Numerical Investigations on Vortical Structures in the Near Tongue Region of a Centrifugal Pump during Transient Operation

Centrifugal pumps are considered to be an integral part of process industries around the world. The flow structure within centrifugal pumps is very complex due to the interaction between the rotating impeller and the geometric features around it, such as tongue. Researchers have been analysing the effects of the interactions between impeller blades and the tongue, however, most of these studies are based on steady-state approximations where the impeller blades are modelled using frozen-rotor approach which leads to discrepancies in the predicted flow fields. In the present study, fully transient numerical investigations, on the generation and dissipation of vortical structures in the vicinity of the tongue region, have been carried out using a commercial Computational Fluid Dynamics (CFD) based solver. The instantaneous behaviour of a centrifugal pump is studied using the Sliding Mesh technique. Simulations have been carried out on both a constant rotating speed and under decelerating conditions. The second invariant of the velocity gradient tensor i.e. Q-criterion, has been employed to identify the generation and dissipation of vortical structures near the tongue region of the pump. The results indicate that the Q-criterion is fairly non-uniform downstream the tongue region due to the complex interaction between the impeller blades and the tongue. Furthermore, it has been observed that as the rotational speed of the centrifugal pump decreases, the Q-criterion in the near tongue region remains constant. The generation, expansion and subsequent mixing of two distinct vortical structures have been noticed downstream the tongue (within the volute), whereby the strength of these structures has been observed to be decreasing as the distance from the tongue increases

Computational Fluid Dynamics based Flow Diagnostics in Hydraulic Capsule Pipeline Bends

Hydraulic Capsule Pipelines (HCPs) are the third generation of pipelines that are based on the transport of hollow spherical, or cylindrical, capsules by the force exerted on them from the carrier fluid, which is water. These hollow capsules can be filled with a variety of cargo goods, such as minerals, jewellery etc. The hydrodynamics of this transport phenomena is quite complex, and researchers around the globe have been trying to analyse the hydrodynamics of such systems. However, most of these studies are based on experimental investigations, which can provide reasonably accurate results for the pressure drop etc. across the pipeline. However, the flow structure within HCPs cannot be easily mapped using experimental facilities. Furthermore, in case of pipe bends, the difficulty level increases exponentially due to a constant curvature in the geometry of the pipeline, and hence mounting the flow measuring instruments can be very challenging. The present study makes use of the advanced Computational Fluid Dynamics (CFD) based solvers, with powerful computing services, in order to analyse the flow structure within HCP bends. It is expected that this information can provide valuable information to the HCP designers, not only to calculate pressure drop across HCP bends, but in order to select the correct size etc. bends for the pipeline

Numerical Investigations on the Transient Performance of a Centrifugal Pump

Centrifugal pumps are an integral part of plants used in process industries. The flow structure within a centrifugal pump is very complex due to the interaction between the rotating impeller and the geometric features around it. In the present study, numerical investigations on a centrifugal pump have been carried out using a Computational Fluid Dynamics (CFD) based solver. This study employs finite volume technique in order to analyse the influence of variations in the rotational speed of the pump on its head. The instantaneous behaviour of a centrifugal pump with varying rotational speeds is studied using the Sliding Mesh technique. The performance parameters of a centrifugal pump have been predicted using numerical simulations. The results indicate that as the rotational speed of the centrifugal pump decreases, the head developed by the pump also decreases, where the effects of varying rotational speeds are dominant in the volute region. Furthermore, the complex interaction between the impeller blades and the tongue region has been analysed in the present study

Numerical Investigations on the Performance Degradation of a Vertical Axis Wind Turbine Operating in Dusty Environment

Rapid increase in global energy requirements has resulted in considerable attention towards energy generation from the renewable energy sources. In order to meet renewable energy targets, harnessing energy from all available resources including those from urban environment is required. Vertical Axis Wind Turbines (VAWTs) are seen as a potential way of utilising distributed wind energy sources. Most of the research on the wind turbines constitutes performance analysis and optimisation of VAWTs, in a clean environment, using steady state approximations where the transient effects are not considered. Operations in dusty environments (such as in desserts) may change the nature of the flow field around the VAWT which could decrease its life cycle. This study is an attempt to use Computational Fluid Dynamic’s based techniques to study and analyse the performance of a wind turbine under dusty environment. For this purpose, a novel modelling technique, known as Discrete Phase Modelling (DPM), has been used in the present study to introduce dust particles in the vicinity of a VAWT. The predicted results show that the instantaneous torque output of the VAWT decreases significantly in dusty environment. This abrupt change in the instantaneous torque output of the turbine may give rise to highly transient loads on the turbine’s structure which may induce heavy stresses on the turbine, leading to structural failure

Numerical Investigations on the Effect of Blade Angles of a Vertical Axis Wind Turbine on its Performance Output

There are many social, political and environmental issues associated with the use of fossil fuels. For this reason, there are numerous investigations currently being carried out to develop newer and renewable sources of energy to alleviate energy demand. Wind is one source of energy that can be harnessed using wind turbines. In this study, numerical investigations using Computational Fluid Dynamics (CFD) solver have been carried out to determine the optimum blade angles of a wind turbine used in urban environment. The effect of these blade angles have been considered to be within the normal operating range (α from 1.689⁰ to 21.689⁰, ϒ from 18.2⁰ to 38.2⁰ and δ from 22.357⁰ to 42.357⁰) while β was kept constant at 90⁰ due to design requirements. The results show that as α increases average torque output increases to a certain point after which it remains constant. On the contrary, as ϒ and δ increase, average torque output decreases. From the results, it can be concluded that the ideal blade angles, for optimal torque output, are α=11.689⁰, ϒ=18.2⁰ and δ=22.357⁰

Effect of solar heat flux and thermal loading on the flow distribution within the riser pipes of a closed-loop solar thermo-syphon hot water system

Solar energy is one of the main sources of renewable energy that is abundantly available throughout the world. Solar energy can be used for useful purposes through a number of mechanical artefacts. One such artefact is known as Thermo-syphon, which typically contains water as its working fluid. One of the major applications of Thermo-syphon is within the residential and industrial units, where a constant supply of hot water is required. The use of Computational Fluid Dynamics (CFD) based solvers has recently been proven capable of predicting the flow behaviour within thermo-syphons with reasonable accuracy. Hence, the present study focuses on using a commercial CFD based solver to predict the flow behaviour within the riser pipes of a thermo-syphon with varying solar heat flux and thermal loading conditions. In order to qualitatively and quantitatively analyse the flow structure within the riser pipes of the thermo-syphon, velocity magnitude and static temperature distributions within these pipes is analysed in detail. The results depict that the solar heat flux has a significant impact on the velocity magnitude and static temperature profiles within the riser pipes. Furthermore, it has been observed that the thermal loading has negligible effects on the velocity magnitude and static temperature profiles within the riser pipes. The data has also been used to develop novel design correlations

Pressure Drop in Capsule Transporting Bends Carrying Spherical Capsules

One of the most important parameters in designing a capsule transporting pipeline is the pressure drop in the pipes carrying capsules and associated pipe fittings such as bends etc. Capsules are hollow containers with typically cylindrical or spherical shapes flowing in the pipeline along with the carrier fluid. The dynamic behavior of a long train of capsules depends on the behavior of each capsule in the train and the hydrodynamic influence of one capsule on another. Researchers so far have used rather simplified empirical and semi-empirical correlations for pressure drop calculations, the range and application of which are fairly limited. Computational Fluid Dynamics (CFD) based techniques have been used to analyze the effect of the presence of solid phase in hydraulic bends. A steady state numerical solution has been obtained from the equations governing turbulent flow in pipe bends carrying spherical capsule train consisting of one to four capsules. The bends under consideration are of 45⁰ and 90⁰ with an inner diameter of 0.1m. The investigation was carried out in the practical range of 0.2 ≤Vb≥ 1.6 m/sec. The computationally obtained data set over a wide range of flow conditions has been used to develop a rigorous model for pressure drop calculations. The pressure drop along the pipe bends, in combination with the pressure drop along the pipes, can be used to calculate the pumping requirements and hence design of the system

Numerical investigations on the propagation of fire in a railway carriage.

In this study, advanced Computational Fluid Dynamics (CFD)-based numerical simulations have been performed in order to analyse fire propagation in a standard railway compartment. A Fire Dynamics Simulator (FDS) has been employed to mimic real world scenarios associated with fire propagation within railway carriages in order to develop safety guidelines for railway passengers. Comprehensive parametric investigations on the effects of ignition location, intensity and cabin upholstery have been carried out. It has been observed that a fire occurring near the exits of the carriage results in a lower smoke layer height, due to the local carriage geometry, than an identical fire igniting at the center of the carriage. This in turn causes the smoke density along the aisleway to vary by around 30%. Reducing the ignition energy by half has been found to restrict combustion, thus reducing smoke density and carbon exhaust gases, reducing the average temperature from 170°C to 110°C. Changing the material lining of the seating has been found to cause the most significant change in output parameters, despite its relative insignificance in bulk mass. A polyester sample produces a peak carbon monoxide concentration of 7500 ppm, which is 27× greater compared with nylon. This difference has been found to be due to the fire spread and propagation between fuels, signifying the polyester’s unsuitability for use in railway carriages

Computational Fluid Dynamics Based Optimal Design of Hydraulic Capsule Pipelines Transporting Cylindrical Capsules

Rapid depletion of energy resources has immensely affected the transportation sector, where the cargo transportation prices are rising considerably each year. Efforts have been made to develop newer modes of cargo transportation worldwide that are both economical and efficient for a long time. One such mode is the use of energy contained within fluids that flows in the pipelines for transportation of bulk solids. After appropriate modifications to these pipelines, bulk solids can be transported from one location to another very effectively. Solid material can be stored in cylindrical containers (commonly known as capsules), which can then be transported, either singly or in a train through the pipeline. Both the local flow characteristics and global performance parameters associated with such pipelines need careful investigation for economical and efficient system design. Published literature is severely limited in establishing the effects local flow features on system characteristics of Hydraulic Capsule Pipelines (HCPs). The present study focuses on using a well validated Computational Fluid Dynamics (CFD) tool to numerically simulate the solid-liquid mixture flow in HCPs, installed both on-shore and off-shore, along-with the pipe bends. Local static pressure fields have been discussed in detail for a wide range of geometrical and flow related parameters associated with the capsules and the pipelines. Numerical predictions have been used to develop novel semi-empirical prediction models for pressure drop in HCPs, which have then been embedded into a pipeline optimisation methodology that is based on Least-Cost Principle. This novel optimisation methodology that has been developed for HCPs is both robust and user-friendly

Performance Comparison of a Vertical Axis Wind Turbine using Commercial and Open Source Computational Fluid Dynamics based Codes

Computational Fluid Dynamics (CFD) is a very effective tool to analyse the flow characteristics within and around different mechanical artifacts such as automotive vehicles, turbomachines etc. CFD based analysis provides beneficial information about the flow behavior within a component, hence reducing the costs involved in the design process of that component. This has led the research-ers to develop an Open Source CFD code, commonly known as Open Field Opera-tion and Manipulation, or OpenFOAM. The development of OpenFOAM has made scientific research in the field of fluid dynamics available for almost no cost. Designers who rely on commercial CFD packages are hesitant on using Open Source CFD codes because of accuracy. They need to be convinced by proving its simulation capability as compared to any commercial CFD package. Hence, this study investigate the flow phenomenon in the vicinity of a Vertical Axis Wind Turbine (VAWT), using such open source code combinations that yields reasona-bly accurate results, which can be compared against any commercial CFD code