جستجوی مقالات مرتبط با کلیدواژه « نازل » در نشریات گروه « مکانیک »

Design, manufacturing and testing of a resistojet suitable for atmospheric conditionsABSTRACTThe purpose of this paper is to design and manufacture a resistojet thruster based on butane propellant with the ability to perform tests in atmospheric conditions. The important sections for designing of this system are heater and nozzle design. The utilized heater is designed for direct heat transfer and the design of the nozzle is based on the thermodynamic relations governing a converging-diverging nozzle which is suitable for the atmospheric outlet pressure. CFD simulation has also been used to investigate the flow of propellant in the nozzle. In the following, the resistojet thruster was built based on the designing and experimental tests were carried out for its validation. By comparing the functional parameters of the thruster, such as thrust force and specific impulse from the experimental results and thermodynamic relationships, the design of the thruster is validated. Considering the heat exchanger power of 30 watts and also the most optimal conditions, the efficiency of the thruster is 21%, the thrust force is 36 millinewtons and the specific impact is computed as 35.9 seconds.

This paper introduces a novel approach to enhance the performance of a two-phase steam and air ejector through primary supersonic nozzle designs with uncircular cross-sections. Experimental tests evaluated the impact of these novel nozzle designs ،which included a star shape ،a simple square ،a square skewed in the direction of the nozzle axis ،a special sketch ،and a simple circular cross-section as the reference nozzle ،on the ejector's performance. The results indicated that the novel nozzles demonstrated the capability to enhance the ejector's entrainment ratio by up to 12% compared to the conventional circular cross-section reference nozzle. To validate and gain further insights into the novel nozzle designs ،computational fluid dynamics (CFD) simulations were also conducted. The integration of CFD simulations and experimental data showcased the potential of these uncircular cross-section nozzles to improve the ejector's performance. The findings offer promising opportunities for optimizing ejector configurations ، paving the way for more efficient and innovative solutions in various engineering applications.

In this paper, the catalyst bed of a 10 N hydrazine monopropellant thruster was designed. The catalyst bed is including iridium granules, which is used to decompose the hydrazine in monopropellant thruster. Hydrazine must be decomposed almost completely in the catalytic chamber, because it is a carcinogenic chemical fuel and on the other hand, achieving the maximum power from the thruster is also an important goal. As a result, the effect of change in catalytic chamber length on the mass fraction of chemical species including hydrazine, ammonia, nitrogen, and oxygen was studied. Also, after determining the length of the catalytic chamber, the diameter of the nozzle throat corresponding to the same length was determined.

Heat transfer plays a major role in the design and performance of missiles and vehicles that have rocket driving. The main importance of this discussion is related to the safety range missile materials, especially in areas such as the combustion chamber and nozzle, which are under critical heat. Only one failure is enough to interfere with the operation of missiles. It may also be due to excessive heat in the nozzle throat, a portion of the sheet metal locally damaged. In which case the exhaust gas flow becomes asymmetrically, which led to the creation of inappropriate force vector direction. This leads to an error in the missile guidance to the target and a lot of fuel consumed on the spacecraft to correct its path by secondary driving system. In this project the amount of heat transferred to the chamber for different sections of engine during the simulation by software is calculated, also the coolant conditions and temperatures have been calculated in accordance with existing heat and cooling operation performed in each section. For this purpose, the engine divided into four parts, the combustion chamber, the convergent nozzle, throat nozzle and the divergent nozzle. The rate of heat transferred from the gas chamber (according to the conditions of gas in different sections) as well as the chamber temperature in the vicinity of the coolant and coolant temperature calculated for different sections of each section. Notably, in this research, ANSYS software package is used to create geometry, mesh and simulations.

In the present study, fuel injection and hydrodynamic behavior of fuel spray has been studied numerically under the cavitation phenomenon inside the injector chamber in the combustion chamber of the diesel engine using AVL-Fire software. Spray simulation involves the phenomenon of two-phase flow and requires the numerical solution of the survival equations for the gas phase and the liquid simultaneously. The cavitation flow inside the nozzle is simulated using the Euler-Eulerian method. In this method, liquid and vapor fuels are considered as continuous two-phase, and the governing equations are solved separately for each phase. Spray development and decomposition are simulated using the Eulerian- Lagrangian method. In this method, the gas inside the combustion chamber is considered in the Eulerian coordinates and fuel droplets in Lagrangian coordinates. In the simulations carried out for compression, two values of 60 and 100 MPa are considered for a pressure of 2 MPa. The results showed that for both injections, the cavitation phenomenon is created, although the cavitation phenomenon continues only for the injection pressure of 100 MPa until the end of the nozzle outlet. Therefore, the high injection pressure causes an increase in fuel velocity in the injector orifice and causes a cavitation phenomenon. At high pressures, cavitation grows rapidly, resulting in better atomization and lower average particle diameter.

The design of a controller for a thrust vector control system of UAV has been studied through the robust  H∞ control method. In the first, the governing space-state equations of the system have been derived using the bond graph approach. Then, the critical performance parameters of the system were evaluated and identified according to the operational feasibility and the range of successful performance of the system. Next, the weight functions of the robust H∞,including the indeterminate weight function under the influence of specified uncertainties, were determined. Finally, the consistency of robust control in the presence of uncertainties was evaluated and the results of deflection of thrust vectoring nozzle were compared with the performance results of an optimized PID controller. The simulation results are determined using the MATLAB environment. The results of this study showed that the bond-graph method has good validity for modeling of this system and the designed robust controller can also meet its mission requirements

Following concerns about air pollution and global warming in recent years, the use of heavy duty gas engines has become favorable in major industries such as the marine industry, power plants, etc. Heavy duty diesel engines designed for similar applications were used and made by modifying their structure or adding new parts or a combination of the two approaches, because of the fact that heavy duty gas engines are more similar to diesel engines with similar emissions. They have less emission and also less power. Various technologies can be used to increase the power of the gas engines. One of these new technologies is the pre-combustion chamber, which results in an increase in power output. The pre-chambers are categorized into two types of refueling in terms of how the refueling is shared with the main chamber and refueling independent of the main chamber. The pre-combustion chamber should be used to increase the efficiency of the pre-chamber and overall engine efficiency, which is suggested after considering the use of the pre-combustion chamber with a stand-alone fuel system.

One of the conventional ways to increase velocity of a fluid flow is using a nozzle in stream wise. In this paper, in order to increase the flow velocity in a low speed wind tunnel, and to carry out experiments at higher velocities. An optimal nozzle profile, by considering constraints such as the nozzle inlet cross section, inlet velocity, and nozzle length has been designed using computational fluid dynamics. Design variables were the nozzle inlet cross section, outlet velocity, the turning point of the nozzle profile, the uniformity of the outlet flow and the effective length of the test section. The performance of the designed nozzle was experimentally investigated. According to the results, the velocity increased by 13 m/s and the uniformity of the flow decreased by ±1%.

Cavitating flow through the nozzle is numerically simulated by using the multiphase lattice Boltzmann method. The pseudo-potential Shan-Chen model is used to resolve inter-particle interactions, modeling phase change between the liquid and vapor phases and imposing the surface tension at the interface. The numerical algorithm implemented is simple for programming and efficient for simulation of multiphase cavitating flows comparing to the traditional Navier-Stokes solvers with complicated cavitation models. Efficiency and accuracy of the multiphase lattice Boltzmann method with Shan-Chen model for simulation of cavitating flows through the nozzle are examined by computing the cavitation inception, growth and collapse and the results obtained are compared with the existing numerical results in the literature. The study shows that the present computational technique is robust and efficient to predict the cavitation phenomena in the geometries studied.

Plume reversion due to missile ascending and related flow expansion and its interaction with missile body especially with missile base has been an important concern of investigators and missile designers. The aim of the current is investigation of effects of different parameters on the interaction of plume and missile body. To do this, heat flux on the missile body at different conditions including different flight conditions, turbulence modeling, base length and nozzle modeling has been studied. In the following, plume induced flow separation is studied. To model flow field, Gambit 2.4.6 and Ansys Fluent 17 are used for grid generation and flow simulation respectively. The results show that with increasing in flight height, plume at the base of missile gradually expands and finally covers the base completely. As well as, it can be seen that plume expands more rapidly in the base region and reduces heat flux when the nozzle is not considered. The reduction of heat flux is different in various parts of the base, ranging from zero to a maximum of 83% in areas far away from or near the nozzle. In the end, the effect of the base length was investigated. The results showed that as the base length is increased, the vortices are further expanded and this expansion leads to increased heat flux so that when the base length is doubled, the heat flux is increased by 20% at most

This study is a try to design a spike nozzle and simulate its flow-field in different conditions. Hence, spike nozzle design methods were studied and accordingly the design code was developed. Then the behavior of flow in this type of nozzle was simulated numerically by means of computational fluid dynamics. In order to conduct the simulations, four turbulence models suitable for solving the flow-field of spike nozzle were used, not only to model the performance of the nozzle in design and off-design conditions, but also to identify the best model for the accuracy of the solutions. To ensure the accuracy of the simulations, numerical results and experimental data were compared. It was found that applied models in case of using high quality grids with proper dimension near the nozzle walls, can predict the nozzle flow pattern with acceptable approximation. Also the comparisons revealed that the amount of pressure on the spike wall calculated by Realizable k-ε model, is generally identical with experimental results and in the worst condition the difference between them is 15%, so this model has the best agreement with experimental results. Besides, comparison of taken photos during experiments and extracted contours from numerical analysis, shows the high ability of applied numerical method to predict spike nozzle flow-field. Therefor it can be claimed that by using the proposed method in this research, there is no need to perform cold-flow tests during the design and construction of spike nozzles.

Lateral jet control systems are being considered as attractive alternatives to conventional control systems in recent years. In present study which is divided in two parts, the effects of lateral jet interaction with supersonic cross flow on aerodynamic behavior of a standard projectile at zero angle of attack has been studied. In the first part, results of the effects of parameters such as jet location, Mach number and nozzle type on pressure coefficient, drag coefficient, drag force and pressure distribution on the fins is presented and analyzed. In the second part, longitudinal static and dynamic stability coefficients of the projectile in presence of lateral jet has been achieved and evaluated according to the mentioned parameters. According to the results, jet location is the most effective parameter. In the first part, the pressure distribution on the fins is much dependent on jet location. Effect of Mach number on pressure coefficient, drag force and drag coefficient is also significant. Besides change of the pressure distribution on the fins comes more into sight at the final locations by variation of Mach number. In the second part, lateral jet effect leads to decreasing longitudinal static stability. Increasing the Mach number is also results in decreasing longitudinal dynamic stability and jet displacement make nonlinear behavior over pitch damping moment coefficient, therefore choosing proper jet location is depend on desired parameters of designer. According to the results, effect of nozzle type has been insignificant for all cases.

In order to decrease construction cost of vertical wind tunnel, it is necessary to reduce the wind tunnel nozzle length. In this regard, it is adequate to reduce the ratio of inlet to outlet diameters of the nozzle and ratio of nozzle length to its inlet diameter. In addition, shifting of the inflection point of the nozzle curves to the flow upstream and reduction of the exit section of the nozzle can result in reduction in nozzle length. These modifications may cause change in the flow quality at the nozzle exit, which has to be studied. In this experimental work, application of hot wire, velocity distribution and turbulence intensity at the nozzle exit have been investigated. When the ratio of inlet to outlet area of the nozzle reduce from 12 to 6.25, the ratio of inlet to outlet turbulence intensity increase from 0.2 to 0.4. Using the results, the nozzle length can be reduced by about 62% so that air quality in the short nozzle output is acceptable

The electrohydraulic valves are commonly used in the engineering applications. These valves, as the medium elements, prepare the hydraulic systems for the electrical control applications. For the precise performance of these valves, disturbances in the valve elements dynamics will disturb the control process of the system. The electrohydraulic servo valves are greatly affected by the external acceleration, for instance in the aerospace applications. In a two stage flapper- nozzle electrohydraulic valve, the external acceleration changes the pressure of the fluid leaving the nozzles and it affects the flapper and spool of the valve like a virtual force. Thus, when the applied current is zero, the acceleration diverts the spool of the valve from the equilibrium point, and unwanted performance in the valve occurs. In this study the pilot pressures of the spool is modeled in unsteady state condition. The effects of the acceleration on the flapper and the spool of the two stage electrohydraulic valve are investigated. At the end, the obtained model is verified by use of the experimental data.

Nozzle is an important component of wind tunnel. Its main functions: conversion of static pressure to dynamic pressure and reduction of turbulence intensity and helping in uniformity of the velocity profile in the test section of wind tunnel. In order to reduction of wind tunnel building costs, in some wind tunnel special vertical type, setting chamber may be replaced by a bell mouth at the nozzle inlet. Experimental methods such as hot wire anemometry have been used in this research. Result show that the effect of nozzle in blowing and suction type of wind tunnels is similar. Effect of bell mouth at the nozzle inlet is not significant for turbulence intensity reduction, but bell mouth of the nozzle inlet reduce the losses of nozzle about 7%.