Research Paper
Aerodynamics
ava shahrokhi; sahar noori
Abstract
The influence of the plug shape on the performance of an aerospike nozzle thrust force is studied in different back pressure conditions. To generate smooth plug contours, Cubic B-Spline technique is employed. In the current research, basis functions are obtained using Deboor’s relation. The flow ...
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The influence of the plug shape on the performance of an aerospike nozzle thrust force is studied in different back pressure conditions. To generate smooth plug contours, Cubic B-Spline technique is employed. In the current research, basis functions are obtained using Deboor’s relation. The flow field around the aerospike nozzle is investigated implementing various shapes and the best of the generated configurations is determined. The flow field is simulated using Navier-Stokes equations and k-ε turbulence model. A triangle unstructured grid is applied for discretization of the governing equations. The computational methodology utilizes steady state density-based formulation and a finite volume cell centered scheme is used to discretize the flow field equations. To accelerate the solution convergence, the flow field is divided into several zones and appropriate initial condition is assigned to each zone. Six different shapes of the plug are generated and the effect of the spike shape on the formation of the shock wave and expansion waves is investigated in each case. The thrust force is calculated for each case and the best configuration is determined in terms of the maximum thrust generation. Eventually, the temperature distribution is calculated along the nozzle for further investigations and it is concluded that the best configurations show a lower temperature rise compared to other designs.
Research Paper
Vibration
Ali Nouri; Sajad Hajirezaee
Abstract
In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. While the other ...
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In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. While the other one is frequency domain impact hammer test which is categorized as an Experimental Modal Analysis method and can be regarded as the most common method in modal analysis. Checking the results obtained by the two methods, one can notice a distinct inconsistency in modal damping ratios extracted by each method. However, based on recent publications on the subject, it can be inferred that the time domain methods have better accuracy in identifying damping ratios of structures. In order to confirm the findings, the effect of excitation is examined for each method by altering the excitation tool. For the operational method, it is concluded that changing the excitation tool will not have a noticeable influence on the identified damping ratios, whilst for the Experimental Modal Analysis method changing the hammer tip leads to inconsistent results for damping ratios. This study exemplifies the deficiency of Experimental Modal Analysis methods in their dependency on excitation techniques.
Research Paper
Fluid Mechanics
Prasannakumara B.C; Shashikumar N.S; Archana M
Abstract
The steady three-dimensional boundary layer flow and heat transfer of a dusty fluid towards a stretching sheet with convective boundary conditions is investigated by using similarity solution approach. The free stream along z-direction impinges on the stretching sheet to produce a flow with different ...
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The steady three-dimensional boundary layer flow and heat transfer of a dusty fluid towards a stretching sheet with convective boundary conditions is investigated by using similarity solution approach. The free stream along z-direction impinges on the stretching sheet to produce a flow with different velocity components. The governing equations are reduced into ordinary differential equations by using appropriate similarity variables. Reduced nonlinear ordinary differential equations subjected to the associated boundary conditions are solved numerically by using Runge–Kutta fourth-fifth order method along with Shooting technique. The effects of the physical parameters like magnetic parameter, velocity ratio, fluid and thermal particle interaction parameter, Prandtl number, Eckert number and Biot number on flow and heat characteristics are examined, illustrated graphically, and discussed in detail. The results indicate that the fluid phase velocity is always greater than that of the particle phase and temperature profiles of fluid and dust phases increases with the increase of the Eckert number.
Research Paper
Forming
Mehdi Bostan Shirin; Ramin Hashemi; Ahmad Assempour
Abstract
An enhanced unfolding Inverse Finite Element Method (IFEM) has been used together with an extended strain-based forming limit diagram (EFLD) to develop a fast and reliable approach to predict the feasibility of the deep drawing process of a part and determining where the failure or defects can occur. ...
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An enhanced unfolding Inverse Finite Element Method (IFEM) has been used together with an extended strain-based forming limit diagram (EFLD) to develop a fast and reliable approach to predict the feasibility of the deep drawing process of a part and determining where the failure or defects can occur. In the developed unfolding IFEM, the meshed part is properly fold out on the flat sheet and treated as a 2D problem to reduce the computation time. The large deformation relations, nonlinear material behavior and friction conditions in the blank holder zone have also been considered to improve the accuracy and capability of the proposed IFEM. The extended strain-based forming limit diagram based on the Marciniak and Kuczynski (M-K) model has been computed and used to predict the onset of necking during sheet processing. The EFLD is built based on equivalent plastic strains and material flow direction at the end of forming. This new forming limit diagram is much less strain path dependent than the conventional forming limit diagram. Furthermore, the use and interpretation of this new diagram are easier than the stress-based forming limit diagram. Finally, two applied examples have been presented to demonstrate the capability of the proposed approach.
Research Paper
Fracture Mechanics
Alireza Hassani; Amin Hassani; Mojtaba Mahmoudi Monfared
Abstract
Abstract: The solution to problem of an orthotropic long cylinder subjected to torsional loading is first obtained by means of separation valuables. The cylinder is twisted by two lateral shear tractions and the ends of the cylinder surface of the cylinder are stress-free. First, the domain under consideration ...
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Abstract: The solution to problem of an orthotropic long cylinder subjected to torsional loading is first obtained by means of separation valuables. The cylinder is twisted by two lateral shear tractions and the ends of the cylinder surface of the cylinder are stress-free. First, the domain under consideration is weakened by an axisymmetric rotational Somigliana ring dislocation. The dislocation solution is employed to derive a set of Cauchy singular integral equations for the analysis of multiple axisymmetric planner cracks. The numerical solution to these integral equations is used to determine the stress intensity factors (SIFs) for the tips of the concentric planar cracks A preliminary comparison between results of this study and those available in the literature is performed to confirm the validity of the proposed technique. Several examples of multiple concentric planner cracks are solved and displayed graphically. Furthermore, Configuration of the cracks and the interaction between cracks is studied.
Research Paper
Aerodynamics
Sarallah Abbasi; Marhamat zienali
Abstract
Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial ...
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Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial compressor rotor blades row. Simulations are carried out on near-stall condition, which is valuable of being studied in detail. In turbomachines, flows are non-isotropic and highly three-dimensional. The reason arises from the complicated structure of bounded walls, tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. As a result, accurate studies on tip leakage flow would be accompanied by many challenges such as adopting suitable turbulence models. So, investigations are carried out numerically utilizing two well-known turbulence models of k-ε and k-ω-SST, separately. It is shown that the k-ε model yields poor results in comparison to the k-ω-SST model. To realize reasons for this discrepancy, turbulence parameters such as turbulent kinetic energy, dissipation and eddy viscosity terms at the tip clearance region were surveyed in detail. It is found out that estimation for eddy viscosity term is too high in the k-ε model due to excessive growth of turbulent kinetic energy, time scale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of flow field at the rotor tip clearance region. Nevertheless, k-ω-SST turbulence model provides results consistent with reality.
Research Paper
Computational Fluid Dynamics (CFD)
Muhim Chutia
Abstract
The aim of this paper is to investigate the effect of the variable thermal conductivity and the inclined uniform magnetic field on the plane Poiseuille flow of viscous incompressible electrically conducting fluid between two porous plates Joule heating in the presence of a constant pressure gradient ...
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The aim of this paper is to investigate the effect of the variable thermal conductivity and the inclined uniform magnetic field on the plane Poiseuille flow of viscous incompressible electrically conducting fluid between two porous plates Joule heating in the presence of a constant pressure gradient through non-uniform plate temperature. It is assumed that the fluid injection occurs at lower plate and fluid suction occurs at upper plate. The governing equations of momentum and energy are transformed into coupled and nonlinear ordinary differential equations using similarity transformation and then solved numerically using finite difference technique. Numerical values for the velocity and temperature have been iterated by Gauss Seidal iteration method in Matlab programming to a suitable number so that the convergent solutions of velocity and temperature are considered to be achieved. Numerical results for the dimensionless velocity and the temperature profiles for different governing parameters such as the Hartmann Number (M) angle of inclination of magnetic field (α), suction Reynolds number (Re) Prandtl Number (Pr), Eckert number (Ec) and variable thermal conductivity (ԑ) have been discussed in detail and presented through graphs.
Research Paper
Solar Energy
hamideh Hoseini; ramin mehdipour
Abstract
Solar chimney power plants are plants based on solar thermal power including three parts of collector, chimney and turbine, which is able to produce electrical energy. One of the effective parameters in increasing the power production is the collector angles versus horizon. In the present study, a numerical ...
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Solar chimney power plants are plants based on solar thermal power including three parts of collector, chimney and turbine, which is able to produce electrical energy. One of the effective parameters in increasing the power production is the collector angles versus horizon. In the present study, a numerical analysis of a solar chimney power plant for different angles of the collector (divergent, convergent and horizontal type collector) is proposed. The introduced numerical model uses mathematical models of heat transfer. In this regard, effect of various angles of the three considered collectors on temperature distribution and power production of the solar chimney is evaluated. Divergent type collectors produce more power than convergent and horizontal collectors, as they produce more velocity and mass flow rates. It will be shown that by increasing the angle of divergent-type collector (keeping the inlet height constant), the power production will be increased and the output temperature will be decreased, in a way that the angle variation of 0.8 to 1 will increase the divergent type collector output power by 11 % and will decrease the output temperature by 0.78%. In the other case, when the output height is kept constant and the collector angle changes, performance of the divergent type collector is better than the other two collectors. Power production in a constant mean height is shown to be 3 times and 1.5 times more than the convergent and horizontal collectors respectively.
Research Paper
Composite Materials
Ali Akbar Azemati; Hossain Khorasanizadeh; Behzad Shirkavand Hadavand; Ghanbar Ali Sheikhzadeh
Abstract
One of the ways to waste energy in buildings is wasting it from the walls. For this reason, insulating materials are used to prevent the loss of energy in buildings. Typically, common insulations are high thickness and thin coatings are used less. The purpose of this research is to introduce nanocomposite ...
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One of the ways to waste energy in buildings is wasting it from the walls. For this reason, insulating materials are used to prevent the loss of energy in buildings. Typically, common insulations are high thickness and thin coatings are used less. The purpose of this research is to introduce nanocomposite thin polymer coatings and its effect on thermal conductivity. For achieving this, chemically modified nano zirconium oxide and nano aluminum oxide in three different weight percentages (1, 3, and 5%) were used in polyurethane matrix for preparing nanocomposite coatings. To study thermal conductivity, the metallic plates are coated with prepared nanocomposites and the thermal conductivity of the samples was measured. The results show that by adding zirconium oxide and aluminum oxide nanoparticles in polyurethane matrix, the thermal conductivity of coatings in all three weight percentages compared to the coating without nanoparticles, decreased. The lowest thermal conductivity was found for 5% nano aluminum oxide composition, which, compared to the conductivity of the pure polyurethane resin, has decreased about 40% that leading to a decrease in the surface heat flux.
Research Paper
Optimization
Omid Fathi; Hadi Kargarsharifabad
Abstract
Improving the efficiency of compressors has been one of the most important goals of researchers over the years. In this paper, three different methods are presented for parameterization and blade optimization of axial flow compressor. All methods consist of flow analysis tool, optimization algorithms, ...
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Improving the efficiency of compressors has been one of the most important goals of researchers over the years. In this paper, three different methods are presented for parameterization and blade optimization of axial flow compressor. All methods consist of flow analysis tool, optimization algorithms, and parametric geometry generation tool, that are different in each approach. Objective function is defined based on the aerodynamic performance of blade in the acceptable incidence angles range. A DCA blade is used as the initial guess for all methods. The performance of optimized blades and the initial blade are compared for evaluating the capability of various methods that a good agreement has been achieved. The results show that the value of performance improvement in each method depends on the number and type of the chosen parameters. All three methods have improved blade performance at the design incidence angle. However, only the first method shows significant performance improvement in off-design conditions.
