Showing 4 results for Mirsajedi
Mohammad Mahdi Gheisari, Seyed Mahdi Mirsajedi,
Volume 14, Issue 15 (Third Special Issue 2015)
Abstract
In this research, three dimensional grain burn-back of solid rocket motors is simulated based on level set method and its accuracy is increased according to marching cube algorithm (MCA). To that end and according to requirements of level set method, grain burn-back is simulated during three steps included grid generation, distance function determination, and calculation of burn-back parameters. In this article, with focus on last step, we will compare strengths and weaknesses of grain burn-back analysis for common methods such as captured cell, three dimensional cut cell, sectional, and Heaviside Delta Dirac and in following, we introduce and run MCA. In order to validation, firstly three simple grains such as cylindrical, quad and hexahedron are considered and the performance of capture cell, 3D cut cell and sectional methods are compared with MCA in terms of accuracy and CPU time. Then, to evaluate the new method facing complex and practical grains, burn-back results of conocyle and NAWC N.13 grains is compared with MCA and heaviside/dirac delta methods. The obtained results show that MCA has a better performance at CPU time and accuracy.
Alireza Rostamzadeh Khosroshahi, Seied Esmaeel Razavi, Seyed Mehdi Mirsajedi,
Volume 18, Issue 6 (10-2018)
Abstract
Present study proposes a new multidimensional artificially characteristic-based (MACB) scheme for simulation of combined convection flows. Multidimensional characteristic structure for energy propagation in incompressible flow is derived for the first time. Four pseudo-waves are selected and equations are discretized along them to observe the physical behavior of domain. Viscous fluxes are computed by variables derivatives at the cell interfaces and for time discretization, a 4th-order Runge-Kutta method was used. According to the new scheme, two-dimensional flow with heat transfer in a square cavity and forced convection around a circular cylinder are solved for a wide range of Reynolds and Grashof numbers. Also, for comparison purposes, the CB scheme with averaging for energy equation is used. It was found that MACB has remarkable faster convergence in comparison with CB scheme and averaging methods. Also, by using MACB scheme, maximum permissible CFL number can be increased 80 percent in comparison to CB scheme. At higher Richardson numbers, the conventional flux averaging was failed to converge properly while MACB scheme presents the most rapid convergence. The computed results of MACB scheme are in good agreement with the benchmark solutions.
N. Heshmati, S.m. Mirsajedi,
Volume 20, Issue 10 (October 2020)
Abstract
In this study, the effects of burner nozzle length changes on combustion characteristics of a swirl premixed flame are investigated. Three nozzles with different lengths (2.5, 4.5, and 7cm) have been used. Also, in order to investigate the effect of swirler geometry on the combustion characteristics of flame along with changes in nozzle length, 7 swirlers with different geometries were examined. In the study of flame stability, certain values of the bulk velocity were selected, which in these values the equivalence ratio of the fuel-air mixture was changed to determine the unfavorable flame condition such as blow-off and flame attachment to the nozzle. By determining these limits, the flame stability map was obtained in a range of different swirlers geometries, different burner nozzle lengths, and different flow mass velocities. The results showed that by increasing the swirlers radius ratio, the blow-off limit of swirlers decreases so that by increasing the radius ratio from 0.57 to 0.71, the blow-off limit decreases about 15%, and the stability of the flame is improved. Reducing the length of the nozzle increases the flame resistance against blow-off. The amount of NOx increased with equivalence ratio and the slope of the increase in NOx increased for the swirler with a higher radius ratio and the in a certain equivalence ratio, the amount of NOx of swirler with a radius ratio of 0.57, which is the lowest radius ratio among other swirlers (about 30%).
Aref Sohrabi, Seyyed Mahdi Mirsajedi,
Volume 24, Issue 12 (December 2024)
Abstract
This study investigates the combustion of hydrogen-methane mixtures in the annular combustion chamber of a C30 microturbine. The primary objective is to evaluate the impact of premixed methane-hydrogen combustion on pollutant emissions and outlet temperature in an annular combustion chamber. Simulations were performed using a partially premixed combustion model and the k-ε turbulence model, employing the Probability Density Function (PDF) approach for chemical reaction modeling. To ensure a detailed analysis of pollutant emissions, comparisons were conducted at a constant turbine inlet temperature. The results indicate that adding hydrogen to methane increases NOx emissions due to the higher flame temperature compared to pure methane, even at constant turbine inlet temperatures. However, this blend can reduce fuel consumption by up to 35%. Additionally, a fuel mixture of 60% methane and 40% hydrogen results in a 61% reduction in CO2 emissions. The study further revealed that, owing to the premixed nature of the fuel-air mixture, the annular geometry, and the swirling flow pattern within the combustion chamber, a fuel blend containing 30% hydrogen can lower NOx emissions to 16.1 ppm—significantly less than the 46 ppm reported in previous studies. Moreover, increasing the hydrogen fraction in the fuel reduced CO emissions by 16%. These findings demonstrate that annular combustion chambers with premixed flows and hydrogen-methane fuel blends have considerable potential for reducing pollutant emissions and optimizing fuel consumption
