Design an affordable eVTOL ambulance that provides emergency medical assistance for small and medium communities in Central Europe and is a scalable competitor to emergency helicopters, and a substitute for ground-based ambulances.

With a symmetric rotor, tip vortex helices develop regularly before interacting, following the leapfrogging instability. The latter can occur earlier when the helices are placed at an initial radial offset, which is realized by considering blades of different lengths. This study investigates the spatio-temporal development of near-wake behavior for rotors with a significant blade length difference. Large eddy simulations and actuator line method on a modified NREL 5MW turbine under various inflow conditions were conducted to evaluate the impact of blade length differences ranging from 5 to 30%. The development of tip vortex helices, the onset of leapfrogging, vortex merging, and ultimately their three-dimensional breakdown were monitored. The analysis is corroborated by using a simplified (two-dimensional vortex-filament model).
The results show that the leapfrogging process begins immediately downstream of the vortex release when blades of different lengths are considered. The instability growth rate obtained from the 2D vortex model agrees with the LES data. Although the rotor asymmetry accelerates the leapfrogging and, in some conditions, the vortex merging process alone, it proves insufficient to cause a large-scale breakdown of the helix system and enhance wake recovery. Under laminar and 5% turbulence inflow conditions, the rotor asymmetry has minimal effect on momentum deficit recovery. In other conditions, no appreciable variations of wake recovery can be observed.

This thesis proposes techniques to produce wall-shear stress estimates from three-dimensional Lagrangian particle tracking (LPT). Several works have already faced the problem of determining near-wall velocity and in particular skin friction for the case of a flat surface. Here, the problem is translated to generic three-dimensional objects. The work makes use of an experimental database, recently produced, with LPT (Hendriksen et al. 2024), that provides in-situ registration of the object, for three shapes of increasing complexity: a cube, an airfoil and a cyclist. Four techniques are examined and compared, including interpolation method as well as local data regression. The uncertainty is evaluated a-posteriori, comparing the results with a local coin-stacking technique, where applicable. All techniques yield accurate and robust representations of the skin friction lines around three-dimensional objects, allowing for an insightful inspection of the near-surface flow topology. Instead, distinct differences are found when the skin-friction magnitude is estimated.

The increasing population density in metropolitan areas, coupled with the faster pace of everyday life, calls for the development of Inter-Urban Air Mobility (UAM) solutions. Currently, there is a gap in the market since there is no competitor that can facilitate all market segments and also provide “last-mile transport” by air. This report aims to identify a promising Inter-UAM design, the Swing, focused on minimising the aircraft’s ground and environmental footprint. The small ground footprint will enable the vehicle to take off from smaller vertiports, helipads or even driveways, allowing it to penetrate urban areas and land where other UAM vehicles cannot.

Particle Tracking Velocimetry (PTV) is an effective and non-intrusive flow measurement technique that is able to provide quantitative information of the full velocity field at a certain instant in time, by tracking each particle individually with high-speed cameras. This permits to have a very high precision in measuring the flow evolutions. The abundant time information can then be leveraged by reconstruction algorithms not only to bring the information into a Cartesian format, but also to increase the space resolution of the original measurements. This thesis aims to explore the enhancement of the Navier-Stokes based reconstruction method called VIC-TSA (Vortex-in-Cell with Time-Segment-Assimilation) through the implementation of Radial Basis Functions (RBF). Moreover, it investigates whether the incorporation of RBFs can enable VIC TSA to match or exceed the accuracy of the VIC+ method. The improvements are evaluated numerically with a synthetic flow field (Taylor-Green sine wave vortex lattice) and experimentally (flow over a bluff body) with a real Lagrangian Particle Tracking (LPT) experiment in the TU Delft W-Tunnel.

Understanding and predicting vortex behavior is crucial to maximize performance using aerodynamic design. Vortex breakdown can be induced to benefit the flow field or has to be prevented to avoid losing performance. It is therefore important to study the dynamics of vortex breakdown.

The main objective of this thesis was to assess the feasibility of measuring a free, streamwise vortex and its breakdown from data acquired with robotic volumetric Particle Image Velocimetry (PIV), whilst analyzing the relation between the local flow properties and the location of the breakdown. Experiments were conducted at the W-Tunnel at the TU Delft High-Speed Lab, where vortex breakdown was induced by the adverse pressure gradient field in front of a cylinder. The robotic Coaxial Volumetric Velocimeter (CVV) was used to assess the feasibility of using this system for vortex breakdown identification, in combination with data processing using a Lagrangian Particle Tracking (LPT) technique (Shake-The-Box), to detect and analyze vortices and their breakdown. The results of this experimental campaign were analyzed to identify vortices and their breakdown from the CVV data by characterizing the vortex’s internal structure. The analysis included establishing the relations of the adverse pressure gradient and the Reynolds number with the breakdown location.

The results showed that vortex breakdown is induced by the adverse pressure gradient. However, the breakdown location is not solely dependent on it. Furthermore, the effect of the Reynolds number at the breakdown location is barely measurable with the robotic volumetric PIV system.

This exploratory and experimental study showed that the CVV in combination with LPT can be used to recognize the structure of the vortex in both its pre- and post-breakdown regimes. However, for the analysis of vortex breakdown, it was found that the data was affected by the low spatial resolution. Thus, robotic volumetric PIV cannot provide conclusive results in terms of the relation between the location breakdown and local flow properties. Several recommendations regarding the experimental set-up are given for future research.

Wind-turbine noise can restrict the growing implementation of renewable energy sources and their application close to urban environments. The largest contributor to the noise of modern turbines is the scattering of the turbulent fluctuations at the blade trailing edge. This source of noise is directly correlated with the turbine’s extracted power. Therefore, operating in noise-restricted environments and at night times entails lower energy production. An extensively applied solution for reducing the noise of wind turbines is the use of trailing-edge serrations, i.e. imposing periodic variations in the geometry of the blade trailing edge. Serrations reduce the effectiveness of the scattering at the trailing edge as the turbulent fluctuations reach the trailing edge at different times along the blade span, consequently reducing the wind-turbine noise. Although extensive literature and knowledge exist on serrations, their measured performance does not compare with the predicted one. Even more problematic, the trends predicted for the geometric alterations of the serrations are not observed in reality. Notably, two things are worth mentioning: first, geometries shown as optimal by theory perform worse than other concepts, and second, the noise from serrations is affected by the angle between the insert and the flow. As a result, the design of trailing-edge serrations still requires dedicated experiments and numerical simulations, hampering the assessment of several geometries necessary for complete optimization of the serration design. This work seeks a physical interpretation of the noise generation mechanisms of trailing edges with serrated add-ons. This interpretation is focused on understanding the underlying physical principles of the flow surrounding a serrated trailing edge. This is carried out in this work with three studies, respectively on the observation, modelling, and control of the flow and acoustic properties of serrated trailing edges...

The available energy density supplied by conventional light sources prohibits the use of time-resolved volumetric Particle Image Velocimetry (PIV) with submillimetre helium-filled soap bubbles (HFSB) on a cubic metre scale. In connection with attempts to expand the maximum attainable measurement domain of PIV, a research project is carried out into the upscale of the seeding particles, capable of scattering more light. The production flexibility and scalability of HFSB is investigated by designing and improving the conventional HFSB nozzle generator used by Delft University of Technology. Experiments are performed on various nozzle designs, focusing on the average bubble diameter. Through geometrical scaling and further developments, the bubble diameter is scaled from 0.5 mm, produced by conventional nozzles, to 2.5 mm. The obtained upscale in bubble diameter corresponds to a 3-fold increase along all dimensions compared to the current operational domain for HFSB experiments. Furthermore, a novel physics-based model is proposed relating particle size to the nozzle orifice and flow rates of air and helium and is benchmarked with the acquired experimental data.

The interaction of an airfoil with incident turbulence is an important source of aerodynamic noise in numerous applications, such as turbofan engines, cooling systems for automotive and construction industries, high-lift devices on aircraft wings, and landing gear systems. In these instances, turbulence is generally produced by elements that are installed upstream of the wing profile and generate inflow distortions. A possible strategy for the reduction of turbulence-interaction noise, also referred to as leading-edge noise, is represented by the integration of porous media in the structure of the airfoil. However, the physical mechanisms involved in this noise mitigation technique remain unclear. The present thesis aims to elucidate these phenomena and, particularly, how porosity affects the incoming turbulence characteristics in the immediate vicinity of the surface. This problem has been addressed from different perspectives, namely from the technological, experimental, and analytical ones. An innovative design for a porous NACA-0024 profile fitted with melamine foam is proposed. The noise reduction performance achieved with such a porous treatment is evaluated through a novel version of the generalized inverse beamforming (GIBF) implemented with an improved regularization technique. The algorithm is first applied to different experimental benchmark datasets in order to evaluate its ability to reconstruct distributed aeroacoustic sources and to assess its accuracy and variability in different conditions. Results indicate that the implemented method provides an enhanced representation of the distributed noise-source regions and higher performance in terms of accuracy and variability if compared with other common beamforming techniques. GIBF is then employed together with far-field microphone measurements to characterize the leading-edge noise radiated by solid and porous NACA-0024 profiles immersed in the wake of an upstream cylindrical rod at different free-stream velocities. A noise reduction of up to 2dB is found for frequencies around the vortex-shedding peak, with a trend that is independent of the Reynolds number, whereas significant noise regeneration is observed at higher frequencies, most probably due to surface roughness. Subsequently, the flow-field alterations due to porosity in the stagnation region of the airfoils are investigated by means of mean-wall pressure, hot-wire anemometry, and particle image velocimetry measurements. The porous treatment mostly preserves the integrity of the NACA-0024 profile’s shape but yields a wider opening of the jet flow that increases the drag force. Moreover, porosity allows for damping of the velocity fluctuations near the surface and has limited influence on the upstream mean-flow field. In particular, the upwash component of the root-mean-square of the velocity fluctuations turns out to be significantly attenuated in a porous airfoil in contrast to a solid one, resulting in a strong decrease of the turbulent kinetic energy in the stagnation region. The present effect is more pronounced for higher Reynolds numbers. The mean spanwise vorticity close to the body appears also to be mitigated by the porous treatment. Furthermore, the comparison between the power spectral densities of the incident turbulent velocities demonstrates that porosity has an effect mainly on the low-frequency range of the turbulent-velocity spectrum, with a spatial extent up to about two leading-edge radii from the stagnation point. In addition, the vortex-shedding frequency peak in the power spectrum of the streamwise velocity fluctuations close to the airfoil surface is found to be suppressed by porosity. The present results show analogies with the outcomes of the aeroacoustic analysis, highlighting the important role played by the attenuated turbulence distortion due to the porous treatment of the airfoil in the corresponding noise reduction. An analytical model based on the rapid distortion theory (RDT) to predict the turbulent flow around a porous cylinder is formulated with the aim of improving the understanding of the effect of porosity on turbulence distortion and interpreting the experimental results. The porous treatment, characterized by a constant static permeability, is modeled as a varying impedance boundary condition applied to the potential component of the velocity that accounts for Darcy’s flow within the body. The RDT implementation is first validated through comparisons with published velocity measurements in the stagnation region of an impermeable cylinder placed downstream of a turbulence grid. Afterwards, the impact of porosity on the velocity field is investigated through the analysis of the one-dimensional velocity spectra at different locations near the body and the velocity variance along the stagnation streamline. The porous surface affects the incoming turbulence distortion near the cylinder by reducing the blocking effect of the body and by altering the vorticity deformation caused by the mean flow. The former leads to an attenuation of the one-dimensional velocity spectrum in the low-frequency range, whereas the latter results in an amplification of the high-frequency components. This trend is found to be strongly dependent on the turbulence scale and influences the evolution of the velocity fluctuations in the stagnation region. The porous RDT model is finally adapted to calculate the turbulence distortion in the vicinity of the porous NACA- 0024 profile leading edge. The satisfactory agreement between predictions and experimental results suggests that the present methodology can improve the understanding of the physical mechanisms involved in the airfoil-turbulence interaction noise reduction through porosity and can be instrumental in designing such passive noise-mitigation treatments.

Turbulent boundary layers are responsible for up to 89 % of the skin friction drag of civil aircraft. This shows that in regard to the current social sensitivity towards climate friendly aviation a reduction of tur- bulent skin friction could have a large impact. On the one side greenhouse gas emissions by aviation could be reduced and on the other hand fuel costs could be saved, an important consideration for air- lines. The research on turbulent drag reduction distinguishes between passive and active techniques. Passive techniques have the advantage that no energy input is necessary. Prominent examples are riblets and dimples which have shown turbulent drag reductions up to 10 %. Active techniques reach turbulent drag reduction percentages of up to 45 %, however it is in doubt if the energy savings are larger than the energy required to operate the control technique. One promising active technique which has proven to partially generate a positive energy effect is spanwise wall oscillation. However, researchers have opposing opinions of the mechanism which leads to the drag reduction. As turbulent boundary layers are strongly three-dimensional, the work of this thesis investigates three-dimensional flow fields of turbulent boundary layers subjected to spanwise wall oscillation by means of tomographic PIV. These are used to study the changes in pointwise statistics and coherent structures in order to derive a descriptive model of the drag reducing mechanism.

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 are around the optimum reported in literature studies (T⁺_osc = [100-700], A⁺_osc= [50, 150]). A high-resolution planar PIV apparatus is employed to measure the drag reduction directly by wall shear stress estimates on the oscillating wall. The measurement uncertainty of the drag estimates from PIV measurements is examined. The results show drag reduction in the order of 15% after 6 boundary layer thicknesses from the beginning of the oscillating section. Variations of the drag reduction follow the trends reported in literature. The PIV measurements enable the analysis in terms of Reynolds shear stresses, turbulence production and allow visualising vortex packets by vorticity. A pronounced drop of turbulence production in the range y⁺ = [5, 30] is observed. The vorticity analysis indicates a distortion from the well-known hairpin-packet arrangement, suggesting that the mechanism of hairpin auto-generation may be inhibited by spanwise wall oscillations

Car industry and motorsport development nowadays strongly rely on wind tunnel testing. As the literature survey shows, in order to fully understand the characteristics of the flow around a car, large-scale and volumetric flow field measurements are required. For its features, PIV can be pointed as a useful technique for automotive wind tunnels. However, its use in an automotive wind tunnel is strongly conditioned by the industrial environment itself, which requires particular efforts for what concerns safety and economic aspects.

The advent of Robotic Volumetric PIV has permitted the measurement of time-averaged properties of large-scale complex aerodynamic flows by the combination of coaxial volumetric velocimetry and robotics. Firstly, the use of Helium Filled Soap Bubbles as seeding permits to enlarge the measurement volume due to their higher scattering capability. Furthermore, the compactness of the coaxial velocimetry probe together with the robotic actuation allows to measure large-scale volumes, partitioning the entire volume and reconstructing the time-averaged flow filed from multiple PIV acquisitions.
Since its presentation, Robotic Volumetric PIV has been used to investigate low velocities flows, with free-stream values ranging between 2 m/s and 14 m/s. More specifically, 15 m/s can be considered the largest velocity that can be analysed with the state-of-the-art of the system due to its hardware limitations in the maximum acquisition frequency.
For this reason, to meet the requirements in terms of flow velocities proper of industrial environments, the range of analysable velocities has to be extended.

To address the identified requirement of high-speed volumetric measurements, a new acquisition technique has been designed and proposed. Even if a standard double-pulse strategy can measure high-speed flows due to the short time that can elapse between the two subsequent pulses, in order to increase the accuracy of the final results, a two-$\Delta t$ method is proposed. Firstly, a predictor is built using a Double-Pulse, Double-Frame acquisition with a short pulse separation time $\Delta t_1$. Afterwards, the predictor is used to allow the stretching of the second pulse separation time $\Delta t_2$ without encountering errors given by the false pairing that would be present due to the longer displacement of the particles.

To test the performance of the new method, the near wake of a $50\%$ replica of the Ahmed body with a 25$^{\circ}$ slant angle has been studied through an experimental campaign in the Open Jet Facility (OJF) of TU Delft. Firstly, a measurement at 12 m/s has been performed in order to be able to assess the performances of the proposed method w.r.t. the time-resolved acquisition strategy and the DP standard -DF approach.
Afterwards, an airspeed of 20 m/s has been considered, in order to demonstrate the capability of the new technique of extending the velocity range of Robotic Volumetric PIV.

The conducted measurements demonstrate the possibility of extending the velocity range of the Robotic Voluemtric PIV system with the proposed method. However, this is achieved at the expense of a lower accuracy, due to the lack of temporal information, and a longer measurement time, given by the necessity of multiple acquisitions.

A new type of tracer is making its entry in the scenario of wind-tunnel measurements: helium-filled soap bubbles (HFSB). The present work discusses the main fluid-dynamic and optical properties of HFSB to evaluate their use for quantitative measurements in aerodynamic experiments.
In the past three decades, particle image velocimetry (PIV) has become a standard measuring technique in experimental fluid mechanics. Advances in both hardware components and software analysis have allowed achieving many milestones in flow diagnostics, mainly time-resolved and instantaneous volumetric measurements. In particular, the extension to the third dimension in space, i.e. tomographic PIV and 3D particle tracking velocimetry (PTV), has been used to provide quantitative visualizations of the coherent structures occurring in various turbulent flows and have provided insight in the spatial organization of the turbulent motions at different scales. The extension of the aforementioned techniques towards industrial practice in wind tunnel testing requires the development of a more efficient approach in terms of scaling and versatility.
The present dissertation tackles the upscaling of PIV experiments towards industrial wind tunnels with the use of HFSB as tracing particles. The reasons and motivations behind this choice are addressed in the first chapter and followed by a description of the state-of-the-art of PIV. The second chapter aims at familiarising the reader with the working principles of PIV, which will be later recalled when presenting the advances towards large-scale experiments. Information on the mechanical behaviour of tracer particles and on the underlying physics are discussed in the third chapter, where also the case of HFSB is examined for use during quantitative measurements in the low-speed flow regime.
The problem of seeding in wind tunnels is discussed in chapter 4, where a system for the injection of HFSB in a large wind tunnel is presented. Here, the relationship between HFSB production rate and the resulting spatial concentration and dynamic spatial range (DSR) are discussed. Specific experiments that examine the tracing fidelity of sub-millimetre HFSB tracers are presented in chapter 5. The behaviour of HFSB is compared to micro-size droplets, yielding a characteristic response time in the range of 10 μs. The latter milestone opens up to the applicability of HFSB tracers for quantitative velocimetry in wind tunnel flows. In chapter 6, a specific case of interest is presented whereby HFSB tracers are used to measure the flow velocity within steady vortices such as those released at the tip of wings. A dedicated experiment shows that the neutrally or slightly buoyant HFSB return a rather homogeneous spatial concentration within the core of vortices, solving the long-standing issue encountered for small heavy tracers, such as fog droplets, that are systematically ejected from highly vortical regions.
An analysis of the light scattering by HFSB was conducted with theoretical and experimental approaches, as described in chapter 7. The light intensity scattered by the HFSB is characterised by two source points: the glare points. The overall scattered light appears to be 104-105 times more intense with respect to the oil-based micro-size droplets. This information is used to retrieve the maximum size of the measurement volume for a given light source.
Chapter 8 closes this dissertation presenting a survey of all the experiments that have been conducted during this PhD research. The scale of experiments varies from the more academic case of a circular cylinder up to the one of a ship model installed in one of the large industrial wind tunnels operated at the German-Dutch Wind Tunnels laboratories (DNW), going through the visualization and quantification of large structures in the rotor region of a vertical axis wind turbine (VAWT).

The research presented in this thesis focuses on boundary layer separation and, more specifically, on the related physical mechanisms, such as laminar to turbulent transition, with a vision towards effective separation control. The work is divided in three parts, each corresponding to a different separation scenario. The supporting data is experimental, obtained by means of particle image velocimetry. The first and major part regards the phenomenon of laminar separation bubbles. The spatial and temporal response characteristics of a flat plate laminar separation bubble to impulsive forcing are first investigated in order to shed light on the processes of flapping and bursting. The impulsive disturbance is introduced twodimensionally with a dielectric barrier discharge plasma actuator. The disturbance develops into a wave packet that causes rapid shrinkage of the bubble in both upstream and downstream directions. This is followed by bubble bursting, during which the bubble elongates significantly, while vortex shedding strength in the aft portion of the bubble is reduced. Duration of the recovery of the bubble to its unperturbed state is independent of the forcing amplitude. At the same time, linear stability analysis shows that the growth rate and the frequency of the most unstable mode decreases for increasing forcing amplitude. Throughout recovery, growth rates are directly proportional to the shape factor, indicating that bursting and flapping mechanisms are driven by altered stability characteristics due to variations in incoming disturbances. It is found that the stability of the flow changes only when disturbances interact with the shear layer breakdown and reattachment processes, supporting the notion of a closed feedback loop.

Aerodynamics research and development often involves large-scale and turbulent flows; may this be a rotor flow, the wake of a car, or the flow passing a human athlete to name a few examples. Volumetric particle image velocimetry (PIV) is well suited for the study of such flows. The introduction of Helium Filled Soap Bubbles (HFSB) for wind tunnel measurements has pushed the achievable measurement domains using state-of-the-art tomographic PIV systems to the order of 50 liters. Despite the dramatic increase in the measurement volume size by the introduction of HFSB, the observation volumes in tomographic PIV are still relatively limited. Further, the system complexity is high, constraining optical access on complex geometries and prohibiting a rapid repositioning of the measurement domain.

To address the identified need of large-scale volumetric flow field measurements around complex geometries, a novel robotic PIV approach is presented. The proposed method relies on a coaxial volumetric velocimetry probe comprising four high speed cameras at low tomographic aperture, aligned with the illumination. The compact system greatly enhances optical access and it gives rise to a universal calibration, meaning that it can take full advantage of robotic manipulations. Therefore, large domains can rapidly be partitioned into a series of adjacent sub-volume measurements, controlling the velocimeter position by means of a robotic arm.

The feasibility of the proposed system is demonstrated in a study of the near flow field around a full-scale replica of a time-trialling cyclist at 14 m/s. 450 time-resolved volumetric PIV measurements are acquired to compound the time-averaged flow field on a 2 m³ domain. The analysis of the flow topology developing around the cyclist shows good agreement with available literature and it indicates the potential of the proposed robotic PIV approach in other engineering applications.

The flow near the surface, and the acoustic emissions of trailing edge serrations are investigated in this work. The use of this family of aerodynamic devices on airfoils is intended for the reduction of turbulent boundary layer-trailing edge noise (TBL-TE noise). This purpose has been well demonstrated in wind tunnel and numerical experiments. Particularly, their use in the wind turbine industry has been of great interest in recent years. A growing number of field measurements have shown that a noticeable noise reduction of TBL-TE noise in state-of-the-art blades is also obtained. A full explanation on the mechanism of how noise is reduced is nevertheless lacking. Existing experimental research on serrations offers only a limited characterization of the relevant flow parameters. Fundamental concerns pertaining to the conditions at which that data has been previously gathered are furthermore recurrent. The persistent use of flow-misaligned serrations creates a situation in which flow structures may be observed and misinterpreted as necessary for the attainment of noise reduction. This circumstance complicates the discussion and isolation of the relevant noise reduction mechanism...

The fundamental properties of computed flow fields using particle imaging velocimetry (PIV) have been investigated, viewing PIV processing as a black box without going in detail into algorithmic details. PIV processing can be analyzed using a linear filter model, i.e. assuming that the computed displacement field is the result of some spatial filtering of the underlying true flow field given a particular shape of the filter function. From such a mathematical framework, relationships are derived between the underlying filter function, wavelength response function (MTF) and response to a step function, power spectral density, and spatial autocorrelation of filter function and noise.
A definition of a spatial resolution is provided independent of some arbitrary threshold e.g of the wavelength response function and provides the user with a single number to appropriately set the parameters of the PIV algorithm required for detecting small velocity fluctuations.
The most important error sources in PIV are discussed and an uncertainty quantification method based on correlation statistics is derived, which has been compared to other available UQ-methods in two recent publications (Sciacchitano et al. 2015; Boomsma et al. 2016) showing good sensitivity to a variety of error sources. Instantaneous local velocity uncertainties are propagated for derived instantaneous and statistical quantities like vorticity, averages, Reynolds stresses and others. For Stereo-PIV the uncertainties of the 2C-velocity fields of the two cameras are propagated into uncertainties of the computed final 3C-velocity field.
A new anisotropic denoising scheme as a post-processing step is presented which uses the uncertainties comparing to the local flow gradients in order to devise an optimal filter kernel for reducing the noise without suppressing true small-scale flow fluctuations.
For Stereo-PIV and volumetric PIV/PTV, an accurate perspective calibration is mandatory. A Stereo-PIV self-calibration technique is described to correct misalignment between the actual position of the light sheet and where it is supposed to be according to the initial calibration procedure. For volumetric PIV/PTV, a volumetric self-calibration (VSC) procedure is presented to correct local calibration errors everywhere in the measurement volume.
Finally, an iterative method for reconstructing particles (IPR) in a volume is developed, which is the basis for the recently introduced Shake-the-Box (STB) technique (Schanz et al. 2016).