Em função de recentes desenvolvimentos no processo de cálculo de sistemas térmicos de proteção contra gelo em aerofólios, foi identificada a importância da camada limite transicional para a correta previsão do coeficiente de troca de calor externo. O presente trabalho discute os métodos utilizados na modelagem numérica de turbulência e transição, testa a capacidade de um modelo k-epsilon de baixo Reynolds avaliar corretamente a transição para o escoamento em uma placa plana bidimensional e mostra que o acoplamento de uma função de transporte de intermitência ao modelo de turbulência de duas equações é uma alternativa eficiente para se aumentar a qualidade da previsão da transição calculada. A filtragem pela variável de intermitência atua corrigindo os níveis de turbulência fornecidos pelo modelo de duas equações durante a transição. Entre os atrativos da função de transporte de intermitência estão a simplicidade das condições de contorno e o fato de serem expansíveis para escoamentos tridimensionais. Uma equação de transporte de intermitência é implementada e acoplada com um modelo de duas equações do programa Fluent. O modelo é testado para três níveis de turbulência do escoamento livre. Os resultados obtidos são comparados com experimentos e com aqueles fornecidos pelo modelo original sem modificações. As distribuições do coeficiente de atrito e de fator de forma ao longo da placa com a função de intermitência mostram boa concordância com os valores verificados experimentalmente, apresentando significativa melhora em relação àqueles obtidos com o modelo \\ke\\ baixo Reynolds. / As a result of recent developments in the field of thermal anti-ice protection in airfoils, was ideintified the relevance of accurately modeling the transitional boundary layer in order to predict the external heat transfer coefficient. The present work reviews the existing alternatives to turbulence and transition modeling, tests the ability of a low-Reynolds \\ke\\ model in the evaluation of transition for a bidimensional flat plate and shows that the coupling of an intemittency transport function with a two equation turbulence model improves the prediction of transition. The filtering with the intermittency function acts correcting the turbulence intensity levels provided by the two equation model during transition. The simple boundary conditions and the expandability to tridimensional flows are other important characteristics of the intermittency functions. An intermittency transport equation is implemented and tested with a two equation turbulence model of the software Fluent. The model is tested for three freestream turbulence levels and the results are compared with experiments and with those obtained with the original model without modifications. The heat transfer coefficient and boundary layer shape factor evolution calculated with the coupled intermittency transport function show good agreement with experiments, improving the quality of the results of the original model.

In this thesis study, Detached Eddy Simulation turbulence model is studied in two dimension mainly for flow over single element airfoils in high Reynolds numbers to gain experience with model before applying it to a three dimensional simulations. For this aim, Spalart-Allmaras and standard DES ,DES97, turbulence models are implemented to parallel, viscous, hybrid grid flow solver. The flow solver ,Set2d, is written in FORTRAN language. The Navier-Stokes equations are discretized by first order accurately cell centered finite volume method and solved explicitly by using Runge-Kutta dual time integration technique. Inviscid fluxes are computed using Roe flux difference splitting method. The numerical simulations are performed in parallel environment using domain decomposition and PVM library routines for inter-process communications. To take into account the effect of unsteadyness after the convergence is ensured by local time stepping technique for four order magnitude drop in density residual, global time stepping is applied for 20000 iterations. The solution algorithm is validated aganist the numerical and experimental studies for single element airfoils in subsonic and transonic flows. It is seen that Spalart-Allmaras and DES97 turbulence models give the same results in the non-seperated flows. Grey area is investigated by changing $C_{DES}$ coefficient. Modeled Stress Depletion which cause reduction of eddy viscosity is observed.

Em função de recentes desenvolvimentos no processo de cálculo de sistemas térmicos de proteção contra gelo em aerofólios, foi identificada a importância da camada limite transicional para a correta previsão do coeficiente de troca de calor externo. O presente trabalho discute os métodos utilizados na modelagem numérica de turbulência e transição, testa a capacidade de um modelo k-epsilon de baixo Reynolds avaliar corretamente a transição para o escoamento em uma placa plana bidimensional e mostra que o acoplamento de uma função de transporte de intermitência ao modelo de turbulência de duas equações é uma alternativa eficiente para se aumentar a qualidade da previsão da transição calculada. A filtragem pela variável de intermitência atua corrigindo os níveis de turbulência fornecidos pelo modelo de duas equações durante a transição. Entre os atrativos da função de transporte de intermitência estão a simplicidade das condições de contorno e o fato de serem expansíveis para escoamentos tridimensionais. Uma equação de transporte de intermitência é implementada e acoplada com um modelo de duas equações do programa Fluent. O modelo é testado para três níveis de turbulência do escoamento livre. Os resultados obtidos são comparados com experimentos e com aqueles fornecidos pelo modelo original sem modificações. As distribuições do coeficiente de atrito e de fator de forma ao longo da placa com a função de intermitência mostram boa concordância com os valores verificados experimentalmente, apresentando significativa melhora em relação àqueles obtidos com o modelo \\ke\\ baixo Reynolds. / As a result of recent developments in the field of thermal anti-ice protection in airfoils, was ideintified the relevance of accurately modeling the transitional boundary layer in order to predict the external heat transfer coefficient. The present work reviews the existing alternatives to turbulence and transition modeling, tests the ability of a low-Reynolds \\ke\\ model in the evaluation of transition for a bidimensional flat plate and shows that the coupling of an intemittency transport function with a two equation turbulence model improves the prediction of transition. The filtering with the intermittency function acts correcting the turbulence intensity levels provided by the two equation model during transition. The simple boundary conditions and the expandability to tridimensional flows are other important characteristics of the intermittency functions. An intermittency transport equation is implemented and tested with a two equation turbulence model of the software Fluent. The model is tested for three freestream turbulence levels and the results are compared with experiments and with those obtained with the original model without modifications. The heat transfer coefficient and boundary layer shape factor evolution calculated with the coupled intermittency transport function show good agreement with experiments, improving the quality of the results of the original model.

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With the continuous growth of the space industry and the introduction of reusable rockets, the number of rocket launches is expected to increase significantly in the following years. During rocket launching, the engine exhaust impinges on the launch structure producing a complex flow field. The rocket jet induces large thermoaerodynamic and acoustic loads on the launch structures and the rocket. This thesis aims to study the physics and numerical considerations behind supersonic flows exhausted from rocket engines. First, the treatment of turbulent compressible flows through the Favre-averaged equations and the SST k-ω model are studied. Next, the numerical modeling of the problem, including solver and meshing theory is presented. Then, a model of a nozzle is explained along with how the performance is assessed to finally design a M=3 two-dimensional nozzle using the method of characteristics (MOC). The two-dimensional results are validated using Ansys Fluent, and the same geometry is used for the following axisymmetrical problems, which include the study of a free and impinging jet. The free jet problem serves to study how the nozzle behaves in a two-dimensional axisymmetric problem and to validate the impinging jet results. To obtain the results, RANS-based simulations of a cold, over-expanded jet with adiabatic walls are performed. Empirical formulas were used to verify the results. Lastly, the impinging jet problem is simulated using the same inlet boundary conditions as for the free jet. The impact that the plate distance to the exit of the nozzle has on the position of the shock waves when the jet impinges on the flat surface is assessed. Finally, an optimization of the shape of a wedge to minimize the maximum turbulence kinetic energy produced during steady-state simulation is carried out. As an appendix to the work, an aeroacoustic study of the impinging jet at 4De distance is presented. The results show the direction of propagation of the acoustic waves but due to the lack of acoustic quality of the mesh, the predicted sound pressure levels do not match the expected behavior.

Internal combustion engines, electric motors and batteries generate a significant amount of heat during operation that needs to be extracted by cooling systems. A cooling system is designed and installed to extract the generated heat and maintain the system temperature in an optimal range. Overheating has several unfavorable outcomes such as less durability and lower energy efficiency. The cooling system consists of several components such as hoses, flow splitters, valves, heat exchangers, coolant, pump, etc. The coolant, as the working fluid, is pumped to different heat generator component to enable the cooling down process. Computational Fluid Dynamics (CFD) is a powerful and cost efficient tool to simulate the cooling processes, design, and evaluate the performance of a cooling system. Generally, one dimensional CFD is a common approach to interpret and explain the cooling processes in the automotive industry due to its high flexibility and computational cost efficiency. Also, three dimensional CFD is employed whenever it is required to study complex physical phenomena and provide detailed information. Additionally, it is possible to couple one dimensional and three dimensional CFD approaches to simulate cooling processes. Not only is the coupled 1D-3D CFD approach able to capture complicated physical processes but also is flexible and cost efficient. The objective of this master thesis is to implement 1D-3D CFD coupled simulation on internal combustion engines’ cooling system and evaluate the advantages and disadvantages of this method. The performance of this method is examined in different case studies with different flow and geometrical characteristics. The effect of various turbulence models and numerical settings are investigated on the quality of the coupled simulations’ results. The coupled simulations are carried out using GT-SUITE and STAR-CCM+ software. The performed simulations show that the coupling method is a convenient approach which is able to capture detailed physics with high precision requiring reasonable computational costs. The results of the coupled simulations depict agreement with the uncoupled 1D CFD simulations, although some discrepancies are observed in complex case studies. Also, it is shown that the coupled simulations are sensitive to numerical settings and physical models, consequently, the case setup should be optimized carefully. / Förbränningsmotorer, elmotorer och batterier genererar en betydande mängd värme under drift som behöver extraheras av kylsystem. Ett kylsystem är utformat och installerat för att extrahera den genererade värmen och hålla systemtemperaturen i ett optimalt intervall. Överhettning har flera ogynnsamma följder, som mindre hållbarhet och lägre energieffektivitet. Kylsystemet består av flera komponenter, till exempel slangar, flödesdelare, ventiler, värmeväxlare, kylvätska, pump etc. Kylvätskan, som arbetsvätska pumpas till olika värmegenerator-komponenter för att möjliggöra nedkylningsprocessen.Computational Fluid Dynamics (CFD) är ett kraftfullt och kostnadseffektivt verktyg för att simulera kylprocesserna, utforma och utvärdera prestanda för ett kylsystem. I allmänhet är endimensionell CFD en vanlig metod för att tolka och förklara kylningsprocesserna i bilindustrin på grund av dess höga flexibilitet och beräkningseffektivitet. Dessutom används tredimensionell CFD när det krävs, för att studera komplexa fysiska fenomen och tillhandahålla detaljerad information. Dessutom är det möjligt att koppla ihop en- och tredimensionell CFD-metod för att simulera kylningsprocesser. Inte bara är den kopplade 1D-3D CFD-metoden möjlig för att betrakta komplicerade fysiska processer, utan är även flexibel och kostnadseffektiv.Syftet med detta examensarbete är att implementera 1D-3D CFD kopplad simulering på förbränningsmotorns kylsystem och utvärdera fördelarna och nackdelarna med denna metod. Uppträdandet av denna metod undersöks i olika fallstudier med olika flöde och geometriska egenskaper. Effekterna av olika turbulensmodeller och numeriska inställningar undersöks genom kvaliteten på resultaten hos kopplingens simuleringar. De kopplade simuleringarna utförs med hjälp av mjukvaran GT-SUITE och STAR CCM +.De utförda simuleringarna visar att kopplingsmetoden är ett bekvämt tillvägagångssätt som kan fånga detaljerad fysik med hög precision till rimliga beräkningskostnader. Resultaten av de kopplade simuleringarna visar överensstämmelse med de frikopplade 1D CFD-simuleringarna, även om vissa avvikelser observeras i komplexa fallstudier. Det visas också att de kopplade simuleringarna är känsliga för numeriska inställningar och fysiska modeller, därför bör fallinställningen optimeras noggrant.

Despite the high cost of memory and CPU time required to resolve the boundary layer, a viscous unstructured grid solver has many advantages over a structured grid solver such as the convenience in automated grid generation and shock or vortex capturing by solution adaption. Since the geometry and flow phenomenon of a helicopter are very complex, unstructured grid-based methods are well-suited to model properly the rotor-fuselage interaction than the structured grid solver. In present study, an unstructured Cartesian grid solver is developed on the basis of the existing solver, NASCART-GT. Instead of cut-cell approach, immersed boundary approach is applied with ghost cell boundary condition, which increases the accuracy and minimizes unphysical fluctuations of the flow properties. The standard k-epsilon model by Launder and Spalding is employed for the turbulence modeling, and a new wall function approach is devised for the unstructured Cartesian grid solver. It is quite challenging and has never done before to apply wall function approach to immersed Cartesian grid. The difficulty lies in the inability to acquire smooth variation of y+ in the desired range due to the non-body-fitted cells near the solid wall. The wall function boundary condition developed in this work yields stable and reasonable solution within the accuracy of the turbulence model. The grid efficiency is also improved with respect to the conventional method. The turbulence modeling is validated and the efficiency of the developed boundary condition is tested in 2-D flow field around a flat plate, NACA0012 airfoil, axisymmetric hemispheroid, and rotorcraft applications. For rotor modeling, an actuator disk model is chosen, since it is efficient and is widely verified in the study of the rotor-fuselage interaction. This model considers the rotor as an infinitely thin disk, which carries pressure jump across the disk and allows flow to pass through it. The full three dimensional calculations of Euler and RANS equations are performed for the GT rotor model and ROBIN configuration to test implemented actuator disk model along with the developed turbulence modeling. Finally, the characteristics of the rotor-fuselage interaction are investigated by comparing the numerical solutions with the experiments.

This study separated two parts: PART ¢¹ Meteorologically adjusted trends of ozone Since meteorological changes strongly affect ambient ozone concentrations, trends in concentrations of ozone upon the adjustment of meteorological variations are important of evaluating emission reduction efforts. This work is to study meteorological effects on the long-term trends of ozone concentration using a multi-variable additive model in Kaohsiung. The long-term trends of ozone concentration were analyzed using the Holland model (without meteorological-adjusted) and the robust MM Regression model (with meteorological-adjusted) based on the data of eight EPA air quality stations from 1997 to 2006 in Kaohsiung area. According to the result of the simulation, the simulated value of the robust MM-Regression model present more valid than the Holland model.The simulated results show that the long-term ozone concentration increases at 13.84% (or 13.06%) monthly (or annually) after meteorological adjustments, less than at 26.10% (or 23.80%) without meteorological adjustments in Kaohsiung county. The simulated results show that the long-term ozone concentration increases at 9.01% (or 6.88%) monthly (or annually) after meteorological adjustments, less than at 22.01% (or 19.67%) without meteorological adjustments in Kaohsiung city. Wind speed, duration of sunshine and pressure are the three dominant factors that influence the ground-level ozone levels in Kaohsiung area. PART ¢º Dispersion of air pollutants in the Hsuehshan Tunnel Concentrations of carbon monoxide (CO) and nitrogen oxides (NOx) were measured from November 14 ¡V 17 2008 in a cross-mountain Hsuehshan traffic tunnel stretching 12.9 km and containing eastward and westward channels. Air pollutants of CO (carbon monoxide) and NOx (nitrogen oxides) will be monitored at the inlet, outlet and vertical shafts of the tunnel. Meanwhile, numerical simulation of three-dimensional turbulent flow will be performed using STAR-CD software. Traffic and pollutant concentrations during the weekends exceeded those during the weekdays. Measured concentrations of CO at the two tunnel outlets (14.5 ¡V 22.8 ppm) were approximately three times higher than those at the two tunnel inlets (3.2 ¡V 7.3 ppm), while concentrations of NOx at the two tunnel outlets (1.9 ¡V 2.9 ppm) were approximately four to five times higher than those at the two tunnel inlets (0.3 ¡V 0.8 ppm). The outlet of vertical draft 2 had the highest pollutant concentrations (CO = 12.3 ppm; NOx = 1.9 ppm), followed by vertical drafts 1 and 3. Three-dimensional turbulence modeling results indicate that airflow in the tunnel was primarily driven by the combined effects of axial fans and vehicles. Results of this study demonstrate that simulated pollutant concentrations increase downstream and are vertically stratified, due to tailpipe exhausts close to tunnel floor. Simulations agreed fairly well with measurements.

In this thesis study, implementation, numerical stability and convergence rate issues of turbulence modeling are explored. For this purpose, a one equation turbulence model, Spalart-Allmaras, and a two-equation turbulence model, SST k-w, are adapted to an explicit, cell centered, finite volume method based, structured / hybrid multi grid flow solver, SENSE2D, developed at TUBITAK-SAGE. Governing equations for both the flow and the turbulence are solved in a loosely coupled manner, however, each set of equations are solved using a coupled, semi-implicit solution algorithm. In multigrid solutions, the semi-implicit solution algorithm and the turbulence model equations are employed only in the finest level grid. As a result, stable and convergent numerical solutions are obtained. In order to validate the turbulence models and the semi-implicit solution algorithm implemented, turbulent flow solutions over a flat plate, RAE2822 airfoil and NLR7301 multi element airfoil are performed. The results are compared with the experimental data and the numerical results of the commercial CFD package FLUENT. It is shown that the numerical results obtained by SENSE2D are in good agreement with the experimental data and the FLUENT results. In addition to the turbulence modeling studies, convergence rate studies are also performed by multigrid and semi-implicit solution methods. It is shown that, the convergence rates of the semi-implicit solutions are increased about 5 times for single grid and 35% for multigrid solutions in comparison to the explicit solutions.