Razi Nalim

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https://hdl.handle.net/1805/6680

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Browsing Razi Nalim by Author "Akbari, Pezhman"

Now showing 1 - 5 of 5
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    Air-Standard Aerothermodynamic Analysis of Gas Turbine Engines With Wave Rotor Combustion
    (2009-09) Nalim, M. Razi; Li, H; Akbari, Pezhman
    The wave rotor combustor can significantly improve gas turbine engine performance by implementing constant-volume combustion. The periodically open and closed combustor complicates thermodynamic analysis. Key cycle parameters depend on complex gas dynamics. In this study, a consistent air-standard aerothermodynamic model with variable specific heat is established. An algebraic model of the dominant gas dynamics estimates fill fraction and internal wave compression for typical port designs, using a relevant flow Mach number to represent wave amplitudes. Nonlinear equations for thermodynamic state variables are solved numerically by Newton–Raphson iteration. Performance measures and key operating conditions are predicted, and a quasi-one-dimensional computational model is used to evaluate the usefulness of the algebraic model.
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    Leakage Assessment of Pressure-Exchange Wave Rotors
    (2008-07) Akbari, Pezhman; Nalim, M. Razi; Donovan, ES; Snyder, PH
    Control of leakage within wave rotors is recognized as a key requirement for efficient operation. Previous studies suggest that experimentally observed performance degradation is substantially due to flow leakage. This work presents a leakage model for predicting leakage-attributed performance degradation of four-port pressure-exchange wave rotors more accurately than previous single-cavity leakage models. The methodology comprehensively considers the leakage paths of the entire device. It combines a wave-rotor quasi-one-dimensional computational fluid dynamics prediction code, experimentally validated for internal gas dynamics with the generalized flow-circuit-modeling capability of a leakage-flow network solver. The computational fluid dynamics program and the network solver step through a series of iterations by sharing common leakage information. Application to a well-instrumented wave-rotor rig is briefly summarized, providing important guidance for the improvement of leakage and performance. The new approach is anticipated to be useful in enhancing the design, operation, and efficiency of a broad class of wave rotors by better understanding leakage and hence designing sealing features to control leakage flows.
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    Performance Enhancement of Microturbine Engines Topped With Wave Rotors
    (2006-01) Akbari, Pezhman; Nalim, M. Razi; Mueller, Norbert
    Significant performance enhancement of microturbines is predicted by implementing various wave-rotor-topping cycles. Five different advantageous cases are considered for implementation of a four-port wave rotor into two given baseline engines. In these thermodynamic analyses, the compressor and turbine pressure ratios and the turbine inlet temperatures are varied, according to the anticipated design objectives of the cases. Advantages and disadvantages are discussed. Comparison between the theoretic performance of wave-rotor-topped and baseline engines shows a performance enhancement up to 34%. General design maps are generated for the small gas turbines, showing the design space and optima for baseline and topped engines. Also, the impact of ambient temperature on the performance of both baseline and topped engines is investigated. It is shown that the wave-rotor-topped engines are less prone to performance degradation under hot-weather conditions than the baseline engines.
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    Review of Recent Developments in Wave Rotor Combustion Technology
    (2009-07) Akbari, Pezhman; Nalim, M. Razi
    For some decades, efforts have been made to exploit nonsteady combustion and gas dynamic phenomenon. The theoretical potential of nonsteady-flowmachines has led to the investigation of various oscillatory flowdevices such as pulse detonation engines, wave rotors, pulse jets, and nonsteady ejectors. This paper aims to provide a progress review of past and current research in developing a particular combustion concept: the wave rotor combustor. This pressure-gain combustor appears to have considerable potential to enhance the performance and operating characteristics of gas turbine and jet engines. After attempts in the mid-twentieth century were thwarted by mechanical problems and technical challenges identified herein, recent successes in Switzerland and efforts in the United States benefited from design expertise developed with pressure-exchange wave rotors. The history, potential benefits, past setbacks, and existing challenges and obstacles in developing these nonsteady combustors are reviewed. This review focuses on recent efforts that seek to improve the performance and costs of future propulsion and powergeneration systems.
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    A Review of Wave Rotor Technology and Its Applications
    (2006-10) Akbari, Pezhman; Nalim, M. Razi; Mueller, Norbert
    The objective of this paper is to provide a succinct review of past and current research in developing wave rotor technology. This technology has shown unique capabilities to enhance the performance and operating characteristics of a variety of engines and machinery utilizing thermodynamic cycles. Although there have been a variety of applications in the past, this technology is not yet widely used and is barely known to engineers. Here, an attempt is made to summarize both the previously reported work in the literature and ongoing efforts around the world. The paper covers a wide range of wave rotor applications including the early attempts to use wave rotors, its successful commercialization as superchargers for car engines, research on gas turbine topping, and other developments. The review also pays close attention to more recent efforts: utilization of such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigeration systems, highlighting possible further efforts on this topic. Observations and lessons learnt from experimental studies, numerical simulations, analytical approaches, and other design and analysis tools are presented.