Wind lens performance investigation at low wind speed

In this research work, we investigated a diffuser augmented wind turbine's performance or better known as a wind lens. The wind lens consists of a circular flanged diffuser and a horizontal axis wind turbine with a diameter of 0.6 m. The diffuser length to the diameter ratio is 0.226, and the flange height to diameter ratio is 0.1. The performance of the wind Lens is investigated numerically by solving the flow field using Reynolds Averaged Navier-Stokes for incompressible flow. The finding of this work shows that the flange's role is significant to the performance; also, it shows that the opening angle of the diffuser is essential if the rotation speed of the turbine is set wisely. The wind lens's output torque at an inlet speed of 5 m/s is superior to the bare turbine by 30-60%, which shows the wind lens's usefulness at low wind speed

Large eddy simulation and preliminary modeling of the flow downstream a variable geometry swirler for gas turbine combustors

This work presents a novel swirler with variable blade configuration for gas turbine combustors and industrial burners. The flow dynamics downstream the swirler was explored using Large Eddy Simulation (LES). The resolved turbulence kinetic energy in the region where the flow exhibits the main flow phenomena was well above 80% of the total turbulent kinetic energy of the flow. It was evidently shown that the new swirler produces a central recirculation zone and a Rankine vortex structure which are necessary for swirl flame stabilization. Two Reynolds-averaged NavierStokes (RANS) simulation cases utilizing the standard and realizable k-ε turbulence models were also conducted for two objectives. The first is to demonstrate the validity of RANS/eddy-viscosity models in predicting the main characteristics of swirling flows with comparison to the LES results. The second objective is to comparatively investigate the flow features downstream the new swirler in both co-rotating and counter-rotating blade configurations. The results show that the counter-rotating configuration produces higher turbulence kinetic energy and more compact recirculation zone compared to the co-rotating configuration

Mathematical modelling of droplet atomization using the population balance equation

This study investigates numerically the atomization process occurring in a plain jet airblast atomizer. The population balance equation is solved for the dispersed phase coupled with a CFD Eulerian multi-fluid model. The Sauter mean diameter values obtained numerically compare favorably with previous experimental data only at certain flow conditions. Finally, this study proposes some enhancements on using the numerical model which were revealed from the model formulation and the results obtained

Heat transfer enhancement in two-start spirally corrugated tube

Various techniques have been tested on heat transfer enhancement to upgrade the involving equipment, mainly in thermal transport devices. These techniques unveiled significant effects when utilized in heat exchangers. One of the most essential techniques used is the passive heat transfer technique. Corrugations represent a passive technique. In addition, it provides effective heat transfer enhancement because it combined the features of extended surfaces, turbulators and artificial roughness. Therefore, A Computational Fluid Dynamics was employed for water flowing at low Reynolds number in spiral corrugated tubes. This article aimed for the determination of the thermal performance of unique smooth corrugation profile. The Performance Evaluation Criteria were calculated for corrugated tubes, and the simulation results of both Nusselt number and friction factor were compared with those of standard plain and corrugated tubes for validation purposes. Results showed the best thermal performance range of 1.8–2.3 for the tube which has the severity of 45.455 × 10−3 for Reynolds number range of 100–700. The heat transfer enhancement range was 21.684%–60.5402% with friction factor increase of 19.2–36.4%. This indicated that this creative corrugation can improve the heat transfer significantly with appreciably increasing friction factor

Passive heat transfer enhancement review in corrugation

The heat transfer is a very interesting field for economical, functional and environmental reasons; it is almost related to each aspect of human lives. Therefor, the enhancement of such field is quite essential. Passive heat transfer represents is the soul of heat transfer enhancement due to the merits of simplicity, cheap and good enhancement with acceptable pressure drop. Corrugation is a method involved within the passive techniques of enhancement, it is important and being adopted in a wide range of applications like a nuclear reactor cooling, refrigeration, heat exchangers, and other industrial applications. The current article presents an extensive review of numerical and experimental studies on heat transfer enhancement, which covers the laminar and turbulent flow regions in the corrugations, especially in corrugated tubes. This paper dealt with 95.74% of papers published in corrugated tubes for different applications to offer one article representing a database stop for the designers and authors whom concerning and dealing with heat transfer enhancement in corrugated tubes

Aerodynamic analysis of horizontal axis wind turbine using blade element momentum theory for low wind speed conditions

All around the world, a rapid growth of energy demand during the last decades. An ideal alternative to meet this additional increasing demand would be through renewable energy resources such as wind energy. With over 300 GW of installed wind capacity worldwide and the target for future increase of capacity of more than 15% per year, the research to improve wind energy technology is further required. For countries around the equator where wind speed is low, the need for new innovative design of wind turbine for low wind speed condition or class 1 wind is of primary urgency. A new type of airfoil for low wind speed turbine blade need to be designed. The objective of this study is to investigate the design parameters influencing the performance of three blades Horizontal Axis Wind Turbine (HAWT). Blade Element Momentum Theory was used to find the optimal performance, in term of the coefficient of power (Cp), which rates the turbine blade’s ability to extract energy from the available wind stream. The result shows the relationship between the changes of the power coefficient with tip speed ratio. The maximum power coefficient found was 0.57 at tip speed ratio 4.8. It was then shown that Cp reduced for higher tip speed ratio

A mathematical model for predicting spray atomization characteristics in an Eulerian-Eulerian framework

A new mathematical model is developed for calculating droplet break-up frequency based on both drag and turbulence induced fragmentation stresses. The droplet break-up model is introduced into a CFD methodology that is based on the Eulerian–Eulerian approach. The CFD solver couples the population balance equation along with the Navier–Stokes equations for predicting the droplets diameter. Finally, preliminary results using this CFD model are presented for the case of a coaxial airblast atomizer and a good agreement with the experimental data is achieved

Large Eddy simulation and prelimiry modeling of the flow downstream a variable geometry swirler for gas turbine combustors

This work presents a novel swirler with variable blade configuration for gas turbine combustors and industrial burners. The flow dynamics downstream the swirler was explored using Large Eddy Simulation (LES). The resolved turbulence kinetic energy in the region where the flow exhibits the main flow phenomena was well above 80% of the total turbulent kinetic energy of the flow. It was evidently shown that the new swirler produces a central recirculation zone and a Rankine vortex structure which are necessary for swirl flame stabilization. Two Reynolds-averaged NavierStokes (RANS) simulation cases utilizing the standard and realizable k-e turbulence models were also conducted for two objectives. The first is to demonstrate the validity of RANS/eddy-viscosity models in predicting the main characteristics of swirling flows with comparison to the LES results. The second objective is to comparatively investigate the flow features downstream the new swirler in both co-rotating and counter-rotating blade configurations. The results show that the counter-rotating configuration produces higher turbulence kinetic energy and more compact recirculation zone compared to the co-rotating configuration