Flow past a circular cylinder is a problem for understanding flow around bluff bodies. This flow has been studied both experimentally and numerically of laminar infinite flow of viscous incompressible fluid around a rotating circular cylinder at Reynolds number 80,120,160 and dimensionless rotation rate, α , (ratio of cylinder surface speed to the free stream velocity) varying from 0 to 6 has been carried out. Navier–Stokes and continuity equations were solved numerically by using finite volume technique is conducted with ANSYS CFX 15 package program. High Speed Photography and LDV, present new experimental results for correlation purposes, captured the flow profile. Rotation can be used as a drag reduction technique. Comparison with previous studies showed good agreement.
Dry Low NOx combustors based on the use of Lean Pre-mixtures and Swirling Flows are widely used in gas turbine combustors to produce systems with low emissions, although the efficiency of reducing emissions is dependant on the techniques used for premixing. Swirling flows are recognized as one of the best systems for stabilizing high intensity flames giving reduced maintenance, increase of turbulent flame speed, wide stability limits and ability to produce low emissions. However, most practical swirling flows are highly complex, three dimensional and time dependant in nature and contain complex coherent structures which are essential to the flame stabilization process. Even though the study of these types of flows has been extensive for several decades , some of the fundamental mechanisms are still barely understood owing to their complexity. Numerical simulations have also tried to explain the development of different regimes, but the extremely complex nature of the former has shown a variety of results whose lack of time dependant validation leaves the results open to question. Due to the high complexity of these flows, parameters such as Re, S, φ and geometry play a crucial role in the development of these structures, interrelation that has been barely studied. This paper thus adopts an experimental approach to characterize large coherent structures in swirl burners under combustion conditions so as to reveal the effects of swirl, Re and φ in a number of geometries. Aided by different techniques such as High Speed Photography (HSP), CH* Photo Chemiluminescence (CH* CL) and Particle Image Velocimetry (PIV), the recognition of several structures was achieved in a 100 kW Swirl Burner model. Several varied, interacting, structures developed in the field as a consequence of the configurations used.
Numerous low-carbon energy initiatives are adopting ammonia as an energy source, with a particular focus on combining ammonia and hydrogen in a 70%/30% volume ratio for gas turbine systems. The ammonia-hydrogen triple generation cycle, a hybrid of a humidified Brayton cycle and a reverse Brayton cycle, has demonstrated outstanding performance, achieving zero carbon and low NOx emissions, while boosting overall efficiency to around 59%, comparable to conventional fossil fuel-based power generation systems. The Aspen Plus software was used to simulate and calculate the system’s efficiency, mainly focusing on the humidification Brayton cycle, reverse Brayton cycle, and waste heat recovery phase of the ammonia-hydrogen triplex production cycle. Three scenarios were developed to evaluate the efficiency of different steam condensation recovery processes, with all three yielding efficiencies of at least 59%, confirming the cycle’s effectiveness and feasibility. Advancements in the system’s structure in the future could further enhance the system’s efficiency.
The objective of this paper is to employ a numerical approach to model a 150kW tangential swirl burner to investigate the consequence of central air injection on the flashback mechanism. The effects of diffusive air injection on flow field characteristics and how these can affect the lower instability limits by altering the flashback mechanism via CIVB are analysed in both experimental and theoretical approaches. Simulations under isothermal conditions are carried out using both premixed and partially premixed species models to compare the flow field behaviour with and without air injection. The experimental data includes LDA measurements for the same burner geometry. CFD and experimental results demonstrated that using diffusive air affects flashback propensity significantly by expanding the stability region in terms of both equivalence ratio and mass flow rate that lead to greater operability at higher power outputs compared to using only a central body injector. The CFD results were verified and correlated to experimental findings with very good agreement
This chapter deals with the current practices, methods, and facilities used to safely store and distribute ammonia safely. As a commodity, ammonia is stored and posteriorly distributed on a global scale over a great variety of distances. It can be used either directly or as a raw material for downstream applications. The ammonia distribution system consists of sea and land transportation routes to and from large storage terminals and/or smaller storage systems at retailer or end-user locations. Ammonia is typically transported in liquid state and therefore needs to be compressed, cooled, or both. Stress corrosion cracking, which can occur under distribution and operating conditions, is a primary concern when storing and handling ammonia. The phenomenon is discussed in this chapter in relation to its impact on common service metals under operational conditions. Furthermore, different approaches to abate this phenomenon are outlined. Finally, a case study discussing the use of current natural gas lines for ammonia transport is also described, demonstrating some contemporary ideas on future utilization of natural gas lines as carriers of different compounds, including ammonia. These results suggest that although such repurposing is possible, several factors would need to be included and reconsidered to enable this distribution path.
A potential enabler of a low carbon economy is the energy vector hydrogen. However, issues associated with hydrogen storage and distribution are currently a barrier for its implementation. Hence, other indirect storage media such as ammonia and methanol are currently being considered. Of these, ammonia is a carbon free carrier which offers high energy density; higher than compressed air. Hence, it is proposed that ammonia, with its established transportation network and high flexibility, could provide a practical next generation system for energy transportation, storage and use for power generation. Therefore, this review highlights previous influential studies and ongoing research to use this chemical as a viable energy vector for power applications, emphasizing the challenges that each of the reviewed technologies faces before implementation and commercial deployment is achieved at a larger scale. The review covers technologies such as ammonia in cycles either for power or CO2 removal, fuel cells, reciprocating engines, gas turbines and propulsion technologies, with emphasis on the challenges of using the molecule and current understanding of the fundamental combustion patterns of ammonia blends.
The objective of this paper is to employ a numerical approach to model a 150kW tangential swirl burner to investigate the consequence of central air injection on the flashback mechanism. The effects of diffusive air injection on flow field characteristics and how these can affect the lower instability limits by altering the flashback mechanism via CIVB are analysed in both experimental and theoretical approaches. Simulations under isothermal conditions are carried out using both premixed and partially premixed species models to compare the flow field behaviour with and without air injection. The experimental data includes LDA measurements for the same burner geometry. CFD and experimental results demonstrated that using diffusive air affects flashback propensity significantly by expanding the stability region in terms of both equivalence ratio and mass flow rate that lead to greater operability at higher power outputs compared to using only a central body injector. The CFD results were verified and correlated to experimental findings with very good agreement
The demand for alternative fuels has increased significantly during the previous decades in order to reduce pollutants and increase the amount of energy that can be generated from nonfossil fuels.However, the use of new fuels faces many issues especially the problem of stability of operation which sometimes can cause severe damages to the system hardware.Thus the development of flexible combustion systems for gas turbines becomes urgent in order to achieve high reliability with these new sources of energy.Swirl stabilized combustion is the most widely spread deployed technology used to stabilize and control combustion in gas turbines and numerous other systems.However, the interaction of the swirling flows with the burner geometries is very complex and it has been proved that any change in the burner geometry can affect the flow field inside the combustion chamber, close to the burner mouth and downstream the combustion zone.Most burners are generally provided with a diffusive injector that centrally delivers well-known fuels allowing the stabilization of the system previous to entirely premixed conditions.Moreover, the injector anchors the central recirculation zone formed downstream of the nozzle.However, the use of injectors can also affect the stability limits of the system, especially the propagation of flashback through changes of shape of the shear layer since other structures such as the Combustion Induced Vortex Breakdown are suppressed due to the presence of this central body.However, the characterization of the flow and its impacts on the propagation of these and other flashback structures using different injectors has been briefly documented.Thus, this paper presents a series of experiments using a well-characterized tangential swirl burner to determine the impact of different central injector geometries on the flow field characteristics which directly affect the flow stagnation point downstream of the burner mouth and consequently the propagation of the Combustion Induced Vortex Breakdown.Results show how the use of various injectors and swirl numbers can impact on the flashback limits with a minimum outside diameter before which the Combustion Induced Vortex Breakdown is altered.
Large scale coherent structures play an important role in the behavior of the combustion regime inside any type ofcombustor stabilized by swirl, with special impact on factors such as flame stability, blow off, emissions and theoccurrence of thermo-acoustic oscillations. Lean premixed combustion is widely used and is known to impact many ofthese factors, causing complex interrelationships with any coherent structure formed. Despite the extensiveexperimentation in this matter, the above phenomena are poorly understood. Numerical simulations have been usedto try to explain the development of different regimes, but their extremely complex nature and lack of time dependentvalidation show varied and debatable results. The precessing vortex core (PVC) is a well-known coherent structurewhose development, intensity and occurrence has not been well documented. This paper thus adopts an experimentalapproach to characterize the PVC in a simple swirl burner under combustion conditions so as to reveal the effects ofswirl and other variables on the latter. Aided by a high speed photography (HSP) system, the recognition and extentof several different types of PVCs were observed and discussed.
