نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و دوم شماره 2 (بهار و تابستان 1400)

Regenerative flow compressors or blowers are rotodynamic machines with the ability to produce high heads at low flow rates. They have performance curves with very stable features. By employing numerical simulation of fluid flow, the effect of using symmetric aerodynamic blades, the number of blades, and the height of the blades on the performance and efficiency of the compressor were analyzed. Due to the complexity of the flow pattern in this type of turbomachinery, the SST turbulence model has been applied. Dimensionless numbers have been used to present the results so that they can be generalized and archived. The results showed that reducing the blade height from 34 mm to 28 mm reduces the pressure ratio and also reduces efficiency. The study of the effect of the number of blades at the design point showed that the highest efficiency occurs in the pitch-to-chord ratio of 0.36. Based on the results of the study of aerodynamic blades with the same inlet and outlet angles, which were presented in five different angles of 20, 30, 40, 50, and 60 degrees, it was found that symmetric aerodynamic blades with an inlet/outlet angle of 46 degrees have the best performance.

The emitted noise (sound) by turbulent supersonic jet flow coming out from convergent or convergent-divergent nozzles has destructive effects on the environment and humans. To prevent these effects, the noise generation mechanisms should be well studied in the near field and behind the nozzle. In this study, a choked nozzle and its emitted noise are studied in two dimensions using the URANS approach and the k-ε Realizble turbulence model. The noise from the turbulent jet in the near field and behind the nozzle is also obtained by solving the Williams-Hawking equation. The effect of nozzle pressure and temperature on the radiated noise has been investigated. The temperature changes affect the shear layer and the length of the jet potential core. The recorded noise close to the nozzle lip and behind the nozzle indicate that the presence of shock cells in the jet plume affects the acoustic waves propagate upstream. It causes broadband shock cell-associated noise. This noise is about 100 db for a cold jet with a temperature of 300 K and about 105 db for a hot jet with a temperature of 600 K. By increasing the nozzle pressure twice the initial value the noise reaches about 124 db.

Aluminum CNG vessels compared with steel ones can lead to lower fuel consumption. Dome forming (spinning) is an important step in seamless CNG vessels fabrication. This paper aims to the process simulation on a 6061-O aluminum tube at an elevated temperature, investigation of feed effect on the stress and strain after the first pass and its effect on the whole of the process. After the whole process simulation and achievement of the final dome shape, to investigate the feed effect on the strain, circumferential, axial and thickness strains after the first pass, on different inner, middle and outer paths of the tube wall are reported in some figures. Feed variation has not a considerable effect on the decrease of increase rate of circumferential strain absolute value and on the strain distribution on the middle path. The primary higher feeds effect on other investigated strains is smoother distribution. This effect is in agreement with a more stable process and less wrinkling at higher feeds. This stability is reported in a higher tested feed in this paper. On the other hand, investigating different feeds shows that the feed increase leads to decrease of maximum stress in the tube after roller separation at the end of the first pass.

In this paper, solar/wind/battery hybrid system for different prime movers including diesel engine, gas engine and gas turbine with hourly analysis during a year is modelled and optimized for Kerman city. Fuel ratio is defined for comparison of system fuel consumption than traditional system. Number of solar panels, wind turbines, batteries as well as nominal capacity of prime movers are considered as design parameters. Fuel ratio and total annual cost (TAC) are selected as two simultaneous objective functions and Fast and Elitism Non Dominated Sorting Genetic Algorithm (NSGA-II) is used to find the optimum value of design parameter. The optimum result showed that hybrid system with diesel engine as prime mover is the optimum system in large zones of Pareto front with lower TAC and higher fuel ratio compared with the other studied prime movers. Fuel ratio and total annual cost in final optimum point for diesel prime mover are obtained 0.735 and 185456.5 ($/year). The optimum number of solar panels, wind turbines and batteries for the diesel-powered hybrid system are determined 1266, 19 and 822, respectively. In addition, nominal power of diesel engine obtained 163 kW.

In this work, a plate heat exchanger with an inconsistent flow is investigated in different working conditions. Four different models in laminar and turbulent flows with rigid and elastic plates at different Reynolds numbers have been studied, and the effect of the separator plate elasticity on the heat transfer rate and the efficiency of the heat exchanger has been investigated. A sinusoidal profile is used at the entrance to the cold passage. The results of this study showed that the elasticity of the intermediate plate in both laminar and turbulent flow has raised the heat transfer rate. Of course, in cases where the middle plane was elastic, the friction coefficient increased relative to the rigid plate. The efficiency of the heat exchanger is defined and is obtained for the heat exchanger to consider both heat transfer rate and pressure drop. Results showed that in most cases, the efficiency of the heat exchanger with elastic separator is more than one. The results showed that the maximum efficiency is 5.2 which was observed in Re=3000 and the minimum efficiency is 0.9 which occurs in Re=200.

In this paper, Frequency analysis of cracked porous functionally graded beams which are resting on elastic foundation based on reddy third order shear deformation theory is studied. Mechanical property gradients defined in accordance with model of exponential law. Governing equations obtained with the aid of third order shear deformation theory and by considering elastic foundation effects within hamilton’s principle. Due to complicating closed form solution of equations, differential equations solved utilizing Generalized Differential Quadrature Method by considering various end conditions. In order to validate the results, comparisons are made with solutions which are available for other papers. This study shows that the difference between the results of this paper and the results of others is negligible. Finally the effects of geometrical parameters, exponential law indexes, crack location and depth, elastic foundation and porosity on natural frequencies of functionally graded beams are studied. The results of this paper and effects of these parameters can be used in the optimum design of functional graded beams and crack prediction, detection and monitoring techniques.

Parameters of core roughness are important in the determination of contact area and performance of engaged surfaces which can be modified using finishing processes. Burnishing is a mechanical behavior on the surface to enhance surface characteristics and work hardening which can change core roughness parameters. In this research, a comprehensive study on the surface roughness parameters especially, peak and valley core roughness, before and after of ball burnishing process is presented on the copper cylindrical parts. Initial surface roughness and a tool with different balls are important inputs of the current research which are studied besides other parameters such as burnishing force and feed. Results showed that the burnishing process has reduced surface roughness by about 90 to 96 percent. Also, ball diameter of 20 mm decreased Ra about 20% in comparison to ball diameter of 12 mm. Peak core roughness (Rpk) and valley core roughness (Rvk) presented decreasing of 80% to 90% and 20% to 80%, respectively which prove lower effectiveness of burnishing process on the Rvk. Hence, an initial condition especially the initial surface roughness has a great effect on the Rvk. Considering other parameters, initial surfaces prepared using sandpaper with a grit size of 60 and turning with a feed of 0.24 mm/rev which associated with the highest surface roughness, presented a significant reduction of roughness parameters after the ball burnishing process.

In the nuclear fuel assembly, the mixing vanes are solid components which are attached to the spacer grid. These vanes would increase heat transfer rate from the fuel wall. The force induced by flow may expose the vanes to excessive stress and bending, which in turn, it impairs the mixing vanes. In order to improve the heat transfer rate and decrease the vibrational forces, vanes are usually positioned at a certain angle regarding to the flow axis. This study investigates displacement of vanes in three angles of 65, 70 and 75 degrees for a specific geometry using the fluid-solid interaction method. First, the fluid flow is solved using a Finite Volume Method (FVM) solver and the forces exposed by the flow to the vanes are estimated. Next, the displacement of the vanes due to the applied forces is calculated by the Finite Element Method (FEM). Comparison between calculated pressure drop in this study and experimental result show a difference less than 10%. The maximum pressure drop is occurred when the vanes have 65° angle. The most turbulence intensity is obtained at the angle of 75°. Also, according to the frequency estimation, it was observed that with increasing frequency the displacement's amplitude would decrease.

The enormous application of nano-tweezes in modern technologies and biological purposes leads to new operation situations for these devices, such as an external magnetic field. In this paper, the pull-in behavior of nano-wire-made tweezers immersed in a longitudinal magnetic field is simulated. As the scale dependency can be dominant in ultra-small structures, the constitutive equation is developed based on the consistent couple stress theory. In addition, the influence of van der Waals force and Casimir force are considered in the developed model. A semi-analytical model based on the Homotopy perturbation method is presented to solve the nonlinear governing equation. The influence of different phenomena including size dependency, Casimir force, van der Waals force, and the magnetic field on the pull-in voltage and tweezering range of nano-wire manufactured tweezers is investigated. The obtained results demonstrated that the magnetic field has a considerable effect on the pull-in instability and operating range of nano-tweezers.

This research is focused on scaling of a radial turbine for turbocharger of a lean combustion engine. One of the methods to decrease pollution is to reduce the exhaust temperature using lean combustion. So, more air should be entered the engine, and by increasing the air, the turbocharger should be changed for increased mass flow rate. In the first step, the turbine performance is simulated using a CFD solver, and the results are compared to the experimental data. Next, the turbine is scaled by four scenarios, and the turbines' performance is simulated using the CFD solver. In the first scenario, only the hub radius is decreased, and the mass flow is increased by 0.5%. In the second scenario, the hub radius decreases, and the shroud radius increases, and a 7% improvement is obtained. In the third scenario, the inlet and shroud radius increase while the hub radius decreases, and the mass flow is improved by 11%. In the fourth scenario, the geometry is changed freely, and a 20% increment is obtained.

The effect of suction jet parameters on the control of the dynamic stall of a NACA0012 has been investigated at Reynolds number of 13500. Average coefficients and average aerodynamic performance were used to compare and evaluate the impact of different jets. Location, velocity amplitude, suction angle and orifice length were considered as the effective and changeable parameters in the suction jet. Angles of 30, 60 and 90 degrees and locations of 1, 4, 6, 10 and 20 percent of the chord length were selected to investigate the effect of the angle and location of the suction jet, respectively. Values of 0.01 and 0.005 of chord length were chosen for the opening length. Values of 0.04, 0.08 and 0.14 were considered for jet momentum coefficient at fixed orifice length. The results showed that the location of 4% of the chord length is more suitable than other locations for placing the suction jet, and by increasing the suction angle and approaching to 90 degrees, the jet had a better effect on the flow control. The effect of jet velocity and orifice size is such that increasing them improves jet performance.

The fast filling process is the main process that occurs in the CNG refueling station. The main objective of the present study is to apply a thermodynamic analysis for a complete modeling of a CNG refueling station with several consecutive refueling . The results of the thermodynamic analysis have been validated against the experimental data and previous studies. The AGA8 Equation of State has been used to calculate the thermodynamic properties of CNG. There are many researches concentrated on the thermodynamic modeling of CNG refueling station, but didn't address the optimal algorithm of priority panel. Filling time minimizing, filling mass maximizing and average specific energy consumption minimizing have been employed as the objective function for the optimization problem. Finally, the optimal algorithm of priority panel has been determined as the main goal of the present study. The conclusive results of the optimization problem are presented. Achieving more accurate modeling and modeling the process of several consecutive refueling is one of the most important results of the present study. The optimal algorithm of priority panel are obtained for PPM225 algorithm . An economic analysis is performed to see the results more clearly. The results of the economic analysis show that 65,700,000,000 Rials (43,800,000 kWh) can be saved in one year.