Identification of Large-Scale Structures in Turbulence

This thesis aims to automatically and reliably detect large-scale structures in turbulent flows. To achieve this, a U-net (a type of neural network) is trained using artificially generated data. From the network output, continuous structures are derived and general statistics, including, volume fraction, relative kinetic energy and length scales...

Determining the topology of hydrogen flame using computed tomography of chemiluminescence

With ongoing research towards clean combustion, hydrogen has been identified as a potential alternative to natural gas fuel, for example in power generation sectors utilizing gas turbines because of their inherent nature of being a carbon-free energy carrier. However, it is crucial to clarify that the ultimate goal is not just carbon-free...

Wall Interference Assessment of Isolated Fixed-Pitch Propeller Tests

The need to reduce greenhouse gas emissions is emergent throughout every industrial sector worldwide. For aviation, this has opened a market gap for small scale electric aircraft configurations (e-V/STOL). These configurations are very diverse and they are classified based on how lift is obtained. However, their flight...

Entrainment Coefficient of a Turbulent Plume: An Experimental Investigation with PIV and LIF

Buoyancy-driven plumes are natural phenomena that occur in widespread applications, such as geological flows or pollutant dispersion from a chimney. One characteristic of plumes is the entrainment process, where the plume stream drags in ambient fluid and mixes with the ambient fluid, and classic plume theory has used an entrainment coefficient...

Fundamental numerical studies of thermal stratification effects in idealized urban areas: Weakly unstable thermal stratification effects on the elongated roll-structures downstream of a high-rise building, and its potential effect on pollutant dispersion in urban areas

Pollution in urban environments is increasingly becoming a major concern for our societies which, together with the increasingly powerful capabilities provided by computational fluid dynamics (CFD), has made pollution dispersion a common topic of research during the last two decades. Several factors are relevant to the dispersion of pollutants...

Translationally Accelerating Wings in Ground Effect: A Numerical Study

Aerodynamics has played a significant role in the industry of motorsports in improving the performance and handling of the race car. Rob Smedley, the former head of vehicle performance at Williams Racing stated that - "Where teams have problems is when their development or simulation environment – so CFD [Computational Fluid Dynamics] or wind...

Spanwise wall oscillation as a drag reduction technique: PIV-based evaluation of turbulent skin-friction drag reduction over a flat plate by spanwise wall oscillation

Reduction of skin-friction drag over a fully developed canonical zero-pressure gradient turbulent boundary layer (ZPGTBL) subjected to spanwise oscillation is measured using planar particle image velocimetry (PIV). The experiments are conducted at Re_θ of 1000 and 1800, the chosen range of spanwise oscillations amplitude and frequency...

The Effect of Nozzle Length and Exhaust Plume on Transonic and Supersonic Axisymmetric Base Flows: An Experimental Study

A combined PIV and Schlieren measurements have been carried out in the transonic-supersonic wind tunnel (TST-27) to investigate the effect of exhaust plume and the variation in nozzle length on the flow topology and mean pressure distribution on the wake of axisymmetric backward facing step model at freestream Mach numbers of 0.76 and 2.20,...

Controlled ring vortex injection into a turbulent pipe flow

In this thesis a vortex generator is presented, that can generate controlled ring-vortex injections into a pipe flow. The performance of the generator and the coherence of its structures is tested by applying a dye visualisation method. Furthermore, iso-contour plots of the 3D velocity field, obtained from Stereoscopic Particle Image Velocimetry...

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...

Self-Sustaining Mechanisms in Wall Bounded Turbulence: Merging & auto-generation of vortices

For channel flow, we explore how a hairpin eddy may reach a threshold strength required to produce additional hairpins by means of auto-generation. This is done by studying the evolution of two eddies with different initial strengths (but both below the threshold strength), initial sizes and initial stream-wise spacing between them. The...

Numerical study of boundary layer transition behind a zigzag trip

In this thesis a numerical investigation was performed to increase our understanding of a low Reynolds number transition behind a zigzag trip. This was done with the use of Direct Numerically Simulation (DNS). This means that the Navier-Stokes equations are solved numerically without any use of a turbulence model. The DNS solver of the CFD...

Investigating the 3D Flow Structure Downstream of a Fence

In this research the experiments were performed in the water tunnel at the Laboratory for Aero and Hydrodynamics to investigate the 3D flow structure over roughness elements as a model for the flow over urban environment. It represents the first phase in an extended study on the dispersion of pollutants in an urban environment, which process is...