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In this paper, molecular level simulations of a one-dimensional (1-D) hydrogen-air flame are performed at pressures of 0.1 MPa and 1 MPa using the Direct Simulation Monte Carlo (DSMC) method. DSMC has been previously used to successfully simulate hydrogen flames using traditional Arrhenius based reaction rates and using a novel quantum-kinetic (QK) model. The latter only uses collision data for determining the reaction outcome and is used in this study. Fundamental studies of combustion at high pressure are challenging and in this paper, the ability of the DSMC method to simulate hydrogen flames at high pressure is demonstrated. Results from DSMC are evaluated using a skeletal 12-step as well as a more detailed 21-step reaction mechanism, and are compared with those from 1-D Direct Numerical Simulation (DNS), showing a reasonable agreement in flame speed, flame temperature and species mass fraction at lower pressure. At high pressure, a good agreement in temperature and species mass fraction is found between DSMC and DNS. However, the flame speed particularly from the 12-step skeletal mechanism is overestimated from DSMC compared to that from the experiments. DSMC shows strong promise to carry out molecular level simulations at higher pressures but require improvements in associated models for better results. [ABSTRACT FROM AUTHOR]

Abstract The validity of Damköhler's first hypothesis, which relates the turbulent flame speed to turbulent flame surface area under the condition where the integral length scale of turbulence is greater than the flame thickness, has been assessed using three-dimensional Direct Numerical Simulations (DNS) of turbulent premixed Bunsen burner flames over a range of values of Reynolds number, pressure and turbulence intensity. It has been found for the Bunsen configuration that the proportionality between volume-integrated burning rate and the overall flame surface area is not strictly maintained according to Damköhler's first hypothesis. The discrepancy is found to originate physically from the local stretch rate dependence of displacement speed, and this helps to explain differences observed previously between flames with and without mean curvature. Approximating the local density-weighted flame propagation speed with the unstrained laminar burning velocity is shown to be inaccurate, and can have a significant influence on the prediction of the overall burning rate for flames with non-zero mean curvature. Using a two-dimensional projection of the actual scalar gradient for flame area evaluation is shown to exacerbate the loss of proportionality between volume-integrated burning rate and the overall flame surface area. The current analysis identifies the conditions under which Damköhler's hypothesis remains valid and the necessary correction for non-zero mean flame curvature. Further, it has been demonstrated that surface-weighted stretch effects on displacement speed need to be accounted for in order to ensure the validity of Damköhler's hypothesis under all circumstances. Finally, it has been found that the volume-integrated density-weighted scalar dissipation rate remains proportional to the overall burning rate for all flames considered here irrespective of the value of Reynolds number, pressure and turbulence intensity. However, this proportionality is lost when the scalar dissipation rate is evaluated using the two-dimensional projection of the actual scalar gradient. [ABSTRACT FROM AUTHOR]

The prospects presented by wavelets in the numerical analysis of chemically reacting turbulent flows are examined. In many flows of industrial relevance, combustion takes place in a stream of turbulent premixed gases. The mode of combustion is said to lie in the laminar flamelet regime. When a combustion process belonging to this regime occurs, it is anticipated that the flow field will be split into two components: reactants, consisting essentially of the fuel–air mixture, and products, typically consisting of carbon dioxide, water vapour, nitrogen and a number of other trace species. The two regions are separated by the flame, which is typically a very small-scale structure containing all of the chemical and molecular transport effects. The length scale disparity between the thin flame and the flow domain as a whole makes efficient discretization with traditional methods difficult, but is ideally suited to the multiresolution paradigm. In this paper, the current state of the art in the application of wavelets to the discretization of turbulent combustion problems is explored. The limitations of the present approaches as well as their strengths are assessed and outstanding problems from both a theoretical and a practical point of view are discussed. Key research directions for future investigations are highlighted. [ABSTRACT FROM AUTHOR]

This paper focuses on the simulation of turbulent reacting flows via recent developments in wavelet-based analyses. The unique data compression properties of wavelet methods render them especially attractive for such simulations, in which the length and time-scales of interest originate from both physical and chemical processes and may span several orders of magnitude. The particular difficulties encountered when representing reacting flow problems on non-periodic domains, and how these difficulties have led to the adoption of a biorthogonal wavelet framework, are discussed. This leads to consideration of interpolating wavelet transforms based on second-generation wavelets, for which a fast transform algorithm is presented. Issues raised by the application of wavelet transform methods to the reacting Navier–Stokes equations, including the calculation of differential operators, the extension to two and three dimensions and the evaluation of non-linear terms, are examined. The implications of the wavelet approachfor the representation of the turbulent energy cascade are explored briefly. Finally, some future directions for research into the extension of wavelet analysis as an underpinning technology for computational fluid dynamics are indicated. [ABSTRACT FROM AUTHOR]

• Anxiety and depression are common during pregnancy. • Massage therapy may be effective in reducing pregnant women's anxiety and depression. • High-quality research is required to properly evaluate the impact of massage therapy on pregnancy related anxiety and depression. To critically appraise and synthesize the best available evidence on the effectiveness of massage to reduce antenatal women's anxiety and/ or depression. Systematic review with meta-analysis Pregnant women over the age of 18 years who receive massage interventions. Eight studies were included in the review; seven were randomized controlled trials. Data were collected via pregnant women's self-reported ratings of anxiety or depression using validated tools. Meta-analysis of four studies revealed a moderate effect of massage therapy on women's depressive symptoms as measured by the Center for Epidemiologic Studies Depression Scale (CES-D) (MD = -5.95, 95%CI = -8.11 to -3.80, I2 = 0%) compared with usual care. A moderate effect of massage interventions on women's anxiety were also found based on five studies using various measures (SMD = -0.59, 95%CI = -1.06 to -0.12, I2 = 75%) when compared with usual care. However, none of the trials had a low risk of bias. Non-pharmacologic treatments for mental health symptoms are an important option for women to use during pregnancy. As shown in meta-analysed data, massage therapy might be more effective in reducing pregnant women's anxiety and depression than usual care, although the current results may be prone to bias. Further high-quality research is required to fully evaluate the impact of massage therapy on pregnant women's mental health symptoms in the immediate and also longer term. Massage therapy may be an acceptable and feasible approach for pregnant women to employ to reduce their anxiety and depressive symptoms. More research evidence examining the safety and effectiveness of massage is required before practice recommendations can be made. [ABSTRACT FROM AUTHOR]