Stereo Particle Image Velocimetry Research Articles

Effects of wind shear and thrust coefficient on the induction zone of a porous disk: A wind tunnel study

AbstractNeglecting the velocity reduction in the induction zone of wind turbines can lead to overestimates of power production predictions, and, thus, of the annual energy production for a wind farm. An experimental study on the induction zone associated with wind turbine operations is performed in the boundary‐layer test section of the BLAST wind tunnel at UT Dallas using stereo particle image velocimetry. This experiment provides a detailed quantification of the wind speed decrease associated with the induction zone for two different incoming flows, namely, uniform flow and boundary layer flow. Operations of wind turbines in different regions of the power curve are modeled in the wind tunnel environment with two porous disks with a solidity of 50.4% and 32.3%, which correspond to thrust coefficients of 0.71 and 0.63, respectively. The porous disks are designed to approximate the wake velocity profiles previously measured for utility‐scale wind turbines through scanning wind LiDARs. The results show that the streamwise velocity at one rotor diameter upwind of both disks decreases 1% more for the boundary layer flow than for the uniform flow. Further, the effect of shear in front of the disk with a higher thrust coefficient can be observed until 1.75 rotor diameter upwind of the disk, whereas for the disk with a lower thrust coefficient, the effect of shear becomes negligible at 1.25 rotor diameter upwind. It is found that at one rotor diameter upwind, for both incoming flows, the disk having a higher thrust coefficient has 2% more velocity reduction than the lower‐thrust‐coefficient disk. The results suggest that the variability in wind shear and rotor thrust coefficient, which is encountered during typical operations of wind turbines, should be considered for the development of improved models for predictions of the rotor induction zone, the respective cumulative effects in the presence of multiple turbines, namely, wind farm blockage, and more accurate predictions of wind farm power capture.

Experimental study on modulation of homogeneous isotropic turbulence by bubbles of different sizes

The mechanism of turbulence modulation by bubbles is crucial for understanding and predicting turbulent bubbly flow. In this study, we conducted an experimental investigation of turbulence modulation by bubbles of different sizes in homogeneous isotropic turbulence using two-phase stereo-particle image velocimetry measurement techniques. Two bubble generation methods, electrolysis and porous medium, were employed to generate bubbles in micrometer and millimeter sizes, respectively. The oscillating grid system was utilized to generate homogeneous isotropic turbulence, allowing precise control of turbulent boundary conditions. The ratio of the fluctuating velocities and the comparison between turbulent kinetic energy and average kinetic energy indicated that the generated turbulence was nearly homogeneous and isotropic. With increasing turbulence intensity, micron-sized bubbles transition from suppressing turbulence to enhancing it, while millimeter-sized bubbles exhibit the opposite behavior. Turbulence modulation by millimeter-sized bubbles appears to be nearly isotropic, whereas micrometer-sized bubbles do not exhibit isotropy.

Experimental study on the synergy of sweeping jets on the afterbody flows of a slanted-base cylinder

The synergistic effects of sweeping jets (SWJs) hold significant potential in controlling afterbody vortex flows of a cargo fuselage. A combination of SWJ pairs, located at various streamwise positions, are employed to investigate the efficiency of their synergy in influencing the afterbody flows of a slanted-base cylinder with a 30° angle at a Reynolds number of 200,000. The total mass flow rate is kept similar resulting in a variation of the momentum coefficient of SWJs from Cμ=4.3×10−3 to 1.0×10−1. Energy efficiency and mass flow interactions were examined through direct force measurement, stereo Particle Image Velocimetry (PIV), and surface pressure measurement. The results show that the jet impingement on the surface is stronger when there is synergy among SWJs positioned more upstream (e.g. the combination of Top and Mid pairs), particularly at low momentum coefficients (Cμ < 0.02); conversely, when considering the synergy of SWJs located more downstream (e.g. the combination of Mid and Bot pairs), a greater reduction in surface pressure is observed at higher momentum coefficients (Cμ > 0.05); a potential net energy saving is achieved in the case of the combination of Top, Mid and Bot pairs (T+M+B). The controlled vorticity distribution observed in the collaborative configurations was mostly sandwiched by curves of individual SWJ cases, which is due to the fact that downstream SWJs (located at Mid and Bot positions in case T+M+B for instance) manage to weaken the enhanced vortex induced by the SWJ at upstream (located at Top position), highlighting a compromise in the synergy effectiveness of the jets with reverse roles at different positions. However, by taking the similar advantages of SWJ at certain positions on the vortex control, at Cμ=1.7×10−2, the vorticity reduced by the case combining Mid and Bot pairs is even 7 % and 13.5 % greater than cases Mid and Bot, respectively, which could serve as a hint on the potential benefit of SWJs’ synergy in the future.

Investigation of pulsed direct-current plasma jets in a turbulent boundary layer

Characteristics of the plasma jet produced by a pulsed direct-current (pulsed-DC) dielectric barrier discharge (DBD) and its interaction with a turbulent boundary layer (TBL) are investigated in detail using stereo particle imaging velocimetry. Quiescent-flow characterization results show that a positive starting vortex and a negative near-wall jet structure are induced by the pulsed-DC DBD plasma actuator. With increasing pulse width and discharge frequency, the jet velocity magnitude increases monotonously, as a direct result of the extension of fluid particle acceleration time. During the interaction with a cross-flow TBL, two streamwise vortices with opposite signs are observed at the two sides of the electrode junction, which essentially originate from the starting vortex and negative jet in quiescent air. The skin-friction drag variations are dominated by the cross-stream momentum transportation of streamwise vortices, with drag reduction in the vortex upwash zone and drag increase in the downwash zone. Compared with the conventional alternating-current DBD plasma actuators, the turbulent fluctuations produced by pulsed-DC DBD are much higher, which also affects the skin-friction drag. Further proper orthogonal decomposition (POD) analysis reveals that two distinctly different flow patterns are produced by pulsed-DC DBD working at small and large pulse widths. The dominant POD modes causing the most velocity fluctuation are the spanwise translation and deformation of plasma-induced streamwise vortices. These results provide insights into the basic phenomenon of pulsed-DC plasma jets in cross flow, which recently has demonstrated its promising applications in turbulent skin-friction reduction.

Three dimensional analysis of the exhalation flow in the proximity of the mouth

The human exhalation flow is characterized in this work from the three-dimensional velocimetry results obtained by using the stereo particle image velocimetry (SPIV) measurement technique on the flow emitted from a realistic airway model. For this purpose, the transient exhalation flow through the mouth of a person performing two different breaths corresponding to two metabolic rates, standing relaxed (SR) and walking active (WA), is emulated and studied. To reproduce the flow realistically, a detailed three-dimensional model obtained from computed tomography measurements on real subjects is used. To cope with the variability of the experimental data, a subsequent analysis of the results is performed using the TR-PIV (time resolved particle image velocimetry) technique. Exhalation produces a transient jet that becomes a puff when flow emission ends. Three-dimensional vector fields of the jet velocity are obtained in five equally spaced transverse planes up to a distance of ▪ from the mouth at equally spaced time instants ▪ which will be referred to as phases (φ), from the beginning to the end of exhalation. The time evolution during exhalation of the jet area of influence, the velocity field and the jet air entrainment have been characterized for each of the jet cross sections. The importance of the use of realistic airway models for the study of this type of flow and the influence of the metabolic rate on its development are also analyzed. The results obtained contribute to the characterization of the human exhalation as a pathway of the transmission of pathogens such as SARS-CoV-2 virus.

Experimental and numerical investigation to elucidate the fluid flow through packed beds with structured particle packings

The present paper presents an experimental and numerical investigation of the dispersion of the gaseous jet flow and co-flow for the simple unit cell (SUC) and body-centred cubic (BCC) configuration of particles in packed beds. The experimental setup is built in such a way that suitable and simplified boundary conditions are imposed for the corresponding numerical framework, so the simulations can be done under very similar conditions as the experiments. Accordingly, a porous plate is used for the co-flow to achieve the uniform velocity and the fully developed flow is ensured for the jet flow. The SUC and BCC particle beds consist of 3D-printed spheres, and the non-isotropy near the walls is mostly eliminated by placing half-spheres at the channel walls. The flow velocities are analysed directly at the exit of the particle bed for both beds over 36 pores for the SUC configuration and 60 pores for the BCC configuration, for particle Reynolds numbers of 200, 300, and 400. Stereo particle image velocimetry is experimentally arranged in such a way that the velocities over the entire region at the exit of the packed bed are obtained instantaneously. The numerical method consists of a state-of-the-art immersed boundary method with adaptive mesh refinement. The paper presents the pore jet structure and velocity field exiting from each pore for the SUC and BCC packed particle beds. The numerical and experimental studies show a good agreement for the SUC configuration for all flow velocities. For the BCC configuration, some differences can be observed in the pore jet flow structure between the simulations and the experiments, but the general flow velocity distribution shows a good overall agreement. The axial velocity is generally higher for the pores located near the centre of the packed bed than for the pores near the wall. In addition, the axial velocities are observed to increase near the peripheral pores of the packed bed. This behaviour is predominant for the BCC configuration as compared to the SUC configuration. The velocities near the peripheral pores can become even higher than those at the central pores for the BCC configuration. It is shown that both the experiments as well as the simulations can be used to study the complex fluid structures inside a packed bed reactor.

Experimental investigation of characteristics and influence of tip leakage vortex wandering in an axial compressor cascade

Vortex wandering is one of the most basic unsteady flow characteristics of the tip leakage vortex (TLV) in compressors. In this study, stereo particle image velocimetry (stereo-PIV) has been conducted in compressor cascades with various tip clearances to investigate the characteristics and influence of TLV wandering. The most effective vortex identification method for stereo-PIV data has been clarified. The wandering characteristics of the TLV are statistically analyzed, and the relationship between the vortex wandering and the dominant proper orthogonal decomposition mode is identified. The results reveal that TLV preferentially wanders along the pitchwise direction in the blade channel and gradually loses the dominant wandering direction downstream of the blade. The large displacement of the vortex center around its mean location is characterized by higher probabilities at small tip clearance size (1% chord length C). The spatial distribution characteristics demonstrate similarly concentric isocontour around the mean vortex center location for large tip clearances (3% and 5% chord length C). The effect of TLV wandering on the secondary velocity distribution, the tip flow blockage, and the distribution of Reynolds stress is explored using the vortex wandering corrected technique. The analysis verifies that the elevated turbulence kinetic energy in the core of the time-averaged uncorrected TLV is caused by vortex wandering rather than vortex deformation. The discussions of the current paper will enhance our knowledge of TLV wandering. Regardless of the reference to TLV, the interpretation of other swirling flows can benefit from the discussions presented here.

In-depth three-component assessment of wind turbine wake using stereo PIV under low tip speed ratio conditions

The behavior of wind turbine wake is unique and has a distinct pattern that often carries crucial information on the nature of wake propagation. This information plays a vital role in dictating the wind turbine wake model and subsequently in the design and placement of multirotor system. In most cases, either analytical or numerical, the representation of wind turbine wake is expressed as a streamwise flow deficit at different downstream locations. Though the result provides valuable information, the representation often lacks three-dimensional characterization, thus ignoring several influential factors that could potentially define the extent of propagation. In this aspect, an in-depth flow field mapping and assessment have been carried out behind a model horizontal-axis wind turbine using stereo particle image velocimetry (SPIV) under low tip speed ratio conditions. The three-component mapping using the time-resolved SPIV data helped to understand the notion of the wake's helical behavior and its relationship with the velocity deficit. Apart from the Gaussian-like (skew) distribution of the streamwise velocity component, the stereo assessment reveals the formation of two opposite crests supporting the helical analogy. Toward the end, a comparative assessment with the existing analytical models have been carried out.

On the unsteady interactions between a sweeping jet and afterbody vortices

In this paper, a sweeping jet was applied to control the afterbody vortices behind a 30° slanted-base cylinder at a Reynolds number of 87 000. Phase-locked stereo particle image velocimetry measurements were conducted during a sweeping jet actuation cycle, and insights of the complex three-dimensional interaction process between the sweeping jet and the afterbody vortices have been obtained for the first time. It is found that in the near-field of the jet orifice (x/c &amp;lt; 0.3), the jet swings from side to side over the endplate between the afterbody vortex pair. An intersection between them around x/c = 0.3 causes the sweeping jet to take on a zigzag pattern as it propagates downstream along the slanted surface. From x/c = 0.6 onwards, the intensity of this interaction decreases as the afterbody vortices become detached from the base. Nevertheless, the sweeping jet continues invading the afterbody vortices from their inner side and pushes its way outwards from the underside of the afterbody vortices causing them to weaken further. Furthermore, the interaction between sweeping jets and afterbody vortices results in a cyclic variation in the circulation of afterbody vortices, which increases in magnitude at downstream locations. Except for the phases where a merger between the afterbody vortex and the sweeping occurs, a reduction in the circulation is observed. Finally, the level of interaction between sweeping jets and afterbody vortices intensifies as the strength of the sweeping jet increases resulting in the afterbody vortices being penetrated by the sweeping jet and their regular shape being momentarily destroyed.

Flow Field Investigations of Two‐Stage Stirrer Configurations Combining Axially and Radially Conveying Turbines

AbstractIn this study, the flow fields of two‐stage impellers, consisting of combinations of different impeller types on one shaft, are investigated using stereo particle image velocimetry. Based on the results of torque measurements, diameters for different impellers are determined in order to achieve matching power input of the individual turbines. When implemented adequately, both selected impellers are able to contribute their respective characteristics, resulting in flow fields that differ significantly from those induced by single‐stage impellers as well as two‐stage setups consisting of identical impellers.

Analysis of the wake flow behind concave curved cylinders with velocity measurements by particle image velocimetry and modal decomposition

The properties of the wake flow behind concave curved cylinders have been investigated analyzing simultaneously the mean velocity profiles extracted along concentric arcs parallel to the cylinder axis and the dynamically most relevant coherent structures obtained by spectral proper orthogonal decomposition. These analyzes have allowed us to determine the position, the extension, and the evolution of the different wake regimes. The velocity measurements have been obtained through the stereo particle image velocimetry (stereo-PIV) technique. The study considers various Reynolds numbers, based on cylinder diameter (240&amp;lt;Re&amp;lt;840), and curvatures. The quarter-of-ring cylinder is first analyzed. Near the cylinder root, the flow exhibits a topology dominated by an oblique vortex shedding, contrary to what is observed in the literature for similar geometric configurations. We attribute this disagreement to differences in the treatment of the free-end conditions that play a role in triggering the shedding regime. We find that the local shedding inclination is driven by the axial velocity, whereas its extension and wavelength depend mainly on the Reynolds number. The near free-end region presents, instead, two counter-rotating standing vortices that induce a cross-wise velocity directed toward the cylinder root and a tip vortex that expands evolving downstream. As the Reynolds number increases, the wake presents irregularities and the shedding spreads becoming nearly normal to the incoming flow. At smaller curvatures, the cylinder free-end becoming more inclined with respect to the incoming flow, and the free-end effects are enhanced. The interaction with the vortex sheets of the standing vortices that develop at the leeward side weakens. As a consequence, these vortices stretch in the stream-wise direction giving rise to the trailing vortices that stem from the cylinder surface and affect the cross-wise velocity distributions.

Aerodynamic Design Modification for Utility Helicopters

Wind tunnel testing and accompanying numerical analyses are the essential methods to improve and optimize the aerodynamic design of helicopters. The focus is on improving the aerodynamic performance and the handling qualities. Of special interest is the parasitic drag as a major factor for the power consumption and the wake flow caused by the rotor head, which can interact with the helicopter tail and influence stability. For this purpose, design modifications and their influence on the aerodynamic characteristics of the helicopter as well as on the flow field are investigated. The design modifications are evaluated by force and moment measurements, stereo particle image velocimetry, and high fidelity computational analysis. This allows us to compare the different investigation methods and design configurations to each other. The investigations are performed on the Kopter AW09, a 2.8-t-class single engine utility helicopter. Design modifications of the upper fuselage are considered for the presented investigations.

Experimental characterization of the flowfield and cavitation physics of a tip-loaded hydrofoil

This paper reports an experimental study of tip vortex flowfield and cavitation inception of a tip-loaded hydrofoil. Vortex strength, wandering, and turbulence statistics are characterized using stereo particle image velocimetry (SPIV) in a water tunnel facility, at a chord Reynolds number of 1.3×106. Cavitation physics are characterized using high-speed videography and dual-hydrophone acoustic cavitation measurements. The loading of the rectangular planform hydrofoil has a maximum at 65% span, 56% greater than that at the root, i.e., the hydrofoil loading is representative of non-elliptically loaded open propellers. Acoustic cavitation inception is quantified and is observed to precede visual cavitation onset using unaided and high-speed imaging. Measurements reported here show that vorticity fluctuations are nearly of the same magnitude as the ensemble vorticity. Instantaneous measurements of vorticity at the trailing edge, 12-chord downstream, and one-chord downstream positions are reported. Their peak magnitudes are located adjacent to the ensemble vortex center and are between four and five times the ensemble mean. The fluctuating vorticity measurements, taken in conjunction with high-speed video observations, provide insight into the hydrodynamic conditions responsible for intermittent cavitation events. The reported measurements elucidate instantaneous and mean turbulence physics associated with vortex cavitation and can provide a validation basis for numerical simulations.

Boundary Layer Investigations for Primarily Axial Flow Over a Stationary and Transversely Oscillating Cylinder

AbstractBoundary layer information local to three longitudinal positions has been characterized for a 122 cm long acrylic cylinder with hemispherical endcaps, via analysis of stereo particle image velocimetry (PIV) measurements made during laterally oscillating motions and for steady, axisymmetric flow. No obvious turbulent flow structures or indications of boundary layer separation were observed at nonzero advance speeds, and skin friction coefficients were subsequently estimated for magnitude relative to the dynamic pressure associated with an axial flow speed of 0.25 m/s. Computational fluid dynamics (CFD) analysis is performed in commercial software to accompany the experimental measurements. Local skin friction coefficients are estimated and deviate, on average, from analytical solutions for zero gradient axisymmetric flows by around 22% and from the accompanying numerical solutions by around 4%. The effects of intermittent boundary layer compression and turbulence inhibition are readily observed for the oscillating cylinder, although vortex shedding is observed for some large amplitude, high frequency cases.

In Vitro Investigation of the Effect of the Timing of Left Ventricular Assist Device Speed Modulation on Intraventricular Flow Patterns.

Thromboembolic events remain a common complication for left ventricular assist device (LVAD) patients. To prevent in-pump thrombosis, third-generation LVADs use speed modulation, which is not synchronized with the native left ventricle (LV) contractility. This study aims to investigate the effect of speed modulation on intraventricular flow patterns, and specifically, the impact of timing relative to pressure variations in the LV. Stereo-particle image velocimetry measurements were performed in a patient-derived LV implanted with an LVAD, for different timings of the speed modulation and speed. Speed modulation has a strong effect on instantaneous afterload and flowrate (-16% and +20%). The different timings of the speed modulation resulted in different flowrate waveforms, exhibiting different maxima (5.3-5.9 L/min, at constant average flowrate). Moreover, the timing of the speed modulation was found to strongly influence intraventricular flow patterns, specifically, stagnation areas within the LV. These experiments highlight, once more, the complex relationship between LVAD speed, hemodynamic resistance, and intraventricular pressure. Overall, this study demonstrates the importance of considering native LV contractility in future LVAD controls, to improve hemocompatibility and reduce the risk of thromboembolic complications.

Experimental investigation of three-dimensional effects in cavitating flows with time-resolved stereo particle image velocimetry

The present paper is devoted to characterizing the three-dimensional effects in a cavitating flow generated in a venturi-type profile. Experimental measurements based on 2D3C (two-dimensional-three-component) stereoscopic particle image velocimetry are conducted to obtain the three components of the velocity field in multiple vertical planes aligned with the main flow direction, from the center of the channel to the side walls. Time-resolved acquisitions are conducted, so not only time-averaged quantities but also velocity fluctuations can be discussed. The attention was focused on configurations of cloud cavitation, where the attached cavity experiences large-scale periodical oscillations and shedding of clouds of vapor. Although the water channel is purely two-dimensional, some significant flow velocities in the third direction (depth of the test section) were measured. Some of those velocities were found to be related to small differences between the boundary conditions on the two sides, such as minor gaps between the sides and the bottom wall, while others reflect intrinsic three-dimensional mechanisms inside the cavitation area, such as side jets that contribute to the periodical instability process. These mechanisms are discussed, and a possible 3D (three-dimensional) structure of the cavitating flow is proposed.

Enhancement of PIV measurements via physics-informed neural networks

Physics-informed neural networks (PINN) are machine-learning methods that have been proved to be very successful and effective for solving governing equations of fluid flow. In this work we develop a robust and efficient model within this framework and apply it to a series of two-dimensional three-component stereo particle-image velocimetry (PIV) datasets, to reconstruct the mean velocity field and correct measurements errors in the data. Within this framework, the PINNs-based model solves the Reynolds-averaged-Navier–Stokes equations for zero-pressure-gradient turbulent boundary layer (ZPGTBL) without a prior assumption and only taking the data at the PIV domain boundaries. The turbulent boundary layer (TBL) data has different flow conditions upstream of the measurement location due to the effect of an applied flow control via uniform blowing. The developed PINN model is very robust, adaptable and independent of the upstream flow conditions due to different rates of wall-normal blowing while predicting the mean velocity quantities simultaneously. Hence, this approach enables improving the mean-flow quantities by reducing errors in the PIV data. For comparison, a similar analysis has been applied to numerical data obtained from a spatially-developing ZPGTBL and an adverse-pressure-gradient TBL over a NACA4412 airfoil geometry. The PINNs-predicted results have less than 1% error in the streamwise velocity and are in excellent agreement with the reference data. This shows that PINNs has potential applicability to shear-driven turbulent flows with different flow histories, which includes experiments and numerical simulations for predicting high-fidelity data.

Laminar and turbulent flow development study in a rectangular duct with 180° sharp bend by using stereo particle image velocimetry and liquid crystal thermography measurements

This work presents a detailed insight into the flow progression and surface heat transfer distribution across the sharp 180° bend of a two-pass rectangular duct for laminar (Re = 800) and turbulent (Re = 6500) in-flow conditions. Stereoscopic particle image velocimetry (stereo PIV) as well as two-dimensional and two-component PIV measurements and liquid crystal thermography techniques are appropriately used for flow and heat transfer characterization across the complete sharp 180° bend. The centrifugal instabilities arise due to the sharp bend, which induces the secondary flows in the form of counter-rotating vortex pairs commonly known as Dean vortices. These secondary vortices play a significant role in the localized laminar–turbulent transition and turbulence augmentations for laminar and turbulent inflow conditions. Subsequently, quantitative analysis shows that complete 180° turning of flow resulted in intense augmentation of spatially averaged turbulence quantities. Root mean square (RMS) fluctuations in the transverse direction V¯T|rms increase by 298% and 186% for respective flow conditions. Augmentation of ∼ 287% (laminar) and 260% (turbulent) in the wall-normal RMS fluctuations (V¯N|rms) are observed. These augments in transverse and wall-normal velocity fluctuations result in a very sharp amplification of spatially averaged turbulent kinetic energy (k¯), that is, 1825% for inlet laminar and 928% for inlet turbulent flow regimes.

Experiment on jet–vortex interaction for variable mutual spacing

The interaction of a line vortex with a collinearly aligned jet is a prototypical configuration for various important applications in aeronautics. The purpose of this study is to analyze the impact of the jet flow on the kinematics and dynamics of a trailing vortex. A particular emphasis is on the effect of a variable relative jet–vortex spacing. To this end, we realized four different jet–vortex configurations in a wind tunnel experiment at a chord-based Reynolds number of 1.7×105 using high-speed stereo particle image velocimetry measurements in five transversal planes located between 2 and 26 chords behind the wing. Stochastic analyses reveal that the jet generally contributes an external excitation to the vortex as a function of the mutual spacing. Compared with the configuration without jets, the vortex amplification increases upon reducing the jet–vortex spacing. Most notably, for all but the closest spacing, the vortex response is qualitatively the same, changing mainly in magnitude. For the closest spacing, however, the dynamics is considerably different, which we suspect to be a consequence of jet entrainment. Proper orthogonal decomposition reveals, for the first time, that the collinearly aligned jet tends to excite a progressively broader range of vortex modes as the jet–vortex spacing is reduced. A close examination of the vortex mean flow seems to preclude linear vortex instabilities, while the vortex characteristics hint toward some form of receptivity mechanism to disturbances being located in the free stream. Our analyses are useful to validate simulation tools on configurations combining simultaneous lift and thrust effects.

Identification and dynamics of coherent structures in a Coanda swirling jet flow

Swirl stabilised flows are the most common technology for gas turbine combustion stabilisation. Although success on the characterisation of these flows is tangible, there are several structures that appear in such flows that are still a concern for fundamental and applied research. One of these structures is the Precessing Vortex Core (PVC), whose ambiguous characteristics make it an adequate mechanism for chemical mixing whilst being a detrimental component for thermoacoustic stabilisation. The PVC has been extensively characterised in swirling jet flows exhibiting vortex breakdown (in this study named Open Jet Flow or OJF). However this has not been the case for swirling Coanda (i.e. wall attached) Jet Flows (CoJF). Therefore, this research presents experimental work detailing the identification and visualisation of coherent structures in both types of jet flows. A generic swirl burner was fitted with a base plate in a position so that any of these two flows, OJF and CoJF, could be obtained within the same burner geometry. High speed stereo particle image velocimetry (S-PIV) was used to obtain a time-resolved flow field of each flow state at different flow rates. Two PVCs were clearly identified in both flows, one in the inner shear layer between the vortex breakdown bubble and the jet and one between the jet and the ambient. Precessing frequencies for the CoJF where ∼8.5% higher (St ∼0.9-1.0) than those of the OJF (St ∼0.8-0.9). Spectral proper orthogonal decomposition was used to identify the coherent structures in the flow. Swirl strength (λci2) analysis was conducted on the coherent modes to establish quantitative and qualitative results and to produce a 3D reconstruction of the flow field. The results indicate that precessing coherent flow structures are present in wall attached Coanda swirling flows and these are similar to the structures found in swirling jet flows undergoing vortex breakdown.