Numerical Investigation on Flow Separation Control of Low Reynolds Number Sinusoidal Aerofoils

The paper presents a computational analysis of the characteristics of a NACA 634- 021 aerofoil incorporated with sinusoidal leading-edge protuberances at Re = 14,000. The protuberances are characterized by an amplitude and wavelength of 12% and 50% of the aerofoil chord length respectively. An unsteady Reynolds Average Navier Stokes (RANS) analysis of the full-span aerofoils was carried out using Transition SST (Shear Stress Transport) turbulence model across five different angles-of-attack (AOA). Comparisons with previous experimental results reported good qualitative agreements in terms of flow separation when the aerofoils are pitched at higher AOAs. Results presented here comprised of near-wall flow visualizations of the flow separation bubble at the peaks and troughs of the protuberances. Additionally, results indicate that the aerofoil with leading-edge protuberances displayed distinctive wall shear streamline and iso-contour characteristics at different span-wise positions. This implies that even at a low Reynolds number, implementations of these leading-edge protuberances could have positive or adverse effects on flow separation

Wideband pulse propagation: single-field and multi-field approaches to Raman interactions

We model the process of ultra broadband light generation in which a pair of laser pulses separated by the Raman frequency drive a Raman transition. In contrast to the usual approach using separate field envelopes for the different frequency components, we treat the field as a single entity. This requires the inclusion of few-cycle corrections to the pulse propagation. Our single-field model makes fewer approximations and is mathematically (and hence computationally) simpler, although it does require greater computational resources to implement. The single-field theory reduces to the traditional multi-field one using appropriate approximations.Comment: 6 pages, two 3-part figure

Characterisation of the dynamical quantum state of a zero temperature Bose-Einstein condensate

We describe the quantum state of a Bose-Einstein condensate at zero temperature. By evaluating the Q-function we show that the ground state of Bose-Einstein condensate under the Hartree approximation is squeezed. We find that multimode Schroedinger cat states are generated as the condensate evolves in a ballistic expansion.Comment: 13 pages, 6 figure

On Approximating the Number of kk-cliques in Sublinear Time

We study the problem of approximating the number of $k$-cliques in a graph when given query access to the graph. We consider the standard query model for general graphs via (1) degree queries, (2) neighbor queries and (3) pair queries. Let $n$ denote the number of vertices in the graph, $m$ the number of edges, and $C_k$ the number of $k$-cliques. We design an algorithm that outputs a $(1+\varepsilon)$-approximation (with high probability) for $C_k$, whose expected query complexity and running time are O\left(\frac{n}{C_k^{1/k}}+\frac{m^{k/2}}{C_k}\right)\poly(\log n,1/\varepsilon,k). Hence, the complexity of the algorithm is sublinear in the size of the graph for $C_k = \omega(m^{k/2-1})$. Furthermore, we prove a lower bound showing that the query complexity of our algorithm is essentially optimal (up to the dependence on $\log n$, $1/\varepsilon$ and $k$). The previous results in this vein are by Feige (SICOMP 06) and by Goldreich and Ron (RSA 08) for edge counting ($k=2$) and by Eden et al. (FOCS 2015) for triangle counting ($k=3$). Our result matches the complexities of these results. The previous result by Eden et al. hinges on a certain amortization technique that works only for triangle counting, and does not generalize for larger cliques. We obtain a general algorithm that works for any $k\geq 3$ by designing a procedure that samples each $k$-clique incident to a given set $S$ of vertices with approximately equal probability. The primary difficulty is in finding cliques incident to purely high-degree vertices, since random sampling within neighbors has a low success probability. This is achieved by an algorithm that samples uniform random high degree vertices and a careful tradeoff between estimating cliques incident purely to high-degree vertices and those that include a low-degree vertex

Performance Of Adipate Diester Synthetic Lubricants In The Hydrodynamic Regime.

Special PaperPg. 139-144Diester based synthetic lubricants provide numerous performance advantages over mineral oils in industrial applications. The synthetics not only .permit significant extension of oil drain intervals and application over a wider 'temperature range than mineral oils, but field experience also indicates that synthetic oils develop thicker and stronger films than their mineral oil counterparts. This results from the combination of the diester basestock and appropriate additives. A laboratory evaluation has been conducted to quantify the performance advantages of the synthetic oils over mineral oils in hydrodynamic lubrication. The power loss, maximum pad temperature, and oil film thickness in a tilting pad thrust bearing were measured for an ISO VG 32 mineral oil and ISO VG 32 and VG 10 diester based synthetic oils. Results of the tests revealed that the comparable grade mineral and synthetic oils yielded similar bearing power losses and pad temperatures, while the synthetic product developed significantly thicker films. Relative to the VG 32 mineral oil, the VG 10 synthetic lubricant yielded lower bearing power losses and cooler operation, while developing a slightly thicker film. These laboratory test results confirm the field experience that replacement of mineral oil with a suitable grade synthetic lubricant can yield significant economic and technical benefits, including reduction in bearing power losses, without sacrificing machine protection