Sharif Digital Repository

The performance of an axisymmetric supersonic mixed-compression air intake has been investigated experimentally. The intake has been designed for free stream Mach number of 2.0. This study has two main goals, firstly to investigate the performance of the intake without boundary-layer bleed in design and off-design conditions and secondly to study the effects of a slot bleed on the intake performance. The intake has been tested at free stream Mach numbers of 1.8, 2.0, and 2.2 and zero degree angle of attack. Total pressure recovery (TPR), mass flow ratio (MFR) and flow distortion (FD) have been selected parameters to assess the intake performance. The bleed slot is located upstream of the... 

The starting behavior of a supersonic axisymmetric mixed compression air intake was numerically investigated. The code solves Reynolds-Averaged Navier-Stokes equations using an explicit finite volume method in a structured grid by the Roe flux difference splitting scheme. Further, it uses the Baldwin-Lomax algebraic model to compute the turbulent viscosity coefficient. The correct method of surveying the intake starting problem and effects of several geometrical parameters such as: intake throat area, cowl lip roundness and spike surface curvature upstream of the throat on the starting and performance of the intake were studied. Results showed that correct combinations of the mentioned... 

The performance of a supersonic mixed compression air intake has been investigated experimentally. The intake is of axisymmetric one and has been designed for a free stream Mach number of 2.0. The present work has two main goals, first to investigate the performance of the intake without boundary layer bleed at design and at off-design conditions and second to study the effects of a bleed slot on the intake performance. The intake has been tested at free stream Mach numbers of 1.8, 2.0, and 2.2 and at zero degrees angle of attack. Total pressure recovery, mass flow ratio, and flow distortion have been selected to assess the intake performance. The bleed slot is located upstream of the intake... 

Buzz phenomenon is shock oscillation ahead of the supersonic air intake when its mass flow rate is decreasing at offdesign condition. The buzz onset and the buzz cycle of an axisymmetric mixed-compression supersonic intake have been experimentally investigated through pressure recording and shadowgraph flow visualization. The intake was designed for a freestream Mach number of 2.0; however, tests were conducted for M∞ = 1.8, 2.0, and 2.2. All tests were performed at 0 deg angle of attack. Results show that there is a strong relation between the acoustic characteristics of the intake and the buzz fluctuations. This relation causes a new pattern for the buzz oscillations, large-amplitude... 

Numerical analysis has been conducted to simulate and capture Buzz phenomenon in a supersonic mixed compression air intake. Buzz is an unsteady self-sustained phenomenon occurred in supersonic intakes, especially when operating its subcritical condition, during which the system of compression and shock waves oscillate and move upstream and downstream along the intake. An axisymmetric and unsteady numerical simulation was used to solve Navier-Stokes equations in combination with URANS SST k-ω turbulence model The simulations were performed at M=2.0 and at a specific subcritical point of the intake operation where buzz was detected experimentally. Results are compared with experimental... 

The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods... 

The paper summarizes recent developments in boundary layer suction for high-speed air intakes. Bleed has been efficiently used in supersonic and hypersonic intakes for three primary reasons: to improve the performance of the intake, to reduce the starting Mach number of the intake, and to postpone the onset of buzz oscillations. A bleed system has many characteristics such as the bleed entrance and exit areas, bleed entrance slant angle and position, and bleed type (slot or porous and ram-scoop or flush). Each of these parameters has significant impacts on the intake performance and stability that have been reviewed in this study. In addition, the effectiveness of other flow control methods... 

Gas turbine has broad applications in variety of industries. The developing gas turbine efficiency is of great engineering concern. This appeals to more precise modeling as somewhat inevitable. Modeling plays a decisive and essential role not only in all design phases, but also in development and manufacturing process to investigate performance of an engine. In this research, components of a gas turbine including air intake, axial and centrifugal compressors, combustion chamber and axial turbine are investigated. A novel dimensionless modeling approach is introduced and then, the engine performance parameters are predicted. Setting up a systematic series of experiments on the existing engine... 

Homogeneous charge compression ignition engines require a smart control system to regulate the input quantities of the engine in various operational conditions. Achieving an optimum combustion needs an appropriate system response for different engine loads and speeds according to the power acquired from the engine, as well as the amounts of emissions present in the exhaust. Therefore, performing a set of experimental tests together with numerical simulations in a wide range of conditions facilitates calibration of the input parameters of the engine. In this study, the effects of the thermodynamic parameters and the thermokinetic parameters on the engine output in the preliminary design stage... 

In this work, a double-high swirl gas turbine model combustor (GTMC) has been experimentally investigated to identify the effects of air partitioning and swirlers geometry on combustion characteristics in terms of flame stability, exhaust gas temperature, NOx generation, and combustion efficiency. This high swirl model combustor is originally developed in the German Aerospace Center (DLR) and known as GTMC and recently reconstructed at Sharif University's Combustion Laboratory (named as SGTMC). Here, SGTMC run for liquefied petroleum gas (LPG) fuel and air oxidizer at room temperature and atmospheric pressure. Eleven different burner geometries, M1-M11, are considered for the aims of this... 

Knowledge of Air-water two phase flows is significant to different engineering systems such as chemical reactors and power plant and petrochemical and petroleum industry. One of the most industrial cases of two phase flow is two phase flow in vertical large pipes. In this paper in order to find two phase flow behavior along vertical large diameter pipes we simulate air inlets with different number of holes and different hole diameters in the same flow rate of air. In addition, flow characteristics such as cross-sectional void fraction and velocity and pressure were considered. To achieve this aim, main equations of flow have been developed for investigation of flow behavior in air-water two... 

The study of air-water, two-phase flows in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions, and similar conduits is of great importance for design purposes. Air can be provided by vortices at water intakes, pumping stations, aerators, steep channels, etc. Under certain conditions, air may also be introduced into pressurized intake systems, which may form large bubbles in portions of the pipe. The bubbles may, in turn, cause an unstable slug flow, or other flow patterns, that leads to sever periodic transient pressure. In this paper, an experimental model (a circular and transparent pipeline, 90 mm in ID and 10 m in length) is used to predict pressure... 

Compartment noise has gained significant importance to meet customer expectation. One of the dominant sources of noise from whole engine as a system is the one which is induced from fresh air intake. Geometrical features in air induction systems (AIS) airflow path are often responsible for unusual noise due to the complex air flow structure and its interaction with the internal acoustic field. To reduce air intake noise basically resonator and expansion chamber are used on automotive vehicles. Resonators are widely used for noise reduction of air induction systems. Although, airflow bench tests are faster to evaluate various alternate design geometries, understanding the mechanism of such... 

One of the sources of disturbance at intakes is the occurrence of free-surface vortices with an air core. The most common solution for avoiding air-entrainment is the use of anti-vortex devices and, especially, plates for large pipe or shaft intakes. If plates are used, then, the geometry and position of them should be studied experimentally. Since only general guidance for use of plates is available, a study for the more precise placement of plates is needed. Hence, a comprehensive set of experiments have been carried out using rectangular plates with different dimensions and at various positions with respect to the vertical outlet pipe intakes and two different pipe diameters (D = 75 and... 

A new experimental facility was designed, fabricated and tested to model and study the possibility of applying the bidirectional swirl flow on the combustion chamber of airbreathing subsonic ramjet engine. Appropriate intake was designed to convert axial external air to tangential swirl flow inside the combustion chamber. Inlets with appropriate angles conduct the swirl flow into the chamber and create bidirectional swirl flow field in the combustion chamber. This flow field has been modeled theoretically to determine the velocity field characteristics by previous researchers. Bidirectional swirl flow in liquid fuel ramjet engines has the proven advantage of keeping the combustion chamber... 

The S-shaped air intakes are very common shapes due to their ease in the engine-body integration or Radar Cross Section, RCS, specifications especially for fighter aircrafts. The numerical shape optimization of an S-shaped air intake using adjoint method is conducted. The flow of a specified air intake that uses S-duct M2129 is simulated using three dimensional (3D) numerical solution of Reynolds-Averaged Navier-Stokes equation along with k-ω SST turbulence model. The main purpose of this optimization scheme is to maximize the total pressure recovery (TPR). Further, the scheme is developed in such a way that would be applicable in industry thru satisfying specified constraint requirements....