Sharif Digital Repository

A Specific process centrifugal compressor is upgraded. The operating range and efficiency pattern are increased. A one-dimensional performance prognosis tool (CCPP) is developed. The tool uses mean streamline method as the analysis model. Since the working media has various components, a complete equation of state is utilized to model the thermodynamic behavior of the real gas in super critical pressures. The performance of the base-line compressor is deyermined. The performance prognosis tool is validated with available experimental data. Upgrade road map and methodology were introduced in accordance to domestic requirements. The performance of the upgraded compressor is investigated and... 

The aim of this work is to design, build and test a laboratory scale flameless combustion chamber. Also, a theoretical model is developed to simulate flameless combustion with a simple model. Flameless combustion is a combustion type with transparent flame which consumes less fuel than typical premix and diffusion flames and emits very low level of NOx. In flameless combustion, recirculation ratio is higher than typical diffusion flames so the flow field is highly turbulent. High recirculation ratio causes low oxygen concentration in combustion zone; thus requiring inlet air to be preheated for flame stabilization at low equivalence ratio and oxygen concentration. We have designed a... 

With everyday increasing application of gas turbine in different industries, fast and accurate tools for design, analysis and performance estimation of gas turbines have found many proponent; Compressors, as one of the most important parts of gas turbines, are no exception to this ordinance. Although development of Computational Fluid Dynamics (CFD) method was a great aid to improve the accuracy of this tools, complexity and being time consume make them uncommon and unpopular during preliminary design and analysis process. So it could be imply that simple analysis methods, such as 1D, 2D and quasi-3D, are not only not abandoned, but also very practical and most applied in preliminary design,... 

The fundamental goal of communication networks is to transfer messages across the network between the nodes. Often, maximizing the information flow which is limited by connectivity of the network could be interesting. The concept of connectivity is divided into edge and vertex connectivity. If our focus were on the vertex-connectivity, connected dominating sets (CDS) could be a valuable tool. Obtaining (fractionally) vertex-disjoint connected dominating sets which are called fractional CDS packing presents a backbone to get an information flow matching the size of connectivity. In this thesis, we will present a distributed algorithm that is given a communication network with n nodes and... 

In general, separation of gas mixtures is grouped in three different methods: adsorption and dissolve methods, membranes and filter methods, and cryogenic methods. One of the most novel and efficient techniques in the latter method, is the supersonic separation where all the expansion, liquefaction, and separation processes are performed within a converging-diverging nozzle with no complex or moving part. This research is focused on methane purification. A one-dimensional model is developed for design and performance analysis of supersonic separators incorporating real gas model, variable specific heat, condensation, and swirling flow. Further, an axisymmetric numerical simulation of the... 

Swept wings are of great interest for achieving high speed as well as increasing the critical Mach number in aircrafts and unmanned flying vehicles. The governing fluid mechanical phenomenon on swept wings is strongly influenced by the chordwise and spanwise components of the cross-flow. Laminar airfoils are employed for drag reduction and postponing the boundary layer transition from laminar to turbulence. Hence, the knowledge about the boundary layer structure and instability modes is of great significance. A series of wind tunnel tests are performed to examine the flow field over a swept wing at various conditions. The wing has a laminar flow airfoil section similar to NACA 6-series ones.... 

The delta wing has proven to be very useful for the study and understanding of the basic features of separation-induced vortex flows since many aspects of these vortex flows can be generated with this simple shape. A phenomenon of special importance to vortical flows is vortex breakdown. Vortex breakdown remains an important and complicated phenomenon that can have negative or positive effects. The delta wing leading edge vortex is emphases in many experiments. Most of these experiments are focused on the delta wing only.In this research, emphasis is on vortex interaction of delta wing-canard-fuselage configuration. A series of low speed wind tunnel tests were carried out to investigate... 

Complex Networks are everywhere, many complex systems can be represented as networks, such as the power grid, the road network, the airline network and the Protein-protein interaction network, delivery and distribution networks, and telephone networks. A fundamental issue concerning complex networks is the robustness of the overall system to the failure of its constituent parts. The robustness of networks against failure, targeted attacks to individuals’ components, and the impact on the performance of the system has become an important issue for practical reasons in the last few years. The failures attacks or errors on networks are not limited to the deletion of vertex, for common... 

Supersonic impinging jets, similar to the jet flows exhausted from a nozzle, generate high unsteady pressure and acoustic loads on the rocket payload or the VTOL aircraft structure with possible mission failure during the launch/starting phase. In the past, experimental studies were concentrated on characterizing the steady impingement flow and not the initial transient process. It was shown that one of the main characteristics of supersonic impinging jets is the dominance of the feedback loop mechanism. The present investigation is an attempt to examine the flow characteristics of a high temperature supersonic impinging jet through a convergent-divergent nozzle during the transient starting... 

Environmental heterogeneity, or environmental interactions in evolutionary graphs can drastically change the population dynamics compared to the uniform environment. Such heterogeneity can be imposed in different ways. In this study we choose periodic pattern for the environmental heterogeneity with different values for amplitude and period. Imposing periodic heterogeneity on cyclic graphs, we studied the fixation probability and time. We use birth-death Moran model as the update rule. We observe that with such heterogeneity, an advantageous type in the uniform environment can turn into deleterious in the presence of heterogeneity. Also, the opposite way can happen. The results show that... 

Natural selection in structured populations is considered a crucial subject in evolutionary and population genetics. There is no explicit relationship between discrete-time stochastic models such as the Moran process and continuous-time models such as the Fisher-Kolmogorov equation. However, under specific conditions and within the limits of natural selection and weak selection, a connection can be found between these two models. To gain a better understanding of the specific relationship between these two models, we obtain partial differential equations for the spatiotemporal dynamics of natural selection by extending the birthdeath and death-birth processes of the Moran process to a... 

Laminar-to-turbulent transition is very important concept in fluid dynamics due to its significant role on skin friction drag and heat transfer. It is more important in the fluid-based systems such as wind turbines. Employing computational fluid dynamics is still not efficient on prediction of flow transition, especially in complex problems such as oscillating airfoils. In one hand, flow transition models are not still suitable for general engineering flows such as oscillating airfoils. On other hand, due to the lack of experimental data, the existing flow solvers have not proven in the accurate simulation of the flow field simulation for complex problems such as oscillating airfoils. This... 

The impact of a method on the turbulence reduction in wind tunnels was evaluated. In this method, by installation of trip strip in the contraction, the unsteady behaviors of flow have controlled, consequently the turbulence intensity and possibility of separations were decreased. Location and diameter of trips were very important in this method. Various sizes of trip strip were installed at different locations in the contraction section of four different wind tunnels to study the most significant aspects of the method. Hot wire anemometry system, 1-D and 2-D probes, were used for turbulence measurement and a new method for direct calibration of a 2-D hot-wire probe was introduced. The new... 

Performance of a multi tube pulse detonation engine has been investigated experimentally. A pulse detonation engine uses detonation phenomena and simply consists of a large narrow tube which has closed head, and has feeding system and ignition system. In this tube, detonation is produced periodically to generate thrust. In multi-tube mode, several tubes are arranged in parallel which detonate sequentially. Our PDE consists of 2 tubes with 70 cm length and 25 mm inner diameter which have several places performed for high speed pressure sensors installation. The premixed hydrogen-oxygen mixture are controlled by solenoid valve and injected on head-end and ignited by conventional spark plug.... 

Control surfaces are used in combat aircrafts to control the pitching moment and to help the aircraft perform high angle of attack manoeuvres. For delta wing configuration, the flow characteristics around the horizontal tail depend on the wing and tail flow field and their interactions. The flow over delta wing is mainly characterised by strong vortices. These vortices move downstream and affect the tail flow field making the problem more complicated. The goal of this research is to study the effect of tail up wash on the horizontal wing-body- tail configurations in subsonic flow. For this purpose a series of wind tunnel tests were conducted on a model containing a moveable horizontal tail... 

Measurements of magnitude and direction of thrust generated by a propulsion engine is important for verification of design, fabrication, assembely and or repare procedure used for a engine. Due to possible simplification in design calculations, human and machine errors in manufacturing process, the resulted thrust generated may be different from those values expected. Also, It is important to determine the dependency of magnitude and direction of thrust forces relative to tolerances and manufacturing processes. It is necessary to have thrust measuring stand with high accuracy with capability to measure the forces in different directions. A new digital engine test stand has been designed,... 

Network methods have had profound influence in many domains and fields in the past decade. Community structure is a very important property of complex networks, but the precise definition of a community remains an unresolved problem and Community detection in complex networks has recently attracted wide attention in several research areas such as social networks, communication networks, and biological systems. Complex network studies grow by the scientific community, thanks to the increasing accessibility of real-world network data. The emphasis of use analysis on the network algorithms and community structure is one of the most important problems in the field of complex network. Many... 

Fire is one of the most important events in nuclear power plants which has a large share of total core damage frequency. For example, the core damage frequency in Bushehr nuclear power plant from fire accidents is 6.1E-6/ year which is equivalent to about 63 percent of core damage frequency from all internal accidents. However, due to the unavoidable presence of flammable materials, e.g. Electrical equipment, cables, gas, flammable liquids, …), it is impossible to prevent fires in these plants . Fire at nuclear power plants may be caused directly or indirectly by one or more initiating events, which the following accidents in turn would threaten the safety of the plant. In this project,... 

Thermoacoustics deals with the conversion of heat energy into sound energy and vice versa. This new and emerging technology has a strong potential towards the development of sustainable and renewable energy systems by utilizing waste heat or solar energy. Although thermoacoustic devices are simple to fabricate; however, the design process is very challenging. The thermoacoustic phenomenon is discovered over a century ago; nevertheless, the rapid advancement in this field occurred during the past three decades when the theoretical understanding of the phenomenon is developed along with the prototype devices. There are several advantages of heat engines and refrigerators based on... 

In this thesis, flow-through (or open cycle), standing wave thermoacoustic refrigerator is investigated. The system has the characteristics that the working fluid travels through the system in an oscillatory mode with a mean flow. This type of thermoacoustic refrigerator enables the working fluid to reach the desired cold temperature without passing through the usually required cold heat exchanger. Consequently, the cold heat exchanger subsystem becomes redundant and the entire system becomes less complex and lower in fabrication costs. In this research, while the hot and cold temperatures are fixed, a parametric study is performed to determine the alteration in performance due to the...