Computational investigations were carried out to evaluate the effectiveness and usability of hybrid RANS/LES techniques for predicting the unsteady separated flow over wings with ice accretion. RANS and hybrid RANS/LES computations were performed using the viscous flow solver CHEM with the SST turbulence model. Two configurations were considered during the study: an extruded wing with a glaze-ice shape and a swept wing with a simulated glaze-ice accretion. Hybrid RANS/LES results, in general, predict a less active shear layer ``roll up' than seen in the experimental data. Qualitative improvements are seen in the hybrid RANS/LES results over corresponding RANS results. The extruded wing results show that the CHEM hybrid RANS/LES results are similar to the AVUS DES results. The use of preconditioning and a different turbulent model in CHEM showed a slight improvement in results.

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Veno-arterial extracorporeal membrane oxygenation (V-A ECMO) is a life saving therapy for critically ill patients experiencing a heart and lung failure. During this therapy, a common complication is limb ischemia in the leg where the return cannula reintroduces the oxygenated blood to the patient. The hemodynamics leading to limb ischemia during V-A ECMO therapy is not yet understood. This work uses computational fluid dynamics to model the interacting blood flows from the V-A ECMO return cannula and the native cardiac output in the abdominal aorta and iliac bifurcation. A two-element Windkessel (WK) model is used to model the downstream vasculature. In total, five simulations of four cardiac cycles are conducted, where either one WK model parameter or the aorta inflow boundary condition (BC) is altered. Results suggest that the outflow distribution between the iliac arteries is dependent on the WK model parameters, but it is independent of the inflow BC imposed at the aorta inlet. Increasing the resistance value of the WK model leads to an increase of pressure in the domain relative to the 0.8 L/min baseline case and increases the outflow through the non-cannulated iliac artery. The opposite effect is reached when decreasing the resistive value or increasing the compliance value. The velocity field close to the aortic bifurcation, where the return cannula flow is redirected, shows large variations and complex, three-dimensional flow structures. At the aorta inlet, the velocity field is sensitive to the aorta inflow BC. In the XY -plane, areas of high sensitivity are located in areas with high unsteady flow motion. The sensitivity analysis of the velocity field in the XY -plane seems to be independent of the BCs. The pressure field is sensitive to the BC since the pressure in the domain is dependent on the WK model parameters. This work can be a starting point to further investigate the influence of a change in BCs on the flow structures and the outflow distribution between the iliac arteries. Those results can develop a framework stating the factors with an increased patient’s risk for developing limb ischemia. / Veno-arteriell extrakorporeal membranoxygenering (V-A ECMO) är en behandling som kan rädda liv på patienter med kraftigt nedsatt hjärt- och lungfunktion. En vanlig komplikation under behandlingen är ischemi i benet där kanylen återför oxygenerat blod till patienten. Hemodynamiken bakom ischemi under V-A ECMO är illa förstådd idagsläget. I det här arbetet används beräkningsströmningsdynamik för att modellera interaktionen mellan blodflödet från returkanylen och blodflödet från patientens hjärta i bukaortan bifurkation med iliak artärerna. En Windkesselmodell (WK) med två element används för att modellera kärlen nedströms från illiakartärerna. Sammanlagt utförs fem simulationer av fyra hjärtcykler, vari antingen en av WK-parametrarna eller randvillkoret för aortans inflöde ändras. Resultatet tyder på att utflödet distribueras mellan iliak artärer beroende på WK parametrarna, men oberoende av randvillkoret för aortans inflöde. Med ett flöde på 0.8 L{min vid ursprungsläget ökas trycket i området och utflödet genom iliak artären utan kanyl om resistansen i WK-modellen ökas, och motsatt effekt nås genom att sänka resistansen eller genom att öka modellens värde för artärernas följsamhet. Hastighetsfältet kring aortabifurkation, där återflödet byter riktning, visar starka och komplexa tre-dimensionella variationer. Hastighetsfältet i ingången till aortan är känsligt för randvillkoret för aortans inflöde. I XY -planet finns områden med hög känslighet där flödet är högostadigt. Hastighetsfältets känslighet i XY -planet verkar vara oberoende av randvillkoren. Tryckfältet är känsligt för randvillkoren då trycket i området beror på WK-modellens parametrar. Det här arbetet kan vara en utgångspunkt för framtida studier i randvillkorens effekt på flödesstrukturer och utflödesdistribution mellan iliak artärer. Resultaten från sådana studier kan användas för att bygga upp en förståelse för hur olika faktorer påverkar en patients risk för ischemi under V-A ECMO behandling.

Flow in the Moderator of a CANDU reactor can be very complex due to the interplay of convective and buoyant effects. Experiments have been performed to measure temperature and velocity fields for these kind of flows, although concerns still exist. As a result a Moderator test facility has been built in order to validate CFD models for future predictions and safety analysis. To properly validate this experiment an accurate set of inlet flow conditions must be established in order to ensure a fair comparison. A series of flow conditions indicative of the header assemblies which feed flow into the moderator test facility have been investigated through experimentation, empirical evaluation and numerical simulation. They include flow through curved tubes, turbulent free jets and flow through dividing manifolds. The goal of the present study is to establish the modelling approach to predict the flow distribution inside the manifold and velocity field out of the J-nozzles. A variety of RANS based turbulence models and computational meshes were employed in the numerical study. The turbulence model that was found to perform best was the realizable k- model. It was also found that the velocity field of the J-nozzles is constant between Reynolds numbers of 6800-9300. These Reynolds numbers are indicative of those expected out of the header assemblies. / Thesis / Master of Applied Science (MASc)