Outer scales and parameters of adverse-pressure-gradient turbulent boundary layers

A clear and consistent framework for the analysis of the outer region of adverse-pressure-gradient turbulent boundary layers is established in this paper based on basic principles and theory, and the help of six adverse-pressure-gradient turbulent boundary layer databases and a zero-pressure-gradient one. Outer velocity and length scales for the mean velocity defect and the Reynolds stresses are discussed first. The conditions of validity of four velocity scales are determined in terms of the shape factor, since one scale is restricted to small velocity-defect boundary layers (the friction velocity ), one to large-defect ones (the pressure-gradient velocity ), while the two others are proper scales for all velocity-defect conditions (the Zagarola–Smits velocity and the mixing-layer-type velocity ). The turbulent boundary layer equations are then used to bring out, in a consistent manner and without assuming any self-similar behaviour, a set of non-dimensional parameters characterizing the outer region of turbulent boundary layers with arbitrary pressure gradients. In terms of a generic outer length scale and velocity scale , these non-dimensional parameters are the pressure-gradient parameter , the Reynolds number and the inertial parameter , where and are respectively the streamwise and wall-normal components of mean velocity at the boundary layer edge. These parameters have a clear physical meaning: they are ratios of the order of magnitude of forces, with the Reynolds shear stress gradient (apparent turbulent force) as the reference force – inertial to apparent turbulent forces for , pressure to apparent turbulent forces for and apparent turbulent to viscous forces for . We discuss at length their significance and determine under what conditions they retain their meaning depending on the outer velocity scale that is considered. The seven boundary layer databases are analysed and compared using the established framework. An astonishing and impressive result is obtained: by choosing , the streamwise evolution of the three ratios of forces in the outer region can be accurately followed with , and in all these flows – not just the order of magnitude of these ratios. This cannot be achieved with and , and only imperfectly with . Consequently, , and can be used to follow – in a global sense – the streamwise evolution of the streamwise mean momentum balance in the outer region

Analysis Of Fluid Mechanic Problems With Finite Element Method

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2004Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2004Üç boyutlu viskoz akış problemlerinin modellenmesinde prizmatik elemanların kullanılmasi literatürde gelişmekte olan bir konudur. Bu çalışmada, sınır tabaka bölgesinin prizmatik elemanlar geri kalan çözüm bölgesinin tetrahedral elemanlar ile modellendigi, üç boyutlu sıkıştırılamaz, viskoz akış problemlerinin çözümünde kullanılacak bir sonlu elemanlar uyarlaması gerçekleştirilmiştir. Daimi olmayan akış problemlerini, birçok mühendislik problemleri ile çözme isteği geometrik olarak kompleks problemlere uygun algoritmalarin geliştirilemesine neden olmaktadir. Bu tip problemleri çözmek için kullanılan yöntemler dört ana başlık altında sınıflandırılabilir: Sonlu Farklar Yöntemi, Sonlu Hacimler Yöntemi, Sonlu Elemanlar Yöntemi ve Sınır Eleman Yöntemi. Bu calışmada bu tip problemleri çözmek için Sonlu Elemanlar yöntemi kullanılacaktır. Sonlu Elemanlar yöntemi akış alanının sonlu küçük elemanlar ile modellenmesi prensibine dayanır. Bu çalışmada sağlıklı bir insana ait üç boyutlu burun geometrisi olusturularak, burun içindeki akış Sonlu Elemanlar yöntemi ile incelenmiştir.Using prismatic elements for the simulations of three dimensional flows is a developing subject in literature. In this study, a finite element adaptation is carried out for the solution of three dimensional incompressible viscous flows which is modeled with prismatic elements in the boundary layer region and tetrahedral elements for the rest of the computational domain. The need to solve unsteady flows for several engineering problems causes to develop new algorithms. The methods for the solutions of this kind of problems can be classified into four branches: Finite Difference Method, Finite Volume Method, Finite Element Method and Boundary Element Method. Finite Element Method is used in this study for the solutions of this kind of problems. Finite Element Method depends on the discritization of the solution domain in to the small pieces, elements. A three dimensional, anatomically accurate representation of a healthy adult human nasal cavity is constructed to simulate the nasal airflow profiles numerically in this study.Yüksek LisansM.Sc

Depression and hopelessness in Turkish healthcare workers: The moderating and mediating roles of meaning in life

gungor, abdi/0000-0002-7945-0906WOS: 000481956300001PubMed: 31429360Healthcare workers who served in southern cities of Turkey have been directly and indirectly affected by the civil war in Syria due to stress and trauma. Hopelessness in these healthcare workers can be a potential contributor to their levels of depression. On the other hand, meaning in life, as both moderating and mediating variable, can serve to counteract depression. This is a study of 286 Turkish healthcare workers who served in a southern border city of Turkey and Syria in February and March of 2018. The study examined the effects of hopelessness and meaning in life on depression level including the moderating and mediating effects of meaning in life on the relationship between hopelessness and depression. A hierarchical regression analysis and bootstrapping procedure were employed to test the research questions. This study found that hopelessness positively predicted depression and meaning in life negatively predicted depression. Meaning in life significantly moderated and partially mediated the association between hopelessness and depression. Healthcare workers who served in a conflict area experienced more depression when they had more hopelessness and less meaning in life. Moreover, meaning in life played a central role as both moderator and mediator. Results are discussed with implications and limitations

Large Eddy Simulation of a Stagnation Point Reverse Flow Combustor

The complex unsteady behavior of a stagnation point reverse flow combustor (SPRF) is investigated numerically with large eddy simulation (LES) approach using an open source flow solver OpenFOAM. The SPRF combustor has a unique design where inflow and outflow ports are located in the same plane. This feature promotes stable and efficient combustion through internal gas recirculation, and also reveals a complex flow field inside the combustor. Instantaneous flow features, statistical behavior of the turbulent flow, the effect of grid resolution and energy spectrum are evaluated to study the capability of the LES approach for this combustor. The non-reacting cold flow results show overall very good agreement with experimental data, giving confidence that LES with k-equation subgrid model could be a very powerful tool for resolving such complex flow dynamics. Further analyses are extended for reacting cases to examine turbulence combustion interaction. The interaction of the flame with turbulent structures clarified the intense internal gas recirculation mechanism