Stereoscopic Particle Image Velocimetry Measurements Research Articles

Turbulent/non-turbulent interface of the turbulent boundary-layer over a spanwise-heterogeneous converging/diverging riblets rough wall

Turbulent boundary layer (TBL) flows over various spanwise-heterogeneous rough walls exhibit spanwise variations in turbulence statistics, implying modifications of the turbulent/non-turbulent interface (T/NTI). In this work, based on the datasets of TBL flows over a spanwise-alternating converging/diverging riblets wall, we investigate behavior of T/NTI, properties of ‘bubble’ and ‘drop’ that are associated with T/NTI, as well as connections between T/NTI and large-scale structures within the boundary layer. The flow datasets were obtained through stereoscopic particle image velocimetry measurements on the cross-stream plane of the TBL flow at a Reynolds number Reθ = 1.3 × 104. The T/NTI and associated ‘bubble’ and ‘drop’ are identified using a kinetic energy criterion, while the large-scale structures by a streak detection algorithm. It is observed that the T/NTI height and the occurrence of ‘bubble’ and ‘drop’ display a spanwise-heterogeneous feature, with lower T/NTI height and higher occurrence probability of ‘bubble’ over the diverging section of riblets than over the converging section of riblets. Results of conditional average show that the ‘bubble’ is associated with positive streamwise fluctuations, common-down flow and a pair of counter-rotating streamwise vortices, while the ‘drop’ with negative streamwise fluctuation, common-up flow and a pair of counter-rotating streamwise vortices. Probability density functions of the ‘bubble’ size and fractal dimensions of the T/NTI are found similar for both the riblets and smooth wall flows. Furthermore, it is observed that the large-scale low-speed structures occurring preferentially over the converging section of riblets play a role in elevating T/NTI while the large-scale high-speed ones over the diverging section of riblets lowering down T/NTI.

Enhancing numerical accuracy in the prediction of rotor wake vortex structures

In modern high-fidelity computational fluid dynamic simulations, the primary vortex system in hover often breaks down into secondary vortices. The sources of numerical error influencing the prediction of the vortex system were studied by performing high-fidelity simulations of the wake of a two-bladed rotor and comparing the predictions to stereoscopic particle image velocimetry measurements in different measurement planes. Various numerical inputs, including sub-iteration convergence, blade pitch offset, and grid resolution, were varied to resolve discrepancies between the measured and predicted vortex characteristics from a previous study done by the authors. A parametric study on near- and off-body solver sub-iteration convergence demonstrated that although the secondary vortex characteristics converged as the sub-iteration convergence of both solvers increased, a large discrepancy in the number of secondary vortices remained. This discrepancy was investigated by varying the thrust, where it was found that the breakdown of the primary vortex is directly linked to the number of secondary vortices. Dissimilarities in the blade pitch angle, which could not be avoided in the experiment, were modeled by intentionally using an offset in the blade pitch angle of the two blades. It was shown that as blade pitch angle offset increases, vortex pairing becomes more distinct. When vortex pairing occurred in both the experiment and simulation, the decay of secondary vortices in the experiment and simulation agreed best. To better match the experimental resolution, grid resolution was increased and comparing the two simulations, the finer mesh simulation agreed best with the measured primary and secondary vortex characteristics.

Columnar-jet to wall-jet state transition in transversely excited swirling flow

The current work investigates the transition of a swirling jet between two flow states, namely, columnar-jet (CJ) and wall-jet (WJ) states, under the influence of external transverse acoustic forcing. Here, we have performed simultaneous time-resolved stereoscopic particle image velocimetry and dynamic pressure measurements to understand the structure and dynamics of these swirling jets under external forcing. It is observed that at low Reynolds number (Re), the swirl flow transitions from CJ to WJ state due to transverse forcing. And the flow returns to the CJ state when the acoustic is turned OFF. However, above a critical flow Re, the swirl flow does transition from CJ to WJ state when subjected to transverse forcing, but upon turning OFF the acoustics, the flow stays in the WJ state. Thus, the swirling flow demonstrates bistability in the flow states only above a critical flow Re. It is observed that upon forcing, there is an increase in the streamwise velocity fluctuations (u′x) near the centerline and in the radial velocity fluctuations (u′r) near the injector lip. This finding is also confirmed through spectral proper orthogonal decomposition analysis. In addition, it is observed that as the flow transitions from CJ to WJ state, the relative contribution of the convective term Ur¯∂Ur¯∂r toward the radial pressure gradient (∂P¯∂r) increases in comparison to the centrifugal force term (U¯θ2r). The study highlights the effect of acoustic-induced velocity fluctuations on the bistability of swirl flows over a range of flow Re.

Self-sustained azimuthal aeroacoustic modes. Part 1. Symmetry breaking of the mean flow by spinning waves

In this paper, we study the aeroacoustic instability which occurs in a deep axisymmetric cavity in a turbulent pipe flow. This phenomenon is the axisymmetric counterpart of the classical whistling of a rectangular deep cavity subject to a grazing flow. The whistling of such axisymmetric cavity originates from the interaction of the coherent fluctuations of the vorticity at the cavity's opening with one of its trapped azimuthal or radial acoustic modes. We focus here on the situation involving the first pure azimuthal mode, which is trapped in the cavity. As a consequence of the rotational symmetry of the configuration, azimuthal modes are actually pairs of degenerate eigenmodes, or almost degenerate in the presence of small asymmetries. Therefore, the aeroacoustic instabilities exhibit more complex mechanisms than in the case of a rectangular deep cavity. In particular, we show that self-sustained spinning modes induce a symmetry breaking of the mean flow and we will elucidate the details of this phenomenon. To that end, simultaneous acoustic and time-resolved stereoscopic particle image velocimetry (PIV) measurements are performed. They reveal that when large-amplitude aeroacoustic waves spin around the cavity, a quasi-steady mean flow starts whirling slowly in the opposite direction to the wave propagation. A linear perturbation analysis around an axisymmetric mean flow confirms the experimental observations: although the incoming pipe flow is not swirling, the hydrodynamic component of the aeroacoustic wave induces such whirling motion of the mean flow because of the forcing from the steady part of the coherent Reynolds stress tensor.

Control of a rectangular impinging jet: Experimental investigation of the flow dynamics and the acoustic field

Passive control techniques of impinging jets are of high interest for many industrial applications and particularly for noise generation issues encountered in such configurations. Thus, an experimental study was carried out to simultaneously show the effect of a mechanism of control on the acoustic and the dynamic fields involved in a rectangular jet of air impinging on a slotted plate. A Reynolds number of Re = 5900 presenting an intense acoustic level was considered. The mechanism of control consists on a thin rod which was introduced in different positions of the flow. A total number of 1085 spatial positions of the rod were tested in order to identify the optimal position for noise reduction. Combined Stereoscopic Particle Image Velocimetry measurements were performed to obtain the kinematic field in the whole area of interest from the both sides of the introduced rod. A new representation of the acoustic levels (cartography of acoustic level as function of the location of the rod) is provided to identify the optimal positions of control. It was found that when the self-sustaining tone loop disappears, the sound pressure levels can drop by almost 23% depending on the location of the rod. A Dynamic Mode Decomposition (DMD) was established and cross-correlations were calculated between temporal modes and acoustic signals for both controlled and not controlled cases. The cross-correlations between the acoustic signal and the temporal modes were found to be insignificant in case of controlled flow. Moreover, in case of controlled flow, spatial modes were found to be significant far from the slot which plays a principal role in the self-sustaining tones by interacting with the passage of vortices through it. These results are of interest since the visualization of the flow dynamics and the corresponding vortex activity explains the disappearance of the self-sustaining loop and the sound pressure level changes. Such results are of high interest for developing new strategies of noise control.

Effect of morphology and an upstream tall building on the mean turbulence statistics of a street canyon flow

The effects on turbulent street canyon flow of the morphological model and the existence of an upstream tall building are investigated in a wind tunnel, using Stereoscopic Particle Image Velocimetry (S-PIV) measurements on two orthogonal vertical planes. The cathedral in the “Rue de Strasbourg, (Nantes, France)” morphological model is regarded as a local tall building and is tested and then replaced by generic, square planform buildings of 4 different heights. The cathedral induces an asymmetrical wake while no obvious different influence on the street canyon flow can be identified, in comparison with a generic building of the same height. A strong along-canyon flow occurs which may be due to the intersections, while the along-canyon ventilation decreases with increasing building height. The higher the building, the stronger its sheltering effect, leading to a reduction of the vertical ventilation and mass transport across the canyon opening, at least in the canyon portion directly downstream of the building.

Inexpensive multi-plane particle image velocimetry based on defocusing: Proof of concept on two-component measurement

This paper presents a method for simultaneous particle image velocimetry (PIV) on parallel planes offset in depth. The method places images from two planes onto a different half of a camera sensor by using image splitting optics with variable optical path lengths. A shallow depth of field is achieved to ensure only one plane is in focus on each half of the sensor. Without needing additional lasers, the method is designed as an inexpensive means to increase the number of measurement plane(s) of single/multi-plane PIV setups and can be combined with existing plane discrimination approaches such as polarization and wavelength. The method is useful for studying instantaneous flow correlations on different planes while retaining high in-plane spatial resolution of typical planar PIV measurement. The measurement uncertainty caused by crosstalk from out-of-focus images is discussed. Experimental results from a laminar flow rig test indicate that the average measurement error of each velocity component is lower than 0.1 pixels per time step, with a 20 mm plane separation in depth and a 35 × 54 mm2 field of view. As an application with varying background scatter and out-of-plane flow motions, in-cylinder flow measurements in an optically accessible internal combustion engine were performed on two swirl planes simultaneously. Characteristics of the proposed method performing stereoscopic PIV measurements will be studied in future.

Analysis on three-dimensional flow characteristics of rotor wake

As the main lift and control component of helicopters, the rotor has a complex flow field structure with unique characteristics, such as unsteadiness, paddle-vortex interference, and tip vortex. Thus, it is challenging to measure the rotor flow field. In addition, the instability of the flow is accompanied by strong flow pulsation, which leads to noise and blade vibration during the formation of tip vortices. A phase-locked Stereoscopic Particle Image Velocimetry (SPIV) technique, SPIV measurement technology, and phase locked technology are adopted in the present study to investigate the blade tip vortex. The blade tip vortex, which is the main flow structure to be characterized in this study about the rotor wake, is measured by the phase-locked SPIV technique. The velocity and vorticity fields at five phases are presented. Then, the main energetic modes of pulsation were extracted by proper orthogonal decomposition to analyze the instability characteristics of the flow. Finally, the three-dimensional structure of the blade tip vortex is reconstructed and presented. It can be seen that the blade tip vortex has a spiral structure and develops toward the rotor axis.

Experimental study of a self-excited jet precession in a sudden expansion flow

This study presents Stereoscopic particle image velocimetry measurements of a precessing motion resulting from a sudden expansion of an axisymmetric jet into a coaxial chamber. The sudden expansion has an expansion ratio of 4.9 and an aspect ratio of 2.03. The velocity profile in the inlet tube is measured upstream of the expansion using Laser doppler anemometry. The Reynolds number (Re) is varied from 3160 to 63,870. The time-averaged flow field exhibits an axisymmetric behavior, and the velocity profile near the expansion resembles that of a jet. The half-width and the opening angle of the jet are similar for all Reynolds numbers measured, with values of $$3.73\pm 0.04^{\circ }$$ and $$8.73\pm 0.19^{\circ }$$ , respectively. Despite its axisymmetry, the flow field contains unsteady coherent structures in nature, which are analyzed using both spectral proper orthogonal decomposition and phase averaging. These structures make the instantaneous flow field asymmetric and create a precession around the central axis of the geometry. The structure of this precession is similar for $$8300 \le \hbox {Re} \le$$ 63,870. For $$3160 \le \hbox {Re} \le 8300$$ , the precession is very weak and hard to extract from the turbulent flow fields. The Strouhal number (St) increases linearly for $$8300 \le \hbox {Re} \le$$ 23,600, after which it reaches a value of around 0.003. Precessing structures of this kind were previously only reported for swirling sudden expansion flows, fluidic precessing jet nozzles or annular free jets. However, this study shows that they also exist in confined, non-swirling sudden expansion flows, without exiting to an ambient fluid.

Fluidic-Oscillator-Based Pulsed Jet Actuation on a Vertical Tail

An industry-relevant vertical tail plane (VTP) model equipped with fluidic-oscillator-based pulsed jet actuators was tested with different active flow control (AFC) settings, rudder deflection, and sideslip angles at a chord Reynolds number of 1.3 million. In addition to pressure and force measurements, tuft visualizations and stereoscopic particle image velocimetry measurements were used to investigate AFC effects. With a total momentum coefficient of 1.5%, the control authority (lateral force) of the VTP was increased by a maximum of 34% when actuators were distributed along the rudder span. Additionally, flow control at dedicated positions on the rudder was investigated by using individual actuator segments. It was found that AFC is particularly effective at the position of the maximum load in the spanwise direction. The measurements also confirmed that local application of AFC actuators may simulate the effect of a boundary-layer fence. Finally, a comparison with existing results obtained with sweeping jet actuators shows that these two specific AFC implementations are most effective in different ranges of the momentum and the power coefficients.

On the wake deflection of vertical axis wind turbines by pitched blades

AbstractWake losses are a critical consideration in wind farm design. The ability to steer and deform wakes can result in increased wind farm power density and reduced energy costs and can be used to optimize wind farm designs. This study investigates the wake deflection of a vertical axis wind turbine (VAWT) experimentally, emphasizing the effect of different load distributions on the wake convection and mixing. A trailing vortex system responsible for the wake topology is hypothesized based on a simplified vorticity equation that describes the relationship between load distribution and its vortex generation; the proposed vorticity system and the resulting wake topology are experimentally validated in the wind tunnel via stereoscopic particle image velocimetry measurements of the flow field at several wake cross‐sections. Variations in load distribution are accomplished by a set of fixed blade pitches. The experimental results not only validate the predicted vorticity system but also highlight the critical role of the streamwise vorticity component in the deflection and deformation of the wake, thus affecting the momentum and energy recoveries. The evaluation of the various loading cases demonstrates the significant effect of the wake deflection on the wind power available to a downwind turbine, even when the distance between the two turbines is only three diameters.

LEGO calibration targets for large-FOV particle image velocimetry

Particle image or particle–tracking velocimetry nonintrusively provides velocity field information, and the proposition large field-of-view (FOV) measurements are highly attractive from an experimental standpoint. Stitching multiple smaller FOVs to achieve the large FOV of interest is an approach that faces challenges rooted in the calibration process. For stereoscopic PIV (SPIV), the use of a multi-level target simplifies calibration. However, this is problematic for large-FOV measurements, as standardised multi-level targets are relatively small and expensive. LEGO® bricks are well-suited to the construction of large, customised multi-level targets due to their high-dimensional tolerance and their stackability with high precision. To evaluate the feasibility of LEGO®-based targets, a two-sided multi-level target covering 380 times 1150 mm was created and used for SPIV measurements of the inflow conditions of the Atmospheric Wind Tunnel Munich. Calibrations were also performed using the Type 31 target for comparison. Analysis of the datasets with both calibration targets shows good agreement in the measurement of the streamwise, out-of-plane component u. A parametric study of different LEGO® target configurations was used to verify the calibration performance of the targets as well as identify optimal configurations for experimental use. Due to the high level of agreement in calibration parameters and quantitative and qualitative flowfield parameters in PIV tests, as well as the consistency observed in the subsequent parametric study, LEGO-based calibration targets show potential for further development and usage in large-FOV measurements.Graphic abstract

Detailed unsteady dynamics of flame-flow interactions during combustion instability and its transition scenario for lean-premixed low-swirl hydrogen turbulent flames

This experimental study elucidates the unsteady dynamics of flame-flow interactions during unique thermoacoustic instability (TI) and the transition mechanism from stable combustion to TI for lean-premixed hydrogen turbulent jet flames in a low-swirl combustor (LSC), where a swirler assembly consists of an unswirled central region (CR) and an annular swirler region (SR). Simultaneous 200-kHz pressure fluctuation p’ measurements and 10-kHz OH* chemiluminescence imaging, as well as 40-kHz stereoscopic particle image velocimetry (SPIV) and two-dimensional PIV measurements for steady-state and transient data acquisitions, respectively, were conducted. The SPIV was performed in multiple planes to explore three-dimensional velocity fields. During TI, periodic flashback was possibly caused by significant axial velocity oscillations, resulting in the local mixture velocity falling below the turbulent flame speed. The large-scale vortex ring generated by the velocity oscillations caused axisymmetric radial velocity Vr oscillations with switching signs during the TI period. Similar to a typical low-swirl flow, the positive Vr away from the combustor axis created diverging flow, whereas unlike the typical flowfield, the negative Vr toward the combustor axis generated converging flow while flattening the axial velocity distributions, which was the signature phenomenon for this TI. Using the transient data and dynamic mode decomposition, variations in delay times between the mixture injection and its convection to a region with positive local Rayleigh indices were investigated. During stable combustion, the mixture jet from the SR predominantly induced thermoacoustic coupling (TC). As the combustion transitioned into the TI, the mixture jet from the CR began to induce TC and, eventually, achieved predominance in inducing TC during fully evolved TI. The transition from the SR jet- into CR jet-dominant TI arising from the dynamic flame-flow interactions resulted from the inherent physical characteristics of hydrogen flames, thereby yielding the larger p’ amplitude compared to typical TIs.

Insight into the flow dynamics of a high shear injector equipped with center-body: Suppression of precessing vortex core oscillations

A precessing vortex core (PVC) is a self-excited helical instability that results from the precession of the vortex core around the flow axis in the upstream region of a vortex breakdown bubble. PVC oscillation in a swirl flow-based combustor aids the thermoacoustic instability that results in hardware damage and poor emission characteristics of the engine. The PVC oscillation can be suppressed intermittently or absolutely in the high shear injector-based combustor with proper design and placement of the fuel nozzle in the injector. A high shear injector is an arrangement of two radial swirlers in general, namely, primary and secondary swirlers, equipped with a fuel nozzle at its center to deliver the fuel. In this study, we examine the impact of the placement of the fuel nozzle/center-body and its design over the dynamics of PVC oscillations in a non-reacting flow in a counter-rotating swirler/high shear injector. Time-resolved high-speed (@ 5 kHz) stereoscopic particle image velocimetry measurements are conducted to elucidate the dynamics of PVC and other coherent structures. Spectral proper orthogonal decomposition of the velocity field data shows that fuel nozzle flushing with the base of the primary swirler has the most robust PVC oscillation that subsequently gets intermittent or suppressed by placing the center-body of diameters, Dc = 7, 9, and 11 mm at constant upstream mass flow rate. The results show that the center-body with the end face flushing to the exit plane would be helpful to avoid PVC with proper selection of the center-body diameter.

Vortex Unsteadiness in the Endwall Region of a High-Lift Low-Pressure Turbine Passage

Abstract Three-dimensional vortical structures within the endwall region of turbine passages directly affect the aerodynamic efficiency and heat transfer characteristics of the turbine. Interactions between the vortical endwall structures and the suction surface flow have been shown to be a significant source of loss generation through passages. One dominant vortex extends from the leading-edge junction region of the blade across the passage, where it interacts with the flow along the suction surface of the adjacent blade. In high-lift low-pressure turbine cascade passages, the vortical structure intermittently loses coherence and exhibits unsteady variations of strength and position as it extends across the passage. The present paper details the temporal behavior through high-speed measurements in a low-speed linear cascade of high-lift low-pressure turbine blades. Stereoscopic particle image velocimetry measurements in the passage are used to evaluate the unsteady behavior of the vortex. Space-time iso-surface plots of Q-criterion clearly show the evolution of the vortex over time. Analysis of the data reveals the various time scales of fluctuations in strength and position. Comparisons of the temporal fluctuations in the high-lift turbine passage are made with similar phenomena found in canonical junction flow papers in the literature. Key findings support the hypothesis that in-passage vortex unsteady characteristics near the endwall are influenced by leading-edge junction flow dynamics, and provide additional insight into the unsteady endwall flow physics that is necessary to further the development of endwall loss reduction techniques.

Higher order dynamic mode decomposition of an experimental trailing vortex

The decay of trailing vortices is a fundamental problem in fluid mechanics and constitutes the basis of control applications that intend to alleviate the wake hazard. In order to progress, we use the recently developed modal-decomposition technique to identify the governing dynamics in an experimental trailing vortex. A particular emphasis is on the difficulty and usefulness of applying such tools to noisy experimental data. We conducted a water-tunnel experiment at a chord-based Reynolds number Re=4×104 using stereoscopic particle image velocimetry measurements over a downstream range of 36 chords. The downstream evolution of the maximum of vorticity suggests that the whole wake can be partitioned into three consecutive regimes. A higher-order dynamic mode decomposition of the streamwise vorticity in each such part of the wake shows that the decay is well approximated by at most three modes. Additionally, our study provides evidence for the existence of several instabilities after the vortex roll up beyond about 6.5 chords.

Effects of nitrogen dilution on flame characteristics and stability of lifted propane fire whirl

Nitrogen dilution effects on flame characteristics and stabilization mechanism were experimentally investigated in lifted propane fire whirls. A small rotating screen facility with finely controlled imposed circulation (Γ) and propane heat release rate (Q˙=2.0–4.0 kW) was used for experiments. The nitrogen volume fractions (φ) in the diluted propane flow ranged from 0 to 90%. The stereoscopic particle image velocimetry (SPIV) technique, as well as the synchronized color imaging technique, was utilized to obtain 3-D instantaneous velocity distributions of fire whirl. It was found that the initially anchored fire whirl (φ=0) could be lifted after attaining a critical value of φ in the propane flow. Three regimes, including the attached flame, the lifted flame, and extinction, were identified in φ-Г coordinates. The fire whirl could exhibit flame liftoff and flame attachment under the same φ and Г, depending on the initial flame state in the φ-Г plot. The flame liftoff height and the flame diameter increased, and the flame length decreased with increasing φ. SPIV measurement results showed that the axial velocity followed an S-shaped distribution in the vertical direction. The mean axial velocity conditioned at the instantaneous lifted flame base decreased with φ and increased with Γ. The stable equilibrium was achieved at the locations where the flame propagation velocity and the axial velocity were roughly balanced, and the axial velocity curve had a negative slope with height. The variations of φ and Γ could change the flame liftoff height by breaking the local balance between flame propagation velocity and gas flow velocity. In addition, the peak value in the axial velocity curve, which was related to Γ, strongly affected the transitions among the different regimes.

Measurements of weak and moderate oblique shock-vortex interactions in supersonic flow

Stereoscopic particle image velocimetry measurements have been performed to quantify the centerline flow field associated with oblique shock-vortex interactions. This novel data set provides a unique view into the time-averaged velocity and turbulence kinetic energy distribution of weak and moderate interactions. Traditionally visualized using qualitative techniques, these data demonstrate that even weak interactions will result in measurable alterations to the flow field.

Analysis of the in-cylinder flow of a DISI engine using high-speed particle image velocimetry

In addition to exploring electric drives, it is crucial to minimize emissions and improve the efficiency of transport based on internal combustion engines (ICE). For these, in particular, a significant reduction of emissions as well as a considerable efficiency of ICE are required. A reliable formation of an effective mixture prior to ignition and a fast, steady combustion process are two key elements that influence emissions and efficiency. While on the one hand, the air-fuel mixture is formed by strongly three-dimensional, time-dependent flow phenomena during the intake and compression stroke, the turbulence level of the flow near the approaching flame front has a direct impact on turbulent flame propagation. The flow field in the combustion chamber, on the other hand, is highly turbulent and sensitive to cycle-to-cycle variations (CCV). In order to understand the fundamental processes and interactions of the flow field, flow measurements with high spatial and temporal resolution are required. To analyze CCV, the resulting flow field data must be decomposed into its scales, since CCVs are different from random fluctuations due to turbulent flow motions. Besides velocity decomposition based on traditional Reynolds decomposition, which provides an average flow velocity and a fluctuation velocity, most studies include statistical and linear approaches such as proper orthogonal decomposition (POD) and Fast Fourier transformation (FFT). In this paper, time-resolved high-speed stereoscopic PIV (HS-SPIV) measurements on an optical single-cylinder engine are processed using a new nonlinear and transient decomposition method, namely the multivariate empirical mode decomposition (NA-MEMD) based on a data-driven decomposition algorithm. The decomposition is based on the inherent scales of the data and generates physically valid modal representations known as intrinsic mode functions (IMFs), which are arranged with respect to the contained scale values. The approach and the IMFs generated are described in detail using one engine cycle as an example. According to the results, three modes are obtained, the measurement noise and extremely tiny short-term scales, the turbulent scales, and the large-scale tumble vortex.

Unsteady Effects of Blowing over Actuated Surfaces Using Phase-Locked Particle Image Velocimetry

An experimental study is conducted to investigate the effects of upper-surface trailing-edge blowing on a low-aspect-ratio rectangular wing with an actively actuated flap. Two wing configurations, the wing with a baseline flap and a dual-radius flap, are wind-tunnel tested at three spanwise locations to investigate the three-dimensional and unsteady effects of blowing during flap actuation at a freestream Reynolds number (based on the airfoil chord) of . Two-dimensional and stereoscopic phase-locked particle image velocimetry (PIV) measurements are used to collect data during flap actuation at different actuation speeds and blowing intensities. Proper orthogonal decomposition and modified Q criterion are used to analyze the PIV data. The wake dynamics reveal that flap actuation contributes to tip-vortex strengthening when active blowing is not present. The combination of flap actuation and active continuous blowing is more effective in controlling the boundary layer compared to the flap at rest for the same blowing intensities.