Stability of a moving radial liquid sheet: experiments

A recent theory (Tirumkudulu & Paramati, Phys. Fluids, vol. 25, 2013, 102107) for a radially expanding liquid sheet, that accounts for liquid inertia, interfacial tension and thinning of the liquid sheet while ignoring the inertia of the surrounding gas and viscous effects, shows that such a sheet is convectively unstable to small sinuous disturbances at all frequencies and Weber numbers. We equivalent to rho(l)U(2)h/sigma). Here, rho(l) and sigma are the density and surface tension of the liquid, respectively, U is the speed of the liquid jet, and h is the local sheet thickness. In this study we use a simple non-contact optical technique based on laser-induced fluorescence (LIF) to measure the instantaneous local sheet thickness and displacement of a circular sheet produced by head-on impingement of two laminar jets. When the impingement point is disturbed via acoustic forcing, sinuous waves produced close to the impingement point travel radially outwards. The phase speed of the sinuous wave decreases while the amplitude grows as they propagate radially outwards. Our experimental technique was unable to detect thickness modulations in the presence of forcing, suggesting that the modulations could be smaller than the resolution of our experimental technique. The measured phase speed of the sinuous wave envelope matches with theoretical predictions while there is a qualitative agreement in the case of spatial growth. We show that there is a range of frequencies over which the sheet is unstable due to both aerodynamic interaction and thinning effects, while outside this range, thinning effects dominate. These results imply that a full theory that describes the dynamics of a radially expanding liquid sheet should account for both effects

Does firm-level political risk affect cash holdings?

We investigate whether firm-level political risk affects corporate cash holdings. Taking a sample of 5,424 US firms with 129,750 firm-quarter observations from 2002Q1 to 2021Q3, we find that cash holdings is higher for firms with greater exposure to firm-level political risk. The positive relationship between firm political risk and cash holdings is consistent for financial constraint and non-constraint firms, high and low growth firms, pro-cyclical and counter-cyclical and competitive industries. Further, our findings are consistent to alternative measures of firm-level political risk and cash holdings. In addition, our findings remain robust with different endogeneity tests: a natural experiment, an instrumental variable approach, and a propensity score matching. Overall, we present novel evidence on the determinants of corporate cash holdings

Does the institutional quality matter for renewable energy promotion in the OECD economies?

This study examines the effect of institutional quality on renewable energy promotion in the OECD economies. The study employs annual data from 1980 to 2014 on 18 OECD economies. The robust panel unit root tests show that all the considered variables have a similar order of integration, indicating that they are nonstationary at their levels but stationary at the first-order differences. The panel cointegration test with structural breaks and cross-section dependence confirms a long-run equilibrium association between institutional quality, renewable energy consumption, and control variables. The analysis of long-run estimations displays that better institutional quality makes a unique and substantial contribution to promoting renewable energy consumption. Overall, the study findings offer important policy implications highlighting the importance of institutional quality for the growth of renewable energy and a sustainable world

Long-run relationship between R&D investment and environmental sustainability:Evidence from the European Union member countries

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The researchers, environmental scientists and policymakers around the world are exerting substantial efforts to mitigate the growth of CO2 emissions to save the planet. A number of measures and initiatives, such as, energy efficiency, renewable energy technologies and emission-control are proposed in order to reduce CO2 emissions. This study examines the long-run relationship between R&D investment and environmental sustainability in a panel of 25 European Union (EU) member countries over a period of seventeen years (1998 to 2014). We use robust and reliable econometric methods to capture the interactions between R&D investment on renewable energy consumption and CO2 emissions. The findings confirm that the growth of R&D expenditures promotes renewable energy consumption and plays a significant role in reducing CO2 emissions in the sample countries. Furthermore, the findings suggest that increasing the share of renewable energy consumption in the total energy mix also reduces CO2 emissions. Given these results, we suggest that the EU policymakers provide more financial and regulatory assistance to the R&D activities, specifically in the energy sector, to ensure promoting low carbon economies in this region

Stability of a moving radial liquid sheet: Time-dependent equations

We study the stability of a radial liquid sheet produced by head-on impingement of two equal laminar liquid jets. Linear stability equations are derived from the inviscid flow equations for a radially expanding sheet that govern the time-dependent evolution of the two liquid interfaces. The analysis accounts for the varying liquid sheet thickness while the inertial effects due to the surrounding gas phase are ignored. The analysis results in stability equations for the sinuous and the varicose modes of sheet deformation that are decoupled at the lowest order of approximation. When the sheet is excited at a fixed frequency, a small sinuous displacement introduced at the point of impingement grows as it is convected downstream suggesting that the sheet is unstable at all Weber numbers (We rho(l)U(2)h/sigma) in the absence of the gas phase. Here, rho(l) is the density of the liquid, U is the speed of the liquid jet, h is the local sheet thickness, and sigma is the surface tension. The sinuous disturbance diverges at We = 2 which sets the size of the sheet, in agreement with the results of Taylor ["The dynamics of thin sheets of fluid. III. Disintegration of fluid sheets," Proc. R. Soc. London, Ser. A 253, 313 (1959)]. Asymptotic analysis of the sinuous mode for all frequencies shows that the disturbance amplitude diverges inversely with the distance from the edge of the sheet. The varicose waves, on the other hand, are neutrally stable at all frequencies and are convected at the speed of the liquid jet. (C) 2013 AIP Publishing LLC

Open water bells

A smooth circular moving liquid sheet is formed by the head-on impingement of two equal laminar water jets. We subject such a liquid sheet to uniform laminar air flow from one side such that the direction of air velocity is perpendicular to the liquid sheet. The pressure of the moving air deforms the liquid sheet giving rise to an open water bell. The water bell is symmetric suggesting that the gas flow around the bell is also symmetric and that the gravitational force is negligible. We have captured the shape of the water bells for varying air flow rates and for varying Weber numbers, and compared the measurements with theoretical predictions obtained from a force balance involving liquid inertia, surface tension, and pressure difference across the sheet. The pressure exerted by the gas phase on the front and the rear surface of the deformed liquid sheet is obtained from known results of flow past flat circular discs. The predicted steady state shapes match well with the measurements at low Weber numbers but differences are observed at high Weber numbers, where the sheet flaps and is no longer smooth. Interestingly, the shape predicted by assuming a constant pressure difference equal to the stagnation pressure over the whole of the front face of the sheet and free stream value over the whole of the rear face yields nearly identical results suggesting that an open water bell is similar to a closed water bell in that, to a good approximation, the pressure on either sides of the water bell is homogeneous. (C) 2016 AIP Publishing LLC