in particular, the power spectral density of the flame front curvature. We use both experimental and numerical datasets of stable and unstable (based on linear stability analysis) flames, in conditions ranging from quasi laminar to significantly turbulent regimes

An efficient modeling framework for wall heat flux prediction in rocket combustion chambers using non adiabatic flamelets and wall-functions

In this work an efficient numerical framework for the prediction of wall heat loads in Liquid Rocket Engine combustion chambers is presented. The proposed framework is based on a new version of the non-adiabatic flamelet model and on wall functions for turbulent boundary layer modeling. Different wall function models are applied to 2D and 3D wall heat flux simulations of an experimental single-element gaseous oxygen-gaseous methane combustor in an Unsteady Reynolds Averaged Navier Stokes context. A systematic analysis and a comprehensive comparison of the selected wall models is carried out. The role of the constant or variable properties assumption on the near-wall turbulent quantities affecting the wall heat flux is assessed and the resulting friction velocity scaling investigated. When the skin friction velocity based on the local turbulent kinetic energy is defined by considering constant properties across the boundary layer, the equilibrium boundary layer assumption is not fulfilled and a significant overestimation of the wall heat flux is observed. Results obtained with the corrected near-wall turbulence modeling, on the other hand, showed a substantial improvement in terms of wall heat flux when compared with both experimental data and higher fidelity simulations results

Updated systematic review and meta-analysis of the comparative data on colposuspensions, pubovaginal slings, and midurethral tapes in the surgical treatment of female stress urinary incontinence

Context Retropubic (RP-TVT) and transobturator miurethral (TO-TVT) midurethral sling (MUS) are popular surgical treatments for female stress urinary incontinence. The long-term efficacy and safety of the procedures is still a topic of intense clinical research and several randomised controlled trials (RCTs) have been published in the last years Objective To evaluate the efficacy and safety of MUS compared with other surgical treatments for female stress urinary incontinence. Evidence acquisition A systematic review and meta-analysis of the literature was performed using the Medline, Scopus, and Web of Science databases to update our previously published analyses. Evidence synthesis Twenty-eight RCTs were identified. In total, the meta-analyses included 15 855 patients. Patients receiving MUS had significantly higher overall (odds ratio [OR]: 0.59, p = 0.0003) and objective (OR: 0.51, p = 0.001) cure rates than those receiving Burch colposuspension. Patients undergoing MUS and pubovaginal slings had similar cure rates. Patients treated with RT-TVT had higher subjective (OR: 0.83, p = 0.03) and objective (OR: 0.82, p = 0.01) cure rates than those receiving TO-TVT. However, the latter had a lower risk of intraoperative bladder or vaginal perforation (OR: 2.4, p = 0.0002), pelvic haematoma (OR: 2.61, p = 0.002), urinary tract infections (OR: 1.31, p = 0.04) and voiding lower urinary tract symptoms (OR: 1.66, p = 0.002). Sensitivity analyses limited to RCTs with follow-up durations >60 mo demonstrated similar outcomes for RP-TVT and TO-TVT. No significant differences in efficacy were identified comparing inside-to-out and outside-to-in TO-TVT but vaginal perforations were less common with the former (OR: 0.21, p = 0.0002). Conclusions The present analysis confirms the superiority of MUS over Burch colposuspension. The studies comparing insertion of RT-TVT and TO-TVT showed higher subjective and objective cure rates for the RP-TVT but at the cost of higher risks of some complications and voiding lower urinary tract symptoms. Efficacy of inside-out and outside-in techniques of TO-TVT insertion was similar, although the risk of vaginal perforation was lower in the inside-to-out TO-TVT. Patient summary Retropubic and transobturator midurethral slings are a popular treatment for female stress urinary incontinence. The available literature suggest that those slings are either more effective or safer than other older surgical procedures. Retropubic tapes are followed with slightly higher continence rates as compared with the transobturator tapes but are associated with higher risk of intra- and postoperative complications

Interrupted versus uninterrupted NOAC peri-implantation of cardiac device: A single-centre randomised prospective pilot trial

BACKGROUND: Many patients requiring cardiac implantable electronic device (CIED) implantation are on long-term oral anticoagulant therapy. While continuation of warfarin has been shown to be safe and reduce bleeding complications compared to interruption of warfarin therapy and heparin bridging, it is not known which novel oral anticoagulants (NOAC) regimen (interrupted vs. uninterrupted) is better in this setting. METHODS: One-hundred and one patients were randomized to receive CIED implantation with either interrupted or uninterrupted/continuous NOAC therapy before surgery. No heparin was used in either treatment arm. The primary end-point was the presence of a clinically significant pocket haematoma after CIED implantation. The secondary end-point was a composite of other major bleeding events, device-related infection, thrombotic events and device-related admission length post device implantation. RESULTS: Both treatment groups were equally balanced for baseline variables and concomitant medications. One clinically significant pocket haematoma occurred in the uninterrupted NOAC group and none in the interrupted group (p = 0.320). There was no difference in other bleeding complications. No thrombotic events were observed in either of the two groups. CONCLUSIONS: Despite the paucity of bleeding events, data from this pilot study suggest that uninterrupted NOAC therapy for CIED implantation appears to be as safe as NOAC interruption and does not increase bleeding complications

Toxicity of antioxidant supplements in patients with male factor infertility: A systematic review and meta-analysis of randomized controlled trials

Treating oxidative stress through antioxidant therapy has been considered an appealing strategy in the management of male infertility. However, evidence regarding the toxicity of an-tioxidant therapy is controversial. We summarized the available clinical evidence on the toxicity associated with the use of antioxidants in infertile males. A systematic review was performed in March 2021. We included randomized controlled trials evaluating the incidence of adverse events in male patients with infertility receiving antioxidant therapy. Thirteen studies involving 1999 male patients were identified. Antioxidant supplementation in patients with male factor infertility was associated with a statistically significantly increased risk of nausea (Odds Ratio: 2.16, 95% Confidence Interval: 1.05–4.43, p = 0.036), headache (Odds Ratio: 3.05, 95% Confidence Interval: 1.59– 5.85 p = 0.001), and dyspepsia (Odds Ratio: 4.12, 95% Confidence Interval: 1.43–11.85, p = 0.009) compared to a placebo. Treatment discontinuation due to adverse events was not significantly higher in patients taking antioxidants compared to a placebo (Odds Ratio: 2.29, 95% Confidence Interval: 0.76–6.88, p = 0.139). When antioxidant supplementation is considered, a more accurate risk/benefit analysis is warranted

Lower urinary tract symptoms and mental health during COVID-19 pandemic

Objective: Coronaviruses (CoVs) are a group of RNA viruses involved in several human diseases affecting respiratory, enteric, hepatic, and neurological systems. COVID-19 was identified in 2020 and was named SARS-CoV-2. To limit worldwide contagion, many countries instituted a lockdown, which conducted to disruption of routine life. In fact, pandemic was associated with several stresses among population, such as loss of employment, deaths of family members, friends, or colleagues, financial insecurity, and isolation. This led to long-lasting psychosocial effects as anxiety and depression, increasing the prevalence of stress and traumarelated disorders in the population. The aim of this study was to investigate the correlation between lower urinary tracts symptoms (LUTS) and stress/depressive symptoms during COVID-19 pandemic. Materials and methods: An anonymous cross-sectional webbased survey (comprehending anthropometric data, education level, occupation status, smoking and alcohol habits, current therapies, quarantine and COVID-19 infection status) was conducted from March to May 2020 in Italy. LUTS were examined through National Institute of Health-Chronic Prostatitis Symptom Index (NIH-CPSI) and Genitourinary Pain Index (GUPI). Hamilton Depression Rating Scale (HDRS) was utilized to evaluate depressive and anxiety symptoms. Non-parametric Kruskal-Wallis H Test was used for statistical analysis. Results: A total of 356 out of 461 subjects fully completed the survey, with a response rate of 77.2%. Data showed that subjects involved in economic difficulties, quarantine measures or with increased HDRS reported a significative statistic worsened urinary symptoms (H(3) = 11.731, p = 0.008), quality of life, (H(3) = 10.301, p = 0.016), total NIH-CPSI/GUPI score (H(3) = 42.150, p = 0.000), and quality of life (H(3) = 48.638, p = 0.000). Conclusions: COVID-19 pandemic provoked several alterations in everyday life. Although general lockdown, quarantine and social distancing have been necessary to prevent virus spreading, this had long term effects on all population in terms of mental and physical health. NIH-CPSI and GUPI scores increased linearly with stress and anxiety levels measured at HDRS, confirming worse LUTS in subjects who suffered anxiety and stress from COVID-19 pandemic

Impact of Circadian Desynchrony on Spermatogenesis: A Mini Review

The purpose of this mini review is to provide data about pre-clinical and clinical evidence exploring the impact of circadian desynchrony on spermatogenesis. Several lines of evidence exist demonstrating that disruption of circadian rhythms may interfere with male fertility. Experimental knock-out or knock-down of clock genes, physiologically involved in the regulation of circadian rhythms, are associated with impairments of fertility pathways in both animal and human models. Moreover, disruption of circadian rhythms, due to reduction of sleep duration and/or alteration of its architecture can negatively interfere in humans with circulating levels of male sexual hormones as well as with semen parameters. Unfortunately, current evidence remains low due to study heterogeneity