The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform
Daniel Weihs - One of the best experts on this subject based on the ideXlab platform.
-
Higher order hydrodynamic interaction between two Slender Bodies in potential flow
Journal of Marine Science and Technology, 2015Co-Authors: Usama Kadri, Daniel WeihsAbstract:In this paper, we apply the Slender body theory to study the effect of higher order hydrodynamic interactions between two Slender Bodies of revolution moving in close proximity, in an unbounded, inviscid, and incompressible fluid. We compare between leading and second-order approximations, as well as approximate and exact separation distances. The total solution is found to be valid for both small and large lateral separation distances. The contribution of the higher order forces is found to be relatively small for large separation distances, though significant for small separation distances. Comparisons with measurements and simulations are satisfactory.
-
Creeping flow around a finite row of Slender Bodies in close proximity
Journal of Fluid Mechanics, 2006Co-Authors: Efrath Barta, Daniel WeihsAbstract:The flow through and around a finite row of parallel Slender Bodies in close proximity moving in a viscous incompressible fluid is studied. The motion occurs under creeping flow ( $\hbox{\it Re}\,{\ll}\,1$ ) conditions. This row is a model of a comb-wing configuration found in insects of the Thrips family and being developed for use for flying vehicles of mm size, operating in the creeping flow regime. We show here that such wings utilize viscous effects to carry along enough fluid to approximate continuous surfaces. The comb is described as a row of rod-like ellipsoids of Slenderness ratio smaller than 0.01 at distances apart of order 10 times the minor axis and the flow field is computed by distributing singularities along the major axes of the ellipsoids. Results for the drag on the individual rods, as well as for the full row are presented. It is shown that above a certain number of rods, dependent on the geometric parameters of the comb, the row acts very much like a continuous surface, with over 95% of the flow moving around, and not through the comb. This allows a potential saving of tens of percents in wing weight. Parametric results for number of rods, rod density (ratio of inter-rod distance to rod length) and Slenderness ratio are presented demonstrating the dependence of the flow field on the configuration. It is found that 50–80 rods are required to approach the asymptotic limit of large number of rods, for various combinations of rod parameters with inter-rod distances of order of the cross-section diameter.
-
Aerodynamic Interactions Between Adjacent Slender Bodies
AIAA Journal, 2006Co-Authors: Daniel Weihs, Mordechai. Ringel, Michael VictorAbstract:Most externally carried aircraft stores are basically Slender Bodies. These stores are usually carried underneath the wings or fuselage (itself a Slender body), and in many cases multiple Bodies are carried in proximity. This proximity introduces new interaction forces, both in the longitudinal and lateral directions. Wind-tunnel experiments on a pair of generic Slender Bodies, ellipsoids of a 6:1 Slenderness ratio placed in parallel in the longitudinal direction, at various lateral spacings and axial displacement, are described. The results show that significant side and axial forces are obtained. The results are then compared to calculations based on a theoretical model applied to the interaction of pairs of such Slender Bodies, with very good agreement, up to the limits of the first-order model. When the Bodies are positioned correctly, the axial interaction force counters all of the viscous drag on one of the Bodies. Nomenclature D = doublet strength d = maximal diameter of Slender body F = force G = normalized force; see definition in Eq. (11) L = nominal length of wind-tunnel models l = length of general Slender body r(x) = local radius of Slender body S = maximal cross section of body S(x) = local body cross-sectional area, πr(x) 2 t = time U , V = speed in x and y directions, respectively X , Y = force in x and y directions, respectively x = Cartesian coordinate along long axis of body y = Cartesian coordinate in plane including the long axes of both Bodies z = third Cartesian coordinate η = distance between centroids in the y direction μ = strength of secondary singularity induced by the other body ξ = distance between centroids in the x direction ρ = density of air ϕ = flow potential Subscripts i = index x =i nx direction y = in y direction 0 = fixed system 1 = related to first body (Fig. 2) 2 = related to second body
-
CREEPING FLOW AROUND A FINITE ROW OF Slender Bodies
Advances in Engineering Mechanics — Reflections and Outlooks, 2005Co-Authors: Efrath Barta, Daniel WeihsAbstract:The flow through and around a finite row of parallel Slender Bodies moving at constant low speed in a viscous incompressible fluid is studied. The motion occurs under creeping flow (R
Efrath Barta - One of the best experts on this subject based on the ideXlab platform.
-
Motion of Slender Bodies in unsteady Stokes flow
Journal of Fluid Mechanics, 2011Co-Authors: Efrath BartaAbstract:The flow regime in the vicinity of oscillatory Slender Bodies, either an isolated one or a row of many Bodies, immersed in viscous fluid (i.e. under creeping flow conditions) is studied. Applying the Slender-body theory by distributing proper singularities on the Bodies’ major axes yields reasonably accurate and easily computed solutions. The effect of the oscillations is revealed by comparisons with known Stokes flow solutions and is found to be most significant for motion along the normal direction. Streamline patterns associated with motion of a single body are characterized by formation and evolution of eddies. The motion of adjacent Bodies results, with a reduction or an increase of the drag force exerted by each body depending on the direction of motion and the specific geometrical set-up. This dependence is demonstrated by parametric results for frequency of oscillations, number of Bodies, their Slenderness ratio and the spacing between them. Our method, being valid for a wide range of parameter values and for densely packed arrays of rods, enables simulation of realistic flapping of bristled wings of some tiny insects and of locomotion of flagella and ciliated micro-organisms, and might serve as an efficient tool in the design of minuscule vehicles. Its potency is demonstrated by a solution for the flapping of thrips.
-
Creeping flow around a finite row of Slender Bodies in close proximity
Journal of Fluid Mechanics, 2006Co-Authors: Efrath Barta, Daniel WeihsAbstract:The flow through and around a finite row of parallel Slender Bodies in close proximity moving in a viscous incompressible fluid is studied. The motion occurs under creeping flow ( $\hbox{\it Re}\,{\ll}\,1$ ) conditions. This row is a model of a comb-wing configuration found in insects of the Thrips family and being developed for use for flying vehicles of mm size, operating in the creeping flow regime. We show here that such wings utilize viscous effects to carry along enough fluid to approximate continuous surfaces. The comb is described as a row of rod-like ellipsoids of Slenderness ratio smaller than 0.01 at distances apart of order 10 times the minor axis and the flow field is computed by distributing singularities along the major axes of the ellipsoids. Results for the drag on the individual rods, as well as for the full row are presented. It is shown that above a certain number of rods, dependent on the geometric parameters of the comb, the row acts very much like a continuous surface, with over 95% of the flow moving around, and not through the comb. This allows a potential saving of tens of percents in wing weight. Parametric results for number of rods, rod density (ratio of inter-rod distance to rod length) and Slenderness ratio are presented demonstrating the dependence of the flow field on the configuration. It is found that 50–80 rods are required to approach the asymptotic limit of large number of rods, for various combinations of rod parameters with inter-rod distances of order of the cross-section diameter.
-
CREEPING FLOW AROUND A FINITE ROW OF Slender Bodies
Advances in Engineering Mechanics — Reflections and Outlooks, 2005Co-Authors: Efrath Barta, Daniel WeihsAbstract:The flow through and around a finite row of parallel Slender Bodies moving at constant low speed in a viscous incompressible fluid is studied. The motion occurs under creeping flow (R
B. W. Skews - One of the best experts on this subject based on the ideXlab platform.
-
Shock wave interactions between Slender Bodies
Shock Waves, 2017Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:A complex interference flowfield consisting of multiple shocks and expansion waves is produced when high-speed Slender Bodies are placed in close proximity. The disturbances originating from a generator body impinge onto the adjacent receiver body, modifying the local flow conditions over the receiver. This paper aims to uncover the basic gas dynamics produced by two closely spaced Slender Bodies in a supersonic freestream. Experiments and numerical simulations were used to interpret the flowfield, where good agreement between the predictions and measurements was observed. The numerical data were then used to characterise the attenuation associated with shock wave diffraction, which was found to be interdependent with the bow shock contact perimeter over the receiver Bodies. Shock-induced boundary layer separation was observed over the conical and hemispherical receiver Bodies. These strong viscous-shock interactions result in double-reflected, as well as double-diffracted shock wave geometries in the interference region, and the diffracting waves progress over the conical and hemispherical receivers’ surfaces in “lambda” type configurations. This gives evidence that viscous effects can have a substantial influence on the local bow shock structure surrounding high-speed Slender Bodies in close proximity.
-
Colour surface flow visualisation of interfering Slender Bodies at Mach 3
Journal of Visualization, 2015Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:A study to understand the flow physics produced by two Slender Bodies in close proximity in high-speed airflow was undertaken. The interference flow field generated by the Bodies is dominated by shock and expansion waves, and of particular significance is the complex interaction of the bow-shock wave emanating from the disturbance generator, striking the surface of the disturbance receiver. To gain insight into the shock wave-body interaction, the traditional surface oil flow visualisation technique was extended to include colour, which assists the eye in tracking the streak lines back to their separation and reattachment regions. In addition, the fine particle sizes of the colour pigment produced crisper and more definitive separation lines over the body, in comparison to the traditional monochrome pigments, such as lamp-black or titanium-dioxide. Subsequently, the dried surface pattern was lifted off the body using matte-acetate tape, digitised and then straightened using datum markings along the sting. This allowed the shock impingement location and shock diffraction path over the body to be established quantitatively, which was used to validate numerical simulations. The experimental and computational data showed good agreement for all configurations considered, providing complementary information about the disturbance-induced effects generated in the interference flow field, and provided detailed insight into the near-surface flow topology produced by the shock wave-Slender body interaction. Graphical Abstract
-
three dimensional curved shock wave interactions with Slender Bodies at incidence
International Symposium on Shock Waves, 2013Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:Consider the pressure wave interaction that occurs between two Slender Bodies in close proximity, in a steady supersonic freestream. The pressure wave systems produced by the Bodies creates an interference flowfield that is dominated by shock and expansion waves
Pavlos P. Vlachos - One of the best experts on this subject based on the ideXlab platform.
-
Unsteady separated flows over three-dimensional Slender Bodies
Progress in Aerospace Sciences, 2004Co-Authors: Matthew Zeiger, Demetri P. Telionis, Pavlos P. VlachosAbstract:Abstract Many review articles have been written on the topic of the aerodynamics of Slender Bodies at incidence, some of which are referenced in this paper. Here, we review the unsteady behavior of these flows. Our aim is to review the material that contributes to our understanding of unsteady phenomena over Slender Bodies at incidence. Natural unsteadiness is explored first. Unexpectedly, we found a large number of contributions in this area. We found the material disjointed, making it difficult to draw general conclusions. Forced unsteadiness is conceptually easier to follow, but the number of contributions on this topic is much smaller. We consider both experimental and numerical contributions but we do not discuss the corresponding methodologies.
S. J. Hooseria - One of the best experts on this subject based on the ideXlab platform.
-
Shock wave interactions between Slender Bodies
Shock Waves, 2017Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:A complex interference flowfield consisting of multiple shocks and expansion waves is produced when high-speed Slender Bodies are placed in close proximity. The disturbances originating from a generator body impinge onto the adjacent receiver body, modifying the local flow conditions over the receiver. This paper aims to uncover the basic gas dynamics produced by two closely spaced Slender Bodies in a supersonic freestream. Experiments and numerical simulations were used to interpret the flowfield, where good agreement between the predictions and measurements was observed. The numerical data were then used to characterise the attenuation associated with shock wave diffraction, which was found to be interdependent with the bow shock contact perimeter over the receiver Bodies. Shock-induced boundary layer separation was observed over the conical and hemispherical receiver Bodies. These strong viscous-shock interactions result in double-reflected, as well as double-diffracted shock wave geometries in the interference region, and the diffracting waves progress over the conical and hemispherical receivers’ surfaces in “lambda” type configurations. This gives evidence that viscous effects can have a substantial influence on the local bow shock structure surrounding high-speed Slender Bodies in close proximity.
-
Colour surface flow visualisation of interfering Slender Bodies at Mach 3
Journal of Visualization, 2015Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:A study to understand the flow physics produced by two Slender Bodies in close proximity in high-speed airflow was undertaken. The interference flow field generated by the Bodies is dominated by shock and expansion waves, and of particular significance is the complex interaction of the bow-shock wave emanating from the disturbance generator, striking the surface of the disturbance receiver. To gain insight into the shock wave-body interaction, the traditional surface oil flow visualisation technique was extended to include colour, which assists the eye in tracking the streak lines back to their separation and reattachment regions. In addition, the fine particle sizes of the colour pigment produced crisper and more definitive separation lines over the body, in comparison to the traditional monochrome pigments, such as lamp-black or titanium-dioxide. Subsequently, the dried surface pattern was lifted off the body using matte-acetate tape, digitised and then straightened using datum markings along the sting. This allowed the shock impingement location and shock diffraction path over the body to be established quantitatively, which was used to validate numerical simulations. The experimental and computational data showed good agreement for all configurations considered, providing complementary information about the disturbance-induced effects generated in the interference flow field, and provided detailed insight into the near-surface flow topology produced by the shock wave-Slender body interaction. Graphical Abstract
-
three dimensional curved shock wave interactions with Slender Bodies at incidence
International Symposium on Shock Waves, 2013Co-Authors: S. J. Hooseria, B. W. SkewsAbstract:Consider the pressure wave interaction that occurs between two Slender Bodies in close proximity, in a steady supersonic freestream. The pressure wave systems produced by the Bodies creates an interference flowfield that is dominated by shock and expansion waves
