Shock Wave-turbulent Boundary Layer Interaction Research Articles

Variation of vortical structures across shock-wave/turbulent boundary-layer interaction region in a compression ramp flow

This paper describes direct numerical simulations of a shock-wave/turbulent boundary-layer interaction (STBLI) process in a compression-ramp flow with a ramp angle of 24° and a free-stream Mach number of Ma∞=2.9. Spectral analysis, two-point cross correlation, convection velocity statistics, and individual vortex identification are used to elucidate the streamwise variation of multiscale turbulent structures in the STBLI process. Typical Lagrangian coherent structures in the turbulent boundary layer before the STBLI region are characterized as hairpin-like vortical structures, with heads that rise together with the separated mean flow in the STBLI region. In the downstream region, the reattached turbulent boundary layer has a two-layer structure. The outer layer is characterized as an intensification of large-scale velocity structures, which is attributed to the shock-wave-induced compression effect on vortical structures. A viscous-dominated layer develops independently in the vicinity of the wall, leading to a gradual restoration of the wall-shear effect that accumulates the inner-layer dynamics of small-to-moderate-scale turbulent motions.

A deep learning super-resolution model for turbulent image upscaling and its application to shock wave–boundary layer interaction

Upscaling flow features from coarse-grained data is paramount for extensively utilizing computational physics methods across complex flow, acoustics, and aeroelastic environments where direct numerical simulations are computationally expensive. This study presents a deep learning flow image model for upscaling turbulent flow images from coarse-grained simulation data of supersonic shock wave–turbulent boundary layer interaction. It is shown for the first time that super-resolution can be achieved using only the coarsest-grained data as long as the deep learning training is performed using hundreds of fine-grained data. The unsteady pressure data are used in training due to their importance in aeroelasticity and acoustic fatigue occurring on aerospace structures. The effect on the number of images and their resolution features used in training, validation, and prediction is investigated regarding the model accuracy obtained. It is shown that the deep learning super-resolution model provides accurate spectra results, thus confirming the approach's effectiveness.

Shock-wave/turbulent boundary-layer interaction with a flexible panel

The dynamic coupling between a Mach 2.0 shock-wave/turbulent boundary-layer interaction (STBLI) and a flexible panel is investigated. Wall-resolved large-eddy simulations are performed for a baseline interaction over a flat-rigid wall, a coupled interaction with a flexible panel, and a third interaction over a rigid surface that is shaped according to the mean panel deflection of the coupled case. Results show that the flexible panel exhibits self-sustained oscillatory behavior over a broad frequency range, confirming the strong and complex fluid–structure interaction (FSI). The first three bending modes of the panel oscillation are found to contribute most to the unsteady panel response, at frequencies in close agreement with natural frequencies of the mean deformed panel rather than those for the unloaded flat panel. This highlights the importance of the mean panel deformation and the corresponding stiffening in the FSI dynamics. The time-averaged flow shows an enlarged reverse-flow region in the presence of mean surface deformations. The separation-shock unsteadiness is enhanced due to the panel motion, leading to higher wall-pressure fluctuations in the coupled interaction. Spectral analysis of the separation-shock location and bubble-volume signals shows that the STBLI flow strongly couples with the first bending mode of the panel oscillation. This is further confirmed by dynamic mode decomposition of the flow and displacement data, which reveals variations in the reverse-flow region that follow the panel bending motion and appear to drive the separation-shock unsteadiness. Low-frequency modes that are not associated with the fluid–structure coupling, in turn, are qualitatively similar to those obtained for the rigid-wall interactions, indicating that the characteristic low-frequency unsteadiness of STBLI coexists with the dynamics emerging from the fluid–structure coupling. Based on the present results, unsteady FSIs involving STBLIs and flexible panels are likely to accentuate rather than mitigate the undesirable features of STBLIs.

TURBULENCE MODELING OF SHOCK BOUNDARY LAYER INTERACTION IN HYPERSONIC FLOW

Computational fluid dynamics (CFD) simulations of shockwave turbulent boundary layer interactions using different turbulence modeling including Reynolds-averaged Navier-Stokes (RANS) with different closures (Menter's <i>k</i>-ω-SST, and Spalart-Allmaras) have been investigated. The objective of the study is to assess the capability of current CFD codes, Ansys Fluent and STARCCM, to model hypersonic flow over a large hollow cylinder flare for Mach 6 with Re<sub>∞</sub> = 5.33 × 10<sup>7</sup> The results of heat transfer and pressure data over the surface are presented for two-dimensional, axisymmetric, and three-dimensional RANS models using experimental data of LENS II high Reynolds number shock/Ludweig tunnel at the CUBRC center. Effects of properties of real gas, perfect gas, and different types of mesh have been considered for the assessment.

Coexistence of different mechanisms underlying the dynamics of supersonic turbulent flow over a compression ramp

Supersonic turbulent flow over a compression ramp is studied using wall-resolved large eddy simulation with a freestream Mach number of 2.95 and a Reynolds number [based on δ0: the thickness of incoming turbulent boundary layer (TBL)] of 63 560. The unsteady dynamics of the present shock wave/turbulent boundary layer interaction (STBLI) flow are investigated by using dynamic mode decomposition techniques, linear and nonlinear disambiguation optimization, local stability analysis (LSA), and global stability analysis (GSA). By analyzing the dynamic system for the STBLI flow, three dynamically important modes with characteristic spanwise wavelengths of 2δ0, 3δ0, and 6δ0 are captured. The 2δ0 mode approximates the spanwise scale of the Görtler-like vortices and Görtler mode of LSA, suggesting the presence of Görtler instability, which is believed to be related to the unsteady motion of streaks downstream of reattachment in the flow. The features of the 3δ0 mode are also observed in large-scale motions of the incoming TBL, implying the existence of a convective mechanism that is excited and maintained by such motions. Additionally, the GSA results show the most unstable mode features a spanwise wavelength of around 6δ0, indicating the existence of global instability that is believed to be related to the oscillating motion of separation shock. The coexistence of these three mechanisms is confirmed. Discussions on the above findings provide an interpretation for low-frequency unsteadiness that the unsteadiness of surface streaks results from the combined effects of the Görtler instability near flow reattachment and the convection of large-scale motions in the incoming boundary layer, while the low-frequency shock motion may be related to a global mode driven by upstream disturbances.

Moving wall effect on normal shock wave–turbulent boundary layer interaction on an airfoil

Purpose This paper aims to describe a proposal for an innovative method of normal shock wave–turbulent boundary layer interaction (SBLI) and shock-induced separation control. Design/methodology/approach The concept is based on the introduction of a tangentially moving wall upstream of the shock wave and in the interaction region. The SBLI control mechanism may be implemented as a closed belt floating on an air cushion, sliding over two cylinders and forming the outer skin of the suction side of the airfoil. The presented exploratory numerical study is conducted with SPARC solver (steady 2D RANS). The effect of the moving wall is presented for the NACA 0012 airfoil operating in transonic conditions. Findings To assess the accuracy of obtained solutions, validation of the computational model is demonstrated against the experimental data of Harris, Ladson & Hill and Mineck & Hartwich (NASA Langley). The comparison is conducted not only for the reference (impermeable) but also for the perforated (permeable) surface NACA 0012 airfoils. Subsequent numerical analysis of SBLI control by moving wall confirms that for the selected velocity ratios, the method is able to improve the shock-upstream boundary layer and counteract flow separation, significantly increasing the airfoil aerodynamic performance. Originality/value The moving wall concept as a means of normal shock wave–turbulent boundary layer interaction and shock-induced separation control has been investigated in detail for the first time. The study quantified the necessary operational requirements of such a system and practicable aerodynamic efficiency gains and simultaneously revealed the considerable potential of this promising idea, stimulating a new direction for future investigations regarding SBLI control.

Simulations of Compression Ramp Shock Wave/Turbulent Boundary Layer Interaction Controlled via Steady Jets at High Reynolds Number

Shock wave/turbulent boundary layer interaction (SBLI) is one of the most common physical phenomena in transonic wing and supersonic aircraft. In this study, the compression ramp SBLI (CR-SBLI) was simulated at a 24° corner at Mach 2.84 using the open-source OpenFOAM improved delayed detached eddy simulation (IDDES) turbulence model and the “Rescaling and Recycling” method at high Reynolds number 1.57×106. The results of the control effect of the jet vortex generator on CR-SBLI showed that the jet array can effectively reduce the length of the separation zone. The simulation results of different jet parameters are obtained. With the increasing jet angle, the reduction in the length of the separation zone first increased and then decreased. In this work, when the jet angle was 60°, the location of the separation point was x/δ=−1.48, which was smaller than other jet angles. The different distances of the jet array also had a great influence. When the distance between the jet and the corner djet=70 mm, the location of the separation point x/δ=−1.48 was smaller than that when djet=65/60 mm. A closer distance between the jet hole and the corner caused the vortex structures to squeeze each other, preventing the formation of a complete vortex structure. On the other hand, when the jet was farther away, the vortex structures could separate effectively before reaching the shock wave, resulting in a better inhibition of SBLI. The simulation primarily focused on exploring the effects of the jet angle and distance, and we obtained the jet parameters that provided the best control effect, effectively reducing the length of the CR-SBLI separation zone.

A high-order fluid–structure interaction framework with application to shock-wave/turbulent boundary-layer interaction over an elastic panel

Within this work, a loosely-coupled high-order fluid–structure interaction (FSI) framework is developed in order to investigate the influence of an elastic panel response on shock-wave/turbulent boundary-layer interaction (SWTBLI). Since high-order methods are expected to determine the future of high-fidelity numerical simulations, they are employed in the construction of both fluid and structure solvers. Specifically, a split-form arbitrary Lagrangian-Eulerian discontinuous Galerkin spectral element method is employed in the fluid solver and a Legendre spectral finite element method in the structure solver. Shock capturing by an improved adaptive filter method, which confines the filtering effect to the vicinity of shocks, is found to be well-behaved in accuracy, efficiency and flexibility.After being validated by two benchmark FSI problems, the developed FSI framework is applied to simulate SWTBLI over an elastic panel. A comparison with a previous simulation of SWTBLI over a rigid panel reveals that: (1) A larger amplitude of the pressure variation, observed on the elastic panel surface, implies a larger threat to the structural integrity; (2) The shock-induced separation flow over the elastic panel changes both in size and shape, leading to a different skin-friction coefficient distribution; (3) A new low-frequency flow unsteadiness of the same magnitude as the elastic panel vibration is detected, which may affect the flow dynamics inside the turbulent boundary layer.

Microramp wake impinging on canonical shock/boundary-layer interaction

We analyze the influence of microramp vortex generators (mVGs) on a canonical oblique shock wave/turbulent boundary-layer interaction (SBLI) in terms of mean flow field and unsteady dynamics. The flow configuration of our wall-resolved large-eddy simulations (LES) reproduces the experiment of Bo et al. [“Experimental investigation of the micro-ramp based shock wave and turbulent boundary-layer interaction control,” Phys. Fluids 24, 055110 (2012)]: a rake of microramps is inserted upstream of the SBLI, protruding by 0.476δ in a turbulent boundary layer (TBL) at free-stream Mach number M = 2.7 and corresponding to a Reynolds number based on the displacement thickness of Reθ=3600. The long integration time of 1672 Lsep/U∞ allows an accurate characterization of the low-frequency dynamics of the SBLI under the influence of the microramps. With respect to the reference SBLI without control devices, the mean flow field shows a new spatial organization of the recirculation bubble due to the mVGs' wake. The alternating high and low-speed zones in the near-wall region of the incoming TBL, induced by the counter-rotating streamwise vortices generated by the mVGs, trigger spanwise corrugations of the separation and reattachment lines and locally alter the reverse flow region. Tornado-like vortices are found in the vicinity of these zones, yielding a new fluid collection mechanism of the reverse flow region. These vortices redirect the fluid coming from regions outside of the wake in the incoming TBL to three key spanwise exit locations located in between the mVGs and at their centerline. Interestingly, power spectral densities of wall-pressure probes show a damping of the low-frequency dynamics of the reflected shock foot for spanwise stations aligned with the mVGs' wake, whereas this activity appears to be reinforced in the planes located in between the mVGs. However, we found no evidence of unsteady forcing linked to the high-frequency shedding of the coherent structures developing in the wake of the microramps. Dynamic mode decomposition highlights a significant change in the low-frequency dynamics, mostly affecting the mass budget of the recirculation bubble. The breathing of the recirculation zone that occurs at StL=0.1 for the SBLI without control devices (with StL=fLsep/U∞) appears to shift toward a lower frequency of StL=0.05. Remembering that the reflected shock foot motion is related to frequencies in the range StL=[0.03−0.05], the SBLI with upstream mVGs seems to highlight a synchronization of this motion with the breathing of the separation bubble.

Interaction of a moving shock wave with a turbulent boundary layer

In the present study, the influence of a uniformly moving impinging shock on the resulting shock wave–turbulent boundary layer interaction is numerically investigated. The relative Mach number of the shock front travelling above a flat-plate model varied between 0 and 2.3, while the quasi-steady inflow conditions remained constant with a Mach number of 3. To quantitatively evaluate the effect of shock travelling speed, a well-known scaling method for interaction length in quasi-steady flows was applied as a reference after significant improvements in modelling the effects of Reynolds number and wall temperature using new and existing data. Moreover, previously obtained experimental results for a limited range of travelling speeds were employed to validate the obtained numerical results. Three ranges of shock travelling speeds with distinctly different properties were extracted and quantitatively described using a developed correlation-based approach built on the extended quasi-stationary scaling law. In the first range, the scaled interaction length reaches its maximum for the given interaction strength and can be directly described by the scaling law obtained for quasi-stationary interactions. In the second travelling-speed range, the dependence of the interaction length on the interaction strength is explicitly influenced by the shock movement. With increasing shock travelling speed, the scaled interaction length here decreases significantly faster than in the quasi-stationary reference case. The end of this speed range is reached when the absolute shock front speed has caught up with the maximum speed of sound in the interaction zone, and thus the interaction length has fallen to zero. This travelling-speed limit signifies the transition to the third range, where upstream influence is no longer possible.

Separation length scaling for dual-incident shock wave–turbulent boundary layer interactions with different shock wave distances

In this study, the length scaling for the boundary layer separation induced by two incident shock waves is experimentally and analytically investigated. The experiments are performed in a Mach 2.73 flow. A double-wedge shock generator with two deflection angles ( $\alpha _1$ and $\alpha _2$ ) is employed to generate two incident shock waves. Two deflection angle combinations with an identical total deflection angle are adopted: ( $\alpha _1 = 7^\circ$ , $\alpha _2 = 5^\circ$ ) and ( $\alpha _1 = 5^\circ$ , $\alpha _2 = 7^\circ$ ). For each deflection angle combination, the flow features of the dual-incident shock wave–turbulent boundary layer interactions (dual-ISWTBLIs) under five shock wave distance conditions are examined via schlieren photography, wall-pressure measurements and surface oil-flow visualisation. The experimental results show that the separation point moves downstream with increasing shock wave distance ( $d$ ). For the dual-ISWTBLIs exhibiting a coupling separation state, the upstream interaction length ( $L_{int}$ ) of the separation region approximately linearly decreases with increasing $d$ , and the decrease rate of $L_{int}$ with $d$ increases with the second deflection angle under the condition of an identical total deflection angle. Based on control volume analysis of mass and momentum conservations, the relation between $L_{int}$ and $d$ is analytically determined to be approximately linear for the dual-ISWTBLIs with a coupling separation region, and the slope of the linear relation obtained analytically agrees well with that obtained experimentally. Furthermore, a prediction method for $L_{int}$ of the dual-ISWTBLIs with a coupling separation region is proposed, and the relative error of the predicted $L_{int}$ in comparison with the experimental result is $\sim$ 10 %.

Turbulence Modelling for SWTBLI with Expansion Wave Interference Inside Scramjet Inlets

An accurate prediction of the flowfield inside the scramjet inlet/isolator is crucial for a stable and reliable aerodynamic design. However, the complex phenomena such as shock wave-expansion wave interactions and shock wave-turbulent boundary layer interactions (SWTBLI) inside the isolator pose great difficulties to the computational modelling community. In the current work, a numerical investigation is carried out for a practical mixed compression scramjet inlet/isolator using the extensively validated SST k − ω turbulence model, and the numerical results are compared against the experimental data. Although the simulations qualitatively predict the overall shock structures, major discrepancies are observed in the predictions of separation region (location, shape, and size) and subsequent positions of the separation and reflected shocks: similar discrepancies are observed in the literature with various models. Analysis reveals that although the turbulence model is capable of predicting SWTBLI, this discrepancy is primarily because of the improper estimation of turbulence levels in the separation region due to upstream expansion wave interference. The predictions are significantly improved by recalibrating a model constant, called structure parameter a 1 , when its value was decreased from the standard value of 0.31 to 0.28. The reduction in a 1 is in contrast to observations in the literature where the structure parameter was suggested to be increased beyond the default value for separated high-speed flows. This behaviour is due to the expansion wave interference whose effects, opposite to that of shock, need to be incorporated into the model for accurate predictions of scramjet flows.

Generalized Scaling Analysis of the Separation Zone Induced by Shock Wave–Turbulent Boundary Layer Interactions

Generalized Scaling Analysis of the Separation Zone Induced by Shock Wave–Turbulent Boundary Layer Interactions

Hypersonic Shock Wave/Turbulent Boundary Layer Interaction over a Compression Ramp

A parametric study of ramp-induced planar shock-wave/turbulent-boundary-layer interactions (SBLIs) is carried out at hypersonic conditions (Mach number 6.0) by means of numerical simulation of the Reynolds-averaged Navier–Stokes (RANS) equations, with the eventual goal of establishing wall temperature and Reynolds number effects. Comparison with available experimental data shows that RANS is capable of predicting the main features of hypersonic oblique SBLI, namely, typical size and distribution of the wall-surface pressure, and heat transfer. A large number of flow cases, at low () and high Reynolds number (), were computed to examine the scaling of the heat transfer over a wide range of wall temperatures. As expected, the interaction zone of hypersonic ramp-induced SBLI is reduced as the wall is cooled. A simple power law for heat transfer originally introduced by Back and Cuffel (AIAA Journal, Vol. 8, No. 10, 1970, pp. 1871–1873) is here considered to account for hypersonic ramp-induced SBLI, which is found to successfully collapse the data to the distributions obtained for supersonic, cold/hot interactions.

Direct numerical simulation of shock wave/turbulent boundary layer interaction in a swept compression ramp at Mach 6

Swept compression ramps widely exist in supersonic/hypersonic vehicles and have become a typical standard model for studying three-dimensional (3D) shock wave/turbulent boundary layer interactions (STBLIs). In this paper, we conduct a direct numerical simulation of swept compression ramp STBLI with a 34° compression angle and a 45° sweep angle at Mach 6 using a heterogeneous parallel finite difference solver. Benefitting from the powerful computing performance of the graphics processing unit, the computational grid number exceeds 5 × 106 with the spatiotemporal evolution data of hypersonic 3D STBLI obtained. The results show that the flow of the hypersonic swept compression ramp follows the quasi-conical symmetry. A supersonic crossflow with helical motion appears in the interaction region, and its velocity increases along the spanwise direction. Fluids from the high-energy-density region pass through the bow shock at the head of the main shock and crash into the wall downstream of the reattachment, resulting in the peaks in skin friction and heat flux. The peak friction and heating increase along the spanwise direction because of the spanwise variation in the shock wave inclination. In the interaction region, the unsteadiness is dominated by the mid-frequency motion, whereas the low-frequency large-scale motion is nearly absent. Two reasons for the lack of low-frequency unsteadiness are given: (1) The separation shock is significantly weaker than the reattachment shock and main shock; and (2) because of the supersonic crossflow, the perturbations propagating at the sound speed are not self-sustaining but flow along the r-direction and toward the spanwise boundary.

Dynamics of Three-Dimensional Shock-Wave/Boundary-Layer Interactions

Advances in measuring and understanding separated, nominally two-dimensional (2D) shock-wave/turbulent-boundary-layer interactions (STBLI) have triggered recent campaigns focused on three-dimensional (3D) STBLI, which display far greater configuration diversity. Nonetheless, unifying properties emerge for semi-infinite interactions, taking the form of conical asymptotic behavior where shock-generator specifics become insignificant. The contrast between 2D and 3D separation is substantial; the skewed vortical structure of 3D STBLI reflects the essentially 2D influence of the boundary layer on the 3D character of the swept shock. As with 2D STBLI, conical interactions engender prominent spectral content below that of the turbulent boundary layer. However, the uniform separation length scale, which is crucial to normalizing the lowest-frequency dynamics in 2D STBLI, is absent. Comparatively, the spectra of 3D STBLI are more representative of the mid-frequency, convective, shear-layer dynamics in 2D, while phenomena associated with 2D separation-shock breathing are muted. Asymptotic behavior breaks down in many regions important to 3D-STBLI dynamics, occurring in a configuration-dependent manner. Aspects of inceptive regions near shock generators and symmetry planes are reviewed. Focused efforts toward 3D modal and nonmodalanalyses, moving-shock/boundary-layer interactions, fluid/structure interactions, and flow control are suggested as directions for future work.

Investigation on the adaptive control of shock wave/turbulent boundary layer interaction based on the secondary circulation jets

The shock wave/turbulent boundary layer interaction (SWBLI) exists widely in the internal and external supersonic flow field. The interaction of shock waves with turbulent boundary layers will induce serious separation. As a result, the flow field structure changes greatly. This leads to an increase in the flow field instability, total pressure loss, local peak heat flux, and other adverse effects. Current research shows that the secondary circulation jet control is effective in the flow field as a passive control method. In this paper, a new secondary circulation jet configuration for variable Mach number flow is designed and optimized. The flow fields of this configuration with the inlet Mach numbers being 2.5, 3, and 3.5 are studied, and an adaptive control method is proposed. For the numerical simulation of the flow field, the three-dimensional implicit Reynolds Averaged Navier-Stokes (RANS) equations coupled with the two-equation shear stress transport (SST) k-ω turbulence model are chosen. The obtained results show that when the inlet Mach number is in the range of 2.5–3.5, the secondary circulation jet configuration and the adaptive control method have positive effects on reducing the volume of the separation zone and the total pressure loss. Meanwhile, the adaptive control method can also be realized by passive control.

Effects of Wall Temperature on Hypersonic Impinging Shock-Wave/Turbulent-Boundary-Layer Interactions

We carry out a parametric study of hypersonic impinging shock-wave/turbulent-boundary-layer interactions (SBLIs) at hypersonic conditions (Mach number 6.0) by means of numerical simulation of the Reynolds-averaged Navier–Stokes (RANS) equations, with the eventual goal of establishing wall temperature and Reynolds number effects. Comparison with available direct numerical simulation and experimental data shows that RANS is capable of predicting the main features of SBLI, namely, typical size and distribution of the wall properties. A large number of flow cases were computed to examine the scaling of the global flow parameters over a wide range of wall temperatures and Reynolds numbers. As expected, the interaction zone is reduced as the wall is cooled, and as the Reynolds number is increased. A modified form of the scaling originally introduced by Souverein et al. [Journal of Fluid Mechanics, Vol. 714, 2013, pp. 505–535] is here considered to account for nonadiabatic wall state, which is found to successfully collapse the data to the distributions obtained for adiabatic flow, with some remaining deviations associated with low-Reynolds-number effects.

Momentum balance based model for predicting the scale of separation bubbles induced by incident shock wave/turbulent boundary layer interactions

The incident shock wave/turbulent boundary layer interactions (SWTBLIs) over a wide range of flow conditions are predicted by the Reynolds-averaged Navier–Stokes (RANS) numerical method to generate detailed two-dimensional steady flow field data. After examining the momentum balance terms over the control volume involving the separation bubble, it is concluded that the values of the pressure-force and the momentum-rate terms are significantly higher than the total stress-force term. Ignoring the effect of those small terms on the control surface, a model for the prediction of SWTBLI separation bubble scale is proposed based on the momentum balance over the two-dimensional control volume. For model prediction, essential correlations for key characteristic physical quantities are given. The predicted normal and streamwise scales of the SWTBLI separation bubble are in good agreement with the experimental results in the literatures.

Fast PSP measurement of three-dimensional low-frequency unsteadiness in sidewall-confined shock wave/turbulent boundary layer interaction

The presence of sidewalls exerts three-dimensional (3D) effects on shock wave/turbulent boundary layer interaction (SBLI), which results in experimental challenges due to the highly unsteady flow with complex 3D patterns. The low-frequency large-scale flow patterns of a 24° sidewall-confined compression ramp interaction were investigated using fast pressure-sensitive paint. The experiment was conducted in a Mach 2.5 wind tunnel, and the unit Reynolds number was Re = 1.12 × 107/m. The sampling rate of the fast pressure-sensitive paint was 4 kHz, and the spatial resolution was 0.175 mm/pixel. In-situ calibration via several pressure transducers was used to determine the time-resolved global pressure distributions. Correlation analysis and proper orthogonal decomposition analysis were used to extract the large-scale unsteady flow patterns. The time-averaged results provide a global view of the typical flow structure, which consists of primary interaction zone and corner interaction zones. The time-resolved results show the asymmetry of the instantaneous pressure distribution induced by the sidewalls, and spanwise differences of the pressure fluctuation amplitudes in the interaction zones are observed. In addition to the common streamwise breathing mode, an interesting spanwise antisymmetric mode is revealed that provides clear evidence of the strong 3D effects in sidewall-confined SBLI.