Aerodynamic Shape Optimization of a NACA0018 Airfoil Using Adjoint Method and Gradient-Based Optimizer

The purpose of this study is to demonstrate the suitability and efficacy of the adjoint method on the aerodynamic shape optimization on a simple symmetrical airfoil NACA0018 at low Reynolds number for wind turbine application. The adjoint method has been used in many pressure-based numerical simulations with various degrees of success leading to optimized geometries in their respective uses. ANSYS Fluent code was used in this simulation. Lift to drag ratio was defined as the observables for which adjoint sensitivities were formulated. The objective function of the optimization was set to maximize the lift to drag ratio of the airfoil by 20%. The optimization regime showed significant increase in lift and drag ratio from the initial baseline NACA0018 value of 0.0211 up to 3.66 for the optimal NACAOpt. The results demonstrate the potential of the adjoint solver paired together with the gradient-based optimizer to improve the geometry for shape optimization in many CFD applications

Performance Enhancement of VAWT using Diffuser for Energy Extraction from Cooling Tower Exhaust Air

Renewable energy generation need to be accelerated to battle climate change and depletion of fossil fuel resources. Innovation to design wind recovery system which are efficient is vital to contribute green energy production. Many advancements in vertical axis wind turbines (VAWT) were made over the years however, it is still not as efficient as conventional turbines, and some countries does not have the luxury of strong consistent wind throughout the year. Therefore, this study focuses on extracting wind energy from unnatural sources, specifically for cooling tower exhaust air energy recovery. In this study, cycloidal diffuser with different shroud lengths was used to study the performance of a 3-bladed H-Darrieus VAWT (HDWT) with S-1046 airfoils under accelerated wind conditions in a 3-dimensional numerical study using shear stress transport k-ω turbulence model. The cycloidal diffuser with shroud length of 0.48D increased the HDWT power coefficient by 26.66% compared to the bare HDWT at tip speed ratio of 2.0. Aerodynamics around the energy extractor system was also discussed and this investigation has provided good understanding of the flow behaviour of the wind augmented HDWT under cooling tower exhaust air

Physical and computation modelling of turbidity currents: the role of turbulence-particles interactions and interfacial forces

Experimental and numerical investigations have been conducted in order to evaluate the accuracy of the Mixture Model, a depth-resolved and time-averaged multiphase numerical model, in predicting the behaviour of dilute surge-type turbidity currents. The effects of turbulent dispersion and turbulence modulation upon sediment transport within turbidity currents are directly modelled via their incorporation into the Mixture Model. Modelled predictions of flow front propagation and deposit density are compared against both experimental data and refined two-fluids model from previous studies. When modelled using the formulation of Chen & Wood (1985), turbulence modulation does not affect on the propagation of dilute turbidity currents significantly. Turbulent dispersion can be modelled by incorporating the formulation of Simonin (1991) into the slip equation of the Mixture Model. Its effect is strongest in dilute flows carrying fine particles and diminishes when either grain size or flow concentration increases. Modelled turbulent dispersion effects are too strong in simulations of flows carrying silicon carbide particles; Mixture Model simulations agree poorly with both experimental data or refined two-fluids model results of the deposit mass profile. Yet turbulent dispersion is essential to ensure that model predictions of flows carrying glass beads compare well with experimental data. The reasons for the discrepancy between modelling approaches best suited to each of these flow types remains poorly understood. A new analytical approach is developed to evaluate the effect of the lift force on particles of small, intermediate and large particle Reynolds number immersed in two-dimensional shear flows. The lift force always reduces the magnitude of the particle settling velocity and may push particles forward or backward, depending on the sign of both the lift coefficient and the flow vorticity. Given plausible velocity profiles within natural turbidity currents, the effect of lift force on the sand-like particles immersed in such turbidity currents is negligible. It may become significant when the ratio of the particle density to the flow density approaches unity. New experiments are presented for flows over the flow concentration range 0.25 – 5% and grain size range 58 - 115μm. The data are used to facilitate a more complete validation of the Mixture Model, based on flow front propagation rates, deposit mass density and deposit grain characteristics. Modelling results for first two variables are in good agreement with the experimental data, when turbulent dispersion effects are incorporated. For reasons which remain unclear, the model cannot simulate the unexpected experimental result that deposit grain size is largely unfractionated if the standard deviation of the source material is less than 11 but significantly fractionated if it exceeds 18. This discrepancy requires further work

Aerodynamic Shape Optimization of a NACA0018 Airfoil Using Adjoint Method and Gradient-Based Optimizer

The purpose of this study is to demonstrate the suitability and efficacy of the adjoint method on the aerodynamic shape optimization on a simple symmetrical airfoil NACA0018 at low Reynolds number for wind turbine application. The adjoint method has been used in many pressure-based numerical simulations with various degrees of success leading to optimized geometries in their respective uses. ANSYS Fluent code was used in this simulation. Lift to drag ratio was defined as the observables for which adjoint sensitivities were formulated. The objective function of the optimization was set to maximize the lift to drag ratio of the airfoil by 20%. The optimization regime showed significant increase in lift and drag ratio from the initial baseline NACA0018 value of 0.0211 up to 3.66 for the optimal NACAOpt. The results demonstrate the potential of the adjoint solver paired together with the gradient-based optimizer to improve the geometry for shape optimization in many CFD applications

Performance Enhancement of VAWT using Diffuser for Energy Extraction from Cooling Tower Exhaust Air

Renewable energy generation need to be accelerated to battle climate change and depletion of fossil fuel resources. Innovation to design wind recovery system which are efficient is vital to contribute green energy production. Many advancements in vertical axis wind turbines (VAWT) were made over the years however, it is still not as efficient as conventional turbines, and some countries does not have the luxury of strong consistent wind throughout the year. Therefore, this study focuses on extracting wind energy from unnatural sources, specifically for cooling tower exhaust air energy recovery. In this study, cycloidal diffuser with different shroud lengths was used to study the performance of a 3-bladed H-Darrieus VAWT (HDWT) with S-1046 airfoils under accelerated wind conditions in a 3-dimensional numerical study using shear stress transport k-ω turbulence model. The cycloidal diffuser with shroud length of 0.48D increased the HDWT power coefficient by 26.66% compared to the bare HDWT at tip speed ratio of 2.0. Aerodynamics around the energy extractor system was also discussed and this investigation has provided good understanding of the flow behaviour of the wind augmented HDWT under cooling tower exhaust air

Performance Comparison of Organic Rankine Cycle and Vapour Compression Cycle Hybrid Cooling-Heating System using Subcritical or Supercritical Working Fluid

This paper presents a mathematical modelling on the evaluation of cooling, heating and power performance of a hybrid system of Organic Rankine Cycle and Vapour Compression Cycle. The system is assumed to be powered through solar parabolic trough collector and is able to generate a cooling power of 10 kW. Refrigerants R134a or R245fa are chosen as the working fluid of the system. The system is constructed using commercial energy modelling tool AspenPlus. Analysis is performed to determine the effect of changing the mass flow rate split ratio on the energy output. The effect of using subcritical and supercritical working fluid is also compared. Particular attention is paid toward the condition where the power output is equivalent to the energy consumption in view of creating a self-powered cooling and heating system. The result shows that the coefficient of performance for system using R245fa is higher compared to that using R134a. However, the system using R134a allows a self-powered cooling and heating system to be achieved to be achieve at a much higher mass split ratio, resulting the system to be 35% more efficient in the performance

Performance Comparison of Organic Rankine Cycle and Vapour Compression Cycle Hybrid Cooling-Heating System using Subcritical or Supercritical Working Fluid

This paper presents a mathematical modelling on the evaluation of cooling, heating and power performance of a hybrid system of Organic Rankine Cycle and Vapour Compression Cycle. The system is assumed to be powered through solar parabolic trough collector and is able to generate a cooling power of 10 kW. Refrigerants R134a or R245fa are chosen as the working fluid of the system. The system is constructed using commercial energy modelling tool AspenPlus. Analysis is performed to determine the effect of changing the mass flow rate split ratio on the energy output. The effect of using subcritical and supercritical working fluid is also compared. Particular attention is paid toward the condition where the power output is equivalent to the energy consumption in view of creating a self-powered cooling and heating system. The result shows that the coefficient of performance for system using R245fa is higher compared to that using R134a. However, the system using R134a allows a self-powered cooling and heating system to be achieved to be achieve at a much higher mass split ratio, resulting the system to be 35% more efficient in the performance