Wake Width Research Articles

Mapping the anisotropic Galactic stellar halo with blue horizontal branch stars

We used Legacy Survey photometric data to probe the stellar halo in multiple directions of the sky using a probabilistic methodology to identify blue horizontal branch (BHB) stars. The measured average radial density profile follows a double power law in the range 5 < rgc/kpc < 120, with a density break at rgc ≈ 20 kpc. This description, however, falls short, depending on the chosen line of sight, with some regions showing no signature of a break in the profile and a wide range of density slopes, such as an outer slope −5.5 ≲ αout ≲ −4, pointing towards a highly anisotropic stellar halo. This explains, in part, the wide range of density profiles reported in the literature owing to different tracers and sky coverage. Using our detailed 3D stellar halo density map, we quantified the shape of the Pisces overdensity associated with the transient wake response of the Galaxy’s (dark) halo to the Large Magellanic Cloud (LMC). Measured in the LMC’s coordinate system, Pisces stands above the background, is 60° long and 25° wide, and is aligned with the LMC’s orbit. This would correspond to a wake width of ∼32 kpc at ∼70 kpc. We do not find a statistically significant signature of the collective response in density as previously reported in the literature measured with K giant stars, despite our larger numbers. We release the catalogue constructed in this study with 95 446 possible BHB stars and their BHB probability.

Effect of background turbulence on the wakes of horizontal-axis and vertical-axis wind turbines

We report a wind tunnel study on the wake generated by a horizontal-axis (HAWT) and a vertical-axis wind turbine (VAWT). Two scaled models, one of each type, have been tested in a wind tunnel, under low blockage and at Reynolds numbers, based on the rotor diameter D, of ReD=265×103 for the HAWT and 330×103 for the VAWT. The models scale with respect to the largest commercially deployed turbines is of 1/383 and 1/65.5, for the HAWT and the VAWT, respectively. Furthermore, two different inflows were tested: low and moderate turbulence conditions. For each type of turbine and inflow, different values of tip-speed ratio and ReD were tested.Hot-wire anemometry was used to characterize the wake at different streamwise positions, exploring the range 1<x/D<30 for the HAWT and 1<x/D<15 for the VAWT.We find that, under a low-turbulence inflow, both turbines generate significantly different wakes, characterized by the velocity deficit, wake width and the profiles of average and rms streamwise velocities. More specifically, in low-turbulence conditions, the VAWT presents faster recovery than the HAWT. Remarkably, we observe that a moderately turbulent inflow results in similar wake shapes for both turbines, presenting similar recovery and structure under all studied conditions.

Modeling the hydrodynamic wake of an offshore solar array in OpenFOAM

Offshore solar is seen as a promising technology for renewable energy generation. It can be particularly valuable when co-located within offshore wind farms, as these forms of energy generation are complementary. However, the environmental impact of offshore solar is not fully understood yet, and obtaining a better understanding of the possible impact is essential before this technology is applied at a large scale. An important aspect which is still unclear is how offshore solar affects the local hydrodynamics in the marine environment. This article describes the hydrodynamic wake generated by an offshore solar array, arising from the interaction between the array and a tidal current. A computational fluid dynamic (CFD) modeling approach was used, which applies numerical large eddy simulations (LES) in OpenFOAM. The simulations are verified using the numerical model TUDFLOW3D. The study quantifies the wake dimensions and puts them in perspective with the array size, orientation, and tidal current magnitude. The investigation reveals that wake width depends on array size and array orientation. When the array is aligned with the current, wake width is relatively confined and does not depend on the array size. When the array is rotated, the wake width experiences exponential growth, becoming approximately 30% wider than the array width. Wake length is influenced by factors such as horizontal array dimensions and current magnitude. The gaps in between the floaters decrease this dependency. Similarly, the wake depth showed similar dependencies, except for the current magnitude, and only affected the upper meters of the water column. Beneath the array, flow shedding effects occur, affecting a larger part of the water column than the wake. Flow shedding depends on floater size, gaps, and orientation.

Numerical investigation on the suppression of vortex-induced vibration system by assembling different rotors based on quasi-active control method

Combining the innovative concept of quasi-active control method, a numerical simulation is conducted to investigate the vortex-induced vibration (VIV) responses. The objects of this study include a main cylinder (MC) and a cylindrical system outfitted with a pair of rotors of different types (with Banki rotors, Darrieus rotors, and Savonius rotors, denoted as WBR, WDR, and WSR), and the VIV responses are analyzed within the Reynolds number range of 0.8 × 103≤Re ≤ 5.6 × 103. The findings indicate that all three kinds of rotors show excellent vibration suppression effect in downstream and cross-flow directions by adjusting the VIV response (amplitude, frequency, hydrodynamic coefficient) and vortex pattern (vortex mode, wake shape). The maximum amplitude suppression rate can reach 99% for the Banki and Savonius cases at high reduced velocity. Within the whole velocity range, the maximum amplitudes of WBR, WDR, and WSR cases in the downstream and cross-flow directions were 0.32 and 0.45 times, 0.73 and 0.65 times, and 0.28 and 0.33 times, respectively, compared to the maximum amplitude of MC. The time-averaged drag coefficient of the controlled cylinder in the WBR case was minimized to about 0.015. The Banki rotor and Savonius rotor significantly reduced the vibration frequency of the VIV system compared to the Darrieus rotor. Especially, the Banki rotor could keep the VIV system vibration frequency within a narrow range at different reduced velocity. Moreover, the vorticity contour of the VIV system with assembled rotors was significantly improved, with a narrower flow wake width and more regular vortex shedding at high reduced velocity. Considering both amplitude suppression and drag coefficient, Banki rotors were recommended.

Investigation of three-dimensional wake width for offshore wind turbines under complex environmental conditions by large eddy simulation

Abstract The wake of wind turbines is a main concern for offshore wind farms, in which the wake width is a key index and needs to be accurately predicted. However, the existing wake width models have shortcomings in predicting the wake of wind turbines in different offshore environments. In view of this, large eddy simulation (LES) is adopted to simulate offshore wind turbines under various environmental conditions. The analyses show that there are evident differences in wake widths between horizontal and vertical directions. The variations of turbulence intensity and wind speed in the environment have significant effects on the wake width. By fitting the simulation results, a three-dimensional (3-D) wake width model is proposed to predict the wake widths in horizontal and vertical directions, which considers the effects of lateral and vertical turbulence intensities on the wake width in different directions, and uses the thrust coefficient to reflect the effect of wind speed. The proposed 3-D model is then compared with existing models through test cases, indicating that it is more accurate in predicting wake widths in horizontal and vertical directions under different environmental conditions, meanwhile shows good applicability in complex offshore environments.

The wake of a large wind turbine in stable atmospheric boundary layer flow, simulated in the EnFlo stratified-flow wind tunnel

The EnFlo stratified-flow wind tunnel is described, and the parameterization of stable atmospheric boundary layers in the context of wind turbines and stability classification is given, as are the scaling constraints for stratified-flow wind tunnel experiments. Wake measurements of mean velocity, Reynolds stresses, and turbulent heat flux were made for three mild stable states, including overlying inversion, and the neutral state. The depth of the atmospheric boundary layer was kept constant, and so the results show the effect of change in stability alone, without the change in scale that would also arise in full scale measurements, an advantage provided by wind tunnel experiments. The simulated boundary-layer wind-speed profile is the same in each case, its height slightly exceeding the blade-tip top height, and the velocity deficit at the turbine is also the same in each, implying a constant thrust coefficient. In the near wake the momentum deficit rises more rapidly in the stable cases, and stays higher further downstream where it is subsequently reduced by turbulent mixing. The wake grows less rapidly in the vertical direction in the stable cases, both above and below the hub height, the height above growing still less rapidly with an imposed inversion, while the height below is unaffected by the inversion. The wake width is largely unaffected by stability. Stability reduces the Reynolds stresses in the wake over and above the reduction in the undisturbed flow; there is not a simple superposition. In the lower part of the wake the stresses are not affected by the inversion, while they are in the upper part. Turbulent heat flux is increased in the bulk of the wake, more so with an inversion, but is reduced to the surface and unaffected by an inversion.

Influence of wind barrier on aerodynamic characteristics of vehicle on railway–highway combined bridge

Wind barriers with different parameters will change the aerodynamic force of the car on the bridge as well as the stability of the vehicle–bridge system, affecting the vehicle’s safety and comfort. A numerical simulation test was conducted on the bridge-deck with three different air permeability wind barriers under three distinct vehicles of varying sizes and wind directions, with a large-span road–rail asymmetric cable-stayed bridge serving as the engineering foundation. The results show that the roll force of the bridge is proportional to the width of the body and inversely related to the height of the train. The roll force of a vehicle is inversely proportional to its height and width. The type of vehicle and the properties of the bridge deck exert minimal influence on the stability of the bridge when a single vehicle is positioned upstream. When a single vehicle is situated downstream, the tri-component force coefficient of the bridge undergoes significant changes, and the vehicle’s impact on the bridge’s stability becomes more pronounced. When the bridge deck’s ventilation rate is at 50%, the drag coefficient of the bridge deck doubles compared to that of a bare bridge deck, and the wind pressure coefficient of the vehicle surface on the bridge approaches zero. In scenarios involving two vehicles, the shielding effect caused by the vehicles positioned upstream and downstream results in a substantial shift in the aerodynamic forces acting on the two vehicles. This increases the wake width of the bridge and generates a visible vortex in the wake.

Direct numerical simulation of temporally evolving stratified wakes with ensemble average

Direct numerical simulations are conducted for temporally evolving stratified wake flows at Reynolds numbers from $10\,000$ to $50\,000$ and Froude numbers from $2$ to 50. Unlike previous studies that obtained statistics from a single realization, we take ensemble averages among 80–100 realizations. Our analysis shows that data from one realization incur large convergence errors. These errors reduce quickly as the number of statistical samples increases, with the benefit of ensemble average diminishing beyond 40–60 realizations. The data with ensemble average allow us to test the previously established scalings and arrive at new scaling estimates. Specifically, the data do not support power-law scaling in the centreline velocity deficit $U_0$ beyond the near wake. Its decay rate increases continuously from 0.1 at the onset of the non-equilibrium regime until the end of our calculations without reaching any asymptote. Additionally, while no power-law scalings could be found in the wake width ( $L_H$ ) and wake height ( $L_V$ ) in the late wake, $L_H\sim (Nt)^{1/3}$ is a good working approximation of the wake's horizontal size, where $N$ is buoyancy frequency and $t$ is time. Besides the low-order statistics, we also report the transverse integrated terms and the vertically integrated terms in the turbulent kinetic energy budget equation as a function of the vertical and transverse coordinates. The data indicate that there are two peaks in the vertically integrated production and transport terms, and one peak when the two terms are integrated horizontally.

Laser-Doppler Anemometry Measurements of Turbulent Swirling Wakes

This study considers the development and evolution of the swirling turbulent wake and their link to the turbulence present in the wake. A wake generator produces swirling wakes with a minimum of artifacts that would complicate the flow. Four swirling wakes have been studied with swirl numbers ranging from 0.19 to 0.37, and the results are compared to those of a nonswirling wake. Two-component laser-Doppler anemometry has been used to measure mean and turbulence quantities in the wake, and the uncertainty of these quantities has been determined. Careful alignment of the laser-Doppler anemometry system and large numbers of independent samples were used to obtain second-order turbulence statistics with low uncertainty. The results indicate that swirl strength impacts wake behavior, and changes in the behavior are linked to modifications in the turbulence. Faster wake width growth and centerline velocity deficit decay have been observed for wakes with higher swirl strength. The results indicate that a minimum swirl level is required to significantly impact wake behavior, and, at some level of swirl, the enhanced wake evolution observed saturates. For the conditions tested, the swirl number that enhances wake diffusion before saturation has been determined to lie between 0.21 and 0.37.

Quantitative evaluation of the damage to RC buildings caused by the 2023 southeast Turkey earthquake sequence

Data from 15 earthquakes that occurred in 12 different countries are presented showing that, without better drift control, structures built with building codes allowing large seismic drifts are likely to keep leaving a wide wake of damage ranging from cracked partitions to building overturning. Following the earthquake sequence affecting southeast Turkey in 2023, a team led by Committee 133 of the American Concrete Institute surveyed nearly 250 reinforced concrete buildings in the area extending from Antakya to Malatya. Buildings ranging from 2 to 16 stories were surveyed to assess their damage and evaluate the robustness of their structures in relation to overall stiffness, as measured by the relative cross-sectional areas of structural walls and columns. The majority of the buildings were estimated to have been built in the past 10 years. Yet, the structures surveyed were observed to have amounts of structural walls and columns comparable with amounts reported after the Erzincan (1992), Duzce (1999), and Bingol (2003) Earthquakes in Turkey. These amounts are, on average, much smaller than the wall and column amounts used in Chile and Japan. Because of that lack of robustness and given the intensities of the motions reported from Antakya to Malatya (with 10 stations with peak ground velocity (PGV) of 100 cm/s or more), it is concluded that structures in this region experienced large drifts. Excessive drift (1) exposed a myriad of construction and detailing problems leading to severe structural damage and collapse, (2) induced overturning caused by p-delta for some buildings, and (3) caused widespread damage to brittle masonry partitions. The main lesson is simple: ductility is necessary but not sufficient. It is urgent that seismic drift limits are tightened in high-seismicity regions worldwide.

An improved dynamic model for wind-turbine wake flow

We present an improved dynamic model to predict the time-varying characteristics of the far-wake flow behind a wind turbine. Our model, based on the FAST.Farm engineering model, is novel in that it estimates the turbulence generated by convective instabilities, which selectively amplifies the inflow velocity fluctuations. Our model also incorporates scale dependence when calculating the wake meandering induced by the passive wake meandering mechanism. For validation, our model is compared with FAST.Farm and large-eddy simulation (LES). For the mean flow, our model agrees well with LES in terms of the wake deficit and wake width, but the FAST.Farm model underestimates the former and overestimates the latter. For the instantaneous flow, our model predicts well the wake-center deflection and turbulent kinetic energy, reducing the discrepancies in the spectral characteristics by more than a factor of two relative to LES, depending on the Strouhal number. By incorporating two key mechanisms governing the far-wake dynamics, our model can predict more accurately the dynamic wake evolution, making it suitable for real-time calculations of wind farm performance.

Wind turbine wake superposition under pressure gradient

We investigate the effect of pressure gradient on the cumulative wake of multiple turbines in wind tunnel experiments spanning across a range of adverse pressure gradient (APG), zero pressure gradient (ZPG), and favorable pressure gradient (FPG). Compared to the upstream-most turbine, the in-wake turbines exhibit lower (higher) wake velocity in APG (FPG) than in the ZPG. The maximum velocity deficit shows a lesser difference for the in-wake turbine between different cases compared to the upstream-most one. This is linked to the effect of the wake of the upstream turbine. Conversely, the wake width varies more for the in-wake turbines. A new analytical approach to model the cumulative wake velocity deficit is proposed. This approach extends the application of the analytical pressure gradient model to multiple turbine wakes. Specifically, the new approach explicitly accounts for the effect of the pressure gradient induced by the wake of the upstream turbine on the wake of the downstream one. The new method is compared to the linear summation approach and experimental data. It agrees well with the experiments and outperforms the linear summation approach.

Particle Image Velocimetry Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade

Abstract Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70–120 k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid. The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier–Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream, around three times higher than PIV. Additionally, PIV estimated turbulence intensity (TI) in the cascade, showing TI decay along a streamline. At the highest Mach number, a peak TI occurred past a shock wave. Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.

Effect of pulsatile flow on hydrodynamic characteristics of vortex induced vibration of square cylinder

Vortex Induced Vibration (VIV) of an elastically mounted square cylinder subjected to pulsatile flow conditions is solved numerically for Reynolds number (Re = 100) and low mass ratio (Mred = 2). The focus of the present work is on investigating the effects of pulsatile frequency on the response of the cylinder. Effects of variation in Keulegan-Carpenter number, KC ϵ [10- 40, step of 10] and reduced velocity, Ured, ϵ [3-25, step of 1], on hydrodynamic characteristics is studied. An Arbitrary-Lagrangian Euler (ALE) formulation is used to write the governing equations in two space dimensions. Maximum cross-flow displacement is observed for Ured = 7 for KC=10. It is found that, the lock-in becomes slightly wider with increase in KC. Different regimes like Initial Branch , Lower Branch and desynchronized have been identified for all KC. Beyond KC = 20, cylinder starts to vibrate with the pulsatile frequency. Moreover, in the Lock-in zone flow amplitude is not always enhanced, and it sometimes gets reduced. This is basically due to state of synchronization between displacement and forcing. For all KCs, in-phase and out-of-phase regimes were also identified for X and Y-direction displacements. Wake width and vortex strength are maximum at the lock-in.

Experimental and numerical investigations on the performance and wake characteristics of a tidal turbine under yaw

This paper presents an extensive examination of the wake characteristics and hydrodynamic performance of a 1:60 scale horizontal axis tidal stream turbine under yawed inflow conditions. Experimental investigations were conducted in a laboratory flume, while numerical simulations utilized the actuator line method and large-eddy simulation technique. The turbine was subjected to an inflow turbulence intensity of 6% and was tested at five different yaw angles (5°, 10°, 15°, 20°, and 30°). The findings demonstrate a substantial reduction in the power coefficient as the yaw angle increases, with a notable drop of 47.1% recorded at a yaw angle of 30°. Furthermore, numerical simulations of wake characteristics, including mean velocity and turbulence intensity, were examined and compared with measurements, yielding satisfactory agreement. The yawed wake flow exhibited asymmetrical distributions of mean velocity and deviations from the centerline. Additionally, distinct deformations of the yawed wake in the y-z cross sections were observed, indicating a discernible curled kidney shape that intensified with larger yaw angles. Moreover, interactions between the turbine wake and support structures affected the width and turbulence intensity of the near wake, introducing additional unsteadiness that accelerated wake recovery.

Experimental study on the characteristics of a novel aerodynamic wake width flameholder

In this study, a novel flameholder named aerodynamic wake width flameholder (AWF) was proposed. The AWF optimized the sidewall profile of conventional bluff body flameholders and widened the downstream recirculation zone through aerodynamic force, while maintaining the same trailing edge width as conventional flameholders. Consequently, the combustion properties were impacted. To investigate the flow field structure, flame stability limits, and flame evolution of the novel flameholder, an aerodynamic wake width evaporating flame holder (AWEF) was designed and compared with a normal evaporating flameholder (EF). Comparative analysis of the downstream flow field structure revealed that the AWEF exhibited a wider zero-velocity contour and a higher reflux rate. Furthermore, the AWEF demonstrated a larger velocity gradient near the trailing edge, indicating the presence of a thicker shear layer. Within the inlet Ma range of 0.1 to 0.17, the AWEF exhibited wider flame stability limits compared to the EF. The ignition fuel-air ratio (FAR) of the AWEF remained relatively constant within this range, suggesting that the novel flameholder could withstand the deterioration of ignition performance caused by an increase in the inlet Ma. Moreover, the AWEF achieved a larger flame projection area and flame width downstream compared to the EF. Finally, by combining the flow field characteristics and flame stability properties of the AWEF, the mechanisms underlying the changes in flame stability characteristics were analyzed. The results of this study can serve as valuable references for enhancing flame stability in current and future advanced augmentor systems.

Numerical study on flow-induced vibration of an oscillating cylinder with an unattached downstream square plate at a low Reynolds number

Based on the Lattice Boltzmann Method, we numerically studied the flow around a transversely oscillating cylinder with a downstream stationary square plate at a Reynolds number Re = 150 and a mass ratio m* = 2.0. This paper initially considered a zero-damping ratio and a wide range of reduced velocities (Ur = 3–30) to investigate the effects of the gap ratio (L/D = 0.3–3.0) and the dimensionless width of the square plate (W/D = 0.5–2.0) on the response characteristics, force coefficients, wake patterns, and pressure distribution. The energy conversion performance is further tested by applying different non-zero damping ratios (ζ = 0.01–0.3). The main conclusions are as follows: (1) Three vibration behaviors are identified: vortex-induced vibration (VIV), wake interference galloping, and a newly reported “bifurcation” phenomenon of oscillation. For L/D = 0.3, at high reduced velocities (Ur ≥ 15), the cylinder experiences the “bifurcation” phenomenon, where it oscillates on one side of the square plate with a small vibration amplitude. Similar behavior is achieved for the system with L/D = 0.5 and 0.7 but requires a wider square plate than one diameter and higher reduced velocities of Ur ≥ 17.5. (2) Considering both the response amplitude and drag coefficient exerted on the square plate, the cylinder-square plate system with L/D = 0.7 and W/D = 1.0 exhibits a wide wake interference galloping response and an expected vibration amplitude with a lower drag coefficient. (3) For L/D = 0.7 and W/D = 1.0, as Ur increases from 10 to 15, the inclusion of the square plate leads to an increased difference in pressure coefficient between the front of the square plate and the rear of the cylinder. The amplified pressure difference enhances the response of the cylinder, potentially explaining the transition from VIV to wake interference-induced galloping. (4) With a non-damping ratio (ζ = 0.01–0.3), the cylinder-square plate system with L/D = 1.0 and W/D = 1.0 achieves the highest maximum energy harvesting efficiency ηM = 12.01% at the optimum damping ratio ζO = 0.2.

Investigation of a Near-Field Cylinder Wake in the Subsonic, Transonic, and Supersonic Regimes

The near wake of a circular cylinder in a high-Reynolds-number regime is investigated using the particle image velocimetry technique for an inflow Mach number spanning 0.3 to 2. The mean flow and turbulent kinetic energy field for different Mach number cases are presented. Furthermore, the influence of the Reynolds and Mach number effects is examined based on the mean separation point along the cylinder surface, which is extracted from complementary schlieren visualization measurements, and the literature. The wake width for the supersonic inflow case is found to be an order of magnitude smaller physically than the subsonic case with an identical cylinder diameter. Additionally, the swirl strength criterion is used to identify the eddies present within the wake, and the eddy size and convection velocity are characterized based on the spatiotemporal correlations. The result suggests that the mean wake features for the subsonic and supersonic cases are very different. Moreover, the interaction of eddies generated at the cylinder’s top and bottom shear layers leads to the large-scale features present in the wake, and the differing paths followed by the eddies between the subsonic and supersonic cases are responsible for the variation in the observed wake width.

Investigating the impact of various operating parameters on blade aeroelasticity and wake characteristics of large-scale wind turbines

The current study endeavors to investigate the impact of various operating parameters on the fluid-structure interaction characteristics of wind turbine blades and wake field characteristics within a wind farm. The observed underperformance of wind farms, attributed to downstream wind turbines being exposed to upstream wake effects, highlights the need for implementing active wake control (AWC). Consequently, in-depth research into the fluid-structure interaction characteristics of wind turbines and wake characteristics under AWC conditions becomes imperative. To address this, a novel aeroelastic analysis model based on geometrically exact beam theory, lifting line theory, and optimization is developed. Numerical simulations utilizing the IEA WIND 10 MW wind turbine, developed by the International Energy Agency, are employed to assess the fluid-structure interaction characteristics of the blades and wake characteristics under various wake control strategies. The results demonstrate that cone angle control in blade attitude alters the wake field width but may reduce velocity loss recovery rate, while pitch angle control significantly improves wake field length at the expense of increased response load. Yaw and tilt control redirect wake flow, with tilt control exhibiting lower thrust and structural response loads. The coupling of yaw and tilt control emerges as a promising approach with enhanced velocity loss recovery and reduced response loads. These findings contribute to understanding the effectiveness of wake control strategies in optimizing large-scale wind turbine performance.

Wake interaction between two spar-type floating offshore wind turbines under different layouts

Limited by layout space and manufacturing costs, wake interaction in offshore wind farms is inevitable and can have adverse effects on the performance of downstream wind turbines. To gain a better understanding of the wake interaction between Floating Offshore Wind Turbines (FOWTs), this paper conducts coupled aero-hydrodynamic simulations for two spar-type FOWTs under different layouts. The Unsteady Actuator Line Model (UALM) is used to analyze the unsteady aerodynamic loads of the wind turbine, while the hydrodynamic responses of the floating support platform are obtained using the Computational Fluid Dynamics (CFD) method. To predict the aero-hydrodynamic performance of the FOWT under combined wind and waves, an in-house CFD code developed at Shanghai Jiao Tong University (SJTU), called FOWT-UALM-SJTU solver, is utilized. First, grid convergence test and time step sensitivity study are performed to determine appropriate simulation parameters. Subsequently, numerical simulations of two FOWTs under tandem and offset layouts are conducted to investigate the influence of wake interaction on the performance of downstream FOWT. The dynamic responses of the FWOT, including aerodynamic loads, platform motions, and wake characteristics, are analyzed in detail. From the simulation results and discussions, several conclusions are drawn. Both platform motions and wake interaction contribute to an increased variation range of inflow wind speed experienced by the downstream FOWT, thereby exacerbating the instability of its aerodynamic loads. Under the tandem layout, the platform motions of the upstream FOWT and the downstream FOWT exhibit opposite effects on the aerodynamic loads of the downstream FOWT. Moreover, platform motions increase turbulence intensity in the wake region, accelerating wake velocity recovery and widening the wake width.