Numerical Laser Energy Deposition on Supersonic Cavity Flow and Sensor Placement Strategies to Control the Flow

In this study, the impact of laser energy deposition on pressure oscillations and relative sound pressure levels (SPL) in an open supersonic cavity flow is investigated. Laser energy with a magnitude of 100 mJ is deposited on the flow just above the cavity leading edge and up to 7 dB of reduction is obtained in the SPL values along the cavity back wall. Additionally, proper orthogonal decomposition (POD) method is applied to the x-velocity data obtained as a result of computational fluid dynamics simulations of the flow with laser energy deposition. Laser is numerically modeled using a spherically symmetric temperature distribution. By using the POD results, the effects of laser energy on the flow mechanism are presented. A one-dimensional POD methodology is applied to the surface pressure data to obtain critical locations for the placement of sensors for real time flow control applications

Parametrical and theoretical design of a Francis turbine runner with the help of computational fluid dynamics

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.A computational fluid dynamics based design system with the integration of blade modeler, mesh generator and Navier- Stokes based CFD codes makes the design optimization of turbine components quick and efficient. This design system is applied to a low head Francis turbine runner. The parameters of turbine runner affect the hydraulic performance of turbines. Its complex parameters cause direct effect on the global parameters which change the efficiency and the output power. The purpose of this study is the investigation of the effects of theoretical turbine runner parameters on the design. To determine the parameter effects on the turbine performance theoretical calculations and analyses of turbine runner were performed. A methodology was followed with the help of CFD to reach the best efficiency operating point of turbine. Starting from the preliminary design to the final design, theoretical calculations were performed and evaluated using the results of the CFD analyses. The CFD analyses were used to visualize the flow characteristics on runner blades induced by runner parameters. At the end, a new runner model is designed with a higher efficiency.dc201

Investigation of the Effects of Length to Depth Ratio on Open Supersonic Cavities Using CFD and Proper Orthogonal Decomposition

Simulations of supersonic turbulent flow over an open rectangular cavity are performed to observe the effects of length to depth ratio (L/D) of the cavity on the flow structure. Two-dimensional compressible time-dependent Reynolds-averaged Navier-Stokes equations with k-ω turbulence model are solved. A reduced order modeling approach, Proper Orthogonal Decomposition (POD) method, is used to further analyze the flow. Results are obtained for cavities with several L/D ratios at a Mach number of 1.5. Mostly, sound pressure levels (SPL) are used for comparison. After a reduced order modeling approach, the number of modes necessary to represent the systems is observed for each case. The necessary minimum number of modes to define the system increases as the flow becomes more complex with the increase in the L/D ratio. This study provides a basis for the control of flow over supersonic open cavities by providing a reduced order model for flow control, and it also gives an insight to cavity flow physics by comparing several simulation results with different length to depth ratios

Rehabilitation of Francis Turbines of Power Plants with Computational Methods

Rehabilitation of existing hydroelectric power plants HEPP by redesigning the hydraulic turbines is usually more elaborate than designing a tailor-made turbine for a new plant. Some of the parts are buried and the space is limited with the size of the old turbine; therefore, this increases the number of constraints imposed on the design. This article presents a Computational Fluid Dynamics CFD based rehabilitation procedure involving the state of the art redesign of the turbine of a hydroelectric power plant for better performance at design and off-design conditions of several head and flow rates. Runner and guide vanes of the Francis turbine are designed per the design head and flow rates available for the turbine at the site. The simulations for the designed parts are performed both separately and using all turbine parts as full turbine analyses. Both the design and off-design conditions are simulated for the newly designed and existing turbines for comparison purposes. Cavitation performance of the new design is also determined. The proposed methodology is applicable to any Francis type turbine and any HEPP that needs rehabilitation

Simulation-based design and optimization of Francis turbine runners by using multiple types of metamodels

In recent years, optimization started to become popular in several engineering disciplines such as aerospace, automotive and turbomachinery. Optimization is also a powerful tool in hydraulic turbine industry to find the best performance of turbines and their sub-elements. However, direct application of the optimization techniques in design of hydraulic turbines is impractical due to the requirement of performing computationally expensive analysis of turbines many times during optimization. Metamodels (or surrogate models) that can provide fast response predictions and mimic the behavior of nonlinear simulation models provide a remedy. In this study, simulation-based design of Francis type turbine runner is performed by following a metamodel-based optimization approach that uses multiple types of metamodels. A previously developed computational fluid dynamics-based methodology is integrated to the optimization process, and the results are compared to the results obtained from on-going computational fluid dynamics studies. The results show that, compared to the conventional methods such as computational fluid dynamics-based methods, metamodel-based optimization can shorten the design process time by a factor of 9.2. In addition, with the help of optimization, turbine performance is increased while cavitation on the turbine blades, which can be harmful for the turbine and reduce its lifespan, is reduced.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study is financially supported by the Ministry of Development of Turkey. The computations are performed at TOBB ETU Center for Hydro Energy Research (ETU Hydro), CFD Laboratory

Hybrid Ventilation System Simulation for Several Cities in Turkey

Hybrid ventilation systems combine the superior properties of natural and mechanical ventilation systems to reduce energy consumption. In this study, hybrid ventilation simulations were performed for several cities in Turkey, which have different climate conditions. Matlab/Simulink was utilized to perform the simulations. The results of these simulations were compared with that of regular air conditioning units in terms of energy consumption. A hybrid ventilation system which shows the general behaviour of a fan-assisted natural ventilation system with temperature-based control and which provides both heating and cooling, is shown to be effective for four cities in Turkey that have different climate conditions. Results showed potential savings of around 25-30% when compared to a regular AC system