Graduate School of Engineering and Science

Permanent URI for this collectionhttps://hdl.handle.net/10679/9877

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Browsing by Author "Alhumairi, Mohammed Khudhair Abbas"

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    Investigation of flame characteristics in a turbulent premixed combustion
    (2018-10) Alhumairi, Mohammed Khudhair Abbas; Ertunç, Özgür; Ertunç, Özgür; Başol, Altuğ; Mengüç, Mustafa Pınar; Koşar, A.; Özdemir, B.; Department of Mechanical Engineering; Alhumairi, Mohammed Khudhair Abbas
    In this thesis, the turbulent flame closure (TFC) model and coherent flame model (CFM) of turbulent premixed flames as steady state flow are used. In addition, large eddy simulation (LES) model as unsteady state flow is used. The effects of different turbulent parameters such as Reynolds number based in a Taylor micro scale , turbulence length scale turbulence intensity and the constant of the TFC model on the combustion are modelled for steady reacting flow. In addition, the characteristics of sinusoidal wave, such as amplitude of pulsation and the frequency are used for unsteady reacting flow to show the behavior of the flame topology and flame location of jet flow combustor of lean propane-air combustion. The simulations are achieved with 3, 5 and 9 kW thermal loads at constant inlet velocity and equivalence ratio. Transport equations for progress variable (c) are shown in terms of Reynolds and Favre averages, and the reaction rate terms are used to calculate heat release at different turbulent flow conditions. The results are compared with existing experimental data from the combustor performance studies. The lean premixed combustion under the influence of active grid turbulence was computationally investigated, and results were compared with the experiments. In the experiments, the transverse and longitudinal active grids generated turbulence. The experiments were conducted to generate a premixed gas flame at a given inlet power 3, 5 and 9 kW. Turbulent burning modelling such as CFM, TFC and LES models were implemented to conduct simulations under different turbulent flow conditions as steady and unsteady state flows, respectively. The turbulent flow conditions obtained in the simulations were specified by the dissipation rate of turbulence ( ) and a turbulent kinetic energy ( ) at the inlet region for steady reacting flow. All simulations were used to simulate the turbulent reacting flows at the equivalence ratios of 0.606 and 0.588 to estimate the combustion conditions of the propane. The heat release field was used for comparison with experimental cases. Acceptable agreement is found between the simulations and the experimental results. The flame topology is more sensitive to turbulence in CFM model than that simulated by the TFC model, and the flame location moved toward to inlet region by increasing . CFM and TFC models were used as a fundamental parameter. In addition, in the LES model, the turbulence was attained by setting the characteristics of a sinusoidal wave such as and . Three numerical models were used to prediction the flame topology and flame location at different turbulent flow conditions, and three different results were found as compared with experiments. Moreover, the fields of heat release, species mass fraction and temperature distribution in the centerline of the combustor were investigated. After the TFC model was calibrated, the best value of constant that matches the experiment was A = 0.37. All numerical simulations were performed in STAR CCM+ v10.02 and v12.04 software. The turbulent flame speed was derived from the Zimont formula, and the results showed that the flame location and topology were influenced solely by , as suggested by the derived new equation for . The results showed that combustion occurs in the wrinkled and corrugated flamelet regions on the Borghi diagram. At a low value, the flame topology in the TFC model was wrinkled and symmetrical with respect to the vertical axis of the combustor, whereas at medium and large values, the flame topology exhibited cusps. By contrast, the flame topology behaviour in the CFM model was not constant at different and was like a mushroom shape, and the flames moved toward inlet regions by increasing . In addition, in the LES model, the V-shape and the corrugated wings of the flame were formed. The flame changed topology and location at different turbulent flow conditions of amplitude of pulsation and frequency. The flame topology investigation for jet flow combustor can be used to modulate effectively well the gas turbine burner design or other turbulent combustion studies. The investigation of the flame topology in the combustor with various turbulent flow conditions is important in controlling the flame location to reduce emissions and increase power efficiency, or even design pioneering production techniques related to flame.