Visualisation of turbulent structures in a centrifugal pump's volute using large eddy simulation.

Centrifugal pumps are an integral part of process and chemical industries around the globe. The flow within vaneless volutes of centrifugal pumps is highly turbulent and three-dimensional. Conventional flow modelling techniques are usually incapable of capturing these complex flow structures. Moreover, use of 2-equation turbulence models in Computational Fluid Dynamics (CFD) cannot resolve the turbulent flow structures in pump’s volutes. Visualisation of these complex and turbulent flow structures is very important in order to design the volutes appropriately. In the present study, Large Eddy Simulation (LES) based turbulence modelling approach has been used to analyse the complex flow structures in the volute of a commercial centrifugal pump. LES is more accurate in resolving larger eddies, while smaller eddies are modelled. Hence, flow predictions using LES are more realistic. It has been noticed that the interaction between the impeller blades and the tongue gives rise to flow non-uniformities in the volute. These flow non-uniformities are caused by the generation and subsequent propagation of three-dimensional complex turbulent flow structures. These flow structures absorb energy from the flow, imparting considerable head losses

Inverse design of functional surfaces through low fidelity modelling.

Functional surfaces are extensively being designed for specific purposes within various industries. The inspiration for many of such surfaces has been derived from biological entities such as shark skin etc. In industry, various surfaces are created by physio-chemical properties of materials with appropriately aligned micro and nanostructures, and sophisticated solutions are found for range of problems. Many drag reducing organisms employ functional surfaces that control near-wall flow characteristics thus affecting their global flow performance. This study focuses on the inverse design of functional surfaces for targeted global flow related effects. At its core, the discussed methodology embeds low fidelity model for surface and corresponding flow events. Desired geometrical parameters are iteratively solved to achieve target flow characteristics

Stability of viscous lubricated thin film down an inclined plane beneath ambient lighter non miscible static liquid.

This paper considers the stability of a thin film propagating beneath a large quantity of ambient static non miscible lighter liquid and over a sloping plane. Such configuration that has never been considered earlier can model the spill of a heavy hydrocarbon into the ocean by a tanker. Equations of conservation of the mass and the momentum were appropriately made non dimensional and a similar solution is proposed in this paper. In this way, an analytical expression of the hydrodynamic field, say velocity field and pressure field is provided. Then, the equation governing the spatiotemporal evolution of the water-oil interface was built and solved by a perturbation method. Also, the time evolution of the wave front position along the inclined plane was built. Finally, the effect of the control parameters on the linear stability of the flow was investigated

Effect of surface roughness on the aerodynamic performance of an articulated truck-trailer assembly.

Aerodynamic drag is the most dominant resistive force to the motion of a vehicle, several methods of drag reduction have been applied over the years; these mainly include shape modification and add-on devices. A novel method to improve drag response of a truck is to modify the flow so that the flow remains uniformly attached to the vehicle. This will result in a smaller wake of the vehicle and consequently reduces drag. The present study investigates the feasibility of employing one such flow modifying technique. Surface roughness has been systematically introduced on the tractor-trailer unit in the form of spherical-shaped structures and the drag of the vehicle has been measured. Computational Fluid Dynamics (CFD) based techniques have been employed to numerically simulate the flow of air over the tractor-trailer unit. The results show that the surface roughness parameters affect the overall fluid flow around the truck-trailer unit, and hence have a significant effect on the aerodynamic drag force of the vehicle. Drag force has been observed to increase by 1% when valleys were introduced as surface roughness. However, drag reduction of 1.9% has been recorded in case of roughness peaks. The results suggest that although the peaks act as a restriction to the local flow, they contribute more towards reducing the overall drag. In case of the roughness valleys, the drag force increases because these valleys introduce more non-uniformity in the flow without any benefit in drag reduction

A comparative study of some properties of cassava and tree cassava starch films

Cassava and tree cassava starch films plasticized with glycerol were produced by casting method. Different glycerol contents (30, 35, 40 and 45 wt. % on starch dry basis) were used and the resulting films were fully characterized. Their water barrier and mechanical properties were compared. While increasing glycerol concentration, moisture content, water solubility, water vapour permeability, tensile strength, percent elongation at break and Young's modulus decreased for both cassava and tree cassava films. Tree cassava films presented better values of water vapour permeability, water solubility and percent elongation at break compared to those of cassava films, regardless of the glycerol content

Stability of Water Lubricated Flow of Yield Stress Fluid in Sloping Pipe

To facilitate the transport of viscous crudes in a pipe, an immiscible lubricating liquid, usually water, is added. In such configuration, the water migrates into the regions of high shear at the pipe wall where it lubricates the flow. The pumping pressures being balanced by wall shear stresses in the water, the flow therefore requires pressures comparable to pumping water alone, at the same total throughput [1]. So significant savings in pumping power can be derived from this process provided that it is well monitored. Indeed, instabilities usually take place at the oil/water interface and they constitute an important source of energy dissipation. Precisely, a core annular flow is known to undergo a long-wave instability of capillary type, modified by shear occuring at low Reynolds. Above a given critical Reynolds number, the flow is unstable to shorter waves which leads to an emulsification system of water droplets in oil. In present work, an experimental study of the stability of sloping plane Poiseuille flow of well characterized viscoplastic mineral oils lubricated by water was performed. The investigation was carried out by means of image analysis based on spatiotemporal diagrams (STD). Notably indicated are the effects of bed slope, flow rates ratio and oil rheology on flow stability

Stability of Water Lubricated Flow of Yield Stress Fluid in Sloping Pipe

To facilitate the transport of viscous crudes in a pipe, an immiscible lubricating liquid, usually water, is added. In such configuration, the water migrates into the regions of high shear at the pipe wall where it lubricates the flow. The pumping pressures being balanced by wall shear stresses in the water, the flow therefore requires pressures comparable to pumping water alone, at the same total throughput [1]. So significant savings in pumping power can be derived from this process provided that it is well monitored. Indeed, instabilities usually take place at the oil/water interface and they constitute an important source of energy dissipation. Precisely, a core annular flow is known to undergo a long-wave instability of capillary type, modified by shear occuring at low Reynolds. Above a given critical Reynolds number, the flow is unstable to shorter waves which leads to an emulsification system of water droplets in oil. In present work, an experimental study of the stability of sloping plane Poiseuille flow of well characterized viscoplastic mineral oils lubricated by water was performed. The investigation was carried out by means of image analysis based on spatiotemporal diagrams (STD). Notably indicated are the effects of bed slope, flow rates ratio and oil rheology on flow stability

Demonstration of the triboelectricity effect by flow of liquid water in the insulating pipe

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