Reynolds Stress Components Research Articles

Entropy and Turbulence Structure.

Some new perspectives are offered on the spectral and spatial structure of turbulent flows, in the context of conservation principles and entropy. In recent works, we have shown that the turbulence energy spectra are derivable from the maximum entropy principle, with good agreement with experimental data across the entire wavenumber range. Dissipation can also be attributed to the Reynolds number effect in wall-bounded turbulent flows. Within the global energy and dissipation constraints, the gradients (d/dy+ or d2/dy+2) of the Reynolds stress components neatly fold onto respective curves, so that function prescriptions (dissipation structure functions) can serve as a template to expand to other Reynolds numbers. The Reynolds stresses are fairly well prescribed by the current scaling and dynamical formalism so that the origins of the turbulence structure can be understood and quantified from the entropy perspective.

Anisotropy of turbulent flow behind an asymmetric airfoil

Feature of turbulent flow anisotropy behavior behind an asymmetric NACA 64-618 airfoil investigated in this paper. Experimental studies were performed using a hot-wire anemometery with X-probe at the chord-based Reynolds number 1.7 times 10^5. The average ensemble velocity and Reynolds stress components are used to determine the wake topology and anisotropy of turbulence. The obtained data allowed to identify the outside wake region, which is characterized by low instability and a high degree of anisotropy of the turbulent flow. This tendency is observed at different angles incident. Further, to gain better insight into the physics of this phenomenon the structure of turbulence have been evaluated. Integral turbulence length and time scales were estimated by the area of the autocorrelation function of velocity fluctuations. Then, using the second-order structural function, we obtained the dissipation characteristics of the flow. In addition, the features of the energy spectrum in the region with high and low degrees of turbulence anisotropy were analyzed.

Application of Advanced RANS Turbulence Models for the Prediction of Turbomachinery Flows

AbstractThe current trend in turbomachinery toward broader operating characteristics requires that operating points in the off-design region can be captured accordingly from the simulation models. Complex processes like separation and vortex formation/dissipation occur under these conditions. Linear two equation models are often not able to represent these effects correctly since their derivation is based on oversimplifications, such as the Boussinesq hypothesis, which makes it impossible to capture anisotropic turbulence. Advanced RANS models are usually not considered in the design process of turbomachines because (1) they are usually more delicate with regards to stability and convergence behavior and (2) require additional computational effort. To make the usage of advanced RANS models more applicable for complex turbomachinery simulations, a selected group of models were implemented into a robust framework of a pressure-based fully coupled solver. To further enhance stability, coupling terms between the turbulent transport equations were derived for several models. Anisotropic turbulence is introduced by computing an algebraic expression or by solving the transport equations for the Reynolds stress components. The evaluation of the models is performed on the RWTH Aachen “Radiver” centrifugal compressor case with vaned diffuser. For design conditions and operation points near the stability limit, all investigated turbulence models predict the compressor characteristic. Operation points in the choking region, on the other hand, are only predicted well by anisotropic models. The good results and improved convergence behavior of the advanced RANS models clearly indicates their applicability in the design process of turbomachines.

Asymmetrical Order in Wall-Bounded Turbulent Flows

Scaling of turbulent wall-bounded flows is revealed in the gradient structures, for each of the Reynolds stress components. Within the “dissipation” structure, an asymmetrical order exists, which we can deploy to unify the scaling and transport dynamics within and across these flows. There are subtle differences in the outer boundary conditions between channel and flat-plate boundary-layer flows, which modify the turbulence structure far from the wall. The self-similarity exhibited in the gradient space and corresponding transport dynamics establish capabilities and encompassing knowledge of wall-bounded turbulent flows.

Shock wave and turbulent boundary layer interaction in a double compression ramp

Direct numerical simulations of shock wave and supersonic turbulent boundary layer interaction in a double compression ramp with fixed ramp angles of 12o and 24o at Mach 2.9 are conducted. The characteristics of the shock interactions are investigated for four different length between the two ramp kinks, corresponding to Lc = 0.9δref, 1.8δref, 2.7δref, and 3.6δref (δref being the upstream turbulent boundary layer thickness). The influence of increasing Lc on flow structures, unsteadiness, Reynolds stress, turbulence kinetic energy, and Reynolds stress anisotropy tensor is assessed. The size of the separation region is significantly decreased and reattached flow appears between the two ramp kinks. Streamwise vorticity contours and streamline curvature show the decreased spanwise width and increased spanwise coherency of Görtler-like vortices. Analysis of fluctuating wall pressure indicates that the low-frequency unsteadiness is strongly suppressed in the interaction region. Profiles of Reynolds stress components and turbulence kinetic energy exhibit different turbulence evolution across the interaction, leading to substantial differences observed in the anisotropy invariant map. It is found that the near wall region is characterized by decreased anisotropy, becoming closer to the axisymmetric compression state, while a significant increase of turbulence is identified in the outer region, following the axisymmetric expansion limit. Moreover, downstream of the interaction, turbulence in the near-wall region experiences a faster recovery and the influence of Lc is found to be marginal. The main effect of Lc is observed in the outer region, an increase of Lc resulting in a monotonic decay of turbulence intensities and an inward movement of turbulent structures.

Three-component flow velocity measurements with stereoscopic picosecond laser electronic excitation tagging.

Nonintrusive three-component (3C) velocity measurements of free jet flows were conducted by stereoscopic picosecond laser electronic excitation tagging (S-PLEET) at 100 kHz. The fundamental frequency of the burst-mode laser at 1064 nm was focused to generate the PLEET signal in a free jet flow. A stereoscopic imaging system was used to capture the PLEET signals. The 3C centroids of the PLEET signal were determined by utilizing simultaneous images from two cameras placed at an angle. The temporal evolutions of the centroids were obtained and used to determine the instantaneous, time-resolved 3C velocities of the flows. The free jets with various inlet pressures of 10-40 bars exhausting into atmospheric pressure air (i.e., underexpanded free jet with large pressure ratios; Reynolds numbers from the jet ranged from 39,000 to 145,000) were measured by S-PLEET. Key 3C turbulent properties of the free jets, including instantaneous and mean velocities, were obtained with an instantaneous measurement uncertainty of about ${\rm{\pm 10}}\;{\rm{m/s}}$, which is about 2% of the highest velocities measured. Computation of higher-order statistics including covariances related to turbulent kinetic energy and the Reynolds stress component was demonstrated. The 3C nonintrusive and unseeded velocimetry technique could provide a new tool for flow property measurements in ground test facilities; the measured high-frequency turbulence properties of free jet flows could be useful for turbulence modeling and validations.

Effects of Axial Casing Grooves on the Structure of Turbulence in the Tip Region of an Axial Turbomachine Rotor

Abstract Challenges in turbulence modeling in the tip region of turbomachines include anisotropy, inhomogeneity, and non-equilibrium conditions, resulting in poor correlations between Reynolds stresses and the corresponding mean strain-rate components. The geometric complexity introduced by casing grooves exacerbates this problem. Taking advantage of a large database collected in the refractive index-matched liquid facility at Johns Hopkins University (JHU), this paper examines the effect of axial casing grooves on the distributions of turbulent kinetic energy (TKE), Reynolds stresses, anisotropy tensor, and TKE production rate in the tip region of an axial turbomachine. The comparisons are performed at flowrates corresponding to prestall and best efficiency points of the untreated machine. Common features include high TKE near the tip leakage vortex center and in the shear layer connecting it to the blade suction side tip corner. The turbulence is highly anisotropic and inhomogeneous, with the anisotropy tensor shifting from one-dimensional (1D) to 2D and 3D structures over small distances. With the grooves, the flow structure, hence the distribution of Reynolds stresses, becomes more complex. Additional sites with elevated turbulence include the corner vortex that develops at the entrance to the grooves, and in the flow jetting out of the grooves into the passage. Consistent with trends of the production rates of normal Reynolds stress components, the grooves increase the axial but reduce the radial velocity fluctuations as the inflow and outflow from the groove interact with the passage flow. These findings might assist the development of Reynolds stress models suitable for tip flows.

Flow structure and turbulence in the near field of an immiscible buoyant oil jet

Simultaneous applications of particle image velocimetry and planar laser-induced fluorescence in a refractive index matched facility are used to visualize the phase distribution and measure velocity in an immiscible low Reynolds number buoyant oil jet injected into water. Initially, mixing involves entrainment of water ligaments inward and oil ligaments outward, followed by phase fragmentation into blobs and then droplets. Phase-based conditioning reveals spatially varying discrepancies between the velocity and all Reynolds stress components in the oil and water phases. Trends are attributed to intermittency and differences in turbulence production rate.

Seasonal evolution of winds, atmospheric tides, and Reynolds stress components in the Southern Hemisphere mesosphere–lower thermosphere in 2019

Abstract. In this study we explore the seasonal variability of the mean winds and diurnal and semidiurnal tidal amplitude and phases, as well as the Reynolds stress components during 2019, utilizing meteor radars at six Southern Hemisphere locations ranging from midlatitudes to polar latitudes. These include Tierra del Fuego, King Edward Point on South Georgia island, King Sejong Station, Rothera, Davis, and McMurdo stations. The year 2019 was exceptional in the Southern Hemisphere, due to the occurrence of a rare minor stratospheric warming in September. Our results show a substantial longitudinal and latitudinal seasonal variability of mean winds and tides, pointing towards a wobbling and asymmetric polar vortex. Furthermore, the derived momentum fluxes and wind variances, utilizing a recently developed algorithm, reveal a characteristic seasonal pattern at each location included in this study. The longitudinal and latitudinal variability of vertical flux of zonal and meridional momentum is discussed in the context of polar vortex asymmetry, spatial and temporal variability, and the longitude and latitude dependence of the vertical propagation conditions of gravity waves. The horizontal momentum fluxes exhibit a rather consistent seasonal structure between the stations, while the wind variances indicate a clear seasonal behavior and altitude dependence, showing the largest values at higher altitudes during the hemispheric winter and two variance minima during the equinoxes. Also the hemispheric summer mesopause and the zonal wind reversal can be identified in the wind variances.

Direct numerical simulation of particle-laden turbulent boundary layers without and with combustion

In the present work, direct numerical simulations of non-reactive and reactive turbulent boundary layers laden with inert particles were performed to investigate the influences of combustion on particle motions in wall-bounded flows. It was found that the coherent vortical structures of turbulent boundary layers are significantly modified by combustion. The streamwise velocity of particles is enhanced, while the velocity fluctuation is reduced in the reactive case due to the relaminarization effects. The preferential concentration of particles in the reactive case was found to be attenuated based on both visualization and the Voronoi analysis. The particle concentration in the outer layer of the reactive case is reduced because of the thermal expansion effects. However, the concentration is increased in the near-wall regions. The quadrant analysis of the Reynolds stress component was applied to explain this behavior. It was revealed that the magnitude of the mean Reynolds stress component is attenuated as a result of relaminarization. The frequency of the sweep event is increased but that of the injection event is reduced in the near-wall regions, which is responsible for the high particle concentration near the wall of the reactive case. The present study improves fundamental understandings of particle behaviors in non-reactive and reactive turbulent boundary layers.

Closure modeling for the conditional Reynolds stresses in turbulent premixed combustion

Turbulence is significantly affected by combustion-induced dilatation in low Karlovitz number premixed flames. Conventional turbulence modeling approaches based on traditional unconditional averaging are limited in accurately capturing combustion heat release effects since they must capture both the direct influence of combustion heat release on turbulence and the flame dynamics. Solving momentum transport equations conditionally averaged with respect to a flame structure variable (progress variable for premixed combustion) could provide a superior framework for modeling combustion-affected turbulence since the flame dynamics are embedded into the flame structure variable conditioning. However, the conditional momentum equations contain numerous unclosed terms that evolve in both physical and phase spaces. Of the many unclosed terms, the conditional Reynolds stresses (conditional analog of the Reynolds stresses) represent the influence of turbulent transport on the conditional velocities. In this work, a new model consisting of two components for the conditional Reynolds stresses in turbulent premixed flames is developed to capture heat release effects on turbulence. The first component is the conditional analog of the Boussinesq model that characterizes turbulent shear effects in physical space. The second component depends on the conditional velocity gradient not in physical space but in phase space and captures the anisotropy in the conditional Reynolds stresses driven by thermal expansion effects that vary within the flame structure. The model is validated a priori using DNS databases of turbulent premixed jet flames at low and high Karlovitz numbers. At low Karlovitz number, the phase space term enables the model to capture direct heat release effects on all conditional Reynolds stress components, specifically the correct anisotropy of the normal components and the sign of the shear component. At high Karlovitz number where heat release effects on turbulence are insignificant, turbulent shear effects are dominant, and the phase space term has a nearly negligible effect.

Investigation on noise from shock/isotropic turbulence interaction using direct numerical simulation

Direct numerical simulation of shock/isotropic turbulence interaction combining Lighthill’s acoustic analogy is conducted to study the influence of shock/turbulence interaction (STI) on the turbulence noise in the farfield. The acoustic statistics are adopted to quantify the influence of STI on the turbulence noise. The results show that STI increases the power spectral density in almost the whole frequency band and obviously amplifies the acoustic intensity. Based on the numerical results and the theoretical analysis, the primary noise sources are identified. The normal Reynolds stress components in the transverse direction contribute greatly to the noise at the observers. By applying the Rankine-Hugoniot relation and the spatial and temporal Fourier analysis on the simplified noise source, the mechanisms of turbulence noise variation under STI are also investigated, which can be divided into three parts. First, the compression effect of the shock wave increases the downstream density. Second, STI increases the value of turbulent kinetic energy spectrum over the entire wavenumber range. Third, the noise sources in the high frequency band are amplified under STI. Additionally, the transverse velocities are filtered in wavenumber space and the influence of STI on turbulence noise is studied from the perspective of the turbulence scales. The contribution of acoustic intensity radiated from “smaller” or “larger” turbulence scales is decreased, and the contribution of acoustic intensity radiated from the interaction of “smaller” and “larger” turbulence scales is increased under STI.

Structure function tensor equations in inhomogeneous turbulence

Exact budget equations for the second-order structure function tensor ⟨𝛿u$_{i}$𝛿u$_{j}$⟩, where 𝛿u is the difference of the i th fluctuating velocity component between two points, are used to study the two-point statistics of velocity fluctuations in inhomogeneous turbulence. The anisotropic generalised Kolmogorov equations (AGKE) describe the production, transport, redistribution and dissipation of every Reynolds stress component occurring simultaneously among different scales and in space, i.e. along directions of statistical inhomogeneity. The AGKE are effective to study the inter-component and multi-scale processes of turbulence. In contrast to more classic approaches, such as those based on the spectral decomposition of the velocity field, the AGKE provide a natural definition of scales in the inhomogeneous directions, and describe fluxes across such scales too. Compared to the generalised Kolmogorov equation, which is recovered as their half-trace, the AGKE can describe inter-component energy transfers occurring via the pressure–strain term and contain also budget equations for the off-diagonal components of ⟨𝛿u$_{i}$𝛿u$_{j}$⟩. The non-trivial physical interpretation of the AGKE terms is demonstrated with three examples. First, the near-wall cycle of a turbulent channel flow at a friction Reynolds number of Re$_{𝜏}$ = 200 is considered. The off-diagonal component ⟨-𝛿u𝛿υ⟩, which cannot be interpreted in terms of scale energy, is discussed in detail. Wall-normal scales in the outer turbulence cycle are then discussed by applying the AGKE to channel flows at Re$_{𝜏}$ = 500 and 1000. In a third example, the AGKE are computed for a separating and reattaching flow. The process of spanwise-vortex formation in the reverse boundary layer within the separation bubble is discussed for the first time.

Heat release effects on the Reynolds stress budgets in turbulent premixed jet flames at low and high Karlovitz numbers

In turbulent premixed flames at low Karlovitz number, combustion heat release can have a significant impact on turbulence. Thermal expansion in flame induces dilatation, and the corresponding pressure–dilatation correlation acts as a primary source of turbulent kinetic energy (TKE). As a consequence, the flame-normal component of the normal Reynolds stresses significantly increases. Additionally, for sheared flames, typical of jet flames, the shear component of the Reynolds stresses exhibits counter-Boussinesq behavior. For flames at low Karlovitz number, where these effects dominate, no models have successfully predicted all Reynolds stress components. To develop more complete turbulence models, heat release effects on the evolution of all Reynolds stress components need to be analyzed. In this work, Reynolds stress budgets are evaluated from Direct Numerical Simulation (DNS) databases of spatially-evolving turbulent premixed planar jet flames at low and high Karlovitz numbers. In the Reynolds stress budgets, the velocity–pressure gradient correlation term is important at both Karlovitz numbers but serves fundamentally different roles in each case. In the budgets for the normal components, the velocity–pressure gradient correlation term is decomposed into a redistribution term and an isotropic term, where the redistribution term acts to redistribute energy between the Reynolds stress components and the isotropic term is the pressure–dilatation source term of turbulent kinetic energy. At high Karlovitz number, the isotropic term is negligible, and the redistribution term acts to isotropize the turbulence as in non-reacting flows. Conversely, at low Karlovitz number, the isotropic term acts as a large source, and the redistribution term preferentially injects energy into the flame-normal component at the expense of other components which acts to make the turbulence less isotropic. In the budget for the shear component, the shear production term dominates the velocity–pressure gradient correlation term at high Karlovitz number, but the opposite is observed at low Karlovitz number. The dominance of the velocity–pressure gradient correlation term at low Karlovitz number is primarily induced by the flame-generated mean pressure gradient and ultimately leads to the counter-Boussinesq behavior of the shear component. The overall analysis indicates that any turbulence model that relies on small-scale isotropy and/or rapid isotropization will fail to capture the heat release effects on turbulence at low Karlovitz number.

Flow characteristics of slat cove fillers

Experimental measurements using Particle Image Velocimetry were carried out to understand the flow characteristics of a 30P30N high-lift airfoil with and without slat cove fillers. The tests were carried out for the 30P30N airfoil with a retracted chord of c=0.35, at angles of attack of α=6∘ and 12∘, and for a chord-based Reynolds number of Rec=7.0×105. The wall pressure fluctuation results show that the use of slat cove fillers eliminates the slat tonal noise component. The results of the mean flow fields such as the normalized mean velocity, Reynolds stress components, and turbulent kinetic energy are presented for the baseline, half-slat cove filler, and slat cove filler configurations. The velocity contour results with streamlines showed a recirculation region within the slat cavity. The use of the half-slat cove filler reduced the size of the recirculation region and the use of the slat cove filler eliminated the recirculation region. The mean velocity and turbulent kinetic energy profiles at the slat wake showed insignificant difference between the three tested configurations. The Particle Image Velocimetry results were further analyzed using Proper Orthogonal Decomposition. The results showed that the first two eigenmodes of the vorticity with the highest energy were contained within the slat shear layer and vortex shedding emanating from the slat cusp for the baseline case. The energy levels were distributed over the slat shear layer for the half-slat cove filler and slat cove filler configurations as the vortex shedding is suppressed by the use of the slat cove fillers.

Rearrangement of secondary flow over spanwise heterogeneous roughness

Turbulent flow over a surface with streamwise-elongated rough and smooth stripes is studied by means of direct numerical simulation (DNS) in a periodic plane open channel with fully resolved roughness. The goal is to understand how the mean height of roughness affects the characteristics of the secondary flow formed above a spanwise heterogeneous rough surface. To this end, while the statistical properties of roughness texture as well as the width and spacing of the rough stripes are kept constant, the elevation of the smooth stripes is systematically varied in different simulation cases. Utilizing this variation, three configurations – representing protruding, recessed and an intermediate type of roughness – are analysed. In all cases, secondary flows are present and the skin friction coefficients calculated for all the heterogeneous rough surfaces are meaningfully larger than what would result from the area-weighted average of those of homogeneous smooth and rough surfaces. This drag increase appears to be linked to the strength of the secondary flow. The rotational direction of the secondary motion is shown to depend on the relative surface elevation. The present results suggest that this rearrangement of the secondary flow is linked to the spatial distribution of the spanwise-wall-normal Reynolds stress component, which carries opposing signs for protruding and recessed roughness.

Non-Equilibrium Scaling Applied to the Wake Evolution of a Model Scale Wind Turbine

The present paper addresses the evolution of turbulence characteristics in wind turbine wakes immersed in a turbulent boundary layer. The study thereby focuses on finding physically consistent scaling laws for the wake width, the velocity deficit, and the Reynolds stresses in the far wake region. For this purpose, the concept of an added wake is derived which allows to analyse the self-similarity of the added flow quantities and the applicability of the non-equilibrium dissipation theory. The investigation is based on wind tunnel measurements in the wake of a three-bladed horizontal axis wind turbine model (HAWT) immersed in two neutrally-stratified turbulent boundary layers of different aerodynamic roughness length. The dataset also includes wake measurements for various yaw angles. A high degree of self-similarity is found in the lateral profiles of the velocity deficit and of the added Reynolds stress components. It is shown that these can be described by combined Gaussian shape functions. In the vertical, self-similarity can just be shown in the upper part of the wake. Moreover, it is observed that the degree of self-similarity is affected by the ground roughness. Results suggest an approximately constant anisotropy of the added turbulent stresses in the far wake, and the axial scaling of the added Reynolds stress components is found to be in accordance with non-equilibrium dissipation theory. It predicts a x − 1 decay of the added turbulent intensity I + , and a x − 2 evolution of the added Reynolds shear stresses Δ u i ′ u j ′ ¯ and the velocity deficit Δ u . Based on these findingsa semi-empirical model is proposed for predicting the Reynolds stresses in the far wake region which can easily be coupled with existing analytical wake models. The proposed model is found to be in good agreement with the measurement results.

Turbulence characteristics of flow past submerged vanes

Submerged vanes are hydrofoils utilized to manage the sediment transport through the river by generating the turbulence in the flow in the form of helical currents. The vanes are placed in the flow with respect to its direction at angle of 10o to 40o. In the current study, an attempt has been made to study the effect of the introduction of vanes in form of rows on parameters like turbulence intensities, Reynolds stresses, turbulent kinetic energy, anisotropy index, and the velocity profile of the flow. It is observed that the profile of variation of turbulence intensities, turbulent kinetic energy, vertical Reynolds stress and velocity over three different marked verticals on a transect are nearly identical whereas a large scatter is observed in the variation of transverse Reynolds stress over the vertical of the aforementioned vertical locations. This observation suggests that flow turbulence is homogeneous over the vertical while scattering in the variation of the transverse Reynolds stress component may be attributed to the presence of secondary currents in the flow. After introducing rows of submerged vanes, the bed turbulence is reduced, hence, helping reduce many scour related phenomenon. It is also observed that a vortex occurred at 0.85 times the height of the vane and the variation of turbulence quantities in the presence of vanes shows the existence of a peak in these quantities. It is observed that as flow moves away from the vane rows, due to the interaction of vortices and the action of vorticity, vortices dampens down and the flow regains homogeneity. After the introduction of submerged vane rows, bed shear stress reduces as fluid from the surface replaces the slow-moving fluid near the bed due to the secondary currents generated by the vanes leading to reduction in the magnitude of turbulence intensities, Reynolds stresses, and turbulent kinetic energy near the bed. The anisotropy index is observed to increase near the bed as induced secondary currents enhanced the turbulence production in the near bed region. All the profiles of parameters obtained in the current study show the existence of a peak or inflexions at a height of 0.85H from bed (Where, H is the height of the submerged vane). Profiles of parameters obtained in the current study suggest that as the vorticity dampens the vane-generated secondary currents, the scattering in the profiles along the vertical reduces and profiles are observed to regain the variation which they had before the introduction of vane rows, suggesting that flow turbulence has regained its homogeneity.

Pulse Frequency Effect on the Flow Structure and Heat Transfer in an Impinging Gas-Saturated Turbulent Jet

The turbulent flow structure and the heat transfer in an unsteady bubbly round impinging jet is numerically simulated for different pulse frequencies. The mathematical model is based on the Eulerian approach for describing the flow dynamics and heat transfer in the disperse phase (air bubbles). The problem is considered in the axisymmetric formulation; the system of unsteady Reynolds-averaged Navier—Stokes equations is solved. The turbulence of the carrier phase (liquid) is described invoking the model of the transport of the Reynolds stress components with account for the bubble effect on turbulence production. The pulse supply frequency effect on the flow structure and the heat transfer in an impinging gas-liquid jet is investigated. The pulsed nature of the jet causes both a considerable (almost twofold) increase in the liquid turbulence and heat transfer during the pulse interval and a considerable suppression of these parameters, when the jet is flow-off, as compared with the case of a steady impinging bubblyjet at the same time-average jet flow fluid rate.

Numerical simulation of flow separation over a backward-facing step with high Reynolds number

Large eddy simulation (LES) explicitly calculates the large-scale vortex field and parameterizes the small-scale vortices. In this study, LES and κ-ε models were developed for a specific geometrical configuration of backward-facing step (BFS). The simulation results were validated with particle image velocimetry (PIV) measurements and direct numerical simulation (DNS). This LES simulation was carried out with a Reynolds number of 9000 in a pressurized water tunnel with an expansion ratio of 2.00. The results indicate that the LES model can reveal large-scale vortex motion although with a larger grid-cell size. However, the LES model tends to overestimate the top wall separation and the Reynolds stress components for the BFS flow simulation without a sufficiently fine grid. Overall, LES is a potential tool for simulating separated flow controlled by large-scale vortices.