Aerodynamic characteristics prediction of HAWT blade S809 airfoil using coupled potential theory of wing sections and boundary layers calculation

The industrial development based on the massive use of fossil fuels has led to an ecological imbalance and to a depletion of natural energy resources. This energy and ecological deficit has given the first important start to renewable energy, in particular wind energy. Therefore, many countries have begun their investigation in wind power generators. Also, several National Institutes such as NREL (USA), ECN (Netherlands), and Riso (Denmark) have conducted many studies in this area. Predicting the HAWT blades loads accurately is one of the most important parts of the wind turbine aerodynamics calculation, and is based on an accurate evaluation of the aerodynamic coefficients and of the upstream velocity field. However, these aerodynamic loads estimations remain a complicated task to perform due to the complex nature of the flow around the blades, and to their cyclical fluctuations, which can be a significant source of fatigue and vibration, resulting from the yaw, stall or turbulent conditions where the HAWT operate mostly. The main aim of this paper is to develop a sophisticated numerical procedure that can predict aerodynamic coefficients without using great amounts of computer time. The problem of interest in the first part of the present work is to calculate the air flow around S809 airfoil, the classical assumption of irrotational flow is adopted, the 2-D pressure potential coefficients and the pattern flow calculations, at the surface of the S809 airfoil for any orientation, were made using the potential theory of arbitrary wing sections and Prandtl-Glauert, Karman-Tsien and Laitone's compressiblity corrections. The two-dimensional aerodynamic coefficients were estimate, for the S809 potential-flow wind-turbine airfoil, from the pressure distribution. This paper gives an exact solution of the problem of theoretical flow of a frictionless incompressible fluid past S809 airfoil. A numerical method is presented, aimed at determining the velocity of the 2-dimensional flow for any point at the surface of the S809 airfoil. From this pattern flow, the pressure distribution around the airfoil is obtained thanks to the Bernoulli's relation for any orientation and for any Reynolds number. Comparisons of the computed aerodynamic coefficients has been made with wind tunnel data from the Delft University 1.8m×1.25m low turbulence wind tunnel, from the Ohio State University Aeronautical and Astronautical Research Laboratory 3m×5m subsonic wind tunnel and also from the Colorado state university environmental wind tunnel 3.66m×1m. Aerodynamic coefficients computed from the pressure distribution can not take account of the effects of skin friction, since only the pressure normal to the surface is predicted, Therefore, we found that they differ somewhat from the directly measured aerodynamic coefficients, especially in the case of the drag component, which is mainly due to shearing stresses at the airfoil surface. The aerodynamics problem of interest in the second part of the present work is to estimate the skin-friction drag component of force acting on an airfoil in a uniform viscous stream. The Navier-Stokes equations were reduced, for analyzing the boundary layer flows, to the continuity equation and to the streamwise momentum balance, which could be used to derive the Von Karman momentum integral equation. This last, is resolved according to the flow regime, laminar or turbulent, for estimating the skin-friction drag coefficient. Numerical solutions of the momentum integral equation were found by using the Thwaites' method for the laminar boundary layer, and the Head's method for the turbulent boundary layer. The shape factor was evaluated, for laminar and turbulent regions, by the Cebeci and Bradshow semi-empirical formulas. The turbulent closure method required an additional semi-empirical relationship, in this work, the Ludwieg - Tillmann empirical formula for skin-friction coefficient evaluation is used. The phenomenon of flow transition from laminar to turbulent flow governed by the viscous effects is investigated, the onset of transition was determined by using Cebeci-Smith relation based on the Michel's criterion, and is incorporated into the viscous formulation. And the boundary layer separation point location is determined from the shape factor. The numerical model developed, for estimating aerodynamic characteristics of Horizontal-axis wind turbine blade S809 airfoil, is based on a strong viscous-inviscid interaction technique using the blowing velocity concept which employs both the displacement thickness and the edge velocity distribution. The numerical results have been benchmarked against experiments for different angle of attack and Reynolds numbers, and generally a good agreement is obtained. A complete computer code package for simulation was developed to obtain accurate numerical values in acceptable computational time

Depositional environments, diagenesis and reservoir characteristics of the Permian Khuff Formation in eastern Saudi Arabia.

Imperial Users onl

Conformational study and vibrational spectra of 18-crown-6 and its complexes with some metals

This study is conducted & Submitted in Partial Fulfillment of the Doctor of Philosophy Degree Department of Chemistry - College of Science King Saud University November 2006 G; Shawal 1427 H.The main goal of this thesis is to investigate the structure and the vibrational spectra of free 18-crown-6 (18c6) and its alkali metal cation complexes using accurate and more reliable experimental and theoretical methods than was used in previous studies. This study consists of two parts. The first part is the search of the possible conformations of free 18c6 and its alkali metal cation complexes and some specific conformations of alkaline earth metal cation complexes. The second part is the study of the vibrational spectra of 18c6 and its alkali metal cation complexes. The conformation in which 18c6 and its alkali metal cation complexes exists in is determined through the comparison between the experimental and calculated vibrational spectra. In the first part, an extensive conformational search was performed using the CONFLEX algorithm at the MM3 level, the number of 18c6 predicted conformations was 3136 conformations. The predicted conformations were geometry optimized at different levels of ab initio methods. Excluding the redundant conformations, optimized geometries and energies were calculated at the MP2 correlated level, the number of conformations was reduced to 47 unique energy conformations. The study concluded that the correlated MP2/6-31+G*//HF/6-31+G* level is the lowest reliable level for the accurate prediction of the conformational energy order. At all correlated levels the S6 conformations, was predicted to be more stable than the experimentally known Ci conformation of 18c6. The S6 conformation is calculated to be more stable by 1.84 kcal/mol than the Ci conformation at the MP2/6-31+G* level. It was rationalized that the S6 conformation is the lowest energy conformation of 18c6 since it has the largest number of CH…O interactions. The effect of hydrogen bonding on the relative energy order of certain conformations is not clear, especially in relation to the dihedral angles. For the 18c6 alkali metal cation complexes, optimized geometries were calculated for the 56 lowest energy conformations of the 18c6 at the HF/STO-3G level with the alkali metal cations positioned at the center of the 18c6 ring plane, in addition, at 3 Ǻ above the ring plane. Optimized geometries and energies of the lowest predicted conformations were determined at the correlated levels, MP2/6-31+G*//HF/6- 31+G*, MP2/6-31+G*//B3LYP/6-31+G*. It is concluded that the lowest energy conformation of the 18c6—Li+ complex is the D2 conformation, for the 18c6—Na+ and 18c6—K+ complexes it is the D3d conformation. For the larger metal cation 18c6—Rb+ and 18c6—Cs+ complexes, the C3v conformation is predicted to be the lowest energy conformation, rather than the D3d conformation. This is attributed to the large size of the Rb+ and Cs+ cations compared to the 18c6 ring cavity displacing both cations out of the ring plane producing a C3v conformation. For the 18c6—K+ complex, the metal cation fits well the 18c6 ring cavity and a D3d conformation is produced. For the 18c6—Na+ complex a folded D3d conformation is obtained since the Na+ cation is slightly smaller than the 18c6 ring cavity. For the 18c6—alkaline earth metal cation complexes assuming only the D3d and C3v conformations. At MP2/6-31+G*//B3LYP/6-31+G* level, the 18c6—Mg2+, 18c6— Ca2+ and 18c6—Sr2+ complexes are predicted to adopt the D3d conformation. The larger alkaline earth metal cation the 18c6—Ba2+ and 18c6—Ra2+ complexes are predicted to adopt the C3v conformation. The smaller cations of the alkali and alkaline earth metal cation complexes were found to bind 18c6 more strongly than the larger cations, and the divalent alkaline earth metal cations bind more strongly to 18c6 than alkali metal cations at all levels of calculations. This is attributed to the larger charge on the former than on the later. The second part of the thesis is the experimental and theoretical study of the vibrational spectra of 18c6 and its alkali metal cation complexes. FT-IR and FTRaman spectra were measured for the free 18c6 and its alkali metal cation complexes. Cartesian coordinate force fields were calculated at the corresponding optimized geometries at the B3LYP/6-31+G* for the Ci, S6, C3, D3d and C2 conformations of the free 18c6 and all of the predicted conformations of its alkali metal cation complexes of symmetries higher than the C1 symmetry. A set of scale factors was used to scale the force fields. The experimental vibrational frequencies were assigned to the calculated frequencies and the scale was varied to minimize the difference between the calculated and experimental vibrational frequencies. The assignment of the fundamental vibrational frequencies of 18c6 and its alkali metal cation complexes depend on highly accurately B3LYP force fields. In addition, for the first time to the best of our knowledge, the assignment of the fundamental vibrational frequencies of 18c6 is being performed using the CCl4 and CS2 solution phase. While that of its alkali metal cation complexes of mainly of the methanol solution phase. The experimental and theoretical study of the vibrational spectra indicated that the free 18c6 exists in the Ci conformation. For the 18c6—alkali metal cation complexes, The 18c6—Na+ and K+ complexes exist in the D3d conformation and the 18c6—Rb+ and Cs+ complexes exist in the C3v conformation. These findings are in agreement with the conformational search and with the previous X—ray results. The vibrational spectra of the 18c6—Li+ complex, is different from the other four 18c6—alkali metal cation complexes. It was not possible to predict in which conformation this complex exists in.1. King Abdul Aziz City for Science and Technology (KACST). 2. Research Center, King Saud University

Synthesis of Propylene Carbonate from Epoxide and CO 2

Carbon nanotubes (CNTs) were functionalized and were then used as supports of Fe1.5PMo12O40 (FePMo) Keggin heteropolyanions catalysts. The characterization of the resulting catalysts was investigated by inductively coupled plasma spectrometry (ICP), Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) light spectroscopy, and transmission electron microscopy (TEM). FTIR and XRD results confirmed that FePMo was bounded on CNTs successfully and the Keggin structure was preserved. Characterization by TEM showed that solids with high FePMo content exhibited aggregation of FePMo in large particles. The as-prepared catalysts were tested in the synthesis of propylene carbonate (PC) from CO2 and propylene oxide (PO) in a solvent-free reaction and under mild conditions. Effects of various parameters, such as reaction temperature, reaction time, FePMo content on the support, and catalyst loading on the reaction, were investigated. It has been found that CNTs supported FePMo achieved 57.7% PO conversion and 99.0% PC selectivity, whereas unsupported FePMo led only to 8.5% conversion and 48.6% selectivity. The remarkable enhancement of the catalytic activity over the supported catalyst can be attributed mainly to the better dispersion and reactivity of the FePMo catalyst in the supported material

Analyses of reaction rate data for the simple hydrolysis of acetic anhydride in the acetonitrile/water and acetone/water cosolvent systems using recently developed thermodynamic rate equations

This article presents reaction rate data for the simple hydrolysis of acetic anhydride in the acetonitrile/water and acetone/water cosolvent systems and regression analyses using recently developed thermodynamic rate equations that contain electrostatic and solvent-solute terms. The isomole fraction plots for these reaction systems are linear, and previous theoretical work has shown that the electrostatic term is negligible for such systems. On the other hand, the reaction rates are dependent upon the cosolvent mole fraction, indicating that the solvent-solute term, which is modeled empirically, is significant. The results of the analyses provide the foundation for a paradigm shift away from the emphasis on electrostatic effects to more tenable explanations of kinetic behavior in solvent systems