D. Mokhtari , M. Hojaji , M. Afrand ,
Volume 19, Issue 5 (5-2019)
Abstract
In this study, the effect of a cylindrical protuberance on the thrust vector of a supersonic jet was investigated as a new method in thrust vector control. For this purpose, a convergent-divergent nozzle was designed and constructed. This nozzle is such that the Mach number is its nominal output in full expansion conditions 2. The wall of the nozzle is equipped with pressurized holes to measure pressure variations. Also, there is a duct wall in the nozzle wall to apply a protuberance inside the nozzle. Pressure sensors for pressure measurement and also the schlieren system are used to check the outlet flow field. The total pressure of the compartment is constant at all tests and is 5.7bar. The results of this study show that the depth of penetration of the protuberance in the flow field has a significant effect on the amount of deviation and even the direction of the deviation of the jet stream exited from the convergent-divergent nozzle. The maximum jet outlet flow from the nozzle is 5.7degrees, which occurred at a rate of H/D*=0/4. In addition, these results indicate that with the increase in bulge penetration within the nozzle, the nozzle axial thrust has slightly decreased.
V. Rezapour Jaghargh , A.m. Mahdavi, E. Roohi,
Volume 19, Issue 7 (7-2019)
Abstract
In this article, rarefied gas flow was investigated and analyzed by the Fokker-Planck approach in different Knudsen numbers and Mach numbers at subsonic and supersonic regimes. The presented Fokker-Planck approach is used to solve the rarefied gas flows in different shear-driven micro/nano geometries like one-dimensional Couette flow and the two-dimensional cavity problem. Boltzmann's equation, and especially statistical technique of the Direct Simulation Monte Carlo (DSMC), are precise tools for simulating non-equilibrium flows. However, as the Knudsen number becomes small, the computational costs of the DSMC are greatly increased. In order to cope with this challenge, the Fokker-Planck approximation of the Boltzmann equation is considered in this article. The developed code replaces the molecular collisions in DSMC with a set of continuous stochastic differential equations. In this study, the Fokker-Planck method was evaluated in the Couette flow in the subsonic Mach number of 0.16 (wall velocity was 50 m/s) and in the supersonic Mach number of 3.1 (wall velocity was 1000 m/s), where Knudsen numbers range from 0.005-0.3. Also, the cavity flow with a wall Mach number of 0.93 (wall velocity was 300 m/s) in Knudsen numbers ranging from 0.05-20 was investigated. The results show that by increasing speed and Knudsen numbers, the accuracy of Fokker-Planck increases. In addition, despite using larger number of simulator particles, the rapid convergence and lower computational costs relative to other methods are the features of this method.
S. Mesgary, M. Bazazzadeh, A.r. Mostofizadeh,
Volume 20, Issue 1 (1-2020)
Abstract
Grain design is the most important part of a solid rocket motor. The aim of this study is finocyl grain design based on predetermined objective function with respect to ballistic curves in order to satisfy various thrust performance requirements through an innovative design approach using a genetic algorithm optimization method. The classical sampling method has been used for design space-filling. The level set method has been used for simulating the evolution of the burning surface in the propellant grain. An algorithm has been developed beside the level set code that prepares the initial grain configuration using Pro/Engineer software to export generated models to level set code. The lumped method has been used to perform internal ballistic analysis. Two meta-models are used to surrogate the level set method in the optimization design loop. The first method is based on adaptive basis function construction and the second method is based on the artificial neural network. In order to validate the proposed algorithm, a grain finosyl sample has been investigated. The results show that both grain design method reduced the design time significantly and this algorithm can be used in designing of any grain configuration. In addition, data have more accuracy in grain design based on the artificial neural network, so this method is the more effective and practical method to grain burn-back training.
M.m. Fakhari, H.r. Bokaei, B. Shahriari,
Volume 20, Issue 2 (1-2020)
Abstract
In this paper, the effect of nozzle divergent section geometry on fluid flow and heat transfer within the convergent-divergent nozzle numerically and experimentally is investigated. Axisymmetric supersonic flow simulation for the converging-diverging nozzle is conducted. The flow field is a steady turbulent two-dimensional flow. The working fluid is a combustion product and is considered as a compressible ideal gas. The flow field is simulated using the commercial code FLUENT. The equations are discretized implicitly with the second order of accuracy. In this study, two convergent-divergent nozzles have been analyzed that the divergent part of one is a cone-shaped and the other is bell-shaped. The calculated parameters in the simulation have been compared with the experimental results. Based on the simulation results and the values obtained in the experimental test, the error is less than 4% that is acceptable and appropriate. According to the results, flow simulation accuracy is appropriate.
Mohsen Mohammadi_sarasia, Hossein Ajam, Ahmad Moloodi,
Volume 21, Issue 7 (7-2021)
Abstract
In the present study, the effect of the porous medium in natural-gas pressure regulators, on the operation and reduce the intensity of the sound produced, is studied. First, it was studied experimentally. Experiments apply for the porous medium 20 ppi (pores per inch) and 10 ppi and non-porous system. To check the validity of the results, experiments were evaluated in four different pressure upstream 20, 10, 5, and 2.5 MPa on the critical pressure ratio. Afterward, for evaluation of the flow parameters on the performance of regulators and the sound intensity level, numerical simulation of fluid flow was performed. The results show that the use of porous media for 10 ppi and 20 ppi, flow coefficient decrease, respectively 7% and 15%, and sound intensity level decrease, respectively 25 and 30 dB. The amount of porosity does not have much effect on the sound intensity. On the other hand, the results of the fluid flow simulation show that placing the porous medium in the flow direction reducing the turbulent intensity and regulating the flow. As well, it decreases the sound intensity by decreasing the maximum velocity and the vortex power.
Mojtaba Haghgoo, Hashem Babaei, Tohid Mirzababaie Mostofi,
Volume 21, Issue 11 (9-2021)
Abstract
Numerical simulation of Eulerian fluid Lagrangian solid interaction incorporating H2-O2 mixture gas detonation plate forming by employing conservative element and solution element immersed boundary method in LS-DYNA software is proposed in this paper. The detonation mechanism includes 7 species and 16 reactions. The chemical reaction mechanism and detonation wave propagation of Eulerian solver and dynamic plastic response of mild steel thin plate of Lagrangian solver are discussed thoroughly. The Johnson-Cook phenomenological material model with failure criterion is used to provide accurate predictions of dynamic response and failure state of detonation loaded steel plates taking into account material strain-rate sensitivity and non-linearities. The 2D numerical model is validated by comparing the simulation results with experimental data for thickness strain. The simulated pressure-time history of combustion cylinder, von Mises stress and deflection pattern of plate are also represented. Furthermore, a series of numerical simulation was carried out to determine the effect of the magnitude of internal detonation pressure on plate, taking into account different combustion cylinder longitudinal capacities, pre-detonation pressures and ignition point locations. Results show that an increase of pre-detonation pressure is conducive to increase the value of maximum detonation pressure while decreasing the combustion duration. Moreover, combustion cylinder with higher longitudinal capacity is more powerful to deform the plate.
Ali Zargarbashi, Soroush Sarrafan Sadeghi, Sadegh Tabejamaat,
Volume 22, Issue 4 (3-2022)
Abstract
An experimental study on the effects of methane-oxygen partially-premixed input flow characteristics in a mesoscale reactor with constant length and geometry was investigated in the present work. For this research, two partially-premixed ratios of 25% and 50% are considered. The reactor is mounted horizontally, made from quartz material and its geometric characteristics are internal diameter: 5 mm, wall thickness: 1 mm, and length: 10 cm. In this research, we have tried to determine the factors affecting flame regimes. The range of flame regimes, flame dynamics, the outer wall temperature distribution of the reactor, frequency, and oscillation of oscillating flames, along with the intensity of the Repetitive Extinction and ReIgnition (RERI) extinguishing sound, were analyzed and reported. This flame's dynamics are more affected by changes in mixing ratio, oxygen volume flow rate, and fuel volume flow rate, causing changes in inlet flow velocity and equivalence ratio, respectively. Examination of the results of acoustic oscillations indicates an increase in oscillating flame velocity with increasing volumetric flow and mixing ratio. Loud extinguishing sound of flames when quenching is caused by converting a portion of the thermal energy of the flame into sound in the flame arrestor and the acoustic vibration waves resulting from the extinguishing of the flame and the difference in gas velocity.
