Tren piston etkisi ile yeraltı taşıma sistemi havalandırması

In this study, the general points of subway ventilation are given, focusing on "Train piston action ventilation". A computer program has been developed to simulate train piston action in underground transportation systems. The program has been named as Trapac (Train piston action). Pressure and velocity distributions are computed along tunnel direction and in time, when a train is passing through a tunnel. inThe partial differential equations that govern the unsteady flow of air in the tunnel are transformed to ordinary differential equations by using the method of characteristics to solve them numerically. Simulations were performed for several cases, including constant and variable speed trains, tunnels with and without ventilation shafts. Case studies are mainly based on Ankara Metro Third Phase Project, so that the results of this study find a basis in the evaluation of station comfort for passengers. The results obtained from simulations were compared with the experimental and numerical studies in literature.Bu tezde, yeraltı taşıma sistemlerinin genel özellikleri, trenin piston etkisi havalandırması üzerinde yoğunlaşarak verilmiştir. Tren piston etkisi havalandırmasının etkilerini canlandırmak için bir bilgisayar programı yazılmıştır. Programa Trapac adı verilmiştir. Tren tünelden geçerken oluşan basınç ve hız dağılımları tünel yönünde ve zamana bağlı olarak hesaplanmıştır. <,/T *4 e t V.Tünel içinde geçici hava akışını tanımlayan kısmi diferansiyel denklemler karakteristik yöntemi kullanılarak adi diferansiyel denklemlere dönüştürülmüş ve sayısal olarak çözülmüştür. Sabit ve değişken hızlı trenler, havalandırma şaftı olan ve olmayan tünelleri de içeren çeşitli durumlar için bilgisayar programı çalıştırılmıştır. Tez, örnek çalışmaları özellikle Ankara Metrosu Üçüncü Aşama Projesi üzerinde yapılarak, yolcular için istasyon konforu değerlendirmesi üzerinde anlam kazanmaktadır. Programdan elde edilen sonuçlar literatürdeki deneysel ve nümerik sonuçlarla karşılaştırılmıştır

Artificial Neural Network Based Prediction Of Time-Dependent Behavior For Lid-Driven Cavity Flows

In this study, computational fluid dynamics (CFD) analyses of the two-dimensional, time-dependent lid-driven cavity flows, for Reynolds numbers ranging from 100 to 10000, are performed by using an in-house developed CFD code. The unsteady behavior of the flow is triggered using a sinusoidal lid velocity profile. The flow structure is further investigated with the application of a reduced order modeling technique, Proper Orthogonal Decomposition (POD), and the structures present in the flow, are separated according to their frequency (energy) content. POD results show that when the stream function formation is used as a data ensemble, about 99% of the total energy content can be modeled by considering only the most energetic first four POD modes; whereas, this value remains at a range between 90 - 95% for the x-direction velocity data ensemble. What is more, an Artificial Neural Network (ANN) based approach is developed to predict mode amplitudes for flows with different Reynolds numbers. Once enough information is obtained with the help of CFD of few flow cases, the ANN integrated approach presented herein helps to predict what is happening in the flow for different flow cases without requiring further CFD simulations, which are not practical in real-time flow control applications.This research is financially supported by Turkish Academy of Sciences Distinguished Young Scientists Awards Programme. (TUBA-GEBIP)

Experimental analysis of a mixed-plate gasketed plate heat exchanger and artificial neural net estimations of the performance as an alternative to classical correlations

In this study, experiments are performed to test the thermal and hydraulic performance of gasketed plate heat exchangers (GPHE). A heat exchanger composed of two different plate types is used for the experiments, for a Reynolds number range of 500-5000. The results are compared to the experimental results obtained for plate heat exchangers which are composed of plates that have the same geometry instead of mixing two different plates. Two methods are used to investigate the thermal and hydraulic characteristics based on the obtained experimental data. One of them is the classical correlation development for Nusselt number and friction factors. Artificial neural networks (ANNs) are also used to estimate the performance as an alternative to correlations. Different networks with various numbers of hidden neurons and layers are used to find the best configuration for predictions. The results show that, artificial neural networks can be an alternative to experimental correlations for predicting thermal and hydraulic characteristics of plate heat exchangers. They give better performance when compared to correlations which are very common in heat transfer applications. Especially for mixed plate configurations studied in this research, where different plate types are used as a combination in the complete heat exchanger, it is difficult to obtain a single correlation that represents all the plates in the heat exchanger. However, when ANN's are used, it is easier to predict the performance of mixed plate HEX and the predictions are more reliable when compared to correlations. (C) 2016 Elsevier Masson SAS. All rights reserved.This work is supported by Turkish Academy of Sciences (TUBA-GEBIP program) and Turkish Scientific and Research Council under grant 112M173

Determination and generalization of the effects of design parameters on Francis turbine runner performance

The runner design is the most challenging part of the turbine design process. Several parameters determine the performance and cavitation characteristics of the runner: the metal angle (flow beta angle), the alpha angle, the blade beta angle, the runner inlet and outlet diameters, and the blade height. All of these geometrical parameters need to be optimized to ensure that the head, flow rate and power requirements of the system are met. A hydraulic designer has to allocate time to optimize these parameters and should be experienced in carrying out the iterative design process. In this article, the turbine runner parameters that affect the performance and cavitation characteristics of designed turbines are examined in detail. Furthermore, turbines are custom designed according to the properties of hydroelectric power plants; this makes the design process even more challenging, as the rotational speed, runner geometry, system head and flow rate vary for each turbine. The effects of the design parameters are examined for four different turbine runners specifically designed and used in actual power plants in order to obtain general results and generalizations applicable to turbine design aided by computational fluid dynamics (CFD). The flow behavior, flow angles, head losses, pressure distribution, and cavitation characteristics are computed, analyzed, and compared. To assist hydraulic designers, the general influences of these parameters on the performance of turbines are summarized and empirical formulations are derived for runner performance characterization

Experimental investigation and CFD analysis of rectangular profile FINS in a square channel for forced convection regimes

Steady-state heat transfer from rectangular fin arrays is examined experimentally and numerically for turbulent fully developed flow. The effects of geometrical parameters on heat transfer coefficient and Nusselt number are investigated. For different inter fin ratios, Reynolds number and Nusselt number dependence of the results is investigated. A generalized empirical correlation for Nusselt number is developed for rectangular fins for a Reynolds number range of 17 x 10(7) < Re < 2.47 x 10(8), and an aspect ratio of 0.089 < d/w < 0.0625, 0.24875 < t/L < 0.729. The correlation can predict the results with a relative rms error of 11.14%. (C) 2016 Elsevier Masson SAS. All rights reserved.The construction of the set-up is financially supported by METU-BAP project (BAP-08-11-2013-035) and the experiments were performed at METU Department of Mechanical Engineering Heat Transfer Laboratory.; The computations are performed using the facilities of TOBB ETU Hydro Energy Research Center CFD Laboratory supported by Turkish Ministry of Development. Some of the results presented here are also presented briefly at International Symposium of Convective Heat and Mass Transfer in July 2014

CFD Aided Design Of Heat Transfer Plates For Gasketed Plate Heat Exchangers

12th ASME Biennial Conference on Engineering Systems Design and Analysis (ESDA2014), JUN 25-27, 2014, Copenhagen, DENMARK, ASMEIn this study, three-dimensional computational fluid dynamics (CFD) analyses are performed to assess the thermal-hydraulic characteristics of a commercial Gasketed Plate Heat Exchangers (GPHEx) with 30 degrees of chevron angle (Plate 1). The results of CFD analyses are compared with a computer. program (ETU HEX) previously developed based on experimental results. Heat transfer plate is scanned using photogrammetric scan method to model GPHEx. CFD model is created as two separate flow zones, one for each of hot and cold domains with a virtual plate. Mass flow inlet and pressure outlet boundary conditions are applied. The working fluid is water. Temperature and pressure distributions are obtained for a Reynolds number range of 700-3400 and total temperature difference and pressure drop values are compared with ETU HEX. A new plate (Plate2) with corrugation pattern using smaller amplitude is designed and analyzed. The thermal properties are in good agreement with experimental data for the commercial plate. For the new plate, the decrease of the amplitude leads to a smaller enlargement factor which causes a low heat transfer rate while the pressure drop remains almost constant

Design And Construction Of An Experimental Test Rig For Hydraulic Turbines

12th ASME Biennial Conference on Engineering Systems Design and Analysis (ESDA2014), JUN 25-27, 2014, Copenhagen, DENMARK, ASMEEvery turbine for every hydroelectric power plant is unique; therefore its model has to be designed using state of the art design techniques and tested before the actual prototype which is costly, is manufactured. In this study, the details of the design and construction of a hydroturbine test facility at TOBB University of Economics and Technology are explained. The facility will be used to test hydroturbine models up 2MWs of power simulating turbine prototypes. The performance and cavitation tests of the turbines will be performed utilizing this facility according to International Electrical Commission (IEC) standards. The test facility is 19 meters long with a base area of around 600 meter squares. The hydraulic analysis of the designed set-up is performed using a system where valves, pipes, structures, water records and connections form an intelligent system, same with the experimental facility. According to the results, system performance is checked, alternative designs are evaluated and operating strategies are defined by minimizing the losses

CFD-driven surrogate-based multi-objective shape optimization of an elbow type draft tube

Draft tube is the part of Francis turbines which is used to both discharge water and recover kinetic energy at the exit of the runner. A design optimization study of an elbow type draft tube based on the combined use of Computational Fluid Dynamics (CFD), design of experiments, surrogate models and multi-objective optimization is presented in this study. The geometric variables that specify the shape of the draft tube are chosen as input variables for surrogate models and the pressure recovery factor and the head loss are selected as output responses. It is determined that, pressure recovery factor, which is the main performance parameter, can be increased by 4.3%, and head loss can be reduced by %20 compared to the initial CFD aided design. Pressure recovery factor, is represented with a second order polynomial regression model in terms of the geometrical parameters based on the optimization results. The verification of the model is also provided by comparison with CFD results for different draft tubes other than that are used in the development of the model. The model is verified using 30 different design points and it can predict the pressure recovery factor with an error of less than 8%. This model allows the fast and correct design and optimization of elbow type draft tubes, without the need for further CFD simulations. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.The computations are performed using the computational cluster and computer infrastructure of TOBB ETU Hydro Energy Research Laboratory, financially supported by Turkish Ministry of Development. The first author was also financially supported by Turkish Scientific and Research Council (Tubitak) BIDEB program for her MS studies which is the subject of this article

Reverse Engineering Design of a Hydraulic Turbine Runner

World Congress on Engineering (WCE 2015), JUL 01-03, 2015, Imperial Coll, London, ENGLAND, Int Assoc EngnReverse engineering is an important method utilized in manufacturing and design process. When there is no technical data of a product or it is unusable, the CAD model is obtained with this method. After obtaining the data of the existing product, rehabilitation studies are carried out for improvement in the design. In this rehabilitation process, numerical methods can be used to optimize the current product. This study presents a reverse engineering process of detecting the reasons for lack of performance of an actual hydraulic turbine runner. Reverse engineering methodology is applied for Kahta H.E.P.P. in Turkey, Adiyaman which has two identical horizontal Francis type turbines. The head and discharge are 125 m and 3.25 m(3)/s per turbine, the power plant capacity is 3.66 MW and overall turbine efficiency is 92%. According to the results of this study, it is determined that the turbine runner blade trailing edge theta angle causes a large recirculation region which drops the performance of the turbine