Sharif Digital Repository

Supersonic intakes with mixed compression has an appropriate performance in the critical point, but in the subcritical performance, when inlet mass flow rate is reduced to a certain amount, a self-sustained instability occurs in the flow. In this case, instability appears in the form of shock waves system oscillation which is called Buzz phenomenon. An axisymmetric supersonic air intake with mixed compression which is designed for a Mach number of 2 has been investigated experimentally in order to study buzz frequency. The intake has been experimented in different Mach numbers, angles of attack and mass flow rates. Besides, the intake with wind tunnel wall has been modeled and analyzed in... 

A projectile was tested in a wind tunnel at various free sream Mach numbers and angles of attack. The tests were carried out at the transonic wind tunnel of the Imam Hussein University.The experiments were performed at subsonic and supersonic speeds and at different angles of attack. The aerodynamic behavior of the model was investigated using force and moment measurements. The results showed that in the range of measured angles of attack the separation did not occurr and variations of lift coefficient remained linear for all Mach numbers except for a free stream Mach number of 2.0. For this Mach number, the asymmetric bow shock makes a pressure difference between leeward and windward sides,... 

This study aimed to estimate and simulate the phenomenon of buzz in a supersonic air intake and examine the effects of turbulence models on the accuracy and quality of modeling this phenomenon was divided into two parts. In the first part, turbulence models and characteristics of each of them in modeling supersonic flow was studied as well as available researches were investigated to achieve appropriate numerical method for numerical analysis of intakes using turbulence models. In the second part, one axial symmetry intake of the compound density type was taken which designed for Mach number of 2.0 in order to achieve accurate numerical methods and validate it to model intakes flow. With ... 

The buzz phenomenon is the shock oscillation ahead of the supersonic air intake when its mass flow rate is decreasing at subcriticaloperating condition. This phenomenon may cause combustion extinguishing, thrust loss and structural damages. To delay the buzz onset and reduce the amplitude and frequency of the buzz oscillations, the method of boundary layer suction has been proposed and studied in this research. The intake has been designed for a freestream Mach number of 2.0, however, wind tunnel tests have been conducted for freestream Mach numbers of 1.8, 2.0, and 2.2. All tests were performed for zero degrees angle of attack. For studying effects of the parameters of boundary layer... 

Creating synchronous conditions of precision and speed in rotating systems is a requirement for the design of these systems. The requirement to create these conditions is essential in various applications, such as machine tools and computer equipment. One of the main sources of error in the motion of the high speed spindles is the occurrence of non-repetitive runouts. The presence of non-repetitive runouts at high speeds greatly affects the accuracy of the rotating motion of rotating systems and reducing its effects is always considered in the design of high speed rotary systems. Usually, one of the most important factors in the occurrence of non-repetitive runouts is related to spindle... 

Buzz is a phenomenon caused by the self-sustained shock oscillations in most supersonic inlets. When the entering mass flow is reduced below a specific value, inlet buzz occurs and results in variations of both inlet mass flow and pressure. An extensive wind tunnel tests were conducted on an axisymmetric supersonic inlet at Mach numbers from 1.8 to 2.2, at different values of mass flow rates, and at various angles of attack, α=0-10 degrees, to study the inlet buzz phenomenon. For each test, pressure distributions over the inlet cowl and spike were measured and the flow was visualized by means of the shadowgraph system and a high speed camera to obtain main performance characteristics of the... 

The main aim of this study is to propose a new structure of compression surfaces of a supersonic inlet in order to improve target performance parameter i.e. total pressure recovery ratio. This idea resulted in developing a new type of supersonic inlet, utilizing four ramps and a cone as compression surfaces simultaneously.A prototype of this type of inlet has been designed for Mach 3 and its performance has been studied via numerical simulation in design point and off design conditions. Eventually the new inlet compared to experimental performance survey data from two cases of two-cone inlets and also analytical calculations of ideal performance of some types of supersonic inlets. Results of... 

Although a lot of research has been done on Carbon-based interconnect, there are many important questions unanswered. For example, there is no compact model for the resistance of bundle of CNTs at high frequencies, at which interconnects will be operating due to the scaling. Also there are many studies comparing CNT, GNR, and Cu wires but there is no study to show how much this will impact the design of a chip at today’s Giga Scale Integration. This comprehensive study should include chip performance, power dissipation and total number of metal levels. These two big questions are investigated in this dissertation. In the first part, high frequency behavior of CNT bundles is studied. A... 

Polymer/layered silicate nanocomposites are good candidates to improve polymer matrices due to enhanced interfaces between nanoclay reinforcement and matrix. So many attempts has been done to improve fabrication methods of these nanocomposites. Polypropylene is a common used engineering material in many industrial applications (general and special). So there is many researches focused on PP/Clay nanocomposites. In this research we tried to investigate the role of clay loading, compatibilizer loading and processing sequence on clay delamination and layer dispersion. We used a blend of two different PPs with different MFI values as matrice. It seems that the blend achieves acceptable... 

Stress whitening is a type of discoloration that can occur in variety of polymers used in automotive and household industries. The current research tries to investigate the effective microstructural parameters such as strain rate, rubber second phase, and branched polypropylene (PP) on the stress whitening in polypropylene in order to propose toughed PP blends with limited stress whitening. It is shown that increasing the strain rate in tensile test results in formation of more visible whitened area within the plastically deformed zone. This is the consequence of further growth of micro-voids at higher strain rates. The results are in accordance with the Mie scattering concepts. Besides, the... 

The aim of this investigation is the experimental study of nozzle exhaust jet flow effects on aerodynamic behavior of an air vehicle at transonic speeds. For this sake, a secondary jet injection is used by the ejector into test model. The ejector total pressure for jet injection varies between 0 (jet off) to 4 bar for simulating nozzle exhaust jet flow and supplying intake’s required mass flow rate. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85 and angles of -4 to 6 deg. The aerodynamic force and pressure results were recorded in order to analyze the exhaust jet flow. This study revealed that the aerial vehicle drag becomes bigger than its free flight... 

This study aims to evaluate aerodynamic coefficients of an airplane with air breathing engine experimentally. In these experiments, an ejector is used to better simulate flying conditions and aerodynamic interferences generated in inlet and exhaust engine. Therefore, at first, an ejector was designed for simultaneous simulation of exit cold flow and inlet flow of engine. All tests were conducted at QRC Trisonic wind tunnel and at Mach number of 0.5 to 0.85, angles of -4 to 6 deg. and for various amounts of pressure ejector and control surfaces angles. Finally, for the Mach number of 0.5, effect of roughness on the aerodynamic coefficients was examined. The results showed that, drag... 

High-altitude simulation lab of chemical thrusters is one of the most important infrastructures for the development of space thrusters technology. In these laboratories, different sections are designed according to the requirements for simulation of the thrusters at specific pressure and temperature. The purpose of this research is to design a subset of the creation and preservation of vacuum for the purpose of ground testing of chemical thrusters. Vacuum preservation is more comprehensive than the vacuum creation and is usually the bottleneck of design, so the design of this subset is intended in the present study. To illustrate this, after introducing the basic concepts required, two... 

Inlets must decelerate the air with lowest loss and drag together with a given pressure and Mach number with best quality and uniformity to the engine. This is done based on flight Mach number, by an arrangement of shock waves and surfaces gradient in the inlet. Any distortion in the flow field and the inlet geometry parameters may disrupt such arrangement and influence on the inlet performance, in addition, under critical conditions, it might affect the stability of the intakes. Any distortion in the flow field and the inlet geometry parameters may disrupt such arrangement and influence on the inlet performance, in addition, under critical conditions, it might affect the stability of the... 

As an essential laboratory instrument in aerospace engineering, wind tunnels need to be calibrated. Therefore, this thesis takes into account the calibration of the subsonic wind tunnel at the Sharif University of Technology, with the test section dimensions of 90 × 42 × 30 cm3. It is necessary to accurately and correctly determine the effective parameters for the wind tunnel results to be reliable. A pitot-static tube, a standard wing, pressure sensors, a force balance, a turbulence sphere, rake, yawhead, a digital level, a protractor, and a data acquisition system were used for this experiment. For calibration, variables including flow uniformity, flow Angularity, turbulence intensity,... 

In this thesis a computational method for the design of optimum nozzle contour with consideration for chemical reactions has been presented. This method combines the method of characteristics, CFD and an optimization algorithm to develop a nozzle suitable for a specific operational condition. First using the method of characteristics an isentropic nozzle contour is achieved. then using the FLUENT solver, this initial contour is solved for flow containing finite-rate reactions and boundary layer effects and by iterating this process combined with an optimization algorithm, an optimum nozzle is found. Properties took into consideration in this method, in addition to chemical reaction between... 

Monopropellant thrusters are one of the most common types of propulsion systems that are used extensively in space applications. Especially thrusters with a capacity of less than 50N, they are used on space satellites and are developing rapidly. Problems such as contamination, toxicity of the propellant, difficulty in storing and custody, as well as price, led to the removal of the hydrazine from the focus of attention and focus on green propulsion. One of these, is the green propellant of hydrogen peroxide, which is decomposed in the proper catalytic vicinity, and the only chemical decomposition products are oxygen and water vapour. The present study aims to design and construct mono... 

The characteristics of unsteady flow field around a low-aspect-ratio pitching wing with an airfoil section used in horizontal axis wind turbine are investigated at Reynolds number 2.8×105 and Mach number 0.06. The major objective of this study was to investigate the effects of reduced frequency, oscillating amplitude, mean angle of attack and 3D effects on aerodynamic coefficients. Using aerodynamic coefficients, the unsteady aerodynamics in pre-, near-, and post-static stall regions are analyzed and the results are validated with the corresponding experimental data. The two-dimensional simulation results demonstrate the significant effects of reduced frequency, mean angle of attack and... 

One of the most modern types of inlets in aircraft is the Diverterless supersonic inlet, which is used in some new UAVs and fighters, and has many advantages over other types of inlets, especially in removing the boundary layer. The most important part of DSI design is the creation of bump geometry, which requires special precision and elegance. There are various methods for designing and creating bump geometry, some of which are mentioned in this report, and finally the method of creating bump geometry is selected based on the flow around the primary cone, which is in accordance with the analytical method and is in fact the most basic and widely used method.In this study, a DSI with cowl...