Journal articles: 'Boundary-Layer Separation'

1

Simpson, R. L. "Turbulent Boundary-Layer Separation." Annual Review of Fluid Mechanics 21, no. 1 (January 1989): 205–32. http://dx.doi.org/10.1146/annurev.fl.21.010189.001225.

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2

Cao, Zhiyuan, Bo Liu, and Ting Zhang. "Control of separations in a highly loaded diffusion cascade by tailored boundary layer suction." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 228, no. 8 (October 10, 2013): 1363–74. http://dx.doi.org/10.1177/0954406213508281.

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In order to explore the control mechanism of boundary layer suction on the separated flows of highly loaded diffusion cascades, a linear compressor cascade, which has separated flows on the whole span and three-dimensional separations over the suction surface/endwall corner, was investigated by tailored boundary layer suction. Three suction surface-slotted schemes and two combined suction surface/endwall-slotted schemes were designed. The original cascade and the cascade with part blade span suction were experimentally investigated on a high-subsonic cascade wind tunnel. In addition, numerical simulation was employed to study the flow fields of different suction schemes in detail. The results shows that while tailored boundary layer suction at part blade span can effectively remove the separations at the suction span, the flow fields of other spans deteriorated. The reasons are the ‘C’ shape or reverse ‘C’ shape spanwise distribution of static pressure after part blade span boundary layer suction. Suction surface boundary layer suction over the whole span can obviously eliminate the separation at the suction surface. However, because of the endwall boundary layer, suction surface boundary layer suction cannot effectively remove the corner three-dimensional separation. The separation over the whole span and the three-dimensional separation at the corner are completely eliminated by combined suction surface/endwall boundary layer suction. After combined boundary layer suction, the static pressure distribution over the blade span just like the shape of ‘C’ is good for the transport of the low-energy fluid near the endwall to the midspan.

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3

Nesteruk, Igor G. "Rigid Bodies without Boundary-Layer Separation." International Journal of Fluid Mechanics Research 41, no. 3 (2014): 260–81. http://dx.doi.org/10.1615/interjfluidmechres.v41.i3.50.

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4

Simpson, Roger L. "Aspects of turbulent boundary-layer separation." Progress in Aerospace Sciences 32, no. 5 (October 1996): 457–521. http://dx.doi.org/10.1016/0376-0421(95)00012-7.

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5

Smith, F. T. "Steady and Unsteady Boundary-Layer Separation." Annual Review of Fluid Mechanics 18, no. 1 (January 1986): 197–220. http://dx.doi.org/10.1146/annurev.fl.18.010186.001213.

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6

Núñez, M. "Boundary layer separation of hydromagnetic flows." ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik 92, no. 6 (February 29, 2012): 445–51. http://dx.doi.org/10.1002/zamm.201100070.

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7

Uruba, V., M. Knob, and L. Popelka. "Control of a boundary layer separation." PAMM 7, no. 1 (December 2007): 4140019–20. http://dx.doi.org/10.1002/pamm.200700945.

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8

Peridier, Vallorie J., F. T. Smith, and J. D. A. Walker. "Vortex-induced boundary-layer separation. Part 2. Unsteady interacting boundary-layer theory." Journal of Fluid Mechanics 232, no. -1 (November 1991): 133. http://dx.doi.org/10.1017/s0022112091003658.

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9

Ren, Xiang, Hua Su, Hua-Hua Yu, and Zheng Yan. "Wall-Modeled Large Eddy Simulation and Detached Eddy Simulation of Wall-Mounted Separated Flow via OpenFOAM." Aerospace 9, no. 12 (November 27, 2022): 759. http://dx.doi.org/10.3390/aerospace9120759.

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Considering grid requirements of high Reynolds flow, wall-modeled large eddy simulation (WMLES) and detached eddy simulation (DES) have become the main methods to deal with near-wall turbulence. However, the flow separation phenomenon is a challenge. Three typical separated flows, including flow over a cylinder at ReD = 3900 based on the cylinder diameter, flow over a wall-mounted hump at Rec = 9.36 × 105 based on the hump length, and transonic flow over an axisymmetric bump with shock-induced separation at Rec = 2.763 × 106 based on the bump length, are used to verify WMLES, shear stress transport k-ω DES (SST-DES), and Spalart–Allmaras DES (SA-DES) methods in OpenFOAM. The three flows are increasingly challenging, namely laminar boundary layer separation, turbulent boundary layer separation, and turbulent boundary layer separation under shock interference. The results show that WMLES, SST-DES, and SA-DES methods in OpenFOAM can easily predict the separation position and wake characteristics in the flow around the cylinder, but they rely on the grid scale and turbulent inflow to accurately simulate the latter two flows. The grid requirements of Larsson et al. (δ/Δx,δ/Δy,δ/Δz≈(12,50,20)) are the basis for simulating turbulent boundary layers upstream of flow separation. A finer mesh (δ/Δx,δ/Δy,δ/Δz≈(40,75,40)) is required to accurately predict the separation and reattachment. The WMLES method is more sensitive to grid scales than the SA-DES method and fails to obtain flow separation under a coarser grid, while SST-DES method can only describe the vortices generated by the separating shear layer, but not within the turbulent boundary layer, and overestimates the separation-reattachment zone based on the grid system in this paper.

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Stieger, R. D., David Hollis, and H. P. Hodson. "Unsteady Surface Pressures Due to Wake-Induced Transition in a Laminar Separation Bubble on a Low-Pressure Cascade." Journal of Turbomachinery 126, no. 4 (October 1, 2004): 544–50. http://dx.doi.org/10.1115/1.1773851.

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This paper presents unsteady surface pressures measured on the suction surface of a LP turbine cascade that was subject to wake passing from a moving bar wake generator. The surface pressures measured under the laminar boundary layer upstream of the steady flow separation point were found to respond to the wake passing as expected from the kinematics of wake convection. In the region where a separation bubble formed in steady flow, the arrival of the convecting wake produced high frequency, short wavelength, fluctuations in the ensemble-averaged blade surface pressure. The peak-to-peak magnitude was 30% of the exit dynamic head. The existence of fluctuations in the ensemble averaged pressure traces indicates that they are deterministic and that they are produced by coherent structures. The onset of the pressure fluctuations was found to lie beneath the convecting wake and the fluctuations were found to convect along the blade surface at half of the local freestream velocity. Measurements performed with the boundary layer tripped ahead of the separation point showed no oscillations in the ensemble average pressure traces indicating that a separating boundary layer is necessary for the generation of the pressure fluctuations. The coherent structures responsible for the large-amplitude pressure fluctuations were identified using PIV to be vortices embedded in the boundary layer. It is proposed that these vortices form in the boundary layer as the wake passes over the inflexional velocity profiles of the separating boundary layer and that the rollup of the separated shear layer occurs by an inviscid Kelvin-Helmholtz mechanism.

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11

Ahmed, Saad, and Argin Nazari. "Numerical Analysis of Boundary Layer Separation Control." International Review of Mechanical Engineering (IREME) 9, no. 1 (January 31, 2015): 90. http://dx.doi.org/10.15866/ireme.v9i1.4490.

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12

Jahnke, Craig C., and Daniel T. Valentine. "Boundary layer separation in a rotating container." Physics of Fluids 8, no. 6 (June 1996): 1408–14. http://dx.doi.org/10.1063/1.868917.

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13

Skåre, Per Egil, and Per-åge Krogstad. "A turbulent equilibrium boundary layer near separation." Journal of Fluid Mechanics 272 (August 10, 1994): 319–48. http://dx.doi.org/10.1017/s0022112094004489.

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The experimental results for an equilibrium boundary layer in a strong adverse pressure gradient flow are reported. The measurements show that similarity in the mean flow and the turbulent stresses has been achieved over a substantial streamwise distance where the skin friction coefficient is kept at a low, constant level. Although the Reynolds stress distribution across the layer is entirely different from the flow at zero pressure gradient, the ratios between the different turbulent stress components were found to be similar, showing that the mechanism for distributing the turbulent energy between the different components remains unaffected by the mean flow pressure gradient. Close to the surface the gradient of the mixing length was found to increase from Kl ≈ 0.41 to Kl ≈ 0.78, almost twice as high as for the zero pressure gradient case. Similarity in the triple correlations was also found to be good. The correlations show that there is a considerable diffusion of turbulent energy from the central part of the boundary layer towards the wall. The diffusion mechanism is caused by a second peak in the turbulence production, located at y/δ ≈ 0.45. This production was for the present case almost as strong as the production found near the wall. The energy budget for the turbulent kinetic energy also shows that strong dissipation is not restricted to the wall region, but is significant for most of the layer.

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14

Khusnutdinova, N. V. "On boundary layer separation under increasing pressure." Siberian Mathematical Journal 40, no. 5 (October 1999): 1017–30. http://dx.doi.org/10.1007/bf02674731.

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15

Goff, J. E., W. H. Smith, and M. J. Carré. "Football boundary-layer separation via dust experiments." Sports Engineering 14, no. 2-4 (October 30, 2011): 139–46. http://dx.doi.org/10.1007/s12283-011-0074-3.

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16

Cheng, W., D. I. Pullin, and R. Samtaney. "Large-eddy simulation of separation and reattachment of a flat plate turbulent boundary layer." Journal of Fluid Mechanics 785 (November 11, 2015): 78–108. http://dx.doi.org/10.1017/jfm.2015.604.

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We present large-eddy simulations (LES) of separation and reattachment of a flat-plate turbulent boundary-layer flow. Instead of resolving the near wall region, we develop a two-dimensional virtual wall model which can calculate the time- and space-dependent skin-friction vector field at the wall, at the resolved scale. By combining the virtual-wall model with the stretched-vortex subgrid-scale (SGS) model, we construct a self-consistent framework for the LES of separating and reattaching turbulent wall-bounded flows at large Reynolds numbers. The present LES methodology is applied to two different experimental flows designed to produce separation/reattachment of a flat-plate turbulent boundary layer at medium Reynolds number $Re_{{\it\theta}}$ based on the momentum boundary-layer thickness ${\it\theta}$. Comparison with data from the first case at $Re_{{\it\theta}}=2000$ demonstrates the present capability for accurate calculation of the variation, with the streamwise co-ordinate up to separation, of the skin friction coefficient, $Re_{{\it\theta}}$, the boundary-layer shape factor and a non-dimensional pressure-gradient parameter. Additionally the main large-scale features of the separation bubble, including the mean streamwise velocity profiles, show good agreement with experiment. At the larger $Re_{{\it\theta}}=11\,000$ of the second case, the LES provides good postdiction of the measured skin-friction variation along the whole streamwise extent of the experiment, consisting of a very strong adverse pressure gradient leading to separation within the separation bubble itself, and in the recovering or reattachment region of strongly-favourable pressure gradient. Overall, the present two-dimensional wall model used in LES appears to be capable of capturing the quantitative features of a separation-reattachment turbulent boundary-layer flow at low to moderately large Reynolds numbers.

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17

Afanasiev, V. N., V. I. Trifonov, S. I. Getya, and D. Kong. "Rib in Turbulent Boundary Layer." Mechanical Engineering and Computer Science, no. 10 (November 20, 2017): 13–35. http://dx.doi.org/10.24108/1017.0001312.

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Experimental and theoretical investigations of the flow structure, with the flow over a variety of protrusions and depressions on the initially smooth surfaces are of considerable practical interest, since the there are constructive or random occurring depressions and cavities found on many different convective surfaces. With the flow over the depressions and protrusions, the boundary layer separation and its reattachment can lead to occurring specific phenomena, which have a significant impact on drag and heat transfer. These phenomena, which are encountered in the course of experimental studies and obtaining adequate mathematical models, are complicated and hard-to-understand.The paper presents experimental results of hydrodynamics and heat transfer in the separation zone before and after a single rectangular rib and a round corner rib with the height of approximately y+ = 100, which are placed on the flat plate that is heated according to the law of qw=const. Experimental studies were conducted using a Pitot-Prandtl microprobe and a hot-wire Dantec Dynamics anemometry system, which allowed us to obtain both the mean and the fluctuating characteristics of the turbulent boundary layer and determine the boundaries of the vortex and separation zones.It is shown that the structure of vertex zones before and after the rib has a strong dependence on the rib shape and size. New experimental data on the mean and fluctuating characteristics in the turbulent boundary layer with the flow over the rectangular ribs with and without round top corners are obtained. Also, the fluctuations of temperature and especially velocity in the boundary layer after the rib are significantly higher than in the layer on the flat plate. The changing characteristic of the friction and heat transfer coefficients indicates that the increase of the heat transfer coefficient exceeds the growth of the friction coefficient after the ribs with the size 30 < y+ < 100.

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18

Khotyanovsky, D. V., A. N. Kudryavtsev, and A. I. Kutepova. "Numerical simulation of the interaction of the disturbed boundary layer with an incident shock." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012005. http://dx.doi.org/10.1088/1742-6596/2057/1/012005.

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Abstract Interaction of the disturbed supersonic boundary layer with an incident oblique shock wave is studied numerically with eddy-resolving numerical simulations. Eigenmodes of the linear stability theory are used to generate the inflow boundary layer disturbances. The evolution of unstable boundary-layer disturbances, effects of the incident shock on the disturbances, effects of the disturbances on the boundary layer separation, flow dynamics in the separation zone, and laminar-turbulent transition are studied.

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19

Malkiel, E., and R. E. Mayle. "Transition in a Separation Bubble." Journal of Turbomachinery 118, no. 4 (October 1, 1996): 752–59. http://dx.doi.org/10.1115/1.2840931.

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In the interest of being able to predict separating–reattaching flows, it is necessary to have an accurate model of transition in separation bubbles. An experimental investigation of the process of turbulence development in a separation bubble shows that transition occurs within the separated shear layer. A comparison of simultaneous velocity traces from comparison of simultaneous velocity traces from probes separated in the lateral direction suggests that Kelvin–Helmholtz waves, which originate in the laminar shear layer, do not break down to turbulence simultaneously across their span when they proceed to agglomerate. The streamwise development of intermittency in this region can be characterized by turbulent spot theory with a high dimensionless spot production rate. Moreover, the progression of intermittency along the centerline of the shear layer is similar to that in attached boundary layer transition. The transverse development of intermittency is also remarkably similar to that in attached boundary layers. The parameters obtained from these measurements agree with correlations previously deduced from turbulence intensity measurements.

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20

Bulatova, P. P., V. N. Samokhin, and G. A. Chechkin. "Equations of Magnetohydrodynamic Boundary Layer for a Modified Incompressible Viscous Medium. Boundary Layer Separation." Journal of Mathematical Sciences 232, no. 3 (June 2, 2018): 299–321. http://dx.doi.org/10.1007/s10958-018-3874-1.

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21

Wu, Wen, and Ugo Piomelli. "Effects of surface roughness on a separating turbulent boundary layer." Journal of Fluid Mechanics 841 (February 26, 2018): 552–80. http://dx.doi.org/10.1017/jfm.2018.101.

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Separating turbulent boundary layers over smooth and rough flat plates are studied by large-eddy simulations. A suction–blowing velocity distribution imposed at the top boundary of the computation domain produces an adverse-to-favourable pressure gradient and creates a closed separation bubble. The Reynolds number based on the momentum thickness and the free-stream velocity before the pressure gradient begins is 2500. Virtual sand grain roughness in the fully rough regime is modelled by an immersed boundary method. Compared with a smooth-wall case, streamline detachment occurs earlier and the separation region is substantially larger for the rough-wall case, due to the momentum deficit caused by the roughness. The adverse pressure gradient decreases the form drag, so that the point where the wall stress vanishes does not coincide with the detachment of the flow from the surface. A thin reversed-flow region is formed below the roughness crest; the presence of recirculation regions behind each roughness element also affects the intermittency of the near-wall flow, so that upstream of the detachment point the flow can be reversed half of the time, but its average velocity can still be positive. The separated shear layer exhibits higher turbulent kinetic energy (TKE) in the rough-wall case, the growth of the TKE there begins earlier relative to the separation point, and the peak TKE occurs close to the separation point. The momentum deficit caused by the roughness, again, plays a critical role in these changes.

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22

SCHLEGEL, FABRICE, DAEHYUN WEE, YOUSSEF M. MARZOUK, and AHMED F. GHONIEM. "Contributions of the wall boundary layer to the formation of the counter-rotating vortex pair in transverse jets." Journal of Fluid Mechanics 676 (April 8, 2011): 461–90. http://dx.doi.org/10.1017/jfm.2011.59.

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Using high-resolution 3-D vortex simulations, this study seeks a mechanistic understanding of vorticity dynamics in transverse jets at a finite Reynolds number. A full no-slip boundary condition, rigorously formulated in terms of vorticity generation along the channel wall, captures unsteady interactions between the wall boundary layer and the jet – in particular, the separation of the wall boundary layer and its transport into the interior. For comparison, we also implement a reduced boundary condition that suppresses the separation of the wall boundary layer away from the jet nozzle. By contrasting results obtained with these two boundary conditions, we characterize near-field vortical structures formed as the wall boundary layer separates on the backside of the jet. Using various Eulerian and Lagrangian diagnostics, it is demonstrated that several near-wall vortical structures are formed as the wall boundary layer separates. The counter-rotating vortex pair, manifested by the presence of vortices aligned with the jet trajectory, is initiated closer to the jet exit. Moreover tornado-like wall-normal vortices originate from the separation of spanwise vorticity in the wall boundary layer at the side of the jet and from the entrainment of streamwise wall vortices in the recirculation zone on the lee side. These tornado-like vortices are absent in the case where separation is suppressed. Tornado-like vortices merge with counter-rotating vorticity originating in the jet shear layer, significantly increasing wall-normal circulation and causing deeper jet penetration into the crossflow stream.

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23

Hamed, A., and A. Kumar. "Flow Separation in Shock Wave Boundary Layer Interactions." Journal of Engineering for Gas Turbines and Power 116, no. 1 (January 1, 1994): 98–103. http://dx.doi.org/10.1115/1.2906816.

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This work presents an assessment of the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists of selected configurations where the only characteristic length in the iteration is the incoming boundary layer thickness. It consists of two-dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the empirical correlations for incipient separation are reviewed. The effects of Mach number, Reynolds number, surface cooling, and the methods of detecting separation are discussed.

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24

Pasha, Amjad A., and Khalid A. Juhany. "Effect of wall temperature on separation bubble size in laminar hypersonic shock/boundary layer interaction flows." Advances in Mechanical Engineering 11, no. 11 (November 2019): 168781401988555. http://dx.doi.org/10.1177/1687814019885556.

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At hypersonic speeds, the external wall temperatures of an aerospace vehicle vary significantly. As a result, there is a considerable heat transfer variation between the boundary layer and the wall of the hypersonic vehicle. In this article, numerical computations are performed to investigate the effect of wall temperature on the separation bubble length in laminar hypersonic shock-wave/boundary-layer interaction flows over double-cone configuration at the Mach number of 12.2. The flow field is described in detail in terms of different shocks, expansion fans, shear layer and separation bubble. The variation of the Prandtl number has a negligible effect on the flow field and wall data. A specific heat ratio of less than 1.4 results in the better prediction of wall pressure and heat flux in the shock/boundary-layer interaction region. It is observed that as the wall temperature is increased, the separation bubble size and hence the separation shock length increases. The high firmness of the laminar boundary-layer at a high Mach number shows that the wall temperature in the shock/boundary-layer interaction region has little effect. The peak wall pressure and heat flux decrease with an increase in wall temperature. An estimation is developed between separation bubble length and wall temperature based on the computed results.

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25

RUBAN, A. I., and I. TURKYILMAZ. "On laminar separation at a corner point in transonic flow." Journal of Fluid Mechanics 423 (November 3, 2000): 345–80. http://dx.doi.org/10.1017/s002211200000207x.

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The separation of the laminar boundary layer from a convex corner on a rigid body contour in transonic flow is studied based on the asymptotic analysis of the Navier–Stokes equations at large values of the Reynolds number. It is shown that the flow in a small vicinity of the separation point is governed, as usual, by strong interaction between the boundary layer and the inviscid part of the flow. Outside the interaction region the Kármán–Guderley equation describing transonic inviscid flow admits a self-similar solution with the pressure on the body surface being proportional to the cubic root of the distance from the separation point. Analysis of the boundary layer driven by this pressure shows that as the interaction region is approached the boundary layer splits into two parts: the near-wall viscous sublayer and the main body of the boundary layer where the flow is locally inviscid. It is interesting that contrary to what happens in subsonic and supersonic flows, the displacement effect of the boundary layer is primarily due to the inviscid part. The contribution of the viscous sublayer proves to be negligible to the leading order. Consequently, the flow in the interaction region is governed by the inviscid–inviscid interaction. To describe this flow one needs to solve the Kármán–Guderley equation for the potential flow region outside the boundary layer; the solution in the main part of the boundary layer was found in an analytical form, thanks to which the interaction between the boundary layer and external flow can be expressed via the corresponding boundary condition for the Kármán–Guderley equation. Formulation of the interaction problem involves one similarity parameter which in essence is the Kármán–Guderley parameter suitably modified for the flow at hand. The solution of the interaction problem has been constructed numerically.

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Prakash, R., L. M. Le Page, L. P. McQuellin, S. L. Gai, and S. O’Byrne. "Direct simulation Monte Carlo computations and experiments on leading-edge separation in rarefied hypersonic flow." Journal of Fluid Mechanics 879 (October 2, 2019): 633–81. http://dx.doi.org/10.1017/jfm.2019.692.

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A comprehensive study of the fundamental characteristics of leading-edge separation in rarefied hypersonic flows is undertaken and its salient features are elucidated. Separation of a boundary layer undergoing strong expansion is typical in many practical hypersonic applications such as base flows of re-entry vehicles and flows over deflected control surfaces. Boundary layer growth under such conditions is influenced by effects of rarefaction and thermal non-equilibrium, thereby differing significantly from the conventional no-slip Blasius type. A leading-edge separation configuration presents a fundamental case for studying the characteristics of such a flow separation but with minimal influence from a pre-existing boundary layer. In this work, direct simulation Monte Carlo computations have been performed to investigate flow separation and reattachment in a low-density hypersonic flow over such a configuration. Distinct features of leading-edge flow, limited boundary layer growth, separation, shear layer, flow structure in the recirculation region and reattachment are all explained in detail. The fully numerical shear layer profile after separation is compared against a semi-theoretical profile, which is obtained using the numerical separation profile as the initial condition on existing theoretical concepts of shear layer analysis based on continuum flow separation. Experimental studies have been carried out to determine the surface heat flux using thin-film gauges and computations showed good agreement with the experimental data. Flow visualisation experiments using the non-intrusive planar laser-induced fluorescence technique have been performed to image the fluorescence of nitric oxide, from which velocity and rotational temperature distributions of the separated flow region are determined.

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SCHEICHL, B., A. KLUWICK, and F. T. SMITH. "Break-away separation for high turbulence intensity and large Reynolds number." Journal of Fluid Mechanics 670 (February 22, 2011): 260–300. http://dx.doi.org/10.1017/s0022112010005306.

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Massive flow separation from the surface of a plane bluff obstacle in an incompressible uniform stream is addressed theoretically for large values of the global Reynolds numberRe. The analysis is motivated by a conclusion drawn from recent theoretical results which is corroborated by experimental findings but apparently contrasts with common reasoning: the attached boundary layer extending from the front stagnation point to the position of separation never attains a fully developed turbulent state, even for arbitrarily largeRe. Consequently, the boundary layer exhibits a certain level of turbulence intensity that is linked with the separation process, governed by local viscous–inviscid interaction. Eventually, the latter mechanism is expected to be associated with rapid change of the separating shear layer towards a fully developed turbulent one. A self-consistent flow description in the vicinity of separation is derived, where the present study includes the predominantly turbulent region. We establish a criterion that acts to select the position of separation. The basic analysis here, which appears physically feasible and rational, is carried out without needing to resort to a specific turbulence closure.

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28

Kerimbekov, R. M., A. I. Ruban, and J. D. A. Walker. "Hypersonic boundary-layer separation on a cold wall." Journal of Fluid Mechanics 274 (September 10, 1994): 163–95. http://dx.doi.org/10.1017/s0022112094002089.

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An asymptotic theory of laminar hypersonic boundary-layer separation for large Reynolds number is described for situations when the surface temperature is small compared with the stagnation temperature of the inviscid external gas flow. The interactive boundary-layer structure near separation is described by well-known tripledeck concepts but, in contrast to the usual situation, the displacement thickness associated with the viscous sublayer is too small to influence the external pressure distribution (to leading order) for sufficiently small wall temperature. The present interaction takes place between the main part of the boundary layer and the external flow and may be described as inviscid–inviscid. The flow in the viscous sublayer is governed by the classical boundary-layer equations and the solution develops a singularity at the separation point. A main objective of this study is to show how the singularity may be removed in different circumstances.

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Cloos, F. J., D. Stapp, and P. F. Pelz. "Swirl boundary layer and flow separation at the inlet of a rotating pipe." Journal of Fluid Mechanics 811 (December 12, 2016): 350–71. http://dx.doi.org/10.1017/jfm.2016.734.

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When a fluid enters a rotating circular pipe, an angular momentum or swirl boundary layer appears at the wall and interacts with the axial momentum boundary layer. In the centre of the pipe, the fluid is free of swirl and is accelerated due to boundary layer growth. Below a critical flow number, defined as the ratio of average axial velocity to circumferential velocity of the pipe, there is flow separation, known in the turbomachinery context as part load recirculation. To describe this phenomenon analytically, we extended boundary layer theory to a swirl boundary layer interacting with the axial momentum boundary layer. The solution of the resulting generalized von Kármán momentum equation takes into account the influence of the Reynolds number and flow number. We show the impact of swirl on the axial boundary layer and conduct experiments in which we vary Reynolds number, flow number and surface roughness to validate the analytical results. The extended boundary layer theory predicts a critical flow number which is analytically derived and validated. Below this critical flow number, separation is expected.

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30

Abramov, Fedor Aleksandrovich, Murad Abramovich Brutyan, and Vladimir Efimovich Kovalev. "FLUID MICROPOLARITY INFLUENCE ON LAMINAR BOUNDARY LAYER SEPARATION." TsAGI Science Journal 48, no. 4 (2017): 331–40. http://dx.doi.org/10.1615/tsagiscij.2017024799.

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31

Geissler, Wolfgang. "Unsteady laminar boundary-layer separation on oscillating configurations." AIAA Journal 23, no. 4 (April 1985): 577–82. http://dx.doi.org/10.2514/3.8953.

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32

Sandborn, V. A. "Boundary-Layer Separation in a Turn-Around Duct." AIAA Journal 42, no. 7 (July 2004): 1483–85. http://dx.doi.org/10.2514/1.4828.

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33

LIU, Kui. "Experiments of low speed fluid boundary-layer separation." Chinese Journal of Mechanical Engineering 44, no. 01 (2008): 139. http://dx.doi.org/10.3901/jme.2008.01.139.

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34

Dandy, D. S., and L. G. Leal. "Boundary-layer separation from a smooth slip surface." Physics of Fluids 29, no. 5 (1986): 1360. http://dx.doi.org/10.1063/1.865701.

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35

Higuera, F. J. "Boundary layer separation due to gas thermal expansion." Physics of Fluids 9, no. 10 (October 1997): 2841–50. http://dx.doi.org/10.1063/1.869397.

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36

Manhart, Michael, and Rainer Friedrich. "DNS of a turbulent boundary layer with separation." International Journal of Heat and Fluid Flow 23, no. 5 (October 2002): 572–81. http://dx.doi.org/10.1016/s0142-727x(02)00153-4.

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37

Dovgal, A. V., V. V. Kozlov, and A. Michalke. "Laminar boundary layer separation: Instability and associated phenomena." Progress in Aerospace Sciences 30, no. 1 (January 1994): 61–94. http://dx.doi.org/10.1016/0376-0421(94)90003-5.

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Mehmood, Ahmer, and Muhammad Usman. "Controlling boundary layer separation in stretching sheet flow." Alexandria Engineering Journal 57, no. 4 (December 2018): 3747–53. http://dx.doi.org/10.1016/j.aej.2018.03.004.

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39

Stead, Brendon, and Clayton Williamson. "Speaker port system for reducing boundary layer separation." Journal of the Acoustical Society of America 128, no. 4 (2010): 2251. http://dx.doi.org/10.1121/1.3500755.

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Veldman, Arthur E. P. "Entrainment and boundary-layer separation: a modeling history." Journal of Engineering Mathematics 107, no. 1 (October 4, 2017): 5–17. http://dx.doi.org/10.1007/s10665-017-9930-x.

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41

Chang, H. C., E. A. Demekhin, and P. V. Takhistov. "Circular Hydraulic Jumps Triggered by Boundary Layer Separation." Journal of Colloid and Interface Science 233, no. 2 (January 2001): 329–38. http://dx.doi.org/10.1006/jcis.2000.7289.

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42

Tampieri, Francesco. "Separation features of boundary-layer flow over valleys." Boundary-Layer Meteorology 40, no. 3 (August 1987): 295–307. http://dx.doi.org/10.1007/bf00117453.

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43

Pereira Lara, Ana Maria, and Tiago Cavalcanti Rolim. "Analysis of the Shock Wave/Boundary Layer Interaction considering a Compression Corner Model Using the MacCormack Method." Journal of Engineering 2023 (March 22, 2023): 1–30. http://dx.doi.org/10.1155/2023/8115465.

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The objective of this paper is to numerically study the shock wave/boundary layer interaction and boundary layer separation. The first stage of this research is the development of methodology, flow simulations, and data analysis. When comparing the plots, it can be seen that the results of the check of the methodology were similar. Following, methodologies were developed and simulations were carried out considering the compression corner model. It was noticed that the shock wave could be identified by the jump on the pressure profile near the leading edge and by analyzing the thermodynamic properties of the plate. An increase in pressure, flow inversion, and boundary layer separation through negative values of the friction coefficient was observed, and negative speed at the wall was observed due to the presence of a plateau on the pressure curves. Flow expansion and further reattachment of the boundary layer were also seen. It is possible to observe type VI shock-shock interference and the triple point T, causing a series of expansion waves to form. Finally, an increase in the Mach number, a decrease in the corner compression angle, and a decrease in the wall temperature interfere and reduce the possibility of separating the boundary layer.

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44

Elliott, J. W., and F. T. Smith. "Dynamic stall due to unsteady marginal separation." Journal of Fluid Mechanics 179 (June 1987): 489–512. http://dx.doi.org/10.1017/s0022112087001629.

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A theoretical investigation into the next stage of dynamic stall, concerning the beginnings of eddy shedding from the boundary layer near an aerofoil's leading edge, is described by means of the unsteady viscous-inviscid interacting marginal separation of the boundary layer. The fully nonlinear stage studied in the present paper is shown to match with a previous ‘weakly nonlinear’ regime occurring in the earlier development of the typical eddy from its initially slender thin state. Numerical solutions followed by linear and nonlinear analysis suggest that with confined initial conditions the strong instabilities in the present unsteady flow tend to force a breakdown within a finite time. This leads on subsequently to an unsteady predominantly inviscid stage where the eddy becomes non-slender, spans the entire boundary layer and its evolution then is governed by the Euler equations. This is likely to be followed by the shedding of the eddy from the boundary layer.

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Ali, Kargar, and Mansour Kamyar. "1165 EXPERIMENTAL INVESTIGATION OF BOUNDARY LAYER TRANSITION AND SEPARATION ON ROTATING SPHERE IN AXIAL FLOW." Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2013.4 (2013): _1165–1_—_1165–6_. http://dx.doi.org/10.1299/jsmeicjwsf.2013.4._1165-1_.

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GANAPATHISUBRAMANI, B., N. T. CLEMENS, and D. S. DOLLING. "Low-frequency dynamics of shock-induced separation in a compression ramp interaction." Journal of Fluid Mechanics 636 (September 25, 2009): 397–425. http://dx.doi.org/10.1017/s0022112009007952.

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The low-frequency dynamics of the shock-induced separation region in a Mach 2 compression ramp interaction is investigated by performing high-speed particle image velocimetry (HSPIV) measurements, at a rate of 6kHz, in a streamwise–spanwise plane. The HSPIV measurements made in the upstream turbulent boundary layer indicate the presence of spanwise strips of elongated regions of uniform streamwise velocity that extend to lengths greater than 30δ, validating previous results based on planar laser scattering measurements obtained by Ganapathisubramani, Clemens & Dolling (J. Fluid Mech., vol. 585, 2007, p. 369). At a wall normal-location of y/δ=0.2, a surrogate for separation based on a velocity threshold is found to fluctuate over a streamwise range of ±1.2δ, consistent with previous studies. The amplitude of unsteadiness has contributions from at least two sources that are related to the incoming boundary layer. First, the velocity threshold based surrogate separation line exhibits large-scale undulations along the spanwise direction that conform to the passage of elongated low- and high-speed regions in the upstream boundary layer. This motion is classified as the local influence of the upstream boundary layer. Second, the spanwise-averaged surrogate separation is found to respond to the overall change in streamwise velocity in the incoming boundary layer and is classified as the global influence of the upstream boundary layer. However, this global influence includes the contributions from the elongated low- and high-speed regions. Preliminary findings based on statistical analysis suggest that the local influence contributes nearly 50% more than the global influence. Regardless, the low-frequency unsteadiness of the separation-region can be attributed to the local and global influences of the incoming boundary layer.

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RUBAN, A. I., D. ARAKI, R. YAPALPARVI, and J. S. B. GAJJAR. "On unsteady boundary-layer separation in supersonic flow. Part 1. Upstream moving separation point." Journal of Fluid Mechanics 678 (April 15, 2011): 124–55. http://dx.doi.org/10.1017/jfm.2011.104.

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This study is concerned with the boundary-layer separation from a rigid body surface in unsteady two-dimensional laminar supersonic flow. The separation is assumed to be provoked by a shock wave impinging upon the boundary layer at a point that moves with speed Vsh along the body surface. The strength of the shock and its speed Vsh are allowed to vary with time t, but not too fast, namely, we assume that the characteristic time scale t ≪ Re−1/2/Vw2. Here Re denotes the Reynolds number, and Vw = −Vsh is wall velocity referred to the gas velocity V∞ in the free stream. We show that under this assumption the flow in the region of interaction between the shock and boundary layer may be treated as quasi-steady if it is considered in the coordinate frame moving with the shock. We start with the flow regime when Vw = O(Re−1/8). In this case, the interaction between the shock and boundary layer is described by classical triple-deck theory. The main modification to the usual triple-deck formulation is that in the moving frame the body surface is no longer stationary; it moves with the speed Vw = −Vsh. The corresponding solutions of the triple-deck equations have been constructed numerically. For this purpose, we use a numerical technique based on finite differencing along the streamwise direction and Chebyshev collocation in the direction normal to the body surface. In the second part of the paper, we assume that 1 ≫ Vw ≫ O(Re−1/8), and concentrate our attention on the self-induced separation of the boundary layer. Assuming, as before, that the Reynolds number, Re, is large, the method of matched asymptotic expansions is used to construct the corresponding solutions of the Navier–Stokes equations in a vicinity of the separation point.

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Cassel, K. W., F. T. Smith, and J. D. A. Walker. "The onset of instability in unsteady boundary-layer separation." Journal of Fluid Mechanics 315 (May 25, 1996): 223–56. http://dx.doi.org/10.1017/s0022112096002406.

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The process of unsteady two-dimensional boundary-layer separation at high Reynolds number is considered. Solutions of the unsteady non-interactive boundary-layer equations are known to develop a generic separation singularity in regions where the pressure gradient is prescribed and adverse. As the boundary layer starts to separate from the surface, however, the external pressure distribution is altered through viscous—inviscid interaction just prior to the formation of the separation singularity; hitherto this has been referred to as the first interactive stage. A numerical solution of this stage is obtained here in Lagrangian coordinates. The solution is shown to exhibit a high-frequency inviscid instability resulting in an immediate finite-time breakdown of this stage. The presence of the instability is confirmed through a linear stability analysis. The implications for the theoretical description of unsteady boundary-layer separation are discussed, and it is suggested that the onset of interaction may occur much sooner than previously thought.

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Ramsay, James, Mathieu Sellier, and Wei Hua Ho. "Eliminating Boundary Layer Separation on a Cylinder with Nonuniform Suction." International Journal of Aerospace Engineering 2020 (July 22, 2020): 1–11. http://dx.doi.org/10.1155/2020/9137369.

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Boundary layer separation negatively influences the performance of aerospace vehicles, for example, by triggering static stall or reducing combustion engine efficiency. Developing effective flow control to delay or eliminate separation is therefore of real use to the field. In this paper, numerical studies were carried out to optimise distributed suction profiles for preventing boundary layer separation on a circular cylinder in the fully laminar regime (Re<188), with the least control effort. Relationships were found between the Reynolds number, the separation angle of the uncontrolled case, and the uniform suction needed to eliminate separation. It was found that for Re>20, the uniform suction required to eliminate separation followed a quadratic profile, as a function of Re. Maximum uniform suction effort was needed at Re=20, requiring a suction coefficient of CQ=49.14 (as a percentage of the free-stream velocity) to eliminate separation. To resolve the best nonuniform suction profile at Re=180, a variety of optimisation studies were performed using the coordinate search method. It was determined that the use of six control segments on each half of the cylinder provided the best control and efficient convergence to the optimal solution. 6-segment nonuniform suction eliminated separation at Re=180 with net suction effort of CQ=13.26 compared to CQ=31.25 for the uniform case. These optimal suction profiles were compared using time-dependent simulations to confirm that both methods eliminate separation when introduced to an already unsteady case. Nonuniform suction eliminated separation faster, though uniform suction was more stable.

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Bich Ngoc, Hoang Thi, and Nguyen Manh Hung. "Study of separation phenomenon in transonic flows produced by interaction between shock wave and boundary layer." Vietnam Journal of Mechanics 33, no. 3 (September 8, 2011): 170–81. http://dx.doi.org/10.15625/0866-7136/33/3/210.

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For compressible flows, the transonic state depends on the geometry, Mach number and the incidence. This effect can produce shock wave. Some studies showed that the interaction between shock wave and boundary layer concerns separation phenomenon. Studies in this report demonstrate conditions of separation in transonic flow and that it is not any interaction between shock wave and boundary layer which can cause boundary layer separation. The studies also show that maximum Mach number in the local supersonic region is not a unique factor influencing the separation, and the separation in transonic flows can occur at the incidence of 0$^{\circ}$. For the calculation of viscous transonic flows, we use Fluent software with serious treatment of application operation based on the physical nature of phenomenon and the technique of numerical treatment. For the calculation of invicid transonic flows, we built a code solving the full potential equation with verification for accuracy. Results calculated from Fluent have been seriously compared with results of present program and published results in order to assure the accuracy of application operation in the domain of investigation. separation in transonic flows; shock wave and boundary layer

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Journal articles on the topic 'Boundary-Layer Separation'

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