Hybrid RANS/LES of flow in a rib-roughened channel with rotation

The aim of the present study is to verify the reliability of a k-ω based hybrid RANS/LES model in reproducing the flow in a rib-roughened rotating channel. The numerical results obtained with the hybrid RANS/LES model are compared to experimental data by Coletti and Arts (2011) and to the results obtained with the RANS k-ω model of Wilcox (2008). We demonstrate that the hybrid RANS/LES model gives realistic results for simulation of the rotating ribbed duct flow, without the necessity to add ad hoc corrections for system rotation to the underlying RANS mode

Hybrid RANS/LES of plane jets impinging on a flat plate at small nozzle-plate distances

A k-omega BASED HYBRID RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) model is tested for simulation of plane impinging jets at various nozzle-plate distances (H/B), where H is the distance and B is the slot's width) and various Reynolds numbers (based on the slot's width and the velocity in the symmetry plane). The studied combinations are H/B = 2 for Re = 10000, H/B = 4 for Re = 18 000 and H/B = 9.2 for Re = 20000. The focus is on small distance of the nozzle exit to the plate. In LES mode, the hybrid RANS/LES model uses two definitions of the local grid size, one based on the maximum distance between the cell faces in the destruction term of the turbulent kinetic energy equation and one based on the cube root of the cell volume in the eddy-viscosity formula. This allows accounting for flow inhomogeneity on anisotropic grids. In RANS mode, the hybrid model turns into the newest version of the k-omega model by Wilcox

Deterministic Secure Positioning in Wireless Sensor Networks

Properly locating sensor nodes is an important building block for a large subset of wireless sensor networks (WSN) applications. As a result, the performance of the WSN degrades significantly when misbehaving nodes report false location and distance information in order to fake their actual location. In this paper we propose a general distributed deterministic protocol for accurate identification of faking sensors in a WSN. Our scheme does \emph{not} rely on a subset of \emph{trusted} nodes that are not allowed to misbehave and are known to every node in the network. Thus, any subset of nodes is allowed to try faking its position. As in previous approaches, our protocol is based on distance evaluation techniques developed for WSN. On the positive side, we show that when the received signal strength (RSS) technique is used, our protocol handles at most $\lfloor \frac{n}{2} \rfloor-2$ faking sensors. Also, when the time of flight (ToF) technique is used, our protocol manages at most $\lfloor \frac{n}{2} \rfloor - 3$ misbehaving sensors. On the negative side, we prove that no deterministic protocol can identify faking sensors if their number is $\lceil \frac{n}{2}\rceil -1$. Thus our scheme is almost optimal with respect to the number of faking sensors. We discuss application of our technique in the trusted sensor model. More precisely our results can be used to minimize the number of trusted sensors that are needed to defeat faking ones

Hybrid RANS/LES of plane impinging jets on a flat plate at small nozzle-plate distances

A k-ω based hybrid RANS/LES (Reynolds Averaged Navier Stokes/Large Eddy Simulation) model is tested for simulation of plane impinging jets at various nozzle-plate distances (H/B, where H is the distance and B is the slot width) and various Reynolds numbers (based on the slot width and the velocity in the symmetry plane). The studied combinations are H/B=2 for Re=10000, H/B=4 for Re=18000 and H/B=9.2 for Re=20000. The focus is on small distance of the nozzle exit to the plate. This means for impact of the jet onto the plate before complete mixing of the shear layers. The centre of the impact zone is then in laminar state and the developing boundary layer on the plate undergoes transition to turbulent state. The transitional flow cannot be correctly simulated with a RANS turbulence model, but we will demonstrate that a hybrid model is basically correct