Water injection into a high speed air flow has been recently investigated by many scientists and is still an important field of research in gas turbine technology. To study the behavior of droplets in gas turbines, expensive experimental tests and their validation with analytical and Computational Fluid Dynamics (CFD) models are necessary. The Euler-Lagrange approach can be used to tackle these problems due to their capability in tracking particles along the domain, relative ease in formulating and applying them to the current industrial problems in terms of acceptable computational cost. However, providing spray boundary conditions using Euler-Lagrange approach is quite challenging because the spray pattern depends upon various parameters like spray angle, velocity, diameter distribution etc. In this paper, to obtain these parameters, two different approaches are described. The first approach depends on an analytical model for velocity and spray angle injection conditions and the second approach depends on an Euler free surface simulation. For diameter distribution, Rosin Rammler distribution function and experimental data are used. When combined together these lead to four particle injection conditions. The results achieved from all the four cases are compared with the experimental data of water droplet evaporation in a high speed air flow obtained from a hot air test rig operating at conditions of real gas turbines.

In aeroengine, an s-shaped annular duct is used to connect the high pressure compressor spool to the upstream low pressure compressor. The intermediate casing duct is required because the compressors are designed with different mean radii. Shortening the length of intermediate casing duct is of important significance for improving the performance of aeroengines. Meanwhile, the struts guiding the flow are installed in the intermediate duct, the inlet flow of the duct is not even, and outlet flow requires sufficient uniformity to ensure good working conditions for the high pressure compressor. So the design and optimization of flow path of intermediate casing duct including struts have very important practical significance. This study builds up a system of numerical optimization 3D model based on genetic algorithm and Kriging agent model on the Matlab platform, which automatically couples pre-processing, solver and post-processing of Numeca CFD software. This tool optimizes the intermediate casing duct including struts and a best flow path profile is obtained under the given constrained conditions. The optimization method is validated through experimental investigation. Four kinds of intermediate casing ducts are test, including the original model, optimization model, as well as two models based on optimization model, respectively. The chord of the struts and the length of flow path are changed for the last two models. The internal flow characteristics and aerodynamic performance of four cases above are measured, and the effects of the geometry structure of flow paths and struts to the aerodynamic performance of the ducts are evaluated, and the results may bring some modifications to the optimization method to make it more perfect. Through the experimental and numerical study, two key factors affecting the design of intermediate duct are brought about, which is the midway offset ratio and the maximum to the minimum area ratio of flow path along streamwise including struts. For the given intermediate casing duct in this study, the midway offset ratio is about 0.41, and the maximum to the minimum area ratio of flow path along streamwise including struts should be small.

The paper presents a detailed computational study of flow patterns and performance indices in a dimpled parallel thrust bearing. The bearing consists of eight pads; the stator surface of each pad is partially textured with rectangular dimples, aiming at maximizing the load carrying capacity. The bearing tribological performance is characterized by means of Computational Fluid Dynamics (CFD) simulations, based on the numerical solution of the Navier-Stokes and energy equations for incompressible flow. Realistic boundary conditions are implemented. The effects of operating conditions and texture design are studied for the case of isothermal flow. First, for a reference texture pattern, the effects of varying operating conditions, in particular minimum film thickness (thrust load), rotational speed and feeding oil pressure are investigated. Next, the effects of varying texture geometry characteristics, in particular texture zone circumferential/radial extent, dimple depth and texture density on the bearing performance indices (load carrying capacity, friction torque and friction coefficient) are studied, for a representative operating point. For the reference texture design, the effects of varying operating conditions are further investigated, by also taking into account thermal effects. In particular, adiabatic conditions and conjugate heat transfer at the bearing pad are considered. The results of the present study indicate that parallel thrust bearings textured by proper rectangular dimples are characterized by substantial load carrying capacity levels. Thermal effects may significantly reduce load capacity, especially in the range of high speeds and high loads. Based on the present results, favorable texture designs can be assessed.

An efficient numerical technique has been developed in order to investigate flow characteristics and global performance of Darrieus rotors. The interest for this kind of vertical axis wind turbines arises from their great capacity for integration within urban areas and for distributed generation. The proposed methodology is based on the solution of the steady three-dimensional governing equations, by means of a robust commercial CFD code. Since the effect of the turbine blades on the flow field is simulated through the introduction of momentum sources in the porous shell representing the volume swept by the turbine blades, any expensive refinement of the grid, near the rotor, is avoided. This approach dramatically reduces the computational costs, with respect to conventional unsteady flow simulations. The model efficiency enables the simulation of the flow field around Darrieus rotors considering complex and realistic computational domains, for instance when these turbines are clustered within a wind farm or placed inside urban areas. The methodology is validated by reproducing the performance of the Sandia 17-meter Darrieus rotor with approximate troposkien shape. Comparisons with other codes are also presented in order to highlight the advantages of the proposed method.

The aerodynamic and acoustic performance of a locomotive cooling module is optimized by a new design strategy for the fan unit. The fan selection or development of the cooling modules is usually based on the specific design point but without consideration of installation effects. The new approach considers the fan development in a more integrated manner. A simplified 1:4 model of the cooling system is constructed and used for system analysis, numerical flow simulations, and experimental validation. The subsequent fan and guide vane optimization is based on numerical simulations embedded in an optimization algorithm taking installation effects into account. The noise emitted by the fan is addressed by a smoothed inflow velocity profile, a new blade sweep strategy, the reduction of secondary flows, and the reduction of fan size and rotational speed. The optimized fan unit is then integrated into the non-simplified full-scale system. Experiments reveal an energy saving of 20% and an overall sound power level reduction of 6 dB with even higher reduction of the tone at blade passing frequency. All results are discussed with respect to transferability to other cooling modules. It is found that a set of general design recommendations originates from this work, whereas the optimization loops would need to be repeated for other cooling module types.

A coarse grid CFD methodology was employed to simulate internal flow passages with full coverage effusion cooling by imposing momentum sinks on effusion cooled surfaces based on a perforated plate pressure loss analogy. The methodology was implemented by specifying 1D Porous Jump boundary conditions (available in ANSYS FLUENT) on the effusion cooled surfaces. Numerical simulations were conducted based on the experimental data of an S-duct diffusing passage where ambient air was passively drawn into the sub-atmospheric passage along the different effusion surfaces with 1 mm diameter holes spaced 4 mm apart. The porous wall simulations were also compared to an alternative CFD approach with mass inlet boundary specified on the effusion surfaces. The proposed porous wall model is promising for practical design applications with the reasonable simulations of the S-duct flow fields with effusion injections. A reasonable accuracy in the results of injection mass flow rates was also obtained for the different effusion configurations. Discrepancies in the simulations of flow momentum components were mainly contributed to the diminishing effects of discrete injections at the aft-section of cooling surface due to the development of a shear layer across the free surfaces (porous jump boundaries) between the main flow and coolant flow.

Recent research has demonstrated that proper use of texture geometries can improve the performance of journal and thrust bearings. In particular, for journal bearings, elliptical and egg-shaped texture patterns appear as promising candidates for improving bearing performance, in terms of load carrying capacity and friction coefficient. The expected advantages should also hold for partial-arc bearings, which, for small scale – high speed applications, are characterized by significant advantages, in comparison to full bearings. In the present paper, a tribological study of partial-arc journal bearings with periodic egg-shaped texture applied on the stator surface is presented. Computational Fluid Dynamics (CFD) simulations are performed and processed to yield the bearing performance indices. Here, the bearing geometry and the texture characteristics are defined parametrically; a wide range of bearing designs is thus accounted for. Flow simulations are based on the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. The effects of dimple shape, bearing eccentricity, bearing arc angle, and slenderness ratio on the bearing performance are investigated. The present results demonstrate that a substantial improvement of journal bearing performance, especially in terms of the friction coefficient, in comparison to that of smooth bearings, is feasible.

In the present paper, a study of stiffness and damping in sector-pad micro-thrust bearings with artificial surface texturing is presented, based on Computational Fluid Dynamics (CFD) simulations. The bearing pads are modeled as consecutive three-dimensional independent micro-channels, each consisting of a smooth rotating wall (rotor) and a partially textured stationary wall (stator). CFD simulations are performed, consisting in the numerical solution of the Navier-Stokes equations for incompressible isothermal flow. The goal of the present study is to characterize the dynamic behavior of favorable designs, identified in previous optimization studies, comprising parallel and convergent thrust bearings with rectangular texture patterns. To this end, a translational degree of freedom (DOF) along the thrust direction and a rotational (tilting) DOF of the rotor are considered. By implementing appropriate small perturbations around the equilibrium (steady-state) position and processing the simulation results, the stiffness and damping coefficients of the bearing are obtained for each DOF. The computed dynamic coefficients of textured thrust bearings are compared to those of conventional (smooth slider) designs. It is found that the dependence of bearing stiffness and damping on geometrical parameters exhibits the same trends for both DOFs. Both stiffness and damping are found to increase with bearing width. In general, increasing the bearing convergence ratio results in increased bearing stiffness and decreased damping. Finally, the present results demonstrate that properly textured parallel sliders are characterized by an overall dynamic performance which is superior to that of smooth converging sliders.

Computational and experimental investigations are reported on a flat plate subjected to combined impingement and film cooling with a (14 × 14) matrix of impingement holes and three (6 × 4) staggered arrays of 35° inclined film holes. Conjugate flow and thermal computations are carried out, by using shear stress transport (SST) κ-ω turbulence model. The combined thermo fluid dynamic features of impinging jets and the coolant-mainstream interactions in presence of impingement and film cooling plates are described. Local values of Nusselt number are presented on the impingement surface and film cooling effectiveness values are plotted along the interaction surface. The computed surface temperature distribution is validated by thermochromic liquid crystal measurements. A comparison between the film cooling and the combined impingement and film cooling shows that the surface effectiveness values for the combined cooling are higher as well as more uniform. As the blowing ratio is increased from M = 0.6 to 1.0, the local streamwise effectiveness values show an increasing trend for both the cases. The effectiveness values are higher for higher conducting material at all blowing ratios. However, in case of lower conducting material, local patches of higher effectiveness are observed close to the jet exit.

The preliminary design tools, for the design and performance analysis of axial flow compressors, has been developed based on reduced-order throughflow model. The in-house numerical tools developed specially for turbomachinery preliminary sizing and calculation of its operational characteristics is being an interesting experience in both under- and graduate lectures. Appropriate loss correlations have been selected aiming at good geometrical initial sizing. Flow properties distribution has been obtained using meanline code combined with a quasi-3D streamline curvature code. Any number of sections from hub to tip of each blade can be used for the determination of the blade shape. The compressor operation map calculated is validated against published test data. Details of the developed methodology and implementation are discussed.

Air cooling via evaporation of water droplets injected at the compressor intake duct is the process known as Fogging System, which is among the most used technologies for increasing output power of gas turbines nowadays. The optimal design of this system must consider numerous variables, such as: air temperature (Ta), air relative humidity (RH), duct geometry, amount of water injected (mw), droplets size (Dd), and nozzles location. Since there are so many variables the flow under study is very complicated. In consequence the analytical determination of an optimal Fogging System design is not feasible. In this paper, a numerical model was developed in order to characterize the injection of water at the air intake duct of a Gas Turbine. First, the expressions characterizing the model were included in the CFD software ANSYS CFX v-11 and simulated in a simple geometry (rectangular duct). Validation of CFD results was carried out by comparison with experimental data. Good agreement between numerical results of a control case and experimental data was achieved (deviation < 2%). Then, the influence of key parameters such as: Ta, RH, Dd, mw over the performance of the air cooling system was investigated. Finally, the model was used to design a Fogging System for an existing 120 MW Gas Turbine. For this gas turbine operating under real conditions, the model predicts a net power increment of 2% [7].

This study investigates the performance and the conditions under which flameless oxidation can be achieved for a given annular adiabatic combustor. Numerical modelling of velocity, temperature and species fields are performed for different flow configurations of air and methane streams injected into a proposed design of a gas-turbine combustor. Parametric analysis was performed by systematically varying several parameters: radius of a recirculation zone, radius of the combustor, location of air and fuel ports, air and fuel velocities magnitudes and injection angles. The analysis was performed initially using a three-step global chemistry model to identify a design (geometry and operating conditions) that yield flameless combustion regime. The selected design was then modelled using a skeletal (46 reactions) and a detailed (309 reactions) chemical kinetics mechanism. The k –ε turbulence model was used in the most calculations. Overall, similar qualitative flow, temperature, and species patterns were predicted by both kinetics models; however the detailed mechanism provides quantitatively more realistic predictions. An optimal flow configuration was achieved with exhaust NO x emissions of < 7.5 ppm, CO < 35ppm, and a pressure-drop < 5%, hence meeting the design criteria for gas turbine engines. This study demonstrates the feasibility of achieving ultra-low NO x and CO emissions utilising a flameless oxidation regime.

The accurate prediction of pulverized coal combustion in industrial application still remains a great challenge. This is mainly due to the lack of high quality experimental data acquired during the operation of industrial plants. This work describes the CFD model used in order to numerically simulate the pulverized coal combustion of a full scale, swirl stabilized, aerodynamically staged, industrial burner. In particular, two different combinations of devolatilization and char burnout models were investigated comparing the numerical results with available experimental data obtained during a burner test carried out, in full-scale configuration, in a 50 MW th , fully instrumented, test rig. In order to avoid any unrealistic assumption on pulverized coal distribution at the burner inlet, the entire primary air duct for pulverized coal transportation has been considered. The main flow is computed solving the steady, incompressible, three-dimensional, Reynolds Averaged Navier-Stokes (RANS) equations, whereas the pulverized coal is simulated as a reacting discrete second phase in a Lagrangian frame of reference, computing the trajectories of the discrete phase entities, as well as heat and mass transfer. The numerical analysis confirms the very good burner performance obtained during the tests with a very low percentage of fixed carbon left in the ashes.

For the CFD community the mesh generation is still one of the most important stages to obtain a good flow solution based on the full Navier-Stokes equations. For turbomachinery blade passages this task is not straightforward mainly due to the 3D domain and the complex geometries involved. The mesh quality and and elements distribution, orthogonality, smoothing, aspect ratio and angles are very important to guarantee a good numerical stability and solution accuracy. Moreover, the structure of the mesh inside the boundary-layer should be built carefully mainly in the regions where there are horseshoe vortices and tip leakage flow. In this work, the 3D turbulent flow is calculated and compared for structured and unstructured meshes including two equation models and Reynolds stress models. A high pressure turbine with 4.0 total-to-total pressure ratio is used in this study. A commercial software is used for mesh generation and flow calculation. The results are presented comparing the pressure ratio and efficiency from numerical solutions and experimental data and flow properties distributions along the blade span.

A computational study is carried out for comparison of the effectiveness of film cooling through holes of different shapes: cylindrical, shaped, trenched cylindrical and trenched shaped hole. Both adiabatic and conjugate wall thermal condition with various blowing ratios (0.6 to 1.4) are considered for the investigation. The coolant-to-mainstream density ratio and temperature ratio are maintained at 1.6 and 0.625 respectively. The κ-ω SST turbulence model is used for computation. The complex flow structures within the film hole, the exit and in the interaction zone of jet with cross flow are reported. Among the configurations studied, the shaped and trenched shaped holes have shown smaller jet lift off and uniform coolant coverage in both lateral and streamwise directions. Further, the results showed a significant difference in the indicated values of centerline surface temperature and effectiveness with the adiabatic and the conjugate conditions; the conjugate values being much lower but more uniform.

The aim of this research is to identify a method of prescribing boundary conditions for CFD studies of vortex ingestion. The work illustrates the use of a validated vortex model which has been shown to give good agreement with experimental data. The model is used to generate the vortex velocity and pressure distributions. Prior knowledge of the vortex strength, core radius, Vatistas model constant, and maximum axial velocity perturbation is required. The model has been generalized, which allows any vortex location on the inlet boundary to be specified. Two examples are given. The first case is for a convecting wing-tip vortex. The second is for a ground vortex prescribed at the inlet of the compressor system. The ground vortex model is based on experimental data as well as previous validated CFD studies. A preliminary assessment of the effect of ground vortex ingestion on the performance of NASA Rotor 67 is carried out using the boundary conditions proposed. Furthermore, a sensitivity analysis on the boundary condition components was completed. The use of such boundary conditions can reduce the resource requirements and enables the independent specification of a vortical flow distortion for controlled parametric investigations of intake or compressor sensitivity studies.

Computational and experimental investigations on a flat circular disk are reported with a constant heat flux imposed on its bottom surface and a shower head of air jets impinging on the top surface. The shower head consists of a central jet surrounded by four neighboring perimeter jets. Lamp black flow visualization technique and computations using shear stress transport (SST) κ-ω turbulence model are employed to describe the complex interaction of the wall jets and the associated flow structure. Thermochromic liquid crystal measurement technique is used for surface temperature measurement. The formations of saddle point, nodal point of attachment, nodal point of separation, flow separation line and the up-wash flow are identified. It is observed that the flow topology is practically independent of Reynolds number within the investigated range but is significantly altered with the spacing between the jet orifice and the target surface. A strong correlation between the Nusselt number and the pressure distribution is noticed. Local variation of heat transfer rate with varying plate spacing to jet diameter ratio is significant but its effect on the area weighted average heat transfer rate is small. When compared with a single jet of equal mass flow rate and Reynolds number, the shower head jets provide higher heat transfer rate but require more power for pumping.

This paper presents a fully-coupled zooming approach for the performance simulation of modern very high bypass ratio turbofan engines developed by Snecma. This simulation is achieved by merging detailed 3D simulations and map component models into a unified representation of the whole engine. Today’s state-of-the-art engine cycle analysis are commonly based on component mapping models which enable component interactions to be considered, while CFD simulations are carried out separately and therefore overlook those interactions. With the methodology discussed in this paper, the detailed analysis of an engine component is no longer considered apart, but directly within the whole engine performance model. Moreover, all links between the 3D simulation and overall engine models have been automated making this zooming simulation fully-integrated. The simulation uses the PROOSIS propulsion object-oriented simulation software developed by Empresarios Agrupados for whole engine cycle analysis and the computational fluid dynamics (CFD) code CEDRE developed by ONERA for the high fidelity 3-D component simulations. The whole engine model is created by linking component models through their communication ports in a graphical user-friendly interface. CFD simulated component models have been implemented in PROOSIS libraries already providing mapped components. Simple averaging techniques have been developed to handle 3D-to-0D data exchange. Boundary conditions of the whole engine model remain the same as for the typical 0-D engine cycle analysis while those of the 3-D simulations are automatically given by PROOSIS to CEDRE. This methodology has been applied on an advanced very high bypass ratio engine developed by Price Induction. The proposed zooming approach has been performed on the fan stage when simulating Main Design Point as well as severe case of off-design conditions such as wind-milling. The results have been achieved within the same time frame of a typical CFD fully-converged calculation. A detailed comparison with upcoming test results will provide a first validation of the methodology and will be presented in a future paper.

Dental air turbine handpieces have been widely used in clinical dentistry for over 30 years, however, little work has been reported on their performance. In dental air turbine handpieces, the types of flow channel and turbine blade shape can have very different designs. These different designs can have major influence on the torque, rotating speed, and power performance. This research is focused on the turbine blade and the flow channel designs. Using CFD and experiments, the key design parameters which influence the performance of dental hand pieces can be studied. Three types of dental air turbine designs with different turbine blades, nozzle angles, nozzle flow channels, and shroud clearances were tested and analyzed. Very good agreement was demonstrated between the CFD analyses and the experiments. Using the analytical model, parametric studies were performed to indentify key design parameters.

The first steps of the turbomachinery design usually rely on numerical tools based on inviscid formulation with corrections using loss models to account for viscous effects, secondary flows, tip clearances and shock waves. The viscous effects are accounted for using semi-empirical correlations specially assembled for the chosen airfoils and range of operating conditions. Fast convergence and good accuracy are required from such design procedures. There are successful models that produce very accurate performance prediction. Among the methodologies commonly used, the streamline curvature (SLC) is used, since those characteristics and the most important properties can be calculated reasonably well at any radial positions, assisting other more complex analysis programs. The SLC technique is, therefore, well suited for the design of axial flow compressors, for reasons like quick access to vital flow properties at the blade edges, from which actions may be taken to improve its performance at the design stage. This work reports the association of a SLC computer program and commercial software for comparison purposes, as well as for grid generation required by a full 3D, turbulent Navier-Stokes computer program, used for flow calculation in the blade passages. Application to a high performance 3-stage axial-flow compressor with Inlet Guide Vane (IGV) demonstrates the methodology adopted. The SLC program is also capable of calculating the compressor performance with humid air and water injection at any axial position along the compressor. The influence of water injection at different axial positions, water particle diameter, temperature of water particles were studied for different humid air conditions. The positions of the evaporating water particles were calculated using their thermo-physical and dynamic properties along the compressor.