Development of computational methodologies for turbulence transitional flow prediction

Turbulence transition modelling is still, albeit the past developments, an active research area of interest for various industry sectors. Its modelling can range from RANS based closures to full DNS computations. The former approach is of course the most feasible simulation methodology. Therefore, RANS based transition models have been developed for industry use. These, range from empirically correlated transition models to physics based phenomenological transition closures. Implementation and validation of these models resulted in a deeper understanding of the processes by which RANS based closures are able to predict turbulence transition onset. The research presented herein on the speci c type of physics in which the transition models are based resulted in an accuracy improvement of an existing turbulence transition closure, the k-kl-!. Additionally, upon gaining a deeper understanding on the role of the pre-transitional ow region, a new turbulence transition model was devised. This is based on a never before applied concept of pre-transitional turbulent vortex deformation due to mean ow shear. This will induce the appearance of a small pre-transitional turbulent viscosity on the edge of the laminar boundary layer. The induced viscosity is a result from the predicted small negative pre-transitional u0v0 values. Although experimentally veri ed, up until now, no model has ever been able to predict this turbulent feature based on a mechanical analogy. The transition V-model was then coupled to a turbulence model, the Spalart-Allmaras closure, resulting in the V-SA transition model. This was validated for a wide range of ow conditions and multiple geometries. It is concluded that the mechanical analogy based closure is a feasible concept with a promising future. Although the developed V-SA turbulence transition model is simple, it is able to predict complex transition phenomenon.A modelação de transição para escoamento turbulento, continua a ser uma área de investigação activa, com interesse para vários sectores industriais. A sua modelação pode abranger desde modelos RANS a simulações DNS. A primeira abordagem é claramente a mais exequível forma de simular transição para turbulência. Como tal, modelos de transição RANS têm vindo a ser desenvolvidos para uso industrial. Estes podem variar desde modelos de correlação empírica a modelos fenomenológicos baseados na física do processo de transição. A implementação e validação destes modelos, resultou num aprofundamento do conhecimento sobre os processos a partir dos quais os modelos RANS têm a capacidade de prever a transição para a turbulência. Para além disto, a pesquisa sobre o tópico especí co de modelos de transição baseados na física do processo de transição, resultou numa melhoria da exactidão de um modelo de transição existente, o k-kl-!. Adicionalmente, após adquirir um conhecimento mais detalhado sobre o papel do escoamento de pré-transição, foi desenvolvido um novo modelo de transição. Este é baseado num conceito nunca antes aplicado de deformação de vórtices presentes na região de pré-transi ção devido ao efeito de corte do escoamento médio. Isto irá induzir o aparecimento de uma pequena viscosidade de pré-transição na fronteira da camada limite laminar. Esta viscosidade é resultante da previsão de pequenos valores negativos de u0v0 na região de pré-transição. Apesar de experimentalmente veri cado, até agora, nenhum modelo conseguiu alguma vez prever este fenómeno turbulento baseando-se numa analogia mecânica. O modelo de transição V-model, foi então acoplado com um modelo de turbulência, o modelo Spalart-Allmaras, resultando no novo modelo de transição, o V-SA. Este foi validado para uma vasta gama de escoamentos assim como com múltiplas geometrias. Conclui-se que, o modelo baseado numa analogia mecânica é um conceito funcional com um futuro promissor. Apesar do modelo de transição desenvolvido, V-SA, ser simples, este tem a capacidade de prever fenómenos de transição complexos

Layout and Assembly Technique of the GEM Chambers for the Upgrade of the CMS First Muon Endcap Station

Triple-GEM detector technology was recently selected by CMS for a part of the upgrade of its forward muon detector system as GEM detectors provide a stable operation in the high radiation environment expected during the future High-Luminosity phase of the Large Hadron Collider (HL-LHC). In a first step, GEM chambers (detectors) will be installed in the innermost muon endcap station in the 1.6 \textless \textbar $\eta$ \textbar \textless 2.2 pseudo-rapidity region, mainly to control level-1 muon trigger rates after the second LHC Long Shutdown. These new chambers will add redundancy to the muon system in the $\eta$-region where the background rates are high, and the bending of the muon trajectories due to the CMS magnetic field is small. A novel construction technique for such chambers has been developed in such a way where foils are mounted onto a single stack and then uniformly stretched mechanically, avoiding the use of spacers and glue inside the active gas volume. We describe the layout, the stretching mechanism and the overall assembly technique of such GEM chambers

Production and validation of industrially produced large-sized GEM foils for the Phase-2 upgrade of the CMS muon spectrometer

The upgrade of the CMS detector for the high luminosity LHC (HL-LHC) will include gas electron multiplier (GEM) detectors in the end-cap muon spectrometer. Due to the limited supply of large area GEM detectors, the Korean CMS (KCMS) collaboration had formed a consortium with Mecaro Co., Ltd. to serve as a supplier of GEM foils with area of approximately 0.6 m$^{2}$. The consortium has developed a double-mask etching technique for production of these large-sized GEM foils. This article describes the production, quality control, and quality assessment (QA/QC) procedures and the mass production status for the GEM foils. Validation procedures indicate that the structure of the Korean foils are in the designed range. Detectors employing the Korean foils satisfy the requirements of the HL-LHC in terms of the effective gain, response uniformity, rate capability, discharge probability, and hardness against discharges. No aging phenomena were observed with a charge collection of 82 mC/cm$^{2}$. Mass production of KCMS GEM foils is currently in progress

Quality Control of Mass-Produced GEM Detectors for the CMS GE1/1 Muon Upgrade

The series of upgrades to the Large Hadron Collider, culminating in the High Luminosity Large Hadron Collider, will enable a significant expansion of the physics program of the CMS experiment. However, the accelerator upgrades will also make the experimental conditions more challenging, with implications for detector operations, triggering, and data analysis. The luminosity of the proton-proton collisions is expected to exceed $2-3\times10^{34}$~cm$^{-2}$s$^{-1}$ for Run 3 (starting in 2022), and it will be at least $5\times10^{34}$~cm$^{-2}$s$^{-1}$ when the High Luminosity Large Hadron Collider is completed for Run 4. These conditions will affect muon triggering, identification, and measurement, which are critical capabilities of the experiment. To address these challenges, additional muon detectors are being installed in the CMS endcaps, based on Gas Electron Multiplier technology. For this purpose, 161 large triple-Gas Electron Multiplier detectors have been constructed and tested. Installation of these devices began in 2019 with the GE1/1 station and will be followed by two additional stations, GE2/1 and ME0, to be installed in 2023 and 2026, respectively. The assembly and quality control of the GE1/1 detectors were distributed across several production sites around the world. We motivate and discuss the quality control procedures that were developed to standardize the performance of the detectors, and we present the final results of the production. Out of 161 detectors produced, 156 detectors passed all tests, and 144 detectors are now installed in the CMS experiment. The various visual inspections, gas tightness tests, intrinsic noise rate characterizations, and effective gas gain and response uniformity tests allowed the project to achieve this high success rate