Showing papers on "Flow separation published in 1968"
TL;DR: In this article, a finite-difference solution to the problem of the interaction between an impinging shock wave and the laminar boundary layer on a flat plate is presented, where boundary layer equations are used to calculate the flow with the Prandtl-Meyer formula being used to determine the pressure.
Abstract: A finite-difference solution to the problem of the interaction between an impinging shock wave and the laminar boundary layer on a flat plate is presented. The boundary-layer equations are used to calculate the flow with the Prandtl-Meyer formula being used to determine the pressure. Two different methods for calculating the region of separated flow are discussed. Comparisons between this theory and experimental results show good agreement. The effects of the viscosity and heat-conduction relationships on the calculated results are determined. Diagrams show the influence of the Mach number and the displacement thickness of the boundary layer at the start of the interaction on the pressure distribution. The insulated plate and the plate with given temperature are considered.
281 citations
TL;DR: In this paper, the authors describe a study concerning the sonic injection of a gaseous jet through a transverse slot nozzle in a wall into an external flow which is uniform outside of a turbulent boundary layer.
Abstract: The paper describes a study concerning the sonic injection of a gaseous jet through a transverse slot nozzle in a wall into an external flow which is uniform outside of a turbulent boundary layer. An analytic model of the flowfield has been constructed in which conservation of
momentum is applied to a control volume at the jet nozzle exit. A series of flat-plate experiments was conducted with normal, sonic jets at external flow Mach numbers of 2.61, 3.50, and 4.54. Pressure data near separation and the plateau were in agreement with existing correlations. Comparisons of the trends predicted by the analysis with two-dimensional force data from these experiments and from other sources showed good agreement. Values
of amplification factor, the upstream interaction force plus the jet thrust divided by the vacuum thrust of a sonic jet, of 2.9 to 3.2 were measured. The amplification factor is relatively insensitive to variations in external flow Mach number and variations in injectant gas properties. A correlation of data obtained from experiments with finite-span slots demonstrates that the effective jet penetration height and the slot span are the important characteristic
dimensions of such flowfields.
238 citations
Patent•
09 Jul 1968TL;DR: Boundary layer control for delay or prevention of flow separation and increase in rate of heat exchange between a surface and a fluid by an arrangement of surface elements which may take the form of either crests or discreet concave depressions in the surface, having effective depths or dimensions of less that of the adjacent boundary layer thickness, to cause the formation of vortices with succeeded surface elements being positioned to cause vortex amplification, for effective boundary layer mixing with less drag, weight penalty, noise, and energy loss than that of conventional vane-type generators as mentioned in this paper.
Abstract: Boundary layer control for delay or prevention of flow separation and/or increase in rate of heat exchange between a surface and a fluid by an arrangement of surface elements which may take the form of either crests or discreet concave depressions in the surface, having effective depths or dimensions of less that of the adjacent boundary layer thickness, to cause the formation of vortices with succeeded surface elements being positioned to cause vortex amplification, for effective boundary layer mixing with less drag, weight penalty, noise, and energy loss than that of conventional vane-type generators.
208 citations
TL;DR: In this paper, a criterion for the onset of reverse transition has been deduced in terms of the mean shear-stress gradient in the wall region of the flow, which is quite general applicable to all fully turbulent shear flows.
Abstract: It has been shown experimentally that quite large departures occur from the universal inner-law velocity distribution in the presence of severe favourable pressure gradients in turbulent boundary layers and that these departures are associated with the tendency for the turbulent boundary layer to revert to a laminar state. From the measurements a criterion for the onset of reverse transition has been deduced in terms of the mean shear-stress gradient in the wall region of the flow. Experiments in fully developed pipe and channel flows suggest that the proposed criterion may be quite generally applicable to all fully turbulent shear flows.
167 citations
TL;DR: In this paper, the boundary layer separation associated with a compression corner was investigated in the GALCIT Mach 6 wind tunnel, and a supplementary study was performed in the JPL supersonic wind tunnel.
Abstract: An experimental investigation of the boundary layer separation associated with a compression corner was conducted in the GALCIT Mach 6 wind tunnel, and a supplementary study was performed in the JPL supersonic wind tunnel. Special emphasis was placed on the development of a wind tunnel model which approximated true two-dimensional flow, and which could be run in either a highly cooled or an adiabatic configuration. The basic measurements consist of the model surface pressure and temperature, and Pitot surveys of the boundary layer. The surface pressure distributions for the adiabatic wall configurations are compared with the theory of Lees and Reeves (modified by Klineberg and Lees). The surface pressure distribution for the cold wall was compared with the adiabatic configuration for a laminar interaction, and the dependence on Reynolds number for both laminar and transitional interactions are observed. The "free interaction" similarity suggested by Chapman is empirically tested and found to be a good approximation for the adiabatic configuration, but it fails to correlate the cooled with the adiabatic case. The scaling suggested by Curle was tested and found to eliminate this deficiency.
160 citations
TL;DR: In this paper, the authors measured the distributions of pressure on a bluff flat plate (fence) correlated with the characteristics of the smooth-wall boundary layer in which it is immersed, and found that the relative extent of upstream influence of the bluff-plate on the boundary layer was found to increase rapidly as h/δ decreases.
Abstract: Measurements of the distributions of pressure on a bluff flat plate (fence) have been correlated with the characteristics of the smooth-wall boundary layer in which it is immersed. For zero pressure-gradient flows, correlations are obtained for the variation of form drag with plate height h which are analogous in form to the ‘law of the wall’ and the ‘velocity-defect law’ for the boundary-layer velocity profile. The data for adverse pressure-gradient flows is suggestive of a ‘law of the wake’ type correlation. Pressures on the upstream face of the bluff-plate are determined by a wall-similarity law, even for h/δ > 1, and are independent of the pressure-gradient history of the flow; the separation induced upstream is apparently of the Stratford-Townsend type. The effects of the history of the boundary layer are manifested only in the flow in the rear separation bubble, and then only for h/δ > ½. The base pressure is also sensitive to free-stream pressure gradients downstream of the bluff-plate. The relative extent of upstream influence of the bluff-plate on the boundary layer is found to increase rapidly as h/δ decreases. One set of measurements of the mean flow field is also presented.
160 citations
129 citations
TL;DR: In this paper, the authors show that the rate of heat transfer in a supersonic, turbulent, boundary layer on a concave wall is increased by the streamwise curvature of the wall.
Abstract: Experiments described here show that the rate of heat transfer in a supersonic, turbulent, boundary layer on a concave wall is increased by the streamwise curvature of the wall. For the arrangement investigated, the pressure is kept constant along the wall, and the increase of about 20% is therefore only due to the wall curvature. For a convex wall, a comparable decrease was found, also with constant pressure along the wall.It is likely that this change in heat-transfer rate is mainly due to an increase or decrease of turbulent mixing by the effect of the curvature. The increase on a concave wall can in principle also be explained by large-scale vortices with axes in the flow direction (Gortler vortices). However, disturbances of this type cannot explain the decrease observed on the convex wall. They cannot therefore be the only cause.A simple criterion indicating the effect of curvature on the turbulent motion normal to the wall is given. It is derived from an inviscid-flow analysis. The criterion shows that, for most Mach numbers and wall temperatures of practical interest, the change in mixing depends mainly on the velocity gradient normal to the wall. For high supersonic and hypersonic Mach numbers, however, there is a layer near the outer edge of the boundary layer where the change depends mainly on the temperature (density) gradient.
116 citations
TL;DR: In this article, the laminar flow of a homogeneous viscous liquid in the inlet of a pipe is investigated numerically for a range of small and moderate Reynolds numbers where the boundary layer approximation is inapplicable.
Abstract: The laminar flow of a homogeneous viscous liquid in the inlet of a pipe is investigated numerically for a range of small and moderate Reynolds numbers where the boundary layer approximation is inapplicable. Velocity profiles and other characteristics of the flow are calculated and the results compared with approximate results obtained by other methods. The limiting case of vanishingly small Reynolds number is also treated analytically.
100 citations
TL;DR: In this paper, a simple model is developed to investigate some of the features of the surface boundary layer of a hurricane, where the flow above the friction layer is represented by a steady cylindrical vortex in which there is gradient flow, specified by suitably choosing the radial pressure profile.
Abstract: A simple model is developed to investigate some of the features of the surface boundary layer of a hurricane. The flow above the friction layer is represented by a steady cylindrical vortex in which there is gradient flow, specified by suitably choosing the radial pressure profile. It is assumed that the flow in the main vortex is approximately geostrophic at large distances from the centre and the Ekman solution is taken as appropriate for the boundary layer flow at these distances. A momentum integral method is used to follow the boundary layer development to the centre regions of the vortex. Radial profiles of boundary layer thickness and induced vertical veolocity are obtained when a constant eddy viscosity, K M , is taken as characteristic of the turbulence in the friction layer. Two surface boundary conditions are examined; the no-slip condition and the condition that the surface stress be in the direction of the surface wind. The former of these is found to be the more satisfactory and gives qualitative agreement with observations. The effects of radial and vertical variations of K M are discussed in relation to the surface condition but an inadequate knowledge of the turbulent structure prevents a more realistic formulation of the layer at this stage. DOI: 10.1111/j.2153-3490.1968.tb00388.x
91 citations
TL;DR: Herrmann, J. et al. as mentioned in this paper presented statistical properties of the Turbulent Wake behind Hypervelocity Spheres, The Physics of Fluids, Vol. 6, No. 10, Oct. 1968, pp. 2027-2029.
Abstract: Turbulent and Laminar Wakes," AIAA Journal, Vol. 6, No. 10, Oct. 1968, pp. 2027-2029. 16 Clay, W. G., Herrmann, J., and Slattery, R. E., "Statistical Properties of the Turbulent Wake behind Hypervelocity Spheres," The Physics of Fluids, Vol. 8, 1965, pp. 1792-1801. 17 Schapker, R. L., "Statistics of High Speed Turbulent Wake Boundaries," AIAA Journal, Vol. 4, No. 11, Nov. 1966, pp. 1979-1987. is Herrmann, J. et al., "Some Statistical Properties of Turbulent Wakes," Specialists' Meeting of the Fluid Dynamics Panel of AGARD, AGARD Conference Proceedings 19, 1967. 19 Townsend, A. A., The Structure of Turbulent Shear Flows, Cambridge University Press, London, 1956. 20 Demetriades, A., "Turbulence Measurements in an Axisymmetric Compressible Wake," Tech. Rept. Pub. UG-4118, Aug. 1967, Philco-Ford Corp. 21 Becker, H. A., Hottel, A. C., and Williams, G. C., "The Nozzle-fluid Concentration Field of the Round, Turbulent, Free Jet," Journal of Fluid Mechanics, Vol. 30, No. 2, 1967, pp. 285303.
TL;DR: In this article, a boundary layer formed adjacent to the free surface, and a classical boundary-layer analysis is applied to find the flow there (for moderate distances downstream); the influence of this boundary layer on the flow in the core of the jet is then investigated.
Abstract: This paper is concerned with the jet of liquid, open to the atmosphere, that emerges from a two-dimensional channel in which there is Poiseuille flow far upstream, the flow being driven by an applied pressure gradient. The problem is discussed with the aid of the method of matched asymptotic expansions; the small parameter involved is the inverse Reynolds number. A boundary layer forms adjacent to the free surface, and a classical boundary-layer analysis is applied to find the flow there (for moderate distances downstream); the influence of this boundary layer on the flow in the core of the jet is then investigated. Higher-order boundary-layer effects, such as indeterminacy and eigensolutions, are also discussed. The first few terms are found of an asymptotic expansion for the equation of the free surface, and considerations of momentum balance are applied to find the asymptotic contraction ratio of the jet.
01 Sep 1968
TL;DR: In this article, the model of a bubble growing progressively from the foot of the shock towards the trailing edge does not include the interaction that sometimes occurs between the disturbance at the bottom of the bubble and a subsonic-type rear separation if one exists, or is incipient, in the continuous adverse gradient further downstream.
Abstract: : Attention is drawn to important restrictions to the range of applicability of the flow model developed in earlier work on shock-induced separation of turbulent boundary-layers on aerofoils and wings, and also corresponding restrictions to the conclusion then drawn that full-scale behaviour could readily be reproduced at low Reynolds numbers These restrictions arise because the model of a bubble growing progressively from the foot of the shock towards the trailing edge does not include the interaction that sometimes occurs between the disturbance at the foot of the shock and a subsonic-type rear separation if one exists, or is incipient, in the continuous adverse gradient further downstream Such interactions are shown to be of increasing importance at wind-tunnel scale (as the possibilities of using thicker and more highly loaded wing sections develop) and to introduce real difficulties in reproducing full-scale behaviour at low or moderate Reynolds numbers (Author)
TL;DR: In this paper, a cylindrical protuberance mounted on a flat plate will cause the plate boundary layer to separate if the cylinder is long compared to the boundary-layer height.
Abstract: A cylindrical protuberance mounted on a flat plate will cause the plate boundary layer to separate if the cylinder is long compared to the boundary-layer height. Tests made at M = 4.9 using an oil-flow technique are employed to determine the upstream extent of cylinder influence on a turbulent boundary layer. The results are found to be in reasonable agreement with data from other investigators for a wide range of flow conditions. A method is given for determining the angle of the oblique shock wave caused by separation. This permits calculation of the location of the triple point of the lambda shock pattern that characterizes the flow. An approximate method of calculating the peak value of the cylinder stagnation pressure and the location of the peak is also presented.
TL;DR: In this article, an approximation that can be used to determine how swirl affects the choking constraint on flow through the throat of a nozzle is obtained, consistent with an experimentally observed flow pattern that contains a recirculating internal cell upstream of the throat.
Abstract: An approximation that can be used to determine how swirl affects the choking constraint on flow through the throat of a nozzle is obtained. The flow model is consistent with an experimentally observed flow pattern that contains a recirculating internal cell upstream of the throat. Results of the approximation are applied to three different flow situations. First, it is found that the choking constraint imposes a limit on the maximum tangential Mach number that can be achieved in a vortex tube even when an infinite pressure ratio is available. Next, analytic expressions are derived for the variation of rocket mass flow in a spinning rocket. The last application is the prediction of a performance curve for a fluidic vortex valve that is consistent with limited experimental data.
TL;DR: In this article, an experimental and analytical study of the separation of a turbulent boundary layer is reported, and two distinct turbulent separation regions, an intermittent and a steady separation, with correspondingly different velocity distributions are confirmed.
Abstract: An experimental and analytical study of the separation of a turbulent boundary layer is reported. The turbulent boundary-layer separation model proposed by Sandborn & Kline (1961) is demonstrated to predict the experimental results. Two distinct turbulent separation regions, an intermittent and a steady separation, with correspondingly different velocity distributions are confirmed. The true zero wall shear stress turbulent separation point is determined by electronic means. The associated mean velocity profile is shown to belong to the same family of profiles as found for laminar separation. The velocity distribution at the point of reattachment of a turbulent boundary layer behind a step is also shown to belong to the laminar separation family.Prediction of the location of steady turbulent boundary-layer separation is made using the technique employed by Stratford (1959) for intermittent separation.
TL;DR: The effect of large mass injection on the compressible, similar laminar boundary with favorable pressure gradient has been examined in this article, where the boundary layer may be divided into two regions: an inner region adjacent to the surface where the viscosity plays a minor role, and a viscous layer where the transition occurs from the inner layer to the inviscid flow outside the boundary surface.
Abstract: The effect of large mass injection on the compressible, similar laminar boundary with favorable pressure gradient has been examined. It is found that for high rates of injection, the boundary layer may be divided into two regions: 1) an inner region adjacent to the surface where the viscosity plays a minor role, 2) the viscous layer where the transition occurs from the inner layer to the inviscid flow outside the boundary layer. Matched asymptotic expansions appropriate for large injection rates have'been constructed for each layer and a uniformly valid solution has been obtained. In the case of the insulated wall, it turns out that the viscous outer layer contributes only small corrections to properties of the boundary layer. In the case of the highly cooled wall, on the other hand, the boundary layer is dominated by the viscous mixing between the inviscid outer flow and the high-density, low-speed gas adjacent to the wall. Simple expressions for heat-transfer rates, skin friction, and approximations for integral properties of the boundary layer have been derived, which are useful in future application in nonsimilar boundary-layer calculations.
TL;DR: In this article, the authors presented numerical computations of exhaust plume flow fields from nozzles with boundary layers along the wall, and treated the problem as the inviscid expansion of a shear flow around the nozzle lip, in a manner reminiscent of treatments of the near wakes of reentry vehicles.
Abstract: Numerical computations of exhaust plume flowfields from nozzles with boundary layers along the wall are presented. The problem is treated as the inviscid expansion of a shear flow around the nozzle lip, in a manner reminiscent of treatments of the near wakes of reentry vehicles. The low-Mach-number gas near the wall expands well beyond the limiting line calculated without boundary-layer effects, and "observables" such as dynamic pressure are greatly increased in the large-angle region over the values predicted for a frictionless nozzle flow. The distributions of dynamic pressure in the large-angle region are not greatly sensitive to the details of the boundary-layer profiles at the exit plane, although there is a noticeable difference in behavior between laminar and turbulent layers. Large-angle (up to 90-100°) effects of fully developed laminar or turbulent layers probably can be predicted to within a factor of 2 or 3, whereas there are order-of-magnitude differences from the flow with no boundary layer.
TL;DR: Laminar compressible boundary layer equations solved by quasi-linearization, considering pressure gradients and hypersonic layers, were solved in this paper, where a quasilinearization method was used to solve the boundary layer equation.
Abstract: Laminar compressible boundary layer equations solved by quasi-linearization, considering pressure gradients and hypersonic layers
TL;DR: In this article, a free-flight simulation was conducted in a range, thereby circumventing the wind tunnel effects, and it has resulted in a demonstration of the variation of transition Reynolds number with range pressure (or unit Reynolds number) under conditions of fixed Mach number and average wall temperature ratio.
Abstract: : For at least 15 yrs it has been known that the Reynolds number characterizing transition form laminar to turbulent boundary-layer flow (based on local properties and wetted length to transition) may be influenced by the local unit Reynolds number or some still unidentified, related quantity under both subsonic and supersonic conditions. Because examples of this were available almost exclusively from wind tunnel work, and because of the possibility that free-stream disturbances were responsible, there has been uncertainty as to whether the so-called unit Reynolds number effect exists in atmospheric free flight. The study described in the report was conducted in a free-flight range, thereby circumventing 'wind tunnel effects,' and it has resulted in a demonstration of the variation of transition Reynolds number with range pressure (or unit Reynolds number) under conditions of fixed Mach number and average wall temperature ratio. Some preliminary measurements of sound pressures in the range air are reported for comparison with published results for wind tunnels.
TL;DR: Study in vitro of the pulsatile flow of human whole blood through branched tubes indicates the presence of boundary layer separation at the point of bifurcation, and implications of the relevance of velocity fluctuations in the region of separation are discussed.
TL;DR: In this article, two approaches to the prediction of turbulent boundary-layer development in compressible flow are explored, starting from Head's semi-empirical method for incompressible flow.
Abstract: Starting from Head's semi-empirical method for incompressible flow, two approaches to the prediction of turbulent boundary-layer development in compressible flow are explored. The first uses Head's incompressible method in conjunction with a compressibility transformation similar to Stewartson's transformation for laminar flow; the second carries over Head's physical arguments to treat the compressible flow directly. Measurements in supersonic flow, both on flat plates and downstream of an abrupt pressure rise, show broad agreement with the predictions of the second method but do not support the compressibility transformation. In particular, measurements on flat plates reveal that as Mach number increases the entrainment rate decreases to a lesser extent than the skin-friction coefficient. Whilst this result is consistent with the second treatment in this paper, it is difficult to reconcile with any of the compressibility transformations discussed, and the validity of these transformations in turbulent flow is therefore questioned.
01 Jan 1968
TL;DR: In this paper, pressure fluctuations on surfaces adjacent to attached and separated turbulent boundary layers, giving power and cross spectra and space-time correlations are reported, and the authors show that these fluctuations can be used to give power and spectra correlations.
Abstract: Statistics of pressure fluctuations on surfaces adjacent to attached and separated turbulent boundary layers, giving power and cross spectra and space-time correlations
TL;DR: In this article, the mean flow properties in near wakes behind several 20° included-angle wedges at zero angle of attack were investigated at Mm = 6 and the results showed that the variation of total pressure along streamlines was initially negligible during the shearlayer turning process, indicating that wake shocks originated from viscous regions of the shear layer.
Abstract: An experimental investigation at Mm = 6 has been conducted to determine mean-flow properties in near wakes behind several 20° included- angle wedges at zero angle of attack. One cold-wall (H = 0.3 in., TW/TQ = 0.19) and two adiabatic-wall (H = 0.15 in., H = 0.3 in.) configurations were tested. Freestream Reynolds numbers were varied from 0.5 X 10 5 to 2 X 105 per in. for each model. Flowfield mappings and flow-property profiles were obtained in the base region for the wedge of 0.3-in. base height with and without cooling by combining Pitot- pressure data with total temperature and mass flux results from hot-wire measurements. The variation of total pressure along streamlines was initially negligible during the shearlayer turning process. Downstream boundaries of these isentropic turns corresponded to viscous-layer edges that were positioned in the outer portions of the shear layers, indicating that wake shocks originated from within viscous regions of the shear layer.
TL;DR: In this article, an analysis is presented which extends the analogy between energy and momentum transport for turbulent pipe flow of purely viscous fluids to include drag reducing, non-Newtonian fluids.
Abstract: An analysis is presented which extends the analogy between energy and momentum transport for turbulent pipe flow of purely viscous fluids to include drag reducing, non-Newtonian fluids. The correlation by Meyer is used to predict friction factor and sublayer thickness for the drag reducing fluids. The use of the friction factor correlation with the heat transfer analogy makes it possible to predict heat transfer rates from simple measurements of pressure drop and flow rate for the drag reducing fluids. Some recent experimental data for two effective drag reducing fluids and for water are compared with the predicted heat transfer rates, and the mean deviation in Nusselt number is found to be +8.5% for all of the data. The heat transfer analysis predicts a reduction in Nusselt number accompanying a reduction in friction factor for a given Reynolds number and for Prandtl numbers greater than 1.
TL;DR: In this article, separated flow in two dimensional and axisymmetric nozzles with various wall contours, determining flow structure and shock-boundary layer interaction is discussed.
Abstract: Separated flow in two dimensional and axisymmetric nozzles with various wall contours, determining flow structure and shock-boundary layer interaction