Vortex Shedding Behavior Research Articles

Ground Effect Investigation on the Aerodynamic Airfoil Behavior Using Large Eddy Simulation

Abstract The underlying physics ever behind the aerodynamics of an airfoil in ground effect (GE) are still not fully resolved. In this work, the aerodynamics for an airfoil in GE is investigated computationally for both transitional and turbulent flow regimes. Large eddy simulation (LES) is employed to explore the flow physics around a NACA0012 airfoil in ground vicinity, which is commonly used in wind energy applications. The angle of attack (AoA) is fixed at AoA = 10 deg, while the flight height to chord ratio (h/c) is variable. An analysis is conducted for the aerodynamic forces, i.e., the lift (CL), and the drag (CD). The behavior for the skin fiction drag (CDf) is explored in the light of the flow physics near the ground. In addition, the vortex shedding behavior is estimated at different height (h/c) for the transitional and turbulent flow regimes. At h/c = 0.2, the friction drag (CDf) is improved by 9.6% and 16.3% for the transitional and turbulent flow regimes, respectively. The results show that the frequencies for the vortex shedding decline significantly near the ground. This decline is correlated with the larger vortical structures and vortex developing mechanism.

Aerodynamic characteristics of a streamlined box girder under shear flow considering oncoming turbulence

Non-synoptic winds, such as typhoons and downbursts, are frequently characterized by shear flow associated with turbulence, which affects the aerodynamic performance of long-span bridges. To reveal the aerodynamic characteristics of streamlined box girders under non-synoptic winds, multi-fan wind tunnel (MFWT) tests were used to investigate the aerodynamic effect around a streamlined box girder considering the action of shear flow with different velocity gradients, turbulence intensities, and integral scales. In the MFWT tests, the high shear rate and large turbulence intensity were observed to magnify the mean wind pressure coefficient, whereas the variation in the turbulence integral scale had a slight effect on the mean wind pressure coefficient distribution. An increase in the shear rate was observed to be beneficial in reducing the drag and moment coefficients, as well as in increasing the lift coefficient. The empirical aerodynamic prediction relationships revealed that the influence of turbulence intensity on the aerodynamic coefficient is non-linear, whereas that of the turbulence integral scale and shear rate on the aerodynamic coefficient is linear. Additionally, the large eddy simulation (LES) method was used to study the vortex-shedding behaviors and aerodynamic spectrum characteristics of the streamlined box girder under shear flow. The LES results showed that larger shear parameters amplify the amplitudes of high-frequency aerodynamic forces. The vortex frequently begins from the low-velocity side of the streamlined box girder, which induces a suction effect on the low-velocity side that is greater than that on the high-velocity side.

Effect of crossflow oscillation Strouhal number on circular cylinder wake

The wake flow features and aerodynamic characteristics of a circular cylinder in an oscillating crossflow were experimentally investigated. The study focused on crossflow oscillation Strouhal numbers that were smaller than the natural wake vortex-shedding Strouhal numbers. Crossflow oscillations were generated using a downstream rotating plate method. The flow evolution processes were observed using laser-light sheet assisted smoke flow visualization technique. Wake instability and time-averaged velocities were assessed using a one-component hot-wire anemometer and particle image velocimetry. Pressure distributions on the cylinder's surface were quantified using a linear pressure scanner, obtaining pressure coefficient distributions and drag forces. The wake instability Strouhal number, velocity vectors, streamline patterns, and recirculation bubble geometries in the wake region of the circular cylinder were determined. The wake turbulence properties were analyzed using the triple-decomposition method, including turbulence intensities and Lagrangian integral length and time scales. The results of natural and oscillating crossflows were compared. The wake vortex-shedding Strouhal number was lower than the natural Strouhal number but higher than the crossflow oscillation Strouhal number. It was primarily influenced by the oscillation Strouhal number and the Reynolds number of the crossflow. Critical crossflow Reynolds and oscillation Strouhal numbers were identified, beyond which the wake vortex-shedding Strouhal number reached a constant value. The crossflow oscillation intensity did not significantly affect the wake vortex-shedding behavior. The study provided quantitative descriptions and discussions of recirculation bubble geometries and statistical turbulence properties. Furthermore, the crossflow oscillations led to a substantial reduction in the drag coefficient experienced by the circular cylinder.

Numerical simulation of flow around circular cylinder near a plane wall: effects of wall proximity, boundary layer and reynolds number

The cylindrical structures in close proximity to a solid surface have diverse and numerous applications within current engineering. While the flow dynamics around an isolated circular cylinder located in a uniform flow are reasonably well understood, this is not the case when the cylinder is positioned near a plane wall. This particular configuration is studied using computational fluid dynamics (CFD) through the Fluent code, which implements the finite volume method. For this purpose, a two-dimensional and transient flow is carry out using the SST-SAS turbulence model. The effects of changing the separation (G) between the cylinder (with diameter D) and the wall are analyzed for different Reynolds numbers and different boundary layer thicknesses. The lift and drag coefficients and the behavior of vortex shedding (Strouhal number, St) are examined. The numerical results are compared with values available in the literature from experimental wind tunnel tests, showing that both the drag and lift coefficients strongly depend on the separation ratio (G/D) and are affected by the boundary layer thicknesses.

Effects of sheltering on the unsteady wake dynamics of tandem cylinders mounted in a turbulent boundary layer

The unsteady wake dynamics of two finite wall-mounted cylinders of unequal height and arranged in tandem are investigated using time-resolved particle image velocimetry (TR-PIV). The cylinders were fully submerged in a turbulent boundary layer with a Reynolds number based on the cylinder diameter (d) of 5540 and boundary layer thickness of$\delta /d = 8.7$. The centre-to-centre spacing between the cylinders was fixed at 4d. The degree of sheltering was studied by varying the height of the upstream cylinder (UC)$(h/d \in [0.7\unicode{x2013} 7.0])$while keeping the height of the downstream cylinder (DC) constant at$H/d\; = \; 7.0$. The resulting height ratios were$h/H = 0.10,0.25,0.50,0.75$and$1.00$denoted as HR10, HR25, HR50, HR75 and HR100, respectively. The wake dynamics of the DC were also compared to those of an isolated single cylinder (SC) with similar Reynolds number, aspect ratio and submergence ratio. TR-PIV measurements were performed in the symmetry plane for all test cases and five spanwise planes along the height of HR75. The results showed that as the height ratio increases, the downwash from the free end of the UC impinges directly on the frontal surface of the DC and induces a strong upwash on the opposite rear side of the DC. The induced upwash impedes the downwash from the free end of the DC much earlier than observed behind the SC, resulting in a reduced reverse flow area and high velocity deficit in the sheltered portion of the DC. Nonetheless, the reverse flow area behind the UC and DC undergoes a quasi-periodic pumping motion with frequencies that are synchronized for HR25 to HR100. Spectral analysis and proper orthogonal decomposition also reveal that the attachment of the shear layers of the UC on the DC also promotes a lock-in anti-symmetric vortex shedding behaviour.

Effect of fin density and fin height on flow-induced vibration behavior of finned tube arrays subjected to water cross flow

PurposeThe prediction of critical velocity at instability threshold for shell and tube heat exchangers is important to avoid failure of tubes as a result of flow-induced vibrations due to water cross flow. The flow-induced vibration in finned tube heat exchangers is affected by various parameters such as fin height, fin pitch, fin material, tube array, pitch ratio, fin type, fluid velocity etc. In this paper, an experimental investigation of fluid elastic instability in shell and tube heat exchangers is carried out by subjecting normal square finned tube arrays of pitch ratio 1.79 to water cross flow.Design/methodology/approachThe five tube arrays, namely plain array, two finned tube arrays with 3 fpi and 9 fpi fin density, and two finned tube arrays with 3 mm and 6 mm fin height are tested in the experimental test setup with water flow loop and vibration measurement system. The research objective is to evaluate the effect of fin density and fin height on the instability threshold. The critical velocity at instability threshold is determined to characterize the fluid elastic instability behavior of different tube arrays. The vortex shedding behavior of the tube arrays is also studied by determining Strouhal number corresponding to the small peaks before fluid elastic instability.FindingsThe fluid elastic instability behavior of the tube arrays was found to be the function of fin tube parameters. The experimental results indicate that an increase in fin density and fin height results in delaying the instability threshold for finned tube arrays. It is also observed that critical velocity at instability is increased for finned tube arrays compared to plain tube arrays of the same pitch ratio. The design modifications in the outer box have resulted in further reduction in the natural frequency. This enabled to reach clear instability for all the five-tube arrays.Originality/valueThe research data add the value to the present body of knowledge by knowing the effect of fin height and fin density on the fluid elastic instability threshold of normal square finned tube arrays subjected to water cross flow.

Comparison of Flow Topology Between Major Groups of Airfoil with Vortex Shedding

The effect of vortex behavior on airfoil aerodynamic performance has been widely debated for many years, and many research studies have been conducted to examine the relationship. This paper highlights the in-depth study of flow topological processes on major airfoil groups with vortex shedding. It considers various typeof corresponding geometriesincludingsymmetrical, asymmetrical, thick, and thin airfoilsin order to showthe differences in flow topology. The study also emphasized the behavior of separationbubbles, vortex shedding and reattachment points. The use of a commercial CFD softwarefor the studygave reliable resultswithinan adequate length of time. The vortex shedding wassuccessfully highlighted either physically or hypothetically. The separation bubble was relatively easier to be identified in all cases of airfoil of interest. The evolution of separation bubble captured by the topology in the case of Eppler169 was the unique, and involved the break of reattachment point.

Investigation of hybridized bluff bodies for flow-induced vibration energy harvesting

Small-scale wind energy harvesting based on flow-induced vibration (FIV) mechanisms has attracted lots of research interest in recent years. Vortex-induced vibration (VIV) and galloping energy harvesters usually outperform each other in different wind-speed ranges. To combine the advantages of VIV and galloping harvesters, this paper explores the idea of using a hybridized bluff body constituting of two cylindrical and one cuboid segment for wind energy harvesting. The total length of the hybridized bluff body was fixed. The cuboid segment length was varied to investigate the effect on the FIV behavior of the bluff body. The results show that, when the cuboid segment is short in length, the bluff body exhibits VIV-like behavior in the low wind-speed range and galloping-like behavior in the high-speed range. In the medium wind-speed range, galloping-VIV coupling appears. However, if the cuboid segment is longer, the galloping-VIV coupling phenomenon disappears; the hybridized bluff body behaves just like a cuboid one and only exhibits a galloping motion. In addition to experiments, computational fluid dynamics (CFD) simulations are also conducted to provide more insights into the aerodynamics of the hybridized bluff body. The simulation results reveal that introducing hybridization into the bluff body changes the vorticity flow behind it and alters the vortex-shedding behavior. The vortex-shedding effect, in turn, affects the vibration of the bluff body, as well as the performance of the harvester.

Investigation on vibration parameters in aluminum finned tube arrays subjected to water cross flow

PurposePredicting the critical velocity is crucial at the instability threshold for shell and tube heat exchangers in order to prevent tube failure due to vibrations. In this study, the vibration response of an aluminum tube bundle subjected to water cross flow was analyzed experimentally. Aluminum tubes are preferred over steel tubes because of aluminum tubes' excellent corrosion resistance, ease of manufacture, and high thermal efficiency.Design/methodology/approachThe fluid elastic instability and vortex shedding mechanisms in a finned tube array of aluminum tubes with a base tube diameter of 19.05 mm and pitch of 34 mm were investigated. The current study considers parallel triangular finned tube arrays with fin heights of 3 mm and 6 mm with a uniform fin thickness and fin pitch. The plain tube array was tested to compare the finned tube array results. The tube vibration response was measured using an accelerometer mounted on the middle tube of the third row. In order to define the fluid elastic instability behavior of various tube arrays, the critical velocity at the instability threshold is measured. By finding the Strouhal number at the small peaks before instability, the vortex shedding behavior of the tube arrays is examined.FindingsThe results reveal that the critical velocity at instability for coarse finned tube arrays increases as the fin height increases. The effect of the tube material is evaluated by comparing the results with those previously reported for parallel triangular tube arrays made of steel. Finally, the occurrence of vortex shedding in a tube array is confirmed based on the Reynolds number and Strouhal number relationship. The instability constant K for the plain tube array of steel and aluminum material are 4.97 and 4.87, respectively.Originality/valueThis paper provides the research findings on the effect of fin height on coarse density finned tube array. This will add substantial knowledge to the literature in the field of fluid elastic instability and vortex shedding, which is needed for the safe functioning of shell and tube heat exchangers.

Transient vortex shedding behaviour of non-reacting flow over V-gutter bluff bodies with a central slit

This study numerically investigates the characteristics of unsteady vortex shedding phenomena behind V-gutter bluff bodies, with an emphasis on their application for achieving reliable and energy-efficient combustion in air-breathing propulsion systems. The study explores the effect of the V-gutter’s semi-span angle and the provision of a central slit on the leading edge of the bluff body, on the modification of the wake, which is critical for flame stabilisation. The transient non-reacting fluid flow over the V-gutter bluff body is modelled with two discrete semi-span angles (60° and 30°) and with four central slit diameters (1, 0.75, 0.5, and 0.25 mm). Based on the characteristics of the wake, the study shows that the V-gutter that has a semi-span angle of 60° and a central slit of 0.25 or 0.5 mm would be the most effective configuration within the range of parameters considered in the study.

The Hydrodynamic Behavior of Vortex Shedding behind Circular Cylinder in the Presence of Group Focused Waves

Vortex shedding behind an elastically mounted circular cylinder in the presence of group focused waves propagating upstream was investigated using a classical approach (time series and FFT) and nonclassical approach (complex 2D Morlet wavelets). Wavelet analysis emerged as a novel solution in this regard. Our results include wave trains with different nonlinearities propagating in different water depths and derived from three types of spectra (Pierson–Moskowitz, JONSWAP (γ = 3.3 or γ = 7)). It was found that the generated wave trains could modify regimes of shedding behind the cylinder, and subharmonic frequency lock-in could arise in particular situations. The occurrence of a lock-in regime in the case of wave trains propagating in intermediate water locations was shown experimentally even for small nonlinearities. Moreover, the application of time-localized wavelet analysis was found to be a powerful approach. In fact, the frequency lock-in regime and its duration could be readily identified from the wavelet-based energy and its corresponding ridges.

Vortex shedding induced vibration of thin strip in confined rectangular channel

To study the basic behavior of vortex shedding of spacer grids, both experiments and numerical simulations of a single flat plate with a high chord-to-thickness ratio in a confined rectangular channel were performed. Frequencies of vortex-induced vibrations were obtained through a laser Doppler vibrometer (LDV), and the upstream velocity distribution was acquired by particle image velocimetry (PIV). Two-dimensional large eddy simulations (LES) were conducted, with the PIV results being used as the inlet boundary conditions. Dynamic mode decomposition (DMD) was applied to the numerical results to identify the vortex shedding modes for a number of cases. The numerical results showed good agreement with the experiments in terms of the vortex shedding frequencies. From the simulations, three vortex shedding modes were obtained: trailing edge shedding without the leading edge–vortices coupling (Type I), weak leading edge–vortices coupled shedding (Type II), and strong leading edge–vortices coupled shedding (Type III). The leading edge vortices showed different types of characteristics, namely those that diffused before reaching the trailing edge (Type I), those that stayed close to the plate surface until they reached the trailing edge (Type II), and those that got detached from the plate surface in the transverse direction, and then moved back (Type III). The results showed that both the Reynolds number based on the plate thickness (Red) and dimensionless width of the channel (h/d) could affect the vortex shedding. A higher Red or lower h/d led to stronger leading edge vortices. Moreover, stronger leading edge vortices led to a smaller dimensionless boundary layer thickness (δ/d) at the trailing edge. Finally, the Strouhal number based on the separation distances between similarly shed rotational vortices (Stλ) and the thickness of the plate together with the boundary layer (Std+2δ) were more robust than that based on the thickness of the plate (Std).

Influence of porous media coatings on flow characteristics and vortex-induced vibration of circular cylinders

The aerodynamic parameters and flow field characteristics of cylinders with and without a porous media coating (PMC) were experimentally investigated in a wind tunnel. This research explored the potential of using a PMC to control vortex-induced vibration (VIV). The PMCs were manufactured with four pores-per-inch values (PPI = 15, 20, 30, and 40) and three depths, (d/D=0.125, 0.25, and 0.5, where d is the depth of the coating and D is the diameter of the bare cylinder). The instantaneous drag and lift forces were measured in static tests. The results showed that all the PMCs could decrease the fluctuation of the forces. The root-mean-square lift force was reduced by up to 98% with a coating of PPI = 15 and d/D=0.5 at Re = 5.2×104. The flow fields were visualized using a particle image velocimetry (PIV) system and analyzed with time-averaged velocity fields, wake velocity profiles, and turbulence kinetic energy distributions. For PMCs with smaller PPI values and greater depths, the wake vortex formed further away from the cylinder. Then the dynamical responses were tested for elastically supported models. Not all the PMCs could suppress the VIV. When PPI < 30, the PMC decreased the VIV amplitude. For each PPI, a greater depth resulted in a lower amplitude. The VIV amplitude for a coated cylinder was reduced to 4% of that for the bare cylinder. When PPI > 30, the PMC enhanced the VIV, with a greater depth resulting in a higher amplitude. When PPI = 30, the PMC could either increase or decrease the VIV amplitude, depending on the depth. The flow fields around the oscillating cylinder were also analyzed to reveal the effect of the PMC on the wake vortex shedding behavior.

Lock-in phenomenon of vortex shedding in flows excited with two commensurate frequencies: a theoretical investigation pertaining to combustion instability

An analytical investigation is performed to study the dynamics of vortex shedding behaviour during two commensurate frequency velocity excitations, with an emphasis on the phenomenon of lock-in. We attempt to theoretically study the dynamical features of lock-in under two-frequency excitations and contrast the behaviour with single-frequency excitation. We employ an existing low-order model to characterise the vortex shedding process behind a step/bluff-body. The continuous-time domain model is transformed to a nonlinear dynamical map that relates time instances of successive vortex shedding. Further, these time instances are converted to phase instances, involving which criteria for a generic p : q phase lock-in is obtained. Four parameters are involved: amplitude and frequency of the two excitation components termed as primary and secondary. Bifurcations occurring are investigated using return maps. The inclusion of secondary excitation leads to the existence of two orders of lock-in within a single lock-in boundary. Furthermore, our results indicate that secondary excitation can be used as a control in order to tailor the 1:1 lock-in region formed by the primary excitation. Finally, analytical expressions are obtained to identify lock-in boundaries and their salient geometrical features. Interesting features such as the occurrence of bistability and change in the order of lock-in are observed, which can be explored further with future experiments.

Suppression of vortex shedding using a slit through the circular cylinder at low Reynolds number

The present article aims to study the suppression of vortex shedding using a passive flow control technique (slit through a circular cylinder) in the laminar regime (Re =100–500). The slit width ratio S/D (slit width/diameter) on the modified cylinder plays an essential role to control the vortex shedding. The additional flow through the slit leads to the suppression of the global instability and vortex shedding, whereas a large amount of flow through the slit drastically alters the behavior of vortex shedding. The nature of vortex shedding remains periodic for all S/D, and the root mean square (rms) value of the lift coefficient decreases (in turn, vortex shedding suppression) with S/D up to Re ≤ 300. For the range Re > 300, the root mean square (rms) value of the lift coefficient decreases up to S/D < 0.15, and the flow exhibits periodic vortex shedding, while the root mean square (rms) increases beyond S/D > 0.15 due to irregular vortex shedding downstream of cylinder. The variation of the Re for the S/D =0.20 shows bifurcation points where the flow changes its behavior from symmetric to asymmetric solution at Re=232 and again becomes symmetric at Re=304. The unsteady flow analysis over the modified cylinder also indicates the suppression in the vortex shedding; however, the analysis provides the qualitative property of suppression. The reduced-order modeling, i.e. Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD), is utilized to quantify suppression and investigate the dominant vortical structure for slit through the cylinder.

INVESTIGATION ON UNSTEADY BEHAVIOR OF NEAR-WAKE FLOW OF A BLUNT-BASE BODY BY AN OPTICAL-FLOW ALGORITHM

In this study, an optical-flow algorithm was applied to analyzing unsteady behavior of nearwake flow. The experiment was conducted at low-speed conditions and at Reynolds number around ReD = 1.97×104 to obtain image database for optical-flow processing. Measurement frequency was at 2000 fps. Results of the optical-flow algorithm were compared to previous studies by a traditional cross-correlation method. The ability of optical flow method to extract flow fields was, thereby, confirmed for blunt-base flow at low-speed conditions. Differing from previous studies and cross-correlation results, opticalflow results showed a dominated Strouhal number at around StD = 0.015, which is connected to vortex shedding behavior of the wake-flow. Additionally, the antisymmetric flow shows the most important behavior at low-speed conditions.

Optical-Flow Algorithm for Near-Wake Analysis of Axisymmetric Blunt-Based Body at Low-Speed Conditions

Abstract In this study, ability of an optical-flow algorithm in extracting wake structure of axisymmetric model was investigated. The initial data for optical-flow processing were obtained in low-speed conditions by particle image velocimetry method. The Reynolds number based on the model diameter was around ReD = 1.97 × 104 in this study. Both the time-averaged and transient flow characteristics of near-wake flow were illustrated and examined by the optical-flow analysis method proposed. The processing results of optical-flow method showed good agreement with conventional cross-correlation methods. The ability of optical-flow method to extract flow fields was, thereby, confirmed for blunt-based flow at low-speed conditions. This study showed that the antisymmetric flow behavior of the near wake is the dominant type at low-speed conditions. Differing to traditional methods and cross-correlation results, the optical-flow results showed a frequency at around StD = 0.015 of the near wake for the first time, which is connected to vortex shedding behavior of the wake flow.

Vortex shedding simulation of hydrofoils with trailing-edge truncation

Vortex shedding behind hydrofoils with trailing-edge truncation was analyzed via numerical simulations. The NACA0009 hydrofoil was analyzed numerically using the Spalart-Allmaras turbulence model. The hydrofoil lift coefficient variation curve was monitored during the simulation, and the vortex-shedding frequency was obtained as the oscillation frequency of the lift coefficient curve. The mode of vortex shedding of the perpendicular truncated and oblique truncated trailing edges were compared. The vortex-shedding behavior under different oblique truncation angles and the impact of the angle of attack on vortex shedding were also explored. The results showed that the oblique truncated trailing edge can substantially change the intensity and frequency of vortex shedding of the hydrofoil. Furthermore, there exists an oblique truncation angle at which the vortex-shedding frequency is minimized. In the presence of an angle of attack, the hydrofoil with oblique truncated trailing edges was less affected by vortex shedding from the tail.

Flow control and vibration response of a circular cylinder attached with a wavy plate

Flow past a circular cylinder fitted with a rear rigid wavy plate at a low Reynolds number of Re = 150 is first numerically studied in this work. The effects of the plate length and the surface undulation on the hydrodynamic forces and vortex shedding behavior of the circular cylinder are examined. The mean drag coefficient and the fluctuation of lift coefficient are reduced up to 27.5% and 54.9%, respectively, in the presence of a wavy plate. Additionally, the vortex formation length is elongated and the wake width is shortened, illustrating the suppression of vortex shedding. According to the flow control performance, the 1.5D-length (D is the cylinder diameter) wavy plate with wavelength of 3D is employed to control the vortex-induced vibration (VIV). The two-degree-of-freedom of flow-induced vibration is computed for a wide range of reduced velocities (Ur = 2–20) in comparison with a bare cylinder. The results indicate the initial and lower branches of VIV are effectively suppressed by the wavy plate with the maximum reduction of cross-flow amplitude up to 92.44%. Nevertheless, the reattachment of shear layers on the wavy plate surface and the asymmetric P + S (a single vortex and a pair of opposite signed vortices released per cycle of shedding) vortex structure stir the galloping instability at Ur > 8, instead of the desynchronization branch. The monotonic increase of vibration amplitude in galloping branch shows a greater potential for energy harvesting.

Development of a second-order dynamic stall model

Abstract. Dynamic stall phenomena carry the risk of negative damping and instability in wind turbine blades. It is crucial to model these phenomena accurately to reduce inaccuracies in predicting design driving (fatigue and extreme) loads. Some of the inaccuracies in current dynamic stall models may be due to the fact that they are not properly designed for high angles of attack and that they do not specifically describe vortex shedding behaviour. The Snel second-order dynamic stall model attempts to explicitly model unsteady vortex shedding. This model could therefore be a valuable addition to a turbine design software such as Bladed. In this paper the model has been validated with oscillating aerofoil experiments, and improvements have been proposed for reducing inaccuracies. The proposed changes led to an overall reduction in error between the model and experimental data. Furthermore the vibration frequency prediction improved significantly. The improved model has been implemented in Bladed and tested against small-scale turbine experiments at parked conditions. At high angles of attack the model looks promising for reducing mismatches between predicted and measured (fatigue and extreme) loading, leading to possible lower safety factors for design and more cost-efficient designs for future wind turbines.