On the response of a lean-premixed hydrogen combustor to acoustic and dissipative-dispersive entropy waves

Combustion of hydrogen or hydrogen containing blends in gas turbines and industrial combustors can activate thermoacoustic combustion instabilities. Convective instabilities are an important and yet less investigated class of combustion instability that are caused by the so called “entropy waves”. As a major shortcoming, the partial decay of these convective-diffusive waves in the post-flame region of combustors is still largely unexplored. This paper, therefore, presents an investigation of the annihilating effects, due to hydrodynamics, heat transfer and flow stretch upon the nozzle response. The classical compact analysis is first extended to include the decay of entropy waves and heat transfer from the nozzle. Amplitudes and phase shifts of the responding acoustical waves are then calculated for subcritical and supercritical nozzles subject to acoustic and entropic forcing. A relation for the stretch of entropy wave in the nozzle is subsequently developed. It is shown that heat transfer and hydrodynamic decay can impart considerable effects on the entropic response of the nozzle. It is further shown that the flow stretching effects are strongly frequency dependent. The results indicate that dissipation and dispersion of entropy waves can significantly influence their conversion to sound and therefore should be included in the entropy wave models

Development of an Augmented Conceptual Design Tool for Aircraft Gas Turbine Combustors

Combustor design is the most unreliable and challenging portion in the design process of a gas turbine. To ensure the proper performance, many experimental tests must be performed on a combustor in the industry. The above mentioned design phase is costly and time consuming. This paper focused on an automated and augmented conceptual design methodology for conventional combustors. The design tool developed for this study employs empirical and semi-empirical models which include two main parts of the combustor, the reference diameter and area as well as the component design. The necessity of this work arose from an urgent need for comprehensive and fast generation data in the conceptual design phase of a combustion chamber. This automated and comprehensive tool, equipped with the capacity to provide many details, has a considerable impact on the reduction of further experimental effort. Also, the said tool is equipped with a geometrical model generation section that has application in the future design phases, e.g., detail design

Large eddy simulation of the destruction of convecting hot fluid pockets through a cold channel flow

Hot fluid pockets or hot spots can be found in many engineering systems, such as chemical reactors, internal heat engines and gas turbines. They are inherently fluid parcels with rapid temperature rising in comparison with the base medium and usually convect with the flow inertia. Due to the higher energy content, hot fluid pockets can change thermal characteristics of the system. Ignoring the destruction of them, which has been mainly missed in the literature, can therefore change the related predictions. The destruction of the hot fluid pockets is so investigated in this paper using a large eddy simulation and some statistical indices are used to reveal the coherence of the pockets. The results show that the convecting hot pocket can be significantly affected by hydrodynamic and thermal conditions, such that it may loss the initial tempo-spacial distribution completely. It is found that the hot spot behavior in lower Reynolds number range is not as regular as that at the higher Reynolds number range. Furthermore, the real thermal boundary conditions of convective heat transfer on the walls can completely change the destruction pattern in comparison to that in the adiabatic combustor. The extent of the destruction is various, depending on the flow conditions. The current results will help better prediction for systems involving hot fluid pockets

The effect of sinusoidal fins' amplitude on the thermo-hydraulic performance of a solar air heater

Solar energy exploitation is growing consistently, as it is the cheapest and most accessible amongst all forms of renewable energies. Increasing the performance of solar air heaters can aid in developing clean energy use and subsiding the greenhouse gas emissions in the world. This study, therefore, seeks to improve the thermo-hydraulic performance of solar air heaters using sinusoidal extended surfaces. The results show that the Reynolds number increment contributes to the enhancement of Nusselt number and thermo-hydraulic performance, while it does not affect the friction factor considerably. The highest value of the Nusselt number belongs to the case with the highest fin amplitude and wavy fins configuration by about 7 times higher value in comparison to the simple solar air heater. It is shown that the wavy configuration can render higher thermo-hydraulic performance than that of raccoon fins, by about 10 percent. The finned configurations feature better fluid flow mixing at the outlet and lower maximum and gradient of temperature on the absorber plate compared to those of simple and common solar air heaters