Sharif Digital Repository

Flame Response to acoustic excitation which plays an important role in combustion chamber stability state may be found through numerical simulation. A finite volume code of higher order accuracy developed for compressible flows was adopted. Species equations along with a single-step irreversible reaction model were added to this non-reacting program. Changes were also made to the energy equation. Premixed methane/air flame in tubes was studied and the same problem was solved with FLUENT software. It was found that whether the Lewis number is considered constant or temperature dependent has a strong effect on flame structure and shape and that using mean values for gas properties yields out... 

Acoustic excitation frequency effect on NACA 0012 airfoil boundary layer and on its wake development was investigated experimentally in two wind tunnels. Airfoils chord lentgh were 100 and 152 mm. Flow Reynolds numbers was 60000 and 160000 in the first wind tunnel and 100000 and 250000 in the second one. Excitation frequency range was chosen between 300 and 2400 Hz. Airfoil flow and sound characteristics was measured using a 1-D hot-wire sensor and two microphones, one mounted on the wind tunnel wall and the other flash mounted on the model at 10 percent of chord length, respectively. Airfoil angle of attack was set at zero degree in the first wind tunnel and at three angles of zero, five... 

Lean premixed combustion is highly susceptible to thermoacoustic instabilities. Such instabilities are compounded in low swirl flames by the fact that low swirl flames are stabilized aerodynamically at a relatively considerable distance downstream of the burner rim, such stabilization mechanism makes the flame more prone to both vertical and acoustic perturbations. The main objective of the present thesis is to evaluate effects of acoustic and hydrodynamic perturbations on low swirl flame features. To such aim, first, low swirl flame characteristics and stabilization mechanism are studied using large eddy simulations along with thickened flame combustion model. The obtained results show that... 

Lean premixed flames bring both benefits and challenges to combustion systems. While they have low emission levels and high efficiencies, they are also very susceptible to combustion instabilities. Low swirl burners have been shown to be very capable in stabilizing lean premixed flames.
In this thesis, behavior of low swirl flames under conditions of variable equivalence ratio (0.6 – 0.8), mean flow velocity (3.5 – 5.5 m/s), and excitation frequency is investigated. In static stability diagram of the flame, a region is observed in which stability mode of the flame is dependent on the path that takes the flame to its operating point (hysteresis region). Increasing the recess distance of... 

The aim of this study was to investigate the response of counter flow flames to acoustic excitations numerically. For this purpose, the one-dimensional and two-dimensional laminar counter flow flames are numerically simulated. Cantera is used to simulate the flame in one dimension. In order to consider the counter flow flame as one-dimensional, limiting assumptions are needed, and coding is also required to stimulate the flame acoustically. As a result, a two-dimensional field can be used to simulate a counter flow flame and its acoustic stimulation. This study used Ansys Fluent software to simulate a two-dimensional counterflow flame. Cold solutions without acoustic excitation are first... 

The primary purpose of the present thesis is to understand the dynamic behavior of partially premixed flames of counterflow burners. In this project, work has been done on the previously designed and built counterflow burner. By setting up partially premixed flames in this burner, acoustic excitation of these flames has been done, and finally data acquisition by taking video of the flame and then using image processing to extract the dynamic response of these flames. The flames that we have examined in this project are all in a laminar regime and the fuel used in these flames is also natural gas. The frequencies that we have examined in these flames are 25 and 40 Hz, and these tests were...