Direct numerical simulation of two-phase stratified flows in the primary coolant of a nuclear reactor

Multiphase flows are very common in many Nuclear engineering applications. During high pressurized conditions there are possibilities of high thermal loads on the pressure vessel, leading to pipe ruptures. As part of breakdown measures, the emergency core cooling system is activated and the coolant is mixed with the fluid in the cold leg, giving...

Direct Numerical Simulation of supersonic flow over resolved and modeled roughness

 Distributed surface roughness elements characterise Thermal Protection Systems (TPS) typical of supersonic and hypersonic flows. The presence of these distributed roughness elements cause an increase in drag and heat transfer.  As opposed to incompressible flow over roughness elements, there are very few experimental and numerical studies on...

Turbulence Decay of a Shear-Thinning Fluid in Pipe Flow: A DNS Study

The human body is the subject of several interesting phenomena and blood flow comes under that category. The main motivator for this thesis is the flow of blood in aneurysms. An aneurysm is a sudden expansion of an artery, with large expansion angles causing an adverse pressure gradient and leading to flow separation. Several studies have shown...

Rotating Discs Actuators: Direct Numerical Simulation for Turbulent Skin­Friction Drag Reduction

In the aviation, maritime and oil&gas sector, the potential benefit in yearly savings deriving from the reduction of turbulent skin-friction drag through active flow control are estimated in the millions of U.S. Dollars and million tonnes of CO2 emissions. Research in this topic has brought forward numerous techniques, offering enticing drag...

Direct Numerical Simulations of Boundary Layer Stability for Non-ideal Fluids

The process in which a smooth laminar flow transits to a chaotic to a chaotic, turbulent state, is a topic of particular interest in the sectors of energy technology and aerodynamics. To study the different paths that can be followed during the transition process, various tools and methods have been developed. A preliminary investigation of the...

DNS of heat transfer in a turbulent channel flow over fractal roughness

Convective heat transfer finds applications in several domains of industry like heat exchangers, gas turbine blades, IC engine surfaces etc. The surfaces of these heat transfer applications are either naturally rough owing to manufacturing techniques or become rough over a period of time during operation. These rough surfaces usually contain...

High fidelity simulations of Taylor bubbles in turbulent co-current flow

The graduation project was conducted at the CFD department of Nuclear Research And Consultancy Group (NRG) in Petten. The modeling and simulation of Taylor bubble flow using CFD can contribute significantly to the topic of nuclear reactor safety and in particular, in the emergency cooling of nuclear reactors during a loss of coolant accident, or...

Micro-Ramp Flow Dynamics

Micro-ramps are passive flow control devices used to delay flow separation. Their use is widespread due to their reduced drag and structural robustness. We reproduce with Direct Numerical Simulations (DNS) recent Particle Image Velocimetry (PIV) experiments of the micro-ramp flow performed at TU Delft to study the wake of a micro-ramp immersed...

Heat transfer in finite sized particles suspensions

Heat transfer is important in many applications. For instance, due to the decrease in size of electronics, it<br/>becomes more necessary to have efficient and smaller cooling systems. In order to increase the effect of the<br/>cooling liquids used, it might be interesting to add extra solid particles with a high conductivity, to possibly<br/...

Analyzing a turbulent pipe flow via the one-point structure tensors: Vorticity crawlers and streak shadows

Efforts to identify and visualize near-wall structures typically focus on the region y⁺≳5, where large-scale structures with significant turbulent kinetic energy content reside, such as the high-speed and low-speed streaks associated with sweep and ejection events. While it is true that the level of the turbulent kinetic energy...

Universal aspects of small-scale motions in non-equilibrium turbulent channel flow

Direct numerical simulations of transient turbulent channel flow were conducted in order to study and characterize the large-small scale interaction in this type of flows. This was achieved by analyzing some well-known universal aspects of turbulence. Additionally, the so called strain-rate-eigenframe analysis was applied to study the local flow...

Quantitative Modeling of Domain Name System Protocol

Numerical Simulation of Turbulent Flow in Concentric Annuli

In this paper we consider a fully developed turbulent flow in a round pipe with a small inner annulus. The diameter of the inner annulus is less than 10% of the diameter of the outer pipe. As a consequence, the surface area of the inner pipe compared to the outer pipe is small. The friction exerted by the wall on the flow is proportional to the...

Particle Sedimentation in Wall-Bounded Turbulent Flows

In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by...

Particle Sedimentation in Wall-Bounded Turbulent Flows

In this work, a comparison between the results of point-particle direct numerical simulations and PIV/PTV experiments of a particle-laden horizontal channel flow is presented. The numerical simulations were preformed trying to mimic as much as possible the experimental conditions. The accuracy of the point-particle approach was evaluated by...