Showing papers on "Flow separation published in 1985"
TL;DR: In this article, experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step in a diverging channel flow and mean velocities, Reynolds stresses, and triple products that were measured by a laser Doppler velocimeter are presented for two cases of tunnel wall divergence.
Abstract: Experimental data have been obtained in an incompressible turbulent flow over a rearward-facing step in a diverging channel flow. Mean velocities, Reynolds stresses, and triple products that were measured by a laser Doppler velocimeter are presented for two cases of tunnel wall divergence. Eddy viscosities, production, convection, turbulent diffusion, and dissipation (balance of kinetic energy equation) terms are extracted from the data. These data are compared with various eddy-viscosity turbulence models. Numerical calculations incorporating the k-epsilon and algebraic-stress turbulence models are compared with the data. When determining quantities of engineering interest, the modified algebraic-stress model (ASM) is a significant improvement over the unmodified ASM and the unmodified k-epsilon model; however, like the others, it dramatically overpredicts the experimentally determined dissipation rate.
635 citations
TL;DR: In this article, it was shown that at angles up to about 80°, the fluid flows mainly along the furrows on each plate and a secondary, swirling motion is imposed on the flow along a furrow when its path is crossed by streams flowing along furrows along the opposite wall.
354 citations
TL;DR: In this article, the authors present a survey of recent experimental results in such situations and recent results and models are discussed, as well as several new results in various stages of publication.
311 citations
TL;DR: In this paper, the authors summarized the aerodynamic behavior of baseballs and cricket and golf balls and concluded that the side forces, once tripped, will increase with spin velocity up to a cut-off point.
Abstract: Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.
258 citations
TL;DR: A vortex-induced unsteady separation was investigated experimentally in the laminar boundary layer produced by an axisymmetric jet impinging normally onto a flat plate in this article.
Abstract: A vortex-induced unsteady separation was investigated experimentally in the laminar boundary layer produced by an axisymmetric jet impinging normally onto a flat plate. By forcing the air jet, primary ring vortices were periodically generated in the jet shear layer. Phase-locked flow visualization showed that the wall-jet boundary layer separated periodically and evolved into a secondary vortex counter rotating with respect to the primary vortex. The unsteady separation is induced by the primary vortex and moves downstream in the radial mean-flow direction. Phase-averaged hot-wire measurements using a parallel-wire sensor in the vicinity of the unsteady separation provided data for locating the onset of separation in space and time. The data revealed that the unsteady separation originated from a local shear layer which was initiated by the unsteady adverse pressure gradient produced by the primary vortex.
218 citations
TL;DR: In this article, a large, low-speed, aerodynamic model of a high-speed core compressor is designed and fabricated based on aerodynamic similarity principles, and the model is then tested at low speed where high-loss regions associated with three-dimensional endwall boundary layers flow separation, leakage, and secondary flows can be located, detailed measurements made, and loss mechanisms determined with much greater accuracy and much lower cost and risk than is possible in small, high speed compressors.
Abstract: A systematic procedure for reducing losses in axial-flow compressors is presented. In this procedure, a large, low-speed, aerodynamic model of a high-speed core compressor is designed and fabricated based on aerodynamic similarity principles. This model is then tested at low speed where high-loss regions associated with three-dimensional endwall boundary layers flow separation, leakage, and secondary flows can be located, detailed measurements made, and loss mechanisms determined with much greater accuracy and much lower cost and risk than is possible in small, high-speed compressors. Design modifications are made by using custom-tailored airfoils and vector diagrams, airfoil endbends, and modified wall geometries in the high-loss regions. The design improvements resulting in reduced loss or increased stall margin are then scaled to high speed. This paper describes the procedure and presents experimental results to show that in some cases endwall loss has been reduced by as much as 10 percent, flow separation has been reduced or eliminated, and stall margin has been substantially improved by using these techniques.
213 citations
TL;DR: In this paper, a model is presented to describe flow in segments of collapsible tube mounted between two rigid tubes and surrounded by a pressurized container, and the model predicts self-excited oscillations whose amplitude is large enough to be observable only if the flow in the collapsible tubes becomes supercritical.
Abstract: A new model is presented to describe flow in segments of collapsible tube mounted between two rigid tubes and surrounded by a pressurized container. The new features of the model are the inclusion of (a) longitudinal wall tension and (b) energy loss in the separated flow downstream of the time-dependent constriction in a collapsing tube, in a manner which is consistent with the one-dimensional equations of motion. As well as accurately simulating steady-state collapse, the model predicts self-excited oscillations whose amplitude is large enough to be observable only if the flow in the collapsible tube becomes supercritical somewhere (fluid speed exceeding long-wave propagation speed). The dynamics of the oscillations is dominated by longitudinal movement of the point of flow separation, in response to the adverse pressure gradient associated with waves propagating backwards and forwards between the (moving) narrowest point of the constriction and the tube outlet.
184 citations
TL;DR: In this paper, the authors present spectral analysis and flow visualization for various velocity ratios and Reynolds numbers of a jet issuing perpendicularly from a developing pipe flow into a crossflow.
Abstract: Spectral analysis and flow visualization are presented for various velocity ratios and Reynolds numbers of a jet issuing perpendicularly from a developing pipe flow into a crossflow. The results are complete with conditional averages of various turbulent quantities for one jet-to-cross-flow velocity ratio R of 0.5. A unique conditional-sampling technique separated the contributions from the turbulent jet flow, the irrotational jet flow, the turbulent crossflow and the irrotational crossflow by using two conditioning functions simultaneously. The intermittency factor profiles indicate that irrotational cross-flow intrudes into the pipe but does not contribute to the average turbulent quantities, while the jet-pipe irrotational flow contributes significantly to them in the region above the exit where the interaction between the boundary-layer eddies and those of the pipe starts to take place. Further downstream, the contributions of the oncoming boundary-layer eddies to the statistical averages reduce significantly. The downstream development depends mainly on the average relative eddy sizes of the interacting turbulent fields.
182 citations
TL;DR: The classical view of these vortices is sketched in Fig. la and has been discussed by Hoerner and Borst among others as discussed by the authors, with a sharp leading edge at an angle of attack a, the flow is separated along the entire leading edge forming a strong shear layer.
Abstract: Introduction: The Classical View T HE flow over delta wings at an angle of attack is dominated by two large bound vortices that result from the flow separation at the leading edge. The classical view of these vortices is sketched in Fig. la and has been discussed by Hoerner and Borst among others. With a sharp leading edge at an angle of attack a, the flow is separated along the entire leading edge forming a strong shear layer. The shear layer is wrapped up in a spiral fashion, resulting in the large bound vortex as sketched. These vortices appear on the suction surface and increase in intensity downstream. The low pressure associated with the vortices produces an additional lift on the wing, often called nonlinear or vortex lift, which is particularly important at large angles of attack. As sketched in Fig. la, small secondary vortices also appear on the wing near the points of reattachment as a result of the strong lateral flow toward the leading edge.
167 citations
TL;DR: In this paper, a detachment criterion for attached cavitation on a wall with continuous curvature is proposed, which takes into account the link between the cavitating potential flow and the boundary layer.
Abstract: Attached cavitation on a wall with continuous curvature is investigated on the basis of experiments carried out on various bodies (circular and elliptic cylinders, NACA 16 012 foil). Visualization of the boundary layer by dye injection at the leading edge shows that a strong interaction exists between attached cavitation and the boundary layer. In particular, it is shown that the cavity does not detach from the body at the minimum pressure point, but behind a laminar separation, even in largely developed cavitating flow. A detachment criterion which takes into account this link between attached cavitation and boundary layer is proposed. It consists of connecting a cavitating potential-flow calculation and a boundary-layer calculation. Among all the theoretically possible detachment points, the actual detachment point is chosen to be the one for which the complete calculation predicts a laminar separation just upstream. This criterion, applied to the NACA foil, leads to a prediction which is in good agreement with experimental results.
166 citations
TL;DR: In this paper, an experimental study of the Lissaman 7769 and Miley MO6-13-128 airfoils at low chord Reynolds numbers is presented, and the influence of disturbance environment and experimental procedure on the low Reynolds number airfoil boundary layer behavior is also presented.
Abstract: An experimental study of the Lissaman 7769 and Miley MO6-13-128 airfoils at low chord Reynolds numbers is presented. Although both airfoils perform well near their design Reynolds number of about 600,000, they each produce a different type of hysteresis loop in the lift and drag forces when operated below chord Reynolds numbers of 300,000. The type of hysteresis loop was found to depend upon the relative location of laminar separation and transition. The influence of disturbance environment and experimental procedure on the low Reynolds number airfoil boundary layer behavior is also presented. The use of potential flow solutions to help predict how a given airfoil will behave at low Reynolds numbers is also discussed.
TL;DR: In this article, the results of turbulence measurements on an infinite swept wing, simulated by a duct attached to a blower tunnel, are presented, showing a significant decrease in the magnitude of shear stress compared with an equivalent two-dimensional boundary layer.
Abstract: The results are presented of turbulence measurements on an ‘infinite’ swept wing, simulated by a duct attached to a blower tunnel. The configuration is close to that used at the Netherlands NLR except that the boundary layer does not quite separate. The measurements include triple products, and a balance of the transport equation for turbulent energy is presented. The results confirm the NLR finding of a significant decrease in the magnitude of shear stress compared with an equivalent two-dimensional boundary layer: this is evidently the effect of crossflow on large eddies that have initially developed in a two-dimensional boundary layer. This unexpected effect of three-dimensionality is at least as important in prediction of real-life flows as the better-known lag between the direction of the shear stress and that of the mean-velocity gradient. Tentative suggestions for modelling the reduction in shear-stress magnitude are advanced.
TL;DR: In this article, the authors proposed several means for visualizing large-scale vortex structure in a turbulent mixing layer, where the observations are recorded along the low-speed side of the mixing layer and external to the rotational portion of the flow.
Abstract: Several means for visualizing large-scale vortex structure in a turbulent mixing layer are proposed. Most of the observations are recorded along the low-speed side of the mixing layer, external to the rotational portion of the flow. Conventional correlation measurements in both the streamwise and spanwise directions indicate that the vortex structure becomes independent of the downstream coordinate in a non-dimensional distance of order λx/θi = 300–400, where is the speed ratio and θi is the initial integral thickness. Simultaneous hot-wire measurements at 12 spanwise positions allow computer reconstruction of the velocity field as a function of span and time. These visualizations show the vortex structures to be primarily aligned across the span of the flow, but to contain irregularities. Spanwise correlation lengths are of the order of 3–5δω (δω is the local vorticity thickness). However, the large vortices typically have lengths of order 20δω when the irregularities along the span are ignored.
01 Jan 1985
TL;DR: In this article, a new and improved wall function method for compressible turbulent flows has been developed and tested, which is applicable to attached and separated flows, to both high and low Reynolds number flows, and to flows with adiabatic and nonadiabatic surfaces.
Abstract: A new and improved wall function method for compressible turbulent flows has been developed and tested. This method is applicable to attached and separated flows, to both high- and low-Reynolds number flows, and to flows with adiabatic and nonadiabatic surfaces. This wall function method has been applied to the Launder-Spalding k-epsilon two-equation model of turbulence. The tests consist of comparisons of calculated and experimental results for: (1) an axisymmetrical transonic shock-wave/boundary-wave interaction flow at low Reynolds number in an adiabatic tube, (2) an axisymmetrical high-Reynolds number transonic flow over a nonadiabatic bump, and (3) a two-dimensional supersonic high-Reynolds number flow on a nonadiabatic deflected flap. Each of these experiments had significant regions of flow separation. The calculations are performed with an implicit algorithm that solves the Reynolds-averaged Navier-Stokes equations. It is shown that the results obtained agree very well with the data for the complex compressible flows tested.
TL;DR: In this article, the influence of periodic perturbations on the development of two-dimensional free shear layers generated by a splitter plate was investigated in cases where the ratios of the two velocities u1 and u2 either side of the plate were such that 0 < u1/u2 < 1.
Abstract: The influence of periodic perturbations on the development of two-dimensional free shear layers generated by a splitter plate was investigated in cases where the ratios of the two velocities u1 and u2 either side of the splitter plate were such that 0 < u1/u2 < 1. Investigations were carried out in both a suction and a blower wind tunnel. Results show that even very weak periodic perturbations caused by the wind tunnel may cause significant nonlinear spreading in the downstream development of the shear layer, a behaviour which is also observed when the shear layer is deliberately excited. Other things being equal, the effect of the disturbance is greater when flow separation at the splitter plate is turbulent than when it is laminar.No self-induced feedback frequencies were measured in the test section. All tonal components that were detected in the flow could be traced to external sources.The influence of trailing-edge thickness on the shear-layer development is found to become significant when it exceeds 50% of the sum of boundary-layer displacement thickness at the point of separation. As the trailing edge becomes thicker, the range over which the shear layer is self-similar is shifted farther downstream. This behaviour may be crucial for predicting the evolution of shear layers in high-speed flows having thin boundary layers at separation.The momentum thickness criterion for estimating the development length of the flow as suggested by Bradshaw is shown to be insufficient for two-stream layers, where additional parameters, e.g. the trailing-edge geometry, have to be taken into account. Discrepancies between previously published observations of shear layers, as well as the considerable scatter in reported measurements, may therefore, to a large extent, be attributable to contamination of the experimental facility.
01 Jan 1985
TL;DR: Etude d'ecoulements sur un gradient tourne vers l'amont and sur un gradin tournevers l'aval are presented in this paper, where they describe the relationship between two gradients.
Abstract: Etude d'ecoulements sur un gradient tourne vers l'amont et sur un gradin tourne vers l'aval
TL;DR: In this paper, a low-speed turbulent boundary layer in zero pressure gradient with an isolated, artificially generated vortex imbedded in it is studied, showing that the circulation around the vortex is almost conserved, being reduced only by the spanwise-component surface shear stress.
Abstract: Detailed mean-flow and turbulence measurements have been made in a low-speed turbulent boundary layer in zero pressure gradient with an isolated, artificially generated vortex imbedded in it. The vortex was generated by a half-delta wing on the floor of the wind-tunnel settling chamber, so that the vortex entering the working section had the same circulation as that originally generated, while axial-component velocity variations were very much reduced, relative to the local mean velocity, from values just behind the generator. The measurements show that the circulation around the vortex imbedded in the boundary layer is almost conserved, being reduced only by the spanwise-component surface shear stress. Therefore the region of flow affected by the vortex continues to grow downstream, its cross-sectional dimensions being roughly proportional to the local boundary-layer thickness. The behaviour of the various components of eddy viscosity, deduced from measured Reynolds stresses, and of the various triple products, suggests that the simple empirical correlations for these quantities used in present-day turbulence models are not likely to yield flow predictions which are accurate in detail.
TL;DR: In this paper, the influence of periodic excitation on a plane turbulent one-stream shear layer with turbulent separation was investigated, and it was found that sinusoidal perturbations with frequencies of order f0 [lsim ] u0/100θ0 (depending on excitation strength), introduced at the trailing edge are always amplified.
Abstract: The influence of periodic excitation on a plane turbulent one-stream shear layer with turbulent separation was investigated. For the qualitative study flow visualization was employed. Quantitative data were obtained with hot-wire anemometry and spectrum analysis. It was found that sinusoidal perturbations with frequencies of order f0 [lsim ] u0/100θ0 (depending on excitation strength), introduced at the trailing edge are always amplified. Maximum amplification factors are observed for the lowest perturbation levels. The frequency and amplitude of excitation determine the downstream location of the amplification maximum in the flow. At sufficient amplitude two-dimensional vortices are formed which subsequently decay without pairing. The development of the periodic r.m.s. values along x follows a universal curve for all frequencies and amplitudes when properly normalized.At high excitation amplitudes the flow development depends strongly on the geometrical conditions of the excitation arrangement at the trailing edge. Thus regular vortex pairing as well as suppression of pairing can be achieved.The excited shear layer has considerably stronger, yet nonlinear, spread than the neutral. The region of vortex formation, irrespective of whether it includes pairing or not, is associated with a step-like increase in width, while after the position of maximum vortex energy, i.e. in the region of decay, the spread is reduced to values below the neutral. There the overall lateral fluctuation energy is increased, while the longitudinal may be decreased as compared with the neutral flow.
12 Mar 1985
01 Feb 1985
TL;DR: In this paper, the authors present the present status and future possibility of airfoil design and evaluation at subcritical speeds to meet the needs for these applications, including remotely piloted vehicles (RPV's), sailplanes, ultra-light man-carrying/man-powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers.
Abstract: : Recent interest in a wide variety of low Reynolds number configurations has focused attention on the design and evaluation of efficient airfoil sections at chord Reynolds numbers from about 100,000 to about 1,000, 000. These configurations include remotely piloted vehicles (RPV's) at high altitudes, sailplanes, ultra-light man-carrying/man-powered aircraft, mini-RPVs at low altitudes and wind turbines/propellers. A study is presented of the present status and future possibility of airfoil design and evaluation at subcritical speeds to meet the needs for these applications. Although the design and evaluation techniques for airfoil sections above chord Reynolds numbers of 500,000 is reasonably well developed, serious problems related to boundary layer separations and transition have been encountered below RC = 500,000. Presently available design and analysis methods need to improve their criteria for laminar separation, transition, and turbulent separation. Improved mathematical models of these complex phenomena require additional, very careful experimental studies. Because of the sensitivity of the low Reynolds number airfoil boundary layer to free stream and surface-generated disturbances, definitive experiments are very difficult. Also the physical quantities measured (i.e., pressure difference and drag forces etc.) are very small and the accuracy of such measurements depends on the method used. The results from numerous experimental studies are presented to illustrate the type of difficulties encountered.
TL;DR: In this paper, a two-dimensional local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been extended for the calculation of transition separation bubbles over infinite swept wings.
Abstract: A previously developed two-dimensional local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been extended for the calculation of transitional separation bubbles over infinite swept wings. As part of this effort, Roberts' empirical correlation, which is interpreted as a separated flow empirical extension of Mack's stability theory for attached flows, has been incorporated into the ALESEP procedure for the prediction of the transition location within the separation bubble. In addition, the viscous procedure used in the ALESEP techniques has been modified to allow for wall suction. A series of two-dimensional calculations is presented as a verification of the prediction capability of the interaction techniques with the Roberts' transition model. Numerical tests have shown that this two-dimensional natural transition correlation may also be applied to transitional separation bubbles over infinite swept wings. Results of the interaction procedure are compared with Horton's detailed experimental data for separated flow over a swept plate which demonstrates the accuracy of the present technique. Wall suction has been applied to a similar interaction calculation to demonstrate its effect on the separation bubble. The principal conclusion of this paper is that the prediction of transitional separation bubbles over two-dimensional or infinite swept geometries is now possible using the present interacting boundary layer approach.
TL;DR: In this article, a detailed experimental investigation has been carried out on the effects of different types of screens on turbulent flow, in particular turbulent boundary layers, and the aerodynamic properties of plastic screens are found to differ significantly from those of the conventional metal screens.
Abstract: A detailed experimental investigation has been carried out on the effects of different types of screens on turbulent flow, in particular turbulent boundary layers. The boundary-layer turbulence is reorganized and the thickness reduced, thus making it less susceptible to separation. The aerodynamic properties of plastic screens are found to differ significantly from those of the conventional metal screens. The "overshoot" in mean velocity profile near the boundary-layer edge is shown to be a result of the effect of screen inclination on pressure drop coefficient. A more accurate formulation for the deflection coefficient of a screen is also proposed.
01 Jan 1985
TL;DR: In this article, the heat transfer mechanism and associated turbulence structure in the near-wall region of a turbulent boundary layer have been investigated experimentally with the aid of temperature sensitive liquid crystal and hydrogen bubble method.
Abstract: Heat transfer mechanism and associated turbulence structure in the near-wall region of a turbulent boundary layer have been investigated experimentally. With the aid of temperature-sensitive liquid crystal and hydrogen bubble method, the wall temperature fluctuation and the flow structure are visualized simultaneously to study directly the heat exchange between the fluid and the wall. The structure of the temperature field near the wall is further studied by the measurement of cross correlation of temperature fluctuations in the spanwise and streamwise directions. All of these experimental results show that the turbulent temperature field near the wall has a feature very much similar to the flow structure in the viscous wall region, e.g., the streamwise elongated structure with a quasiperiodicity in the spanwise direction, and are compatible with what is known about the streamwise sublayer vortices previously studied.
TL;DR: In this paper, the relative importance of the terms in the transport equations for mean momentum and turbulence energy are quantified and the implications for procedures which solve potential-flow and boundary-layer equations and for alternative calculation methods are discussed.
Abstract: Experimental techniques, including flying-hot-wire anemometry, have been used to determine the pressure and velocity characteristics of a flow designed to simulate the trailing-edge region of an airfoil at high angle of attack. Emphasis is placed on the region of recirculating flow and on the downstream wake. It is shown that the effect of this recirculation is large even though the details of the flow within it may be unimportant. Normal stresses and cross-stream pressure gradients are important immediately upstream and downstream of the recirculating flow and are associated with strong streamline curvature. The relative importance of the terms in the transport equations for mean momentum and turbulence energy are quantified and the implications for procedures which solve potential-flow and boundary-layer equations and for alternative calculation methods are discussed.
TL;DR: In this article, the mean and fluctuating velocities in a turbulent boundary layer on a cylinder have been experimentally characterized for the case where the boundary layer is thick compared to the radius of transverse curvature.
Abstract: The mean and fluctuating velocities in a turbulent boundary layer on a cylinder have been experimentally characterized for the case where the boundary layer is thick compared to the radius of transverse curvature. The mean velocity measurements suggest a mixed scaling for the ‘‘log law of the wall’’ using the wall coordinate yUτ/ν and the ratio of the local boundary layer thickness to the radius of the cylinder δ/a. A relation for the slope and intercept of the log law of the wall as functions of δ/a based on empirical results and simple analysis is presented. Measurements of the Reynolds stress for δ/a of order 10 show that the Reynolds stress drops off much more quickly with distance from the wall than for a turbulent boundary layer on a flat plate. Both the Reynolds stress data and the turbulent intensity in the mean flow direction data are functions of the inverse radial distance from the center of the cylinder.
TL;DR: In this paper, the nature of the viscous boundary-layer flow induced near a wall, caused by a pair of counter-rotating vortices above the wall, is investigated.
Abstract: The nature of the viscous boundary‐layer flow induced near a wall, caused by a pair of counter‐rotating vortices above the wall, is investigated. Solutions for the unsteady flow that develops near the wall are obtained numerically for a variety of cases. The vortices are taken to be of equal strength with cores located at equal distances from the wall; depending upon the assumed sense of rotation, the vortices either move toward the wall or recede from it, creating a region of either inflow or outflow near the wall, respectively. The calculated results show that the adverse pressure gradient near the wall induced by the vortex motion gives rise to explosively growing regions of recirculating flow near the wall. The possible relevance of these results to Gortler vortex instability and turbulent flow near walls is discussed.
TL;DR: In this paper, the boundary layer separation upstream of cylinders mounted normal to a flat plate leads to the formation of horseshoe vortices around the bases of these cylinders, which can be either laminar or turbulent, depending upon the state of the upstream boundary layer.
01 Jan 1985
TL;DR: In this paper, an experimental study of the unsteady nature of a shock wave/turbulent boundary layer interaction using an unswept compression ramp was carried out, where an array of flush mounted miniature high frequency pressure transducers was used to make multi-channel measurements of the fluctuating wall pressure within the interaction.
Abstract: This paper presents the results of an experimental study of the unsteady nature of a shock wave/turbulent boundary layer interaction. The interaction was generated using an unswept compression ramp. The incoming freestream Mach number was 2.9 and the flow was separated at the corner. An array of flush mounted miniature high frequency pressure transducers was used to make multi-channel measurements of the fluctuating wall pressure within the interaction. From the present results, an overall picture of the instantaneous structure of the unsteady shock system (as inferred from the wall pressure signals) can be constructed. The flow ahead of the corner can be considered as composed of two regions, namely the 'intermittent' region where there is essentially a single leading shock which exhibits significant streamwise 'flapping' and spanwise 'rippling', and the separated region where the flow experiences continuous compression.
TL;DR: In this paper, the effect of rotation on low-Reynolds-number turbulent boundary layers developing in a zero pressure gradient on the sidewall of a duct was examined and the mean-velocity profiles affected by rotation were described in terms of a common universal sublayer and modified logarithmic and wake regions.
Abstract: Measurements are presented for low-Reynolds-number turbulent boundary layers developing in a zero pressure gradient on the sidewall of a duct. The effect of rotation on these layers is examined. The mean-velocity profiles affected by rotation are described in terms of a common universal sublayer and modified logarithmic and wake regions.The turbulence quantities follow an inner and outer scaling independent of rotation. The effect appears to be similar to that, of increased or decreased layer development. Streamwise-energy spectra indicate that, for a given non-dimensional wall distance, it is the low-wavenumber spectral components alone that are affected by rotation.Large spatially periodic spanwise variations of skin friction are observed in the destabilized layers. Mean-velocity vectors in the cross-stream plane clearly show an array of vortex-like structures which correlate strongly with the skin-friction pattern. Interesting properties of these mean-flow structures are shown and their effect on Reynolds stresses is revealed. Near the duct centreline, where we have measured detailed profiles, the variations are small and there is a reasonable momentum balance.Large-scale secondary circulations are also observed but the strength of the pattern is weak and it appears to be confined to the top and bottom regions of the duct. The evidence suggests that it has minimally affected the flow near the duct centreline where detailed profiles were measured.