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This work aims at developing a strategy how the energy which has to be applied to transport incompressible and Newtonian fluids through straight ducts can be reduced. Based on the physical properties of laminar and turbulent flow, models are derived which theoretically lead to the reduction of the dissipated energy. The possibility to implement the proposed state due to appropriate design aspects in the cross section shape of the duct is investigated based on numerical simulations of the flow

Strömungskontrolle --- direkte numerische Simulation --- direct numerical simulation --- turbulente Strömungflow control --- turbulent flow --- drag reduction --- Reibungsreduktion

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The work presents an attempt to improve the understanding of reactive drag reducing control of near-wall turbulence with respect to limitations present in a realistic application scenario. The reference reactive control scheme of opposition control is studied using direct numerical simulation through the consideration of various application oriented restrictions, i.e. local control application, limited spatial and temporal resolution of the scheme, sensor noise and control elements arrangement.

turbulence control --- direct numerical simulation --- turbulent boundary layers --- Direkte Numerische Simulation --- Reibungsminderung --- drag reduction --- Turbulente Grenzschichten --- Turbulenzkontrolle

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The transition of boundary layer from laminar to turbulent is more probable to happen across various components of a turbomachine. If narrowed down to a case of low-pressure turbine cascade, the transition of flow in boundary layer is due to separation induction. Due to this, blade losses are observed and it depends on various physical characteristics such as size and the length of the separation bubble. The physical characteristics can vary based on the variation of flow Reynolds number, expansion ration of the flow and the inlet flow turbulence intensity. Such characteristics can be studied using computational techniques, CFD analysis. Various computational techniques can be used for this scope of study, ranging from Reynolds Averaged Navier Stokes to Direct Numerical Simulation modelling, and each technique have its own set of advantages and disadvantages. 

The objective of this thesis is to present and acknowledge on how these separation bubble physical characteristics vary due to the variation of flow expansion ratio and variation of exit isentropic Reynolds number for a SPLEEN blade cascade. Direct Numerical Simulation technique will be adapted for this thesis, due to its ability to accurately predict separation bubble location and size but compromising to relatively high computational power requirement.

Low pressure turbine --- Flow separation bubble --- Boundary layer --- Flow transition --- Turbulence --- Reynolds stress --- Direct Numerical Simulation --- Discontinous Galerkin method --- Ingénierie, informatique & technologie > Ingénierie aérospatiale

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This book contains original peer-reviewed articles written by some of the most prominent international physicists active in the field of hydrodynamics. The topic is entirely devoted to the study of the transitional regimes of incompressible viscous flow found at the onset of turbulent flows. Nine articles written for this 2020 Special Issue of the journal Entropy (MDPI) have been gathered at the crossroads of fluid mechanics, statistical physics, complexity theory, and applied mathematics. They include experimental, analytic, and computational material of an academic level that has not been published anywhere else.

Research & information: general --- Technology: general issues --- subcritical phenomenon --- transition to turbulence --- direct numerical simulation --- spatio-temporal intermittency --- channel flow --- hibernating turbulence --- hot-film anemometry --- turbulence --- turbulent bands --- obliqueness --- advection speed --- wave generation --- inflectional instability --- transition to/from turbulence --- wall-bounded shear flow --- plane Poiseuille flow --- spatiotemporal intermittency --- directed percolation --- critical phenomena --- subcritical transition --- turbulence fraction --- moment --- unsteady shear flow --- turbulence intermittency --- helical instability --- puff dynamics --- phase transition --- Couette flow --- lifetimes