Showing papers on "Flow separation published in 2022"

Physics and Modeling of Large Flow Disturbances: Discrete Gust Encounters for Modern Air Vehicles

Abstract: Gusts of moderate and large magnitude induce flow separation and other complexities when they interact with the lifting surfaces of air vehicles. The presence of these nonlinear gusts are becoming ...

Aeroacoustic Investigation of a Propeller Operating at Low Reynolds Numbers

Abstract: This paper presents an experimental investigation of a propeller operating at low Reynolds numbers and provides insights into the role of aerodynamic flow features on both propeller performances and noise generation. A propeller operating at a tip Reynolds number regime of is tested in an anechoic wind tunnel at an advance ratio ranging from 0 to 0.6. Noise is measured by means of a microphone array, while aerodynamic forces are measured with load and torque cells. Oil-flow visualizations are used to show the flow patterns on the blade surface, whereas phase-locked stereoscopic particle image velocimetry (PIV) measurements are carried out to analyze the flow at 60% of the blade radius. The pressure field around the blade section has been computed from the PIV velocity data. Results reveal a complex flowfield with the appearance of a laminar separation bubble at the suction side of the blade. The separation bubble moves toward the leading edge and reduces in size as the advance ratio decreases. At an advance ratio equal to 0.6, the flowfield is characterized by a laminar separation without reattachment. This causes vortex shedding responsible for a high-frequency hump in the far-field noise spectra.

Effect of varying frequency of a synthetic jet on flow separation over an airfoil

Abstract: An experimental investigation on the effects of the synthetic jet actuator (SJA) was conducted on a National Advisory Committee for Aeronautics 0025 airfoil in a low-speed recirculating wind tunnel at a chord Reynolds number of 100 000 and at an angle of attack 12°. Particle image velocimetry was used to visualize the flow separation for the uncontrolled baseline flow, and the flow attachment for the SJA controlled flows. The location of the SJA was at −1.3% from the separation point, and a blowing ratio of 0.8 was chosen for this study. The blowing ratio proved to be effective in suppressing the separation of the flow. The reduced frequency ( Ste) was varied between 1, 2, 14, and 58. The momentum bursts from the SJA based on the reduced frequency determined the effectiveness of the control method. The Reynolds stresses and turbulence production decreased dramatically with increasing frequency up to the shear layer frequency ( Ste= 14), but further excitation ( Ste= 58) resulted in a regain of turbulence levels. Proper orthogonal decomposition was performed which showed that the low frequency operations globally affect the modes in the shear layer while the high frequency operations are confined to the airfoil surface.

Three-dimensionality of hypersonic laminar flow over a double cone

Abstract: Abstract Hypersonic laminar flow over a canonical 25°–55° double cone is studied using computational fluid dynamics and global stability analysis (GSA) with a free-stream Mach number of 11.5 and various unit Reynolds numbers. Axisymmetric simulations reveal that secondary separation occurs beneath the primary separation bubble beyond a critical Reynolds number. The numerical results agree well with existing experiments and the triple-deck theory with the axisymmetric effect on the incoming boundary layer treated by the Mangler transformation. The GSA identifies a three-dimensional global instability that is azimuthally periodic immediately prior to the emergence of secondary separation. The criterion of the onset of global instability in terms of a scaled deflection angle established for supersonic compression corner flows (Hao et al., J. Fluid Mech., vol. 919, 2021, A4) can be directly applied to double-cone flows. As the Reynolds number is further increased, the flow is strongly destabilized with the coexistence of multiple stationary and low-frequency oscillating unstable modes. Direct numerical simulations confirm that the supercritical double-cone flow is intrinsically three-dimensional, unsteady and exhibits strong azimuthal variations in the peak heating.

Momentum Coefficient Governing Discrete Jet Actuation for Separation Control

Abstract: Amplitude scaling laws for active control of boundary layer separation using discrete jet forcing are not fully established. Momentum coefficient is the most widely accepted scaling parameter, but accurate measurement and assessment of the employed assumptions are often not documented or even attempted. This work discusses various methods for experimentally determining the momentum coefficient produced by fluidic oscillators. Complementary simulations of the actuator are performed using delayed detached eddy simulations to validate the methods and offer explanations for shortcomings in the experiments. Scaling methods are applied to the experimental study of separation control on the suction side of a type II Glauert airfoil, otherwise known as the NASA hump model. An array of fluidic oscillators is located at and used to control separation over a range of Reynolds numbers for various actuator sizes and spacings . Integrated surface pressure measurements are used to determine the suitability of various momentum coefficient definitions for scaling the flow control efficacy. It is found that the momentum coefficients obtained using direct measurements of actuator plenum or throat pressure govern scaling with respect to both Reynolds number and actuator size. This is independent of the sweeping frequency in the range surveyed.

Numerical Investigation of Plasma Actuator Effects On Flow Control Over a Three-Dimensional Airfoil with a Sinusoidal Leading Edge

Abstract: The impetus of the present bio-inspired work is to investigate the impact of simultaneously using wavy leading-edge (WLE) airfoils in combination with curved multi dielectric barrier discharge (DBD) plasma actuators as hybrid passive and active flow control mechanisms, respectively. A precise distinction of the produced frequency and noise signals, altogether with the acoustic effect of using WLE and DBD plasma actuators are herein analyzed with precision. Two specific DBD plasma actuators are designed to actuate at x/C= 3% and x/C= 30% on a NACA 634-021 airfoil with sinusoidal WLE that bears a wavelength of 25% and an amplitude of 5% of the mean chord length and straight-leading-edge (SLE). A large eddy simulation (LES) turbulence model was used. This includes the dynamic control of unsteady flow separation, the three-dimensional vortical structure and induced trains of vortices, the aerodynamic forces, the velocity variation, and also the spanwise flow. The momentum transfer between the main flow and boundary layer was improved by the DBDs induced vortices train and formed streamwise counter-rotating pair-of-vortices over the tubercle. Also, both the continuous wavelet transform (CWT) and fast Fourier transform (FFT) methods were used to investigate the induced plasma flow spectral content for the WLE and SLE geometries. We witnessed an optimized flow control, by using DBD plasma actuators with the WLE airfoil, that resulted in less massive flow separation, faster turbulent transition and a robust earlier flow reattachment. This modification was beneficial in increasing the efficiency and decreasing the noise for low Reynolds number operational conditions.

Experimental study on drag reduction of the turbulent boundary layer via porous media under nonzero pressure gradient

Abstract: The complex surface of an aircraft generates a nonzero pressure gradient flow. In this study, the boundary conditions of favorable and adverse pressure gradients are constructed in a small low-turbulence wind tunnel test section. Hot-wire anemometers and time-resolved image velocimetry are used to analyze the flow structure in a fully developed turbulent boundary layer with porous media. The effects of the porous surface on the statistical characteristics of the turbulent flow field and turbulent flow structure are analyzed and discussed. The results show that porous media reduce the velocity gradient in the linear layer, and the friction drag reduction effect is higher downstream of the porous wall. The drag reduction effect decreases along the flow direction. A wall with a 10 pores per inch produces a slightly better drag reduction effect than smooth wall. The maximum local drag reduction effect of a 10-pores-per-inch porous wall is 43.7% under a favorable pressure gradient and 42.3% under an adverse pressure gradient. The velocity streaks in the inner layer show that the porous wall widens the low-velocity streaks, making them more stable, while the high-speed streaks decrease in size under the pressure gradient. In the case of the adverse pressure gradient, the structure of the streaks becomes blurred, and their strength weakens. Under both favorable and adverse pressure gradients, the porous media lift up the coherent structures near the wall, thus weakening the large-scale coherent wall structures.

On the synchronisation of three-dimensional shock layer and laminar separation bubble instabilities in hypersonic flow over a double wedge

Abstract: Linear global instability of the three-dimensional (3-D), spanwise-homogeneous laminar separation bubble (LSB) induced by shock-wave/boundary-layer interaction (SBLI) in a Mach 7 flow of nitrogen over a $30^{\circ}-55^{\circ}$ double wedge is studied. At these conditions corresponding to a freestream unit Reynolds number, $Re_1=5.2\times 10^{4}$ m$^{-1}$, the flow exhibits rarefaction effects and comparable shock-thicknesses to the size of the boundary-layer at separation. This, in turn, requires the use of the high-fidelity Direct Simulation Monte Carlo (DSMC) method to accurately resolve unsteady flow features. We show for the first time that the LSB sustains self-excited, small-amplitude, 3-D perturbations that lead to spanwise-periodic flow structures not only in and downstream of the separated region, as seen in a multitude of experiments and numerical simulations, but also in the internal structure of the separation and detached shock layers. The spanwise-periodicity length and growth rate of the structures in the two zones are found to be identical. It is shown that the linear global instability leads to low-frequency unsteadiness of the triple point formed by the intersection of separation and detached shocks, corresponding to a Strouhal number of $St\sim0.02$. Linear superposition of the spanwise-homogeneous base flow and the leading 3-D flow eigenmode provides further evidence of the strong coupling between linear instability in the LSB and the shock layer.

Characteristics of forced flow past a square cylinder with steady suction at leading-edge corners

Abstract: We experimentally investigate the characteristics of a dynamic wake and of flow separation for a square cylinder with steady suction at its leading-edge corners. The wind tunnel experiments were conducted at a Reynolds number of 5946, and suction slots were manufactured symmetrically at the leading corners of the square cylinder. Steady suction was characterized with a suction momentum coefficient Cμ varying from 0.0227 to 0.3182. A time-resolved particle image velocimetry system was used to evaluate the control of leading-edge suction at different Cμ. Next, the measurements were analyzed by applying a proper orthogonal decomposition (POD) to study the control effectiveness. The POD results suggest that the first four modes of wake vortex shedding are transformed in controlled cases and that periodic Karman vortex shedding is suppressed. The results also show that, even with a very small momentum coefficient, the steady suction at the leading-edge corners stabilizes the cylinder wake. The wake region becomes longer and narrower in comparison with the baseline case. In addition, modifications of separation flow were visualized. At quite small Cμ, flow separation at the leading-edge corners is considerably suppressed. Upon increasing the suction momentum coefficient to 0.1364, flow separation at the leading edges is almost eliminated. Finally, we estimate the effect of drag reduction due to the leading-edge suction.

Study of the streamwise location of a micro vortex generator for a separation-control mechanism in supersonic flow

Abstract: A shock wave/boundary layer interaction is a common phenomenon in supersonic (hypersonic) flows, and it usually occurs in an airbreathing propulsion system. It induces a large separation bubble and a local peak heat flux, and means of controlling it have attracted increasing attention. In this paper, the three-dimensional Reynolds-averaged Navier-Stokes equations and the shear stress transfer k-ω model are employed to study the flow control mechanism of a micro vortex generator in a supersonic flow with a freestream at a Mach number of 2.9; the influence of the streamwise location is taken into consideration. At the same time, due to the size of the separation bubble induced by the shock wave/boundary layer interaction, the total pressure recovery coefficient and the wall heat flux density are used to evaluate the control performance. The results show that the size of the separation bubble is greatly reduced, the area of the separation bubble is reduced by 29.63%, and its volume is reduced by 63.27%. However, this entails a total pressure loss and a large peak heat flux, and this should be dealt with through multi-objective design optimization approaches.

Experimental study of laminar-to-turbulent transition in pipe flow

Abstract: This paper describes an experimental study of the unforced laminar-to-turbulent transition in pipe flow. Two pipes with different length-to-diameter ratios are investigated, and the transition phenomenon is studied using pressure measurements and visual observations. The entropy change and force balance are examined, and the peak powers are measured through fast Fourier transform analysis at various Reynolds numbers. Visual observations show that the flow structure changes at the Reynolds numbers corresponding to the peak powers. There is no clear dependency of the transition on the ratio of pipe length to diameter. The flow conditions are classified as laminar flow, transitions I, II, and III, and turbulent flow, separated by Reynolds numbers of approximately 1200, 2300, 7000, and 12 000, respectively. The transition at a Reynolds number of 1200 is caused by the force balance between the laminar and turbulent flows. The other transitions are related to the flow condition in the development region upstream of the pipe flow region. That is, the laminar-to-turbulent transition in the development region affects the transition condition in the downstream pipe flow. The laminar and turbulent development length ratios derived from the entropy changes are in reasonable agreement with the formulas for both laminar and turbulent flows. At large Reynolds numbers, the laminar flow condition will be established through the creation of a laminar-flow velocity profile at the entrance to the pipe.

Laminar Separation Bubble Noise on a Propeller Operating at Low Reynolds Numbers

Abstract: This paper explains the presence and relevance of noise caused by a laminar separation bubble (LSB) on a propeller operating at a low Reynolds number. Microphone measurements of a propeller with both clean and forced boundary-layer transition blades are carried out in an anechoic wind tunnel by varying the propeller advance ratio from 0 to 0.6, corresponding to a tip Reynolds number ranging from to . The flow behavior on the blade surface and around the propeller is investigated with oil-flow visualizations and particle image velocimetry. At and 0.6, vortex shedding from the LSB causes high-frequency noise that appears as a hump in the far-field noise spectra. Forcing the location of the boundary-layer transition suppresses the LSB and, consequently, the hump, reducing the noise emission of about 5 and 10 dB at and 0.6, respectively. The fact that the hump is caused by LSB vortex shedding noise is further assessed by using a semi-empirical noise model; it shows that the hump is constituted by tones of different amplitudes and frequencies, emitted at different spanwise sections along the blade.

High-Fidelity Simulation of Turbulent Flow Past Gaussian Bump

Abstract: A spanwise-periodic computation of a turbulent flow past a Gaussian bump is performed in the form of a hybrid direct numerical simulation and wall-resolved large-eddy simulation. A fourth-order spatially accurate flow solver is employed to perform the simulation, using 10.2 billion grid points for a Reynolds number of 170,000 based on the bump height. The key findings from the simulation are reported in the acceleration and deceleration flow regions associated with the bump shape. Significant anisotropy in the normal Reynolds stresses, along both the wall-normal and streamwise directions, is observed within the acceleration region. The ratio between the Reynolds shear stress and turbulent kinetic energy in that region also experiences significant deviations from the norms of a zero pressure gradient turbulent boundary layer. The chosen Reynolds number generates strong flow separation in the adverse pressure gradient region, which is in contrast with a previous simulation at half the Reynolds number that only indicated incipient separation. An internal layer generated in the acceleration region evolves into a free shear layer that develops in the deceleration region and separates. Proper modeling of this inner layer appears crucial to predict the flow separation. Surface curvature effects on the attached flow development are also discussed.

Control mechanism of the three-dimensional shock wave/boundary layer interaction with the steady and pulsed micro-jets in a supersonic crossflow

Abstract: The separation induced by shock wave/boundary layer interactions (SWBLI) is detrimental to the performance of the flow field, and thus, needs to be reduced by using passive or active approaches. In this study, the authors numerically evaluate flow control induced by steady and pulsed micro-jets to capture the mechanism of control of three-dimensional (3D) SWBLIs. The volume of the separation zone is accurately calculated to assess the control effect. The results predicted by the 3D Reynolds-averaged Navier–Stokes equations coupled with the two-equation κ- ω turbulence model of shear stress transport show that the proposed method of using steady or pulsed micro-jets can significantly reduce the volume of the separation zone induced by shock wave/boundary layer interactions. The best comprehensive effect of control over the flow field was obtained by using a high frequency angled jet—namely, case P5—as it reduced the volume of the separation zone by 19.43% with only a small loss in the total pressure. The upwash and downwash motions induced by the streamwise counter-rotating vortex pairs of the jet constituted a key factor influencing the control of the separation zone.

Heat transfer characteristics of plasma actuation in different boundary-layer flows

Abstract: The coupling characteristics of the aerodynamic and thermal effects of a surface dielectric barrier discharge plasma actuator and its transfer characteristics in different boundary-layer flows are studied experimentally. The actuator is attached to the surface of a flat-plate airfoil and driving by an alternative-current signal. Different boundary-layer flows are achieved in the wind tunnel by adjusting the airfoil's angle of attack with a Reynolds number of 2.02 × 105. The spatial temperature-rise distributions and velocity fields induced by plasma actuation in quiescent air show that the influence range of temperature is consistent with that of the induced velocity field. The aerodynamic and thermal effects induced by plasma actuation have strong coupling characteristics. The heat around the actuator is limited within the boundary-layer flows with a 15 m/s incoming flow. The temperature rise outside the boundary layer is close to zero. In the turbulent boundary-layer flow, the temperature is lower than that in the laminar boundary-layer flow as a whole. The maximum temperature-rise difference exceeds 10 °C. In the leading-edge separation-bubble flow, most heat generated by the plasma actuation is restricted inside the separation bubble. The results provide references for the mechanism detection of related plasma icing-control and flow-control research.

Supersonic compressor cascade flow control using plasma actuation at low Reynolds number

Abstract: To control the supersonic compressor cascade flow at low Reynolds numbers, this paper describes the use of nanosecond dielectric barrier discharge (NS-DBD) plasma actuation for flow control, and presents the results of large-eddy simulations conducted to investigate the corresponding flow control effects. NS-DBD plasma actuation on both the blade pressure surface and suction surface induces a distorted flow structure (DFS) within the blade passage. In the case of NS-DBD plasma actuation on the blade pressure surface, the influence of the DFS on the flow is suppressed by a shock wave. Even so, the DFS can still trigger the instability in the shear layer between the separated flow and the mainstream flow. Shock-wave-induced large-scale flow separation on the blade pressure surface is then suppressed, and the overall total pressure loss of the blade passage is reduced by 7.4%, despite the increased shock wave loss from the reduced flow blockage within the blade passage. In the case of NS-DBD plasma actuation on the blade suction surface, the DFS is less effective in suppressing the shock-wave-induced small-scale flow separation on the blade suction surface. However, the DFS on the blade suction surface enhances the shock wave oscillations within the blade passage, and this suppresses the flow separation on the blade pressure surface.

Swept shock wave/boundary layer interaction control based on surface arc plasma

Abstract: Swept shock wave/boundary layer interactions occur widely in the internal and external flows of supersonic and hypersonic aircraft. Based on the conventional S-A turbulence model, this study investigates surface arc plasma actuation for regulating swept shock wave/boundary layer interactions at Mach 2.95 to explore the ability and three-dimensional shock wave/boundary layer interactions control method of plasma actuation. First, the flow control effect is explored in terms of indirect control by applying actuation in the upstream boundary layer or in front of the separation line, and in terms of direct control by applying actuation in the separation region. These three methods all achieve clear control effects. Control results show that the first method is more effective in regulating the wall pressure and friction coefficient, and can improve the friction and heat transfer of the wall in a wide range of flow direction and cone direction. The second method is more effective in regulating separated shock waves. The third aspect is more effective in regulating reattachment region. The associated control mechanisms are then refined. The control effects of the first control method depend on the transmission of vortices, those of the second are based on the virtual surface generated by actuation, and those of the third rely on energy injection. Finally, the application scenarios of the different control methods are determined according to the flow control requirements of aircraft and the corresponding control mechanisms. This study provides a reference method for solving more complex three-dimensional shock boundary layer interaction problems.

Numerical Analysis of Energy Expenditure for Co-Flow Wall Jet Separation Control

Abstract: This paper numerically investigates the energy expenditure of the co-flow wall jet for separation control by analyzing the widely studied NASA hump with 2D unsteady Reynolds averaged Navier-Stokes equations. Co-flow wall jet is shown to be effective in both adverse and favorable pressure gradients, but is more efficient in adverse pressure gradients due to lower velocity, lower entropy increase, and more enhanced mixing. An energy-efficient way to devise a co-flow wall jet flow control is two-fold: 1) place the injection near the separation onset point at a slightly downstream location; 2) place the suction slot further downstream with sufficiently long distance in adverse pressure gradient region for a thorough mixing and energy transfer. The vanishing of the counter-clockwise wall jet vorticity appears to indicate a sufficient mixing distance. In that case, the injection plays the dominant role. The suction makes a small contribution with a weak coupling effect, but primarily serves as the flow source for the mass conservation of the zero-net-mass-flux flow control, which is essential to be energy efficient. The co-flow wall jet is also compared with the injection-only and suction-only flow controls, which are effective if the slots are placed at the desirable position slightly downstream of the separation onset point. But if they are not placed near the separation onset locations, the co-flow wall jet is much more efficient and effective than the injection-only or suction-only flow controls due to the coupling effect between the injection and suction.

Large Eddy Simulation and Combined control of Corner Separation in a Compressor Cascade

Abstract: Due to the demand for higher aerodynamic performance of compressors, thoroughly investigating the high-loss flow in the corner region and effectively controlling it is important. In this paper, a novel parameterization method based on the Extended Free Form Deformation (EFFD) technique and the constraints for EFFD's control points is proposed. Then, considering the features of typical control techniques and the degrees of freedom of both the blade and hub geometries, the combined control approach is implemented in corner region of a linear cascade. Furthermore, large eddy simulation is used to simulate the flow, verify the effects of the combined control approach, and explore the underlying physical mechanisms of corner separation. The numerical results show that the combined control can significantly decrease the mean total pressure loss. The loss reduction at the design point reaches 6.05%, while it decreases by almost 2.5% near the stall/blockage operating conditions. The combined control increases the radial pressure gradient at the rear of blade by depressing the hub and stretching the suction surface. Consequently, although the radial flow slightly increases the mixing loss in mainstream at large incidences, the accumulation of low energy flow in boundary layer and corresponding development of corner vortex is significantly restrained. Moreover, by redistributing the static pressure on hub, the combined control weakens the migration of crossing flow and obstructs the low velocity flow from the pressure side involving in the separation. Overall, the combined control contributes to reducing the corner separation and improving the aerodynamic performance.

Role of phase-difference between two adjacent rectangular synthetic jet actuators in active control of flow over a rounded ramp

Abstract: In the current study, the role of phase-difference between signals of two adjacent synthetic jet actuators (SJAs) in active control of flow over a rounded ramp geometry has been investigated. In order to accurately predict the separation and reattachment locations, wall-resolved large eddy simulation has been utilized to capture the locations of separation and reattachment. The two adjacent SJAs were placed upstream of the separation point. Six phase-differences between the two SJAs were considered, and two momentum coefficients were applied. First, the role of phase-difference in active flow control of a separation bubble behind a ramp-down region was investigated. Furthermore, the impact of an increased momentum ratio on the size and length of the separation zone was investigated to assess the effectiveness of phase-difference with respect to a higher velocity ratio. The effect of increased momentum ratio on the wall pressure fluctuations was also explored. As the second objective of this study, the flow and turbulent features were discussed to unveil the SJA actuation impact on the downstream flow. The time-averaged velocity and turbulent kinetic energy profiles and the turbulent production were examined and compared to the uncontrolled baseline case. It was found that a higher velocity ratio tremendously increased the turbulent energy before the separation point, while further downstream, the level of turbulent energy was uncoupled from the SJA momentum coefficient. Our study showed that by increasing the momentum ratio, the role of phase-difference in reducing the separation thickness lessened. Nevertheless, applying either a positive or a negative phase-difference of pi/2 still postponed the separation point.

Large-Eddy Simulations of Idealized Shock/Boundary-Layer Interactions with Crossflow

Abstract: An idealized shock/boundary-layer interaction problem that is two dimensional in the mean but with a three-component mean velocity field is studied using large-eddy simulations. The problem isolates some aspects of three-dimensionality while avoiding others and can thus offer insights into the differences between two- and three-dimensional problems. The addition of a crossflow increases the size of the separation bubble quite substantially when normalized by the boundary-layer thickness or the momentum thickness but less substantially when normalized by the displacement thickness. All cases studied are found to have a very thin precursor separation bubble before the point of true separation that extends for at least one boundary-layer thickness but remains fully within the viscous sublayer. Simulations at different Reynolds numbers show that the flow reattaches after the precursor bubble at sufficiently high Reynolds number.

Machine learning building-block-flow wall model for large-eddy simulation

Abstract: Abstract A wall model for large-eddy simulation (LES) is proposed by devising the flow as a combination of building blocks. The core assumption of the model is that a finite set of simple canonical flows contains the essential physics to predict the wall shear stress in more complex scenarios. The model is constructed to predict zero/favourable/adverse mean pressure gradient wall turbulence, separation, statistically unsteady turbulence with mean flow three-dimensionality, and laminar flow. The approach is implemented using two types of artificial neural networks: a classifier, which identifies the contribution of each building block in the flow, and a predictor, which estimates the wall shear stress via a combination of the building-block flows. The training data are obtained directly from wall-modelled LES (WMLES) optimised to reproduce the correct mean quantities. This approach guarantees the consistency of the training data with the numerical discretisation and the gridding strategy of the flow solver. The output of the model is accompanied by a confidence score in the prediction that aids the detection of regions where the model underperforms. The model is validated in canonical flows (e.g. laminar/turbulent boundary layers, turbulent channels, turbulent Poiseuille–Couette flow, turbulent pipe) and two realistic aircraft configurations: the NASA Common Research Model High-lift and NASA Juncture Flow experiment. It is shown that the building-block-flow wall model outperforms (or matches) the predictions by an equilibrium wall model. It is also concluded that further improvements in WMLES should incorporate advances in subgrid-scale modelling to minimise error propagation to the wall model.