Showing papers in "Journal of Fluids Engineering-transactions of The Asme in 1991"
TL;DR: The status and outlook of separation control for both steady and unsteady flows are reviewed and both passive and active techniques to prevent or to provoke flow detachment are considered.
Abstract: Under certain conditions, wall-bounded flows separate. To improve the performance of natural or man-made flow systems, it may be beneficial to delay or advance this detachment process. The present article reviews the status and outlook of separation control for both steady and unsteady flows. Both passive and active techniques to prevent or to provoke flow detachment are considered and suggestions are made for further research.
383 citations
TL;DR: In this paper, it was shown that vortex shedding resonance or lock-on is observed also when a bluff body is placed in an incident mean flow with a periodic component superimposed upon it.
Abstract: The results of recent experiments demonstrate that the phenomenon of vortex shedding resonance or lock-on is observed also when a bluff body is placed in an incident mean flow with a periodic component superimposed upon it. This form of vortex shedding and lock-on exhibits a particularly strong resonance between the flow perturbations and the vortices, and provides one of several promising means for modification and control of the basic formulation and stability mechanisms in the near-wake of a bluff body. Examples are given of recent direct numerical simulations of the vortex lock-on in the periodic flow. These agree well with the results of experiments. A discussion also is given of vortex lock-on due to body oscillations both normal to and in-line with the incident mean flow, rotational oscillations of the body, and of the effect of sound on lock-on. The lock-on phenomenon is discussed in the overall context of active and passive wake control, on the basis of these and other recent and related results, with particular emphasis placed on active control of the circular cylinder wake.
215 citations
TL;DR: The results of an earlier investigation that demonstrated the significance of the particle diameter/fluid length scale ratio in determining whether or not the addition of a dispersed phase would cause an increase or decrease in the carrier phase turbulent intensity are extended to radial locations other than the centerline.
Abstract: The results of an earlier investigation that demonstrated the significance of the particle diameter/fluid length scale ratio in determining whether or not the addition of a dispersed phase would cause an increase or decrease in the carrier phase turbulent intensity are extended to radial locations other than the centerline.
143 citations
TL;DR: In this paper, a mathematical formulation developed for aerodynamic sensitivity coefficients based on a discretized form of the compressible 2D Euler equations is presented, and a new flow prediction concept is developed and illustrated with an example.
Abstract: This study presents a mathematical formulation developed for aerodynamic sensitivity coefficients based on a discretized form of the compressible 2D Euler equations. A brief motivating introduction to the aerodynamic sensitivity analysis and the reasons behind an integrated flow/sensitivity analysis for design algorithms are presented. The finite difference approach and the quasi-analytical approach are used to determine the aerodynamic sensitivity coefficients. A new flow prediction concept, which is an outcome of the direct method in the quasi-analytical approach, is developed and illustrated with an example. Surface pressure coefficient distributions of a nozzle-afterbody configuration obtained from the predicted flowfield solution are compared successfully with their corresponding values obtained from a flowfield analysis code and the experimental data.
136 citations
TL;DR: In this article, it was shown that in uniform shear flow near equilibrium, local isotropy can never constitute a systematic approximation, even in the limit of infinite Reynolds number, and an estimate of the level of mean strain rate for which local isotropic approximation is a good approximation was provided.
Abstract: It is shown that the hypothesis of local isotropy is implausible in the presence of significant mean rates of strain. In fact, it appears that in uniform shear flow near equilibrium, local isotropy can never constitute a systematic approximation, even in the limit of infinite Reynolds number. An estimate of the level of mean strain rate for which local isotropy is formally a good approximation is provided.
122 citations
TL;DR: The object was to obtain a consensus on the capabilities of present-day turbulence models, and identify which types most deserve future support, and the results support the view that Reynolds-stress transport models are the most accurate.
Abstract: A review is given of an ongoing international project, in which data from experiments on, and simulations of, turbulent flows are distributed to developers of (time-averaged) engineering turbulence models. The predictions of each model are sent to the organizers and redistributed to all the modelers, plus some experimentalists and other experts (total approx. 120), for comment. The 'reaction time' of modelers has proved to be much longer than anticipated, partly because the comparisons with data have prompted many modelers to improve their models or numerics.
109 citations
TL;DR: Recommendations are presented with regard to the most appropriate technique for various flow regimes and types of turbomachinery, incompressible and compressible flows, cascades, rotors, stators, liquid- handling, and gas-handling turbomachineries.
Abstract: Various computational fluid dynamic techniques are reviewed focusing on the Euler and Navier-Stokes solvers with a brief assessment of boundary layer solutions, and quasi-3D and quasi-viscous techniques. Particular attention is given to a pressure-based method, explicit and implicit time marching techniques, a pseudocompressibility technique for incompressible flow, and zonal techniques. Recommendations are presented with regard to the most appropriate technique for various flow regimes and types of turbomachinery, incompressible and compressible flows, cascades, rotors, stators, liquid-handling, and gas-handling turbomachinery.
106 citations
TL;DR: In order to perform mathematically equivalent calculation without approximations, the authors have developed a new method which requires much less computation time and computer storage than Zielke’s method.
Abstract: Zielke’s technique of using a method of characteristics to simulate transient phenomena of a liquid transmission line is accurate, easy to apply to complicated systems and therefore, frequently used. However, it requires a very large amount of computation time and computer storage to simulate frequency-dependent friction in a transient liquid flow. Searching for a way to counteract these disadvantages, the authors took note of the fact that the weighting function, which is the root of the above problems, is given by exponential functions or other functions depending on dimensionless time. In order to perform mathematically equivalent calculation without approximations, they have developed a new method which requires much less computation time and computer storage than Zielke’s method. The calculation process is shown by a block diagram to facilitate visual understanding of the method.
89 citations
TL;DR: A review of progress in research during the period 1979-1989 on the fundamental physical mechanisms of hydrodynamic cavitation inception can be found in this article, where the authors identify the physical phenomena and techniques have been developed to reproduce on laborotory scale selected forms of full scale Cavitation inception.
Abstract: A review is made of progress in research during the period 1979-1989 on the fundamental physical mechanisms of hydrodynamic cavitation inception. During that decade identification of the physical phenomena has been made, and techniques have been developed to reproduce on laborotory scale selected forms of full scale cavitation inception. Understanding of the mechanisms remains shallow, and analytical/numerical prediction methods are nonexistent except for the restricted case of travelling bubble cavitation inception in a passive pressure field.
89 citations
TL;DR: In this paper, the results of a flow visualizalion study which concerns three-dimensional vortex structures in a leading-edge separation bubble formed along the sides of a blunt flat plate were described.
Abstract: We describe the results of a flow visualizalion study which concerns three-dimensional vortex structures in a leading-edge separation bubble formed along the sides of a blunt flat plate. Dye and hydrogen bubbles were used as tracers. Reynolds number, based on the plate thickness, was varied from 80 to 800.
78 citations
TL;DR: In this paper, the mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique.
Abstract: The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0-300 rpm and the flow rate varied from 7.0-15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.
TL;DR: In this paper, the authors reported measurements for the separted reattaching flow around a long rectangular plate placed at zero incidence in a low-turbulence stream, which exhibits all of the important features of two-dimensional flow separation with reattachment.
Abstract: Measurements are reported for the separted reattaching flow around a long rectangular plate placed at zero incidence in a low-turbulence stream. This laboratory configuration, chosen for its geometric simplicity, exhibits all of the important features of two-dimensional flow separation with reattachment. Conventional hot-wire anemometry, pulsed-wire anemometry and pulsed-wire surface shear stress probes were used to measure the mean and fluctuating flow field at a Reynolds number, based on plate thickness, of 5 × 104 . The separated shear layer appears to behave like a conventional mixing layer over the first half of the separation bubble, where it exhibits an approximately constant growth rate and a linear variation of characteristic frequencies and integral timescales. The characteristics of the shear layer in the second half of the bubble are radically altered by the unsteady reattachment process. Much higher turbulent intensities and lower growth rates are encountered there, and, in agreement with other reattaching flow studies, a low frequency motion can be detected.
TL;DR: In this paper, the oscillation of horseshoe vortex systems around the base of wall mounted obstacles in the transition range is considered, and existing experimental data from a variety of sources is reanalyzed in the light of two hypotheses-that vortex oscillations are caused by oscillations of the entire vortex system, and by vortex core instabilities.
Abstract: The oscillation of horseshoe vortex systems around the base of wall mounted obstacles in the transition range is considered. Existing experimental data from a variety of sources is reanalyzed in the light of two hypotheses-that vortex oscillations are caused by (a) oscillations of the entire vortex system, and (b) by vortex core instabilities.
TL;DR: In this article, a small circular cylinder (the control cylinder) was used to suppress the fluid forces by controlling a shear layer on one side separated from a square prism, and the results showed that the maximum reduction of the time-mean drag and fluctuating lift and drag occurred when the control cylinder was located near what would ordinarily be considered the outer boundary of the shear layers.
Abstract: This paper deals with the suppression of the fluid forces by controlling a shear layer on one side separated from a square prism. The control of the separated shear layer was established by setting up a small circular cylinder (the control cylinder) in it on one side. Experimental data were collected to examine the effects on the fluid forces and vortex shedding frequency due to variation of the position and diameter of the control cylinder. The results show that (i) the maximum reduction of the time-mean drag and fluctuating lift and drag occurred when the control cylinder was located near what would ordinarily be considered the outer boundary of the shear layer; (ii) the control of the separated shear layer by means of a small cylinder appeared to be effective in suppressing the fluctuating lift and drag rather than the time-mean drag; (iii) in the case of the control cylinder of 6 mm in diameter, the time-mean drag was reduced to about 30 percent, and the fluctuating lift and drag were reduced to approximately 95 and 75 percent, respectively; (iv) the fluid forces and the frequency of vortex shedding of the square prism were mainly dependent on the characteristics of a very thin region near the outer boundary of the shear layer.
TL;DR: In this article, the characteristics of the flow around a bluff body of square cross-section in contact with a solid-wall boundary are investigated numerically using a finite difference procedure.
Abstract: The characteristics of the flow around a bluff body of square cross-section in contact with a solid-wall boundary are investigated numerically using a finite difference procedure. Previous studies have shown qualitatively the strong influence of solid-wall boundaries on the vortex-shedding process and the formation of the vortex street downstream. In the present study three cases are investigated which correspond to flow past a square rib in a freestream, flow past a rib on a fixed wall and flow past a rib on a sliding wall. Values of the Reynolds number studied ranged from 100 to 200. Comparisons between the sliding-wall and fixed-wall cases show that he sliding wall has a significant destabilising effect on the recirculation region behind the rib. Results show the onset of unsteadiness at a lower Reynolds number for the sliding-wall case and both the freestream and fixed-wall cases. At moderate Reynolds numbers the sliding-wall results show that the rib periodically sheds vortices of alternating circulation in much the same manner as the rib in a freestream; as in, for example, Davis and Moore (1982). The vortices are distributed asymmetrically downstream of the rib and are not of equal strength as in the freestream case. However, the sliding-wall case shows no tendency to develop cycle-to-cycle variations at higher Reynolds numbers, as observed in the freestream and fixed-wall cases. Thus, while the moving wall causes the flow past the rib to become unsteady at a lower Reynolds number than in the fixed-wall case, it also acts to stabilise or "lock-in" the vortex-shedding frequency. This is attributed to the additional source of positive vorticity immediately downstream of the rib on the sliding wall.
TL;DR: A practical method of uncertainty analysis is based on sensitivity analysis, which indicates that when CFD is used to design fluid dynamic systems, sensitivity-uncertainty analysis is essential.
Abstract: Uncertainties are inherent in computational fluid dynamics (CFD). These uncertainties need to be systematically addressed and managed. Sources of these uncertainty analysis are discussed. Some recommendations are made for quantification of CFD uncertainties. A practical method of uncertainty analysis is based on sensitivity analysis. When CFD is used to design fluid dynamic systems, sensitivity-uncertainty analysis is essential.
TL;DR: In this article, the mean and turbulence characteristics of wall jets generated from orifices having the shapes of various segments of a circle are investigated and the influence of the geometry of the orifice on the various wall jet properties is presented and discussed.
Abstract: This paper reports experimental investigations on mean and turbulence characteristics of three-dimensional, incompressible, isothermal turbulent wall jets generated from orifices having the shapes of various segments of a circle. In Part 1, the mean flow characteristics are presented. The turbulence characteristics are presented in Part 2. The influence of the geometry on the characteristic decay region of the wall jet is brought out and the differences with other shapes are discussed. Mean velocity profiles both in the longitudinal and lateral planes are measured and compared with some of the theoretical profiles. Wall jet expansion rates and behavior of skin-friction are discussed. The influence of the geometry of the orifice on the various wall jet properties is presented and discussed. Particularly the differences between this class of geometry and rectangular geometries are critically discussed.
TL;DR: In this paper, the authors compare numerical simulations of the large amplitude stage of the Kelvin-Helmholtz instability of a relatively thin vorticity layer with fully viscous finite difference calculations of the Navier-Stokes equations, and compare the limiting behavior of the viscous simulations for high Reynolds numbers and small initial layer thickness with the limiting solution for the roll-up of an inviscid vortex sheet.
Abstract: Numerical simulations of the large amplitude stage of the Kelvin-Helmholtz instability of a relatively thin vorticity layer are discussed. At high Reynolds number, the effect of viscosity is commonly neglected and the thin layer is modeled as a vortex sheet separating one potential flow region from another. Since such vortex sheets are susceptible to a short wavelength instability, as well as singularity formation, it is necessary to provide an artificial “regularization” for long time calculations. We examine the effect of this regularization by comparing vortex sheet calculations with fully viscous finite difference calculations of the Navier-Stokes equations. In particular, we compare the limiting behavior of the viscous simulations for high Reynolds numbers and small initial layer thickness with the limiting solution for the roll-up of an inviscid vortex sheet. Results show that the inviscid regularization effectively reproduces many of the features associated with the thickness of viscous vorticity layers with increasing Reynolds number, though the simplified dynamics of the inviscid model allows it to accurately simulate only the large scale features of the vorticity field. Our results also show that the limiting solution of zero regularization for the inviscid model and high Reynolds number and zero initial thickness for the viscous simulations appear to be the same.
Abstract: The present study is devoted to the interaction between a swarm of bubbles and a turbulent field in a linear shear flow. The transversal and longitudinal evolutions of the void fraction and of the Reynolds stress tensor have been measured. When the air bubbles are blown uniformly into the shear, the void fraction profiles exhibit a strong gradient which can be explained by kinematical effects. No void migration has been observed. The behavior of the Reynolds tensor indicates that the nonisotropy induced by the mean velocity gradient decreases when the void fraction increases. A simple mechanism is proposed to interpret this fact, and a turbulence model based on one-point closures is compared to the experimental data.
TL;DR: In this article, a numerical method for the solution of the Reynolds-averaged Navier-Stokes equations, together with a two-layer turbulence model, has been used to describe steady flow in a 2D channel with a wavy wall.
Abstract: A numerical method for the solution of the Reynolds-averaged Navier-Stokes equations, together with a two-layer turbulence model, has been used to describe steady flow in a two-dimensional channel with a wavy wall. Comparisons of calculations with experiments demonstrate the effects of alternating pressure gradients induced by alternating surface curvatures, and multiple separations and reattachments. The numerical method and the turbulence model are shown to capture the overall features of such a flow, including the breakdown of the logarithmic law of the wall in strong pressure gradients and in separated flow.
TL;DR: In this paper, an optical interferometric technique has been used to determine the 3D shape of cavitation erosion pits, which is particularly suitable to the determination of pit diameter and pit depth.
Abstract: An optical interferometric technique has been used to determine the 3-D shape of cavitation erosion pits. The method which is particularly suitable to the determination of pit diameter and pit depth is used for a statistical analysis of cavitation erosion pits. We analyzed numerous samples which were eroded at various velocities with two different fluids (mercury and water) on two geometrically similar venturi test sections of different length scales. General properties of histograms of pit size are pointed out.
TL;DR: In this paper, the authors studied the details of the horseshoe vortex formation around a cylinder to determine the flow parameters that effect the flow separation in front of the cylinder, using a wind tunnel test section.
Abstract: Details of the horseshoe vortex formation around a cylinder were studied to determine the flow parameters that effect the flow separation in front of the cylinder. An experimental setup, consisting of a circular cylinder vertically mounted on the floor of a wind tunnel test section, was assembled. The approaching turbulent boundary layer was 4cm thick. Pressures were measured on the cylinder surface and the tunnel floor with surface static pressure taps.Surface flow visualisations were accomplished to locate singular points and the size of separation region on the end wall surface. Other details of the study are given.
TL;DR: In this article, the analytic solution to the fully developed oscillatory fluid flow through a porous medium channel bounded by two impermeable parallel plates is presented in the absence of the inertia effects.
Abstract: In the absence of the inertia effects, the analytic solution to the fully developed oscillatory fluid flow through a porous medium channel bounded by two impermeable parallel plates is presented.
TL;DR: In this paper, a four equation model of axial wave propagation with Poisson coupling, including viscous damping to account for structural energy dissipation, is evaluated and compared with experimental data.
Abstract: A four equation model of axial wave propagation with Poisson coupling which includes viscous damping to account for structural energy dissipation is evaluated. Comparison of the predictions with experimental data indicates that the model can satisfactorily predict fluid pressure and structural velocity.
TL;DR: In this paper, phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets, and the Sauter mean diameter distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet.
Abstract: Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.
TL;DR: In this paper, a computational investigation of subsonic and transonic flows past three-dimensional deep and transitional cavities was performed using time-accurate solutions of the Reynolds averaged, full Navier-Stokes equations, using the explicit MacCormack scheme.
Abstract: Presented in this paper is a computational investigation of subsonic and transonic flows past three-dimensional deep and transitional cavities. Simulations of these self-induced oscillatory flows have been generated through time-accurate solutions of the Reynolds averaged, full Navier-Stokes equations, using the explicit MacCormack scheme. The Reynolds stresses have been included through the Baldwin-Lomax algebraic turbulence model with certain modifications. The computational results include instantaneous and time averaged flow properties. The results of an experimental investigation have been used not only to validate the time-averaged results, but also to investigate the effects of varying the Mach number and the incoming boundary-layer thickness. Time series analyses have been performed for the instantaneous pressure values on the cavity floor and compared with the results obtained by a predictive formula. While most of the comparisons have been favorable, some discrepancies have been observed, particularly on the rear face. The present results help understanding the three-dimensional and unsteady features of the separations, vortices, the shear layer, as well as some of the aeroacoustic phenomena of compressible cavity flows.
TL;DR: The tip vortex structure of a three-dimensional hydrofoil at high Reynolds number was measured experimentally in both the 48 in. (1.22 m) diameter water tunnel and the 48in. ( 1.22m) wind tunnel at the Applied Research Laboratory, Penn State as discussed by the authors.
Abstract: The tip vortex structure of a three-dimensional hydrofoil at high Reynolds number was measured experimentally in both the 48 in. (1.22 m) diameter water tunnel and the 48 in. (1.22 m) wind tunnel at the Applied Research Laboratory, Penn State. The flow on and near the hydrofoil was measured in both facilities using a number of flow visualization techniques and laser velocimetry. The downstream tip vortex was measured with a three-component laser velocimeter at a number of streamwise positions
TL;DR: In this paper, the complete Navier-Stokes equations are solved for a steady, incompressible, fully developed laminar flow in a curved duct of elliptic cross section.
Abstract: The complete form of the Navier-Stokes equations is solved in this paper for a steady, incompressible, fully developed laminar flow in a curved duct of elliptic cross section. This is achieved by the use of the control volume-based finite difference method via the numerically generated boundary fitted coordinate system. The curvature ratio is included in the primitive variable governing equations, which are solved based on the SIMPLE algorithm. Solutions are obtained for the minor-axis to major-axis ratios of the elliptic duct, 0.2, 0.5, and 0.8, and for Dean numbers ranging from 11.41 to 635.7. It is found that only one pair of vortices appears on the cross-section, even at a Dean number of 635.7. The friction factor and the ratios of the curved duct to straight duct are tabulated and the correlation equation is developed. Furthermore, the distribution of the axial velocity is displayed graphically to illustrate its variations with the Dean number and the minor-axis to major-axis ratio of the elliptic duct on the horizontal symmetry line and on the half-vertical symmetry line. The present method is also applied to solve for a fully developed laminar flow in a curved square flow. The results are compared with the data available in the literature and very close agreement is observed.
TL;DR: In this paper, the influences of valve disk angle, valve/elbow spacing, and valve orientation on the dimensionless pressure drop, mass flow coefficient, and aerodynamic torque coefficient characteristics of the valve were investigated.
Abstract: Primary emphasis is given the influences of valve disk angle, valve/elbow spacing, and valve/elbow orientation on the dimensionless pressure drop, mass flow coefficient, and aerodynamic torque coefficient characteristics of the valve.
TL;DR: In this paper, a finite-difference study of sinusoidally oscillating flow past a fixed circular cylinder is made using vorticity and stream function as the dependent variables.
Abstract: A finite-difference study of the sinusoidally oscillating flow past a fixed circular cylinder is made using vorticity and stream function as the dependent variables. Calculations are performed for conditions which lead to both a symmetric wake and an unsymmetric wake. The Reynolds number ranges from 100 to 3000 and the Keulegan-Carpenter number ranges from 1 to 12. A hybrid differencing scheme is introduced to provide a stable for large values of the parameters. Good comparison to flow visualisation results and calculated force coefficients is found. The results are given a physical interpretation for the various vortex patterns observed.