Jose A. Jimenez-Bernal

Data Transmission Strategies for Event Reporting and Continuous Monitoring Applications in Wireless Sensor Networks

Wireless Sensor Networks (WSNs) can be typically used to achieve Continuous Monitoring (CM) or Event-Detection inside the supervised area. In CM applications each sensor node transmits periodically its sensed data to the sink node while in Event-Detection Driven (EDD) applications, once an event occurs, it is reported to the sink node by the sensors within the event area. Applications using both continuous monitoring and event driven reporting can also be considered. In this paper, we investigate such hybrid WSNs. Specifically, we propose two different strategies that explicitly assign a time period for the event reporting data by means of the NP-CSMA random access protocol. Both strategies take advantage of the clustered based architecture which assign a TDMA schedule for the continuous monitoring data transmission. By doing so, the continuous monitoring clusters are also used for the event reporting. Hence, no extra energy is consumed for separate event clusters. The performance of these strategies is analyzed for low and high event rate occurrence. These strategies are compared to both continuous monitoring protocols (such as LEACH) and event driven reporting protocols (such as TEEN).

Large Eddy Simulation of the Subcritical Flow over a U-Grooved Circular Cylinder

With the aim of numerically replicating a drag reduction phenomenon induced by grooves presence, this paper presents a comparative large eddy simulation study of the flow over a smooth circular cylinder, and the flow over a U-grooved cylinder, at Re = 140,000, which is near transition between the subcritical and critical flow regimes. The grid densities were 2.6 million cells and 20.7 million cells for the smooth and the U-grooved cylinder, respectively. Both meshes were composed of hexahedral cells disposed in a structured form with additional refinements in near-wall regions, in order to obtain y+< 5 values. The cases were simulated during 25 vortex shedding cycles with the purpose of obtaining significant statistic data through the commercial software FLUENT V.12.1, which solved the Navier-Stokes equations in their unsteady and incompressible forms. Regarding the U-grooved cylinder flow, parameters such as the drag coefficient, lengths of recirculation, the transition from subcritical to critical flow, and the formation of a wake formed by secondary vortices of smaller sizes were predicted satisfactorily by the LES technique. From the manner in which the flow separates at different angles for both valleys and peaks of the U-grooves, a distinctive transitional mechanism induced by grooves presence is conjectured.

Computational Fluid Dynamics in Turbulent Flow Applications

This chapter is intended to present to readers a general scope of the technical, theoretical, and numerical applications of computational fluid dynamics using the finite volume method, restricted to incompressible turbulent flows (Ma < 0.3). The main objective of this chapter was to provide readers of a starting point to select an adequate numerical model for the flow regime of interest. Such knowledge could be a key at the moment of extending the analysis to more complex problems, for example, the ones found in heat transfer and fluid flows, multiphase flows, and compressible flows.

Numerical Simulation of the Subcritical Flow Over a Circular Cylinder With “U” and “V” Grooves

In this paper the comparative results of three numerical simulations of the subcritical turbulent flow over a circular cylinder (Re = 140,000) for the cases of a “U” grooved cylinder, a smooth cylinder, and a “V” grooved cylinder are presented. Due to the high resolution capabilities of the LES model, it was preferred over the RANS or URANS turbulence models. The simulation was carried out using the commercial CFD code ANSYS FLUENT V.12.0. The grid sizes were: 2.6 million cells for the smooth cylinder, and 14.5 and 13 million for the “U” grooved and “V” grooved cylinders respectively. In order to improve the quality of the solutions, the grids were structured and composed of hexahedral cells. Due to the requirements of the LES technique, the lower y+ values obtained were below 5. With the aim of capture the non-steady characteristics of this kind of flows, the simulations were performed over 8 vortex shedding cycles. Although the cross sections of the V and U grooves have almost the same shape, the resulting flow structures and calculated quantities such as the separation point, turbulent intensity in the normal and streamwise direction and recirculating bubble length were different for both cases. Apparently, the flow configuration resulted from the V grooves is similar to the smooth cylinder flow, being the U grooved cylinder flow different from both of them. This could be related to the drag reduction of about 27% obtained for the U grooved cylinder flow For the V grooved cylinder flow, the obtained drag presented an increase of about 7%.© 2013 ASME

Turbulent Flow Over a Facing Step at Several Reynolds Numbers

An experimental study was performed over forward facing step (FFS). It was located within a transparent rectangular acrylic channel (1.4 m in length, 0.1 m in width and 0.02 m in height). The step is 0.01 m in height and 0.1 m in width, and was located 0.7 m downstream (fully developed region); a spanwise aspect ratio, w/h = 10 was used. The experiments were carried out using particle image velocimetry (PIV), which is a non intrusive experimental technique. The experimental water flow conditions include three Reynolds numbers based on the step height, Reh = 1124, 1404 and 1685. These flow conditions correspond to turbulent flow. Measurements were carried out in two zones; zone A begins at x = 8 cm (measured from the step base), and zone B starts at x = 0, y = 0, the visualization region corresponds to an area of 22.76 mm × 16.89 mm. 100 instantaneous velocity fields were obtained for each Reh . A temporal and spatial average was performed to obtain a velocity profile in zone A; likewise, the corresponding turbulence intensity and shear stress distribution were evaluated. The average velocity profile was evaluated for each Reh . Regarding the vortex center location, it was observed that as Reh increases, the y-direction coordinate moves towards bottom of wall channel. For zone B, it was also observed a reduction of the shear stress as Reh increases.Copyright

Laminar Flow through a Rectangular Horizontal Channel with Asymmetrical Contraction

Numerical simulation for the three-dimensional laminar flow through a forward facing step channel was simulated by Fluent 6.3 code. Four Reynolds numbers and four step lengths were analyzed. The results showed that the length of the recirculation zone upstream the step depends on Reynolds number, as well as on the step height (h), while the height of the recirculation zone extends about 70% of the step height. In addition, it was found that the velocity profile in the stream direction at the channel exit presents a fully developed profile for the axial component. Nonetheless, the profile along the transversal direction does not have a parabolic profile, even for a length of 60h

Influence of the Alignment of Two Airfoils in the Losses Generation

A numerical simulation of a flow passing throw two NACA 0012 airfoils is presented in this paper. Aerodynamics, drag forces, and pressure drop is quantified when both profiles are axially aligned and then when one of them is vertically displaced. NUMECA code and Spalart-Allmaras turbulence model were used for this purpose. The results showed that aerodynamic losses are present in both profiles, meaning that the presence of the back profile plays an important role in the aerodynamic behavior of the frontal profile.

Turbulence Intensity Evaluation in a Radial-Tangential Plane Within a Cyclone Separator Using PIV

Experimental results for turbulence intensity measurements within a cyclone separator are presented in this work. Experimental data was obtained in a tangential-radial plane located 5 mm from the top wall of the cyclone separator. PIV technique was used to obtain experimental data at three different flow conditions (Re = 3.66×104 , Re = 9.15×104 , and Re = 1.46×105 ). Reynolds number calculations was carried out using flow inlet velocity and cyclone diameter as characteristic length. Although the flow inside a cyclone separator is a swirling flow, velocity fields obtained using the PIV technique are reported in an orthogonal coordinate system. Therefore, turbulence intensity measurements presented are for u and v velocity components. Maximum values for turbulence intensities increase as Reynolds number increases; however, this increase is not a proportional one.Copyright

Análisis Numérico de la Convección Mixta en un Conducto Horizontal de Sección Rectangular Tridimensional que Encierra un Escalón

Laminar mixed convection over a backward-facing step is studied and presented in this work. A finite volume discretization technique is used to solve the momentum and energy equations. The SIMPLE algorithm is used to link the pressure distribution and velocity field inside the computational domain. The buoyancy forces affecting the velocity and temperature distributions are simulated for constant air flow and constant Reynolds number (Re=200) for a mixed convective flow (Ri=3) and the results are compared with those of pure force convective flow (Ri=0). The results indicate that the re-circulation zones at the vicinity of the back step are reduced if the buoyancy effects are considered. It is concluded that the flow is highly tridimensional.

Experimental Visualization in a Cyclone Separation System

Cyclones are one of the most used equipment for gas cleaning. These devices are widely used because of their simple construction, low energy requirements and their ability to work with high temperature and pressure levels. In this work, a flow visualization of a cyclone separation system is carried out. For that purpose, smoke particles and a laser beam were used to show the flow patterns within the separation system. The objective of this work is to visualize the flow within a cyclone separation system to elucidate the effect of the flow patterns in the gas-particle separation and the optimization of the cyclone.Copyright