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 performance and the buzz onset of a supersonic mixed-compression axisymmetric intake are experimentally investigated. Effectsof the slot bleed position, angle, and width onthe intake performance and onthe buzz initiation at three different Mach numbers of 1.8, 2.0, and 2.2 and at a zero degree angle of attack are studied. The intake performance is assessed using the total pressure recovery, mass flow ratio, flow distortion, and bleed mass flow ratio. The results show that applying the bleed at a position near the intake entrance and reducing the bleed entrance slant angle and width all improve the intake performance considerably. Moreover, these parameters postpone the buzz onset. In... 

Advanced gas turbine cycles use advanced blade cooling technologies to reach high turbine inlet temperature. Accurate modeling and optimization of these cycles depend on blade cooling model. In this study, different models have been used to simulate gas turbine performance. The first model is the continuous model and the second is stage-by-stage model with alternative methods for calculating coolant, stagnation pressure loss and SPR. Variation of specific heat and enthalpy with temperature are included in both models. The composition of gas stream in turbine is changed step by step due to air cooling. These models are validated by two case study gas turbine results, which show good agreement... 

Gas turbine performances are directly related to site conditions. The use of gas turbines in combined gas-steam power plants, also applied to cogeneration, increases such dependence. In recent years, inlet air cooling systems have been introduced to control air temperature at compressor inlet, resulting in an increase in plant power and efficiency. In this paper, the dependence of outside conditions for a simple gas turbine and a combined cycle plant is studied, using absorption chiller as inlet air cooling system. We used, as case study, a simple plant equipped with one frame E gas turbine and a combined cycle with a two pressure level heat recovery steam generator (HRSG). It was found that... 

A computational fluid dynamics code was developed to compute the flow inside and around a supersonic external compression axisymmetric intake. The code solves the Reynolds-averaged Navier-Stokes equations using an explicit finite volume method in a structured grid and uses the Baldwin-Lomax algebraic model to compute the turbulent viscosity coefficient. Experiments were performed to validate the predicted results and good agreements are achieved. In the next part of the research, a parametric study was undertaken using the designed base case at a constant Mach number of 2 and at 0° angle of attack. The effects of various important parameters such as free stream Mach number, spike deflection... 

This Paper presents simulation of Electroosmotic phenomenon in a capillary using an extended hybrid finite-volume-element method. Most of the last electroosmotic phenomenon studies in microchannels do not take into consideration the effect of reservoirs and pressure drops occurred at the inlet and outlet of the microchannel. This neglect may lead to a few drawbacks. For example, the incorrect pressure drops can significantly alter the flow patterns and mass flow rates in microchannels. As a remedy the use of reservoirs at the two ends of a microchannel has been recently practiced as a novel strategy to overcome this drawback. However, this remedy needs careful attention because the resulting... 

The current article presents conceptual, preliminary and detailed aero-thermal redesign of a typical high pressure turbine nozzle guide vane. Design targets are lower coolant consumption, reduced manufacturing costs and improved durability. These goals are sought by 25% reduction in vane count number and lower number of airfoils per segment. Design challenges such as higher airfoil loading, associate aerodynamic losses and higher thermal loads are discussed. In order to maximize coolant flow reduction and avoid higher aerodynamic losses, airfoil Mach distribution is carefully controlled. There has been an effort to limit design changes so that the proven design features of the original vane... 

In a vortex engine, oxidizer issues tangentially at the end of the chamber, consequently a cool vortex flows toward the head, being mixed with fuel, a secondary vortex of combustible reactants swirls coaxial with the first vortex to the nozzle exit. Therefore radiation heat transfer from flame to the chamber wall causes to increase wall temperature; meanwhile highly convective coolant flow of outer vortex reduces the wall temperature. In this paper the rate of total heat transfer and radiative heat are measured experimentally and convective cooling is calculated as the difference between the above mentioned quantities. The rate of heat transfer to the chamber wall is calculated using... 

Radiation heat transfer as an important phenomenon in combustion applications is an interesting subject for scientists and combustion researchers. Heat release and luminous radiative transfer phenomena in an experimental vortex engine are compared with a similar axial flow type engine. A detector sensitive to emission from C2* excited radically is utilized for the measurement of chemiluminescence emission at the centerline of chamber along all axial positions. The filtered photographs of flame are used to compare total C2* emission from flame. Mixtures of Propane and Butane with air enriched by oxygen are used as fuel and oxidizer. The effects of equivalence ratio and oxidizer mass flow rate... 

The performance characteristics of an axisymmetric inlet at its design and off-design operational conditions are experimentally investigated. The model is tested for wide ranges of free stream Mach numbers, M∞ = 1.5-2.5, and mass flow rates. For each test, the pressure recovery, the mass flow passing through the inlet and the pressure distribution over the spike and the cowl are measured. In addition, the shock wave formed in front of the inlet is visualized. The characteristic curve of the inlet is then obtained for each free stream Mach number. As the Mach number is increased, the pressure recovery is reduced, but the maximum value of the mass flow rate grows up. Variations of the mass... 

A new flow model of high performance light water reactor (HPLWR) is discussed in the present study. HPLWR involves a negative density reactivity coefficient with high time delay. This factor decreases the stability of such reactors when transient and abnormal accidents happen. A new design for enhancing safety and efficiency in such reactors is presented. In the new design, the fluid passing through the moderator channels and the assembly gaps (known as a moderator) flows in channels detached from coolants. It is possible to control the moderator mass flux. Increasing or decreasing the moderator mass flux will modify the moderation capacity, which results in a change in the reactor power.... 

In this paper, a novel method of retrofit design in total site cogeneration systems based on constructal theory is presented. In this regard, the total site cogeneration system is decomposed into three constructs: turbines, turbine arrays, and steam generators. The objective function to be minimised is the total annual cost of existing total site. Using constructal theory simplifies the optimisation procedure of total site in addition to reaching better conceptual design especially in more sophisticated systems. A case study from literatures has been taken up to examine the applicability of the algorithm and excellent agreement has been observed. Copyright  

An optimal performance film cooling implies a high cooling effectiveness along with a wide surface cooling coverage. During the past decades, film cooling effectiveness has been well defined with a specific formula to evaluate the quality of a cooling system. However, despite numerous research on film cooling, there is still no explicit parameter to quantify how well a coolant film is spread over a hot surface. This work introduces a new coefficient namely cooling uniformity coefficient (CUC) to evaluate how well a coolant film is spread over a surface that is being cooled. Four different cases at two blowing ratios of 0.5 and 1.5 are studied. Three cases are ordinary single jets with... 

This paper presents the application of a relatively new technique of fluidic thrust-vectoring (FTV), named Co-flow, for a small gas-turbines. The performance is obtained via experiment and computational fluid dynamics (CFD). The effects of a few selected parameters including the engine throttle setting, the secondary air mass-flow rate and the secondary slot height upon thrust-vectoring performance are provided. Thrust vectoring performance is characterised by the ability of the system to deflect the engine thrust with respect to the delivered secondary air mass-flow rate. The experimental study was conducted under static conditions in an outdoor environment at Cranfield University workshop... 

Advanced gas turbine cycles use advanced blade cooling technologies to reach high turbine inlet temperature. Accurate modeling and optimization of these cycles depend on blade cooling model. In this study, different models have been used to simulate gas turbine performance. The first model is the continuous model and the second is stage-by-stage model with alternative methods for calculating coolant, stagnation pressure loss and SPR. Variation of specific heat and enthalpy with temperature are included in both models. The composition of gas stream in turbine is changed step by step due to air cooling. These models are validated by two case study gas turbine results, which show good agreement... 

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... 

This article investigates the effect of nanoparticles on mass transfer in the liquid–liquid extraction for the chemical system of n-butanol–succinic acid–water. For this purpose, nanofluids containing various concentrations of ZnO, carbon nanotubes (CNT), and TiO2 nanoparticles in water, as base fluid, were prepared. To examine the flow mode effect on mass transfer rate, different fluid modes including dropping and jetting were employed in the process. Results show that mass transfer rate enhancement depends on the kinds and the concentration of nanoparticles and the modes of flow. It was observed that after adding nanoparticles, the mass transfer rate significantly increases up to two-fold...