Sharif Digital Repository

Unsymmetrical Dimethyl hydrazine (UDMH) is used as stabilizer, fuel promoter, chemical in photography, and liquid fuel for fighter jet engines. Catalytic liquid phase hydrogenation of nitrosodimethylamine (NDMA) is one of the most efficient methods for the production of UDMH. Hydrogenation of NDMA to UDMH using a commercial 5% Pd/C catalyst in aqueous solution of NDMA was studied under constant temperature at 40°-70°C, ≤ 15 bar, and NDMA concentrations of 40-70 wt %. The effects of temperature, pressure, and NDMA concentration on NDMA conversion and yield of UDMH product in presence of undesired Dimethylamine (DMA) were studied. At NDMA concentration of > 50 wt %, the UDMH yield was < 0.89,... 

We use a third-order perturbation theory and Melnikov's method to prove the existence of chaos in spinning circular disks subject to a lateral point load. We show that the emergence of transverse homoclinic and heteroclinic points lead, respectively, to a random reversal in the traveling direction of circumferential waves and a random phase shift of magnitude π for both forward and backward wave components. These long-term phenomena occur in imperfect low-speed disks sufficiently far from fundamental resonances. © 2007 American Institute of Physics  

The manufacturing process of a directionally solidified (DS) IN738LC turbine blade, produced with the liquid metal cooling (LMC) process was improved based on process modelling. The improvement involved varying the system dimensions in the baffle area and optimising the mould thickness, design and the withdrawal parameters. The grain structure of the DS blades produced exhibits a well defined <001> texture with a few stray grains near the blade top compared to the previous design. Some blades were given to a two stage heat treatment followed by tension tests at 25 and 650°C as well as creep tests at 152 MPa/982°C and 340 MPa/850°C. The yield and tensile strength of improved DS blades were... 

A series of low speed wind tunnel tests on a section of a 660 Kw wind turbine blade which is under constructer were conducted to examine the effects of distributed surface contamination on its performance characteristics. At first model was tested in the clean condition and after that it was tested with tree different types of roughness. The data shows that this particular airfoil is very sensitive to the applied surface roughness. For the contaminated model the roughness, 0.5mm height was distributed over the entire upper surface of the airfoil such that the distribution pattern was denser in the vicinity of the leading edge and thinner in the trailing edge area. Statistical data show that... 

An extensive experimental study is conducted to investigate the effects of reduced frequency on a harmonically pitching wing where its cross section is used in a 660 kW wind turbine under construction in Iran. The corresponding lift coefficient and real time pressure signatures at three sections of the model at various reduced frequencies are examined. The test covers a wide range of angles of attack at prestall, stall, and deep stall regions. Pressure distributions at tip, middle, and root sections of the wing were recorded and from these distributions the lift coefficients are computed. The results show great role of the reduced frequency in altering the maximum lift coefficients, lift... 

This paper presents a state of the art design for the blade tip injection. The design includes the means, to inject high-pressure gas jet directly into a circumferential casing groove formed in the shroud adjacent to the blade tip. The casing groove is positioned over the blade tip and exceeds 30% of the blade axial chord beyond the impeller to both upstream and downstream directions. In order to validate the multi block model used in the tip gap region, main flow characteristics are verified with the experimental data for smooth casing with a design clearance of 0.5% span. Three arbitrary mass flow rates (1.75%, 2.45%, and 4.35% of choked mass flow) have been studied. The results indicate... 

A series of low speed wind tunnel tests on a section of a 660 Kw wind turbine blade were conducted to examine the effects of distributed surface contamination on its performance. The airfoil was a section of a wind turbine blade under construction. The performance of the section was measured in the following conditions: 1. Clean airfoil 2. Two types of zigzag roughness 3. Strip tape 4. Distributed contamination roughness Our preliminary data shows that the airfoil is very sensitive to the applied surface roughness. For the contamination model the roughness, 0.5mm height, is distributed over the entire upper surface of the airfoil. By putting the contamination roughness on the airfoil the... 

Over the recent decades, many different ducted turbines have been designed to augment efficiency of wind turbines. The design and number of blades are the most important parameters to optimize efficiency of wind turbines. In this paper, effects of design, number and attack angles of blades on rotational speed are experimentally studied in a duct which increases wind velocity up to 2.46 times numerically and 2.32 times experimentally as great as far-field flow. In order to realize this, 3 different types of aerodynamic blades were designed and then, 2-bladed, 3-bladed and 4-bladed impellers were created by these blades; finally, 9 impellers were built on aggregate. The rotational speed of... 

The study deals with the design and optimization of external and internal geometry of micro-wind turbines blades. A specified objective function which consists of the power coefficient and the starting time was defined and the genetic algorithm optimization technique in conjunction with the blade-element momentum theory was adopted to find the geometry of the blades including the distributions of the chord, the twist angle and also the shell thickness. Moreover, the allowable stress of the blades was considered as a constraint to the objective function. Results show that a reasonable compromise is achievable such that the starting time of the blades reduces noticeably in return for a small... 

In this paper, the effect of blade number on the vibration behavior of industrial fans has been studied experimentally and numerically. Two similar industrial fans with similar specifications and only different blade numbers were chosen in a plant. The vibration levels were measured on these fans and the results revealed that the blade passage phenomenon is the main cause of vibrations on both fans. Both fans and their structures were modeled numerically and the performance characteristics, vibratory forces and vibration response of structure were calculated. The results showed that the number of blade has small effect on vibratory forces compared to the performance characteristics. The... 

A series of tests were carried out to study the unsteady wake behaviour behind an aerofoil which is a section of a wind-turbine blade. The model is oscillated in pitch about its quarter chord axis at various reduced frequencies, amplitudes, and mean angles-of-attack. Instantaneous and mean velocity profiles were obtained using total and static pressure at 35 vertically aligned points behind the aerofoil via two similar rakes. The rakes were located at a distance of 1.5 chord length behind the model. An estimation of the real time and average variations of the linear momentum deficit during the oscillation cycle is obtained and has been compared with the corresponding static data. The results... 

Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are... 

Jet into crossflow has numerous technological applications, such as in film cooling of gas turbine blades. It has been more than half a century that people have been studying this problem and research is still underway due to its importance and its complexities. This paper is a computational study concerned with film cooling of gas turbine blades. A novel near-wall flow control technique of using staggered arrangement of small injection ports near a film-cooling hole (combined triple jet) is introduced. The fluid injected from the small ports changes the flow pattern downstream, resulting in a considerable enhancement of cooling efficiency. The flowfield computations, governed by the... 

Extensive wind tunnel tests have been conducted to investigate effects of turbulence intensity variations on the behavior of a section of a wind turbine blade in an oscillatory motion. Special emphasize was applied on the aerodynamic characteristics when oscillating the model in the vicinity of its static stall angle of attack and in the post stall condition. The model had 0.25m chord and was pitched about its quarter-chord. Data were acquired at various Reynolds number, and reduced frequency. Results show that turbulent intensity has strong effect on the unsteady load coefficients, hence aerodynamic performance of this model. Furthermore, free stream turbulence has different effect on the... 

Improvements in sealing mechanism between the rotating and the stationary parts of a rurbomachine can extensively reduce the endwall leakage flow. In this regard, abradable seals are incorporated into compressor and turbine blade-tip region. In a gas turbine, equipped with abradable seals, tip of the rotor blade is designed to cut into the material coating of the casing and to form a close fitted circumferential groove for the movement of the blade tip. As a result, the resistance to the leakage flow in the tip gap region increases due to smaller tip clearances (available without any rub-induced damages). Minimizing the tip clearance size can lead to an increase in performance and stability....