Three-dimensional instabilities in flow past a rotating cylinder

Flow past a spinning circular cylinder placed in a uniform stream is investigated via three-dimensional computations. A stabilized finite element method is utilized to solve the incompressible Navier-Stokes equations in the primitive variables formulation. The Reynolds number based on the cylinder diameter and freestream speed of the flow is 200. The nondimensional rotation rate, α, (ratio of the surface speed and freestream speed) is 5. It is found that although the two-dimensional flow for α=5 is stable, centrifugal instabilities exist along the entire span in a three-dimensional set-up. In addition, a "no-slip" side-wall can result in separation of flow near the cylinder ends. Both these effects lead to a loss in lift and increase in drag. The end conditions and aspect ratio of the cylinder play an important role in the flow past a spinning cylinder. It is shown that the Prandtl's limit on the maximum lift generated by a spinning cylinder in a uniform flow does not hold

Interactive free convection from a pair of vertical tube-arrays at moderate Rayleigh numbers

Steady laminar free convection from a pair of vertical arrays of equally-spaced, horizontal isothermal cylinders set in free air, is studied numerically. A specifically developed computer-code based on the SIMPLE-C algorithm is used for the solution of the mass, momentum and energy transfer governing equations. Simulations are performed for pairs of tube-arrays consisting of 1-4 circular cylinders, for center-to-center horizontal and vertical spacings from 1.4 to 24 cylinder-diameters, and from 2 to 12 cylinder-diameters, respectively, and for values of the Rayleigh number based on the cylinder-diameter in the range between 10(2) and 10(4). It is found that any cylinder may exhibit either enhanced or reduced Nusselt numbers with respect to the case of single tube-array, depending on its location in the array, on the geometry of the array, as well as on the Rayleigh number. Heat transfer dimensionless correlating equations are also proposed. (c) 2006 Published by Elsevier Ltd

Calculation of clamping device machine-tools with the spiral corrugated elements

Виведені аналітичні залежності для визначення сили тяги штока затискного гвинтового патрона з пневматичним приводом, а також радіальної сили затиску циліндричних заготовок по зовнішньому діаметрі гвинтовими гофрованими елементами від конструктивних і технологічних факторів. Встановлені залежності нормальної сили деформації гофр гвинтових гофрованих елементів від товщини матеріалу спіралі і радіуса гофра при затиску циліндричних заготовок по зовнішньому діаметру, які дали можливість здійснювати вибір затискних патронів в залежності від потреб виробництва.Shown analytical dependences out for determination of tractive force of clamping spiral patron with a pneumatic occasion, and also radial force of clamp of cylinder semiss on an external diameter by the spiral corrugated elements from structural and technological factors. Set dependences of normal force of deformation of flutes of the spiral corrugated elements on the thickness of material of spiral and radius of the clamp of cylinder semiss on an external diameter, which enabled to carry out the choice of clamping patrons depending on the necessities of production

Correlating equations for free convection heat transfer from horizontal isothermal cylinders set in a vertical array

Steady laminar free convection from flat vertical arrays of equally-spaced, horizontal isothermal cylinders set in free air, is studied numerically. A specifically developed computer-code based on the SIMPLE-C algorithm is used for the solution of the mass, momentum and energy transfer governing equations. Simulations are performed for arrays of 2–6 circular cylinders, for center-to-center separation distances from 2 up to more than 50 cylinder-diameters, and for values of the Rayleigh number based on the cylinder-diameter in the range between 500 and 500.000. It is found that the heat transfer rate at the bottom cylinder remains the same as a single cylinder. In contrast, the downstream cylinders may exhibit either enhanced or reduced Nusselt numbers depending on their location in the array and on the geometry of the array. Heat transfer dimensionless correlating equations are proposed both for any individual cylinder in the array and for the whole tube-array. New correlation-equations for the calculation of the heat transfer rate from a single cylinder to the surrounding air are also proposed and compared to those available in the open literature

Measurements of the Flowfield Interaction Between Tandem Cylinders

This paper presents the most recent measurements from an ongoing investigation of the unsteady wake interference between a pair of circular cylinders in tandem. The purpose of this investigation is to help build an in-depth experimental database for this canonical flow configuration that embodies the effects of component interaction in landing gear noise. This new set of measurements augments the previous database at the primary Reynolds number (based on tunnel speed and cylinder diameter) of 1.66 105 in four important respects. First, better circumferential resolution of surface pressure fluctuations is obtained via cylinder "clocking". Second, higher resolution particle image velocimetry measurements of the shear layer separating from the cylinders are achieved. Third, the effects of simultaneous boundary layer trips along both the front and rear cylinders, versus front cylinder alone in the previous measurements, are studied. Lastly, on-surface and off-surface characteristics of unsteady flow near the "critical" cylinder spacing, wherein the flow switches intermittently between two states that are characteristic of lower and higher spacings, are examined. This critical spacing occurs in the middle of a relatively sudden change in the drag of either cylinder and is characterized by a loud intermittent noise and a flow behavior that randomly transitions between shear layer attachment to the rear cylinder and constant shedding and rollup in front of it. Analysis of this bistable flow state reveals much larger spanwise correlation lengths of surface pressure fluctuations than those at larger and smaller values of the cylinder spacing

CYLINDRICAL ARRANGEMENTS OF UNIFORM SPHERES.

Cylindrical arrangements of uniform spheres have been discussed on a general basis where the ratio of cylinder diameter to sphere diameter is large. These papers have been directed at the study of the filing of cylindrical containers to achieve maximum density without regard for the systematic geometric arrangements which might occur. This paper deals primarily with the systematic arrangements of uniform spheres such that the envelope of the set of uniform spheres is an infinite cylinder

Pressure Distribution of Fluid Flow through Triangular and Square Cylinders

A flow current passing through a triangular cross section bar and rectangular crosssection\ud \ud bar is often found in structural engineering and transportation. Pressure\ud coefficient distribution around a rectangle bar at the top and bottom of the bar is\ud relatively the same, while the biggest pressure coefficient occurs at the frontal side\ud of the square bar. The interference of the double bar distance against the pressure\ud coefficient indicates that a distance between the bar increase will lift up the pressure\ud coefficient at the surface of the bar back pressure. The maximum pressure point moving\ud forward, and the bar separation would no longer be reduced. If the cross section of the\ud bar becomes larger at a constant fluid velocity, then the point of maximum bar pressure\ud is directed to both sides of the front bar. The separation point of the second cylinder\ud pressure occurs at a point that is almost similar but with a different value. Pressure\ud distributions of fluid flow through triangular and square cylinders were analyzed\ud experimentally at various Reynolds numbers, ReD = 48.708; 64.435; 94.480; 119.509\ud and 152.449. This Reynolds number is calculated based on the square cylinder\ud diameter. Ratio of distances between the two cylinders to the diameter of the square\ud cylinder (L/D) was varied as 0.5; 1.0 and 1.5. Diameter ratio between triangular and\ud square cylinders, (d/D), was set constantly at 0.5. Also, pressure distributions were\ud analyzed using CFD. Experimental and numerical results showed that the pressure\ud distribution pattern around tested objects and the pressure coefficient decreases as\ud increasing the L/D.The lowest value of the pressure coefficient occurs at the L/D = 1.0\ud for all Reynolds numbers. Coefficient of pressure is dominantly negative at the front\ud side of the square cylinder, suggesting that arrangement of the triangular cylinder in\ud front of the square one is very effective in drag reduction at square cylinder

GROUTED SLEEVE CONNECTION FOR PRECAST CONCRETE MEMBERS

Precast concrete structures have gained preference in the modern construction industry because of the multiple advantages they offer. The connection of precast members is an important aspect to consider in the design of structures with precast components. Grouted Sleeve connection, one of the famous connector types, is made of the trio of reinforced bars, high strength grouting materials and a ductile iron cylinder. This article compares the finding of recent experimental research findings on grouted sleeve connection and establishes the relationship between the three components of the connector to enhance the performance of the splicing agent. It is found that the tensile performance of the connector increases with the embedded length of the bar for a normal sleeve. An effective embedded length set between 6 and 8 times the diameter of the bar will maximize the tensile performance of the connector. The increase in diameter of the sleeve cylinder, the compressive strength of the grout and the length of the bar embedded and its surface will affect the bond performance and the mode of failure under tensile load

Vibroacoustic Response Data of Stiffened Panels and Cylinders

NASA has collected vibroacoustic response data on a variety of complex, aerospace structures to support research into numerical modeling of such structures. This data is being made available to the modeling community to promote the development and validation of analysis methods for these types of structures. Existing data from two structures is described, as well as plans for a data set from a third structure. The first structure is a 1.22 m by 1.22 m stiffened aluminum panel, typical of a commercial aircraft sidewall section. The second is an enclosed, stiffened aluminum cylinder, approximately 3.66 m long and 1.22 m in diameter, constructed to resemble a small aircraft fuselage with no windows and a periodic structure. The third structure is a filament-wound composite cylinder with composite stiffeners. Numerous combinations of excitation and response variables were measured on the structures, including: shaker excitation; diffuse acoustic field; velocity response from a laser vibrometer; intensity scans; and point acceleration