@article { author = {}, title = {Performance prediction of twin-entry turbocharger turbines}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {145-155}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.956}, abstract = {In this paper, the performance of the twin-entry radial flow turbine under steady state and partial admission conditions is modeled. The method, which is developed here, is based on one-dimensional performance prediction. In one-dimensional modeling, the flow properties are assumed constant on a plane normal to the flow direction. This assumption is in contrast with the flow at the rotor entry of a twin-entry turbine under partial admission condition. In this study the one-dimensional performance prediction method for a single-entry turbine is modified to analyze the twin-entry turbine. In particular, the loss coefficients due to friction, clearance and blade loading, which are already developed for single-entry turbines, are modified. Also, additional losses in the rotor are considered because of twin-entry rotor inlet conditions and the rotor-mixing losses. Indeed, in a single-entry turbine with symmetric volute, the flow tends to move toward the shroud. A correlation for the radial velocity profile at the rotor entry for this case is obtained and is considered to be optimum. Then the rotor mixing loss is estimated. Finally a model based on the above mentioned matters is developed. The results obtained from the model are compared with the experimental results and good agreements are obtained. In this paper, special behaviors of the flow in the twin-entry turbine are also investigated and some physical interpretations are presented.           }, keywords = {Turbocharger,radial flow,turbine,twin-entry,one-dimensional modeling,performance prediction}, url = {https://ijstm.shirazu.ac.ir/article_956.html}, eprint = {} } @article { author = {}, title = {Finite element, modal testing and modal analysis of a radial flow impeller}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {157-169}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.957}, abstract = {This paper is concerned with the finite element analysis and modal testing of an industrial radial flow impeller. The goal is to determine and verify the vibration characteristics of the impeller using both experimental and analytical techniques. The finite element model of the impeller with tapered blades was built using a 3D solid element. The convergence properties of the FE model was then verified by mesh refinement and mass distribution methods. Next, a pre-test plan was performed before conducting a modal test in order to select the proper suspension points, driving point(s) and response points on the impeller. Impact testing using hammer excitation and laser Doppler vibrometer (LDV) response measuring techniques were used to measure the vibration properties of the impeller. Using a scanning laser Doppler vibrometer enabled the backplate modes to be described in terms of their nodal diameter components. The nodal diameters versus natural frequencies graph was then compared with the same results obtained from FE and hammer testing and showed good agreement. Finally, a parametric study was conducted on disc thickness, blade thickness, blade trailing, leading edge profiles and blade mistuning. It was found that the effect of varying disc thickness on the lower modes of the impeller was not significant. However, significant natural frequency shifts were observed for the higher modes. It was also concluded that varying the blade leading edge position had a marked effect on the natural frequencies while the lower modes were somehow insensitive to the variation of trailing edge position.          }, keywords = {Radial flow impeller,modal analysis,laser Doppler vibrometer,test planning,finite element}, url = {https://ijstm.shirazu.ac.ir/article_957.html}, eprint = {} } @article { author = {}, title = {A numerical investigation on convective film boling of the single component refrigerant as alternative of cfcs in a vertical pipe}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {171-185}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1017}, abstract = {In the present work, a numerical analysis has been done to calculate the heat and mass transfer during boiling based on the two-phase annular single component refrigerants in a vertical pipe. The conservation equations of mass, momentum, energy and turbulence models of k-e for each phase have been solved through a numerical finite volume method. A specific wave model has been used for considering the effects of interfacial wavy instabilities in the transport phenomena. The numerical results of heat transfer for R–113 show a good agreement with the available experimental results reported by the others investigators. To compare the R-12 with its suggested alternative, R-134a, the numerical results have been achieved at the same boundary conditions for both of them. Results show that the behaviors of these refrigerants are similar. In addition, the heat transfer coefficient in the case of R-134a is greater than that of R-12, nearly 30 percent.         }, keywords = {Convective boiling,refrigerants,gas–liquid annular flow,vertical pipe,turbulent flow}, url = {https://ijstm.shirazu.ac.ir/article_1017.html}, eprint = {} } @article { author = {}, title = {Airflow in buildings with courtyards}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {187-206}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1018}, abstract = { The airflow rate through a two-story building with a courtyard, with and without trees, was estimated and compared with that of a building without a courtyard. The building and the courtyard were of square shapes, each 10 m to the side. The courtyard walls were 3m high and two separate trees of spherical, cylindrical and conical shapes were considered in the yard. The courtyard was directly south of the building and a wind angle of zero degree was considered when the wind was blowing directly from the south.  It was found that when the wind angles were between 0 to 90 degrees, the airflow rate through the building was reduced when compared with the building without a courtyard. The presence of trees in the courtyard further reduced the airflow rate. When the wind angle was 180 degrees, i.e., when the courtyard was in the lee-ward side of the wind, the airflow rate through the building was increased, and the presence of the trees in the courtyard further increased the flow rate. By considering the wind speeds and directions for the cities of Ahwaz, Kerman, Mashad, Shiraz, Tabriz and Tehran, Iran, the airflow rates were estimated for the buildings located in these cities. The effect of a courtyard and its trees in reducing the airflow rates (or increasing it, under special wind directions) were then determined}, keywords = {Courtyards,wind pressure coefficients,Infiltration}, url = {https://ijstm.shirazu.ac.ir/article_1018.html}, eprint = {} } @article { author = {}, title = {A transient two-dimensional model of thermal and oxidative degradation of pmma}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {207-218}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1019}, abstract = {In the present work, numerical computations of the flow and thermal fields have been carried out for a transient, two-dimensional model of thermal and oxidative degradation of polymethylmethacrylate (PMMA) subjected to a monochromatic, radiant heat flux. An external thermal radiation source is used to simulate the primary mode of energy transfer in a room fire. An incompressible SIMPLE code is used with a staggered grid arrangement. The equations for the fluid and solid (fuel) phases are solved simultaneously using a segregated technique. At the outlet of the computational domain, a convective boundary condition is compared with a traditional Neumann condition. The convective boundary condition is shown to be more effective in reducing the CPU time. A study in the effects of spatial resolution and different time steps are provided. A theory is developed to account for thermal and oxidative degradation. The theory is based on differences in polymer degradation behavior in inert and non-inert environments. A number of quantities such as surface temperature and mass flux of PMMA are calculated by an external source of 40 kW/m2. The predictions of the model are in a good agreement with the experimental results. It is found that an increase in gas-phase oxygen concentration obviously decreases the surface temperature and increases the gasification rate of PMMA.           }, keywords = {Thermal and oxidative degradation,polymers,PMMA,gasification rate,in-depth absorption}, url = {https://ijstm.shirazu.ac.ir/article_1019.html}, eprint = {} } @article { author = {}, title = {Thermal behavior of a large salinity-gradient solar pond in the city of Mashhad}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {219-229}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1020}, abstract = {By applying a model of finite differences, the thermal behavior of a large solar pond in the city of Mashhad in the north east of Iran, is studied in this paper. The 32-year data of sunny hours to day-length ratio are used for the estimation of global radiation. The temperature data of a similar duration are used for evaluating the ambient temperature. The effects of the variation of different zone thicknesses on pond performance are studied. It is observed that the upper convective zone thickness should be as thin as possible, the non-convective zone might be from 1 to 2 m and the lower convective zone thickness may be designed based on the application needs. A thicker non convective zone provides more insulation against heat losses, and a thicker lower convective zone supplies a higher storage capacity, though with a lower operating temperature. The heat may be extracted from the pond by either a constant or a variable loading pattern. The appropriate loading pattern can be selected based on the needs and operational temperature. The LCZ temperature of the pond, under several heat extraction patterns, is also presented for practical applications.           }, keywords = {Salt gradient solar pond,Solar energy}, url = {https://ijstm.shirazu.ac.ir/article_1020.html}, eprint = {} } @article { author = {}, title = {Finite element simulation of hot forming process by using flow stress prediction model}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {231-240}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1021}, abstract = {In hot forming processes, the evolution of microstructural features such as deformation texture and dislocation substructure and their mechanical properties are affected by thermo-mechanical history. In order to analyze these processes, both the plastic deformation of the workpiece and its microstructural changes should be taken into consideration. In this paper, application of the flow stress prediction model to the simulation of hot forming is presented. The model is implemented in the thermo-viscoplastic finite element simulation for the hot upsetting process, temperature, strain rate and flow stress distributions, therefore the geometry of the workpiece at each time step can be calculated. Validation of the model and typical examples of simulation are presented.       }, keywords = {Hot forming process,microstrucral change,finite element,Flow stress,Dynamic recrystallization}, url = {https://ijstm.shirazu.ac.ir/article_1021.html}, eprint = {} } @article { author = {}, title = {The mechanics of normal and oblique penetration of conical projectiles into multi layer metallic targets}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {241-251}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1022}, abstract = {This paper introduces an analytical model for oblique and normal penetration of conical projectiles into multi-layer thin metallic targets. Target layers could be arranged either in space or in direct contact to each other. They could also be selected from the same or different types of materials. This theory could be used for penetration in monolithic thin targets as well. In the case of perfect penetration in multi-layer metallic targets with optional angles of impact, this model could estimate ballistic limit and residual velocities, and the duration time of penetration. In this model, the energy required for the deformation of the target material and petalling formation (which includes plastic, dynamic and bending works) have been calculated. The results obtained from the above model have been compared with experimental and theoretical results of other researchers and good agreements were observed.           }, keywords = {Oblique penetration,multi layer target,ballistic limit velocity,conical projectile}, url = {https://ijstm.shirazu.ac.ir/article_1022.html}, eprint = {} } @article { author = {}, title = {Finite element dimensional design and modeling of an ultrasonic transducer}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {253-263}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1023}, abstract = {Transducers as a heart of ultrasonic heads are one of the most important parts of systems. Among them, sandwiching, adhesive and screw transducers are more applicable, so the applications of ultrasonic waves will widely improve if they are designed correctly. The calculations of dimensions, especially the lengths of pieces, are very important in transducer designing because even a very small miscalculation causes differences in vibration conditions, and afterwards, decreasing or appliance malfunctions will result. The differential equation of the longitudinal vibration mode with its boundary conditions is solved to determine the length of the transducer. After that, the transducer is modeled with the finite element method to evaluate the theoretical calculations, and their resonance frequency is also determined by modal analysis. Finally a prototype transducer is manufactured and tested. The results of theoretical, finite element modeling and experimental tests are very close to each other, so this method was found to be a suitable base for transducer designing.           }, keywords = {Ultrasonic,transducer,piezoelectric,resonance,frequency}, url = {https://ijstm.shirazu.ac.ir/article_1023.html}, eprint = {} } @article { author = {}, title = {Convergence acceleration of shock wave boundary layer interaction flow calculations}, journal = {Iranian Journal of Science and Technology Transactions of Mechanical Engineering}, volume = {29}, number = {2}, pages = {265-268}, year = {2013}, publisher = {Shiraz University}, issn = {2228-6187}, eissn = {}, doi = {10.22099/ijstm.2013.1024}, abstract = {Convergence of the shock wave boundary layer interaction flow calculations is accelerated using a two-dimensional hybrid flux splitting scheme in conjunction with a time-derivative preconditioning method. The ideas of low-Mach-number preconditioning and artificial compressibility are combined to a unified approach designed not only to enhance the convergence rate of high velocity flow field calculations with embedded regions of low Mach number, but also to remove the stiffness of the equations. Results are presented for two sample cases with the various Reynolds numbers and are shown that a 30% to 50% savings in computer time is usually achieved.          }, keywords = {Convergence acceleration,Navier Stocks,shock wave,AUSM}, url = {https://ijstm.shirazu.ac.ir/article_1024.html}, eprint = {} }