Journal of Aerospace Mechanics
Year:2013 | Volume:9 | Issue:1 (31) (HEAT TRANSFER AND PROPULSION)|Papers Count:9

In this paper, the effects of engine operating parameters on knock occurrence crank angle, knock-limited operating conditions and also octane requirement for knock prevention were studied. To predict knock occurrence crank angle and knock intensity, an experimentally based Knock Integral Method is optimized according to experimental results and is incorporated with the qausi-dimensional thermodynamic model. Comparison of the results of this study and experimental results indicates that the model is able to predict the knock-limited operating conditions with minimum error in magnitudes (1.7o). As shown in previous works and literature an increase in the octane number of the fuel allows approximately an equal increase in the spark advance. The effects of intake air temperature and pressure, air/fuel ratio and compression ratio on octane requirement were studied and a good agreement with the literature is observed. The results of this study show that the knock occurence can be predicted by the numerical method via experimental ones, which are very expensive.

Heat recovery steam generator (HRSG) is a major component of combined cycle power plant. This component is often subject to gas turbine exhaust temperature and mass flow rate variation. If the power plant works on the island mode, this variation will be more and special attention is needed. In this paper, we predict the island mode operation of HRSG. At first, thermal modeling is done and a code to predict the transient behavior of the HRSG is generated. Then HRSG’s performance with regard to changes in GT’s load will be investigated. We use different strategies for gas turbine load reduction and compare HRSG’s performance. To ensure the correct performance of developed code, the steady-state numerical output of the model will be checked with the output of THERMOFLOW software.

this paper presents a two-dimensional numerical analysis of an evaporative drying process of the porous bodies in a row, considering effects of configuration on heat and mass transfer in assembly. Drying process simulation of three rectangular porous material subject to forced convection, was carried out by employing N-S, energy and concentration equations for external air flow; along with moisture conservation and energy equations for the porous zone. Numerical predictions indicate that the first porous body encountered with flow dries faster in comparison to the others, while for next bodies average moisture contents are approximately equal in all the drying time. Moreover, it was observed that for the first body, both of top surface and opposite surface to the flow direction have equal importance in heat and mass transfer; while top surface of next bodies, have major role in drying process. Also moisture and temperature profiles of the first body have shown essential difference with the other objects. It can be concluded that no significant change in heat and mass transfer and drying rate will be achieved through the change in distance between porous bodies.

In this paper, heat transfer and entropy analysis are carried out for Couette Poiseuille flow between two parallel plates containing porous media, considering the viscous effect and constant heat flux at the walls. The considered flow is with a temperature jump and slip. The momentum and energy equations are solved analytically. The solution was performed at three situations of channel upper plate movement (V-=0, V-=1, V-=-1). Explicit expressions are obtained for velocity and temperature distributions and Nusselt number has been calculated through numerical integration. The results show that, as the Brinkman number increases and Knudsen number decreases the Nusselt number increases. However, the upper plate situation is a determinant factor in establishing the effect of porous media shape parameter on the Nusselt number. It was observed that, as the ratio (Br/W) and the porous media shape parameter increase the entropy generation increases. In addition, decreasing (Br/W) and increasing S results in an increase of Be number. Moreover, with increasing Kn number, the non-dimensional entropy generation number decreases and Be number increases.

In the present study, the turbulent convective heat transfer and pressure drop characteristic of alumina (Al2O3) nanoparticle dispersions in water is studied experimentally in a horizontal tube. The boundary condition imposed on the tube wall is that of uniform heat flux. Ten temperature sensors are also used to measure the surface temperature. One differential pressure transmitter (DPT) is employed to measure the differential pressure between inlet and outlet of the tube. A flow loop facility is constructed to conduct the experiments. To do this, Al2O3 nanoparticles of 40 nm size are characterized and dispersed in distilled water to form stable suspension containing 1.0%, 1.5% and 2.0% by volume concentrations of nanofluids. Results indicate that heat transfer coefficients increase with nanofluid volume concentration. The enhancement of the Nusselt number is about 22% at Re=13500 using 2% alumina nanoparticles compared to distilled water. The experimental data are also compared to predictions made by using the traditional single-phase convective heat transfer pressure drop in turbulent regime. The measured pressure loss when using nanofluids is almost equal to that of the base fluid.

In this paper, an investigation to understand the effects of geometry variability of blades including maximum thickness and blade surface roughness on the axial transonic compressor performance parameters including efficiency and pressure ratio has been studied. A CFD code, which solves the Reynolds-averaged Navier-Stokes (RANS) equations, was used to simulate the complicated 3D flow field of the axial compressor. The code was validated against experimental data of the axial compressor. Numerical data showed good agreement with experimental data. Then, the effects of geometry variability on the axial compressor blade performance curves, was analysed. Results show that increasing surface roughness and blade thickness lead to decrease in the compressor efficiency, pressure ratio and mass flow significantly.

In this paper, forced convective flow and heat transfer between two parallel plates which partially filled with a porous medium are investigated numerically using the lattice Boltzmann method (LBM). In addition, porous medium is constructed by adiabatic square obstacles with regular arrangement in the computational domain. The effect of varying Reynolds number on the velocity and temperature profiles, and also the Nusselt number are studied. In this simulation velocity and temperature field are calculated using density and temperature distribution functions simultaneity. The flow pattern and temperature distribution in the porous medium are also shown at different Reynolds number. The results show that the average Nusselt number is increased by insertion of some fixed blocks in the channel. The obtained results, in some simplified cases, are compared with analytical solution.

In this work, three-dimensional turbulent forced convection flow through a flattened pipe, partially and completely filled with a porous material, was investigated numerically. Here, the effects of permeability and thickness of the porous layer on the rate of heat transfer and pressure drop were investigated. For this purpose, porous material was inserted in two geometrical arrangements: central and boundary. Also, the pipe had constant-temperature condition. The results for central arrangement show that the rate of heat transfer first increases and then decreases with increasing the thickness of the porous layer, while the pressure drop is monotonically increasing. While for the porous medium boundary arrangement, the rate of heat transfer first decreases and then increases with increasing the thickness of the porous layer. Also the maximum of Nusselt number is occurred for the fully porous pipe configuration.