Drag Coefficient Of Circular Cylinder Research Articles

Drag coefficient of circular cylinder in axial flow of water for a wide range of length to diameter ratios

ABSTRACT An experimental campaign was conducted to determine drag coefficients of circular cylinders in axial flow of water for a wide range of length-to-diameter ratios (L/D) from 2 to 35. Drag force acting on the circular cylinders was acquired at a velocity of 2 to 6 m/s, which corresponds to the Reynolds numbers of 2.2 × 105 to 7.0 × 105. The experimental data were validated by analysis using the commercial CFD code, Star-CCM+. The measured drag coefficients increased monotonically as the L/D increased with the range of Reynolds numbers, and were almost constant regardless of the Reynolds number. The drag coefficient was decomposed by the term of form drag and skin friction. As the value of L/D increased, the drag coefficient increased due to the skin friction drag term. The drag coefficient correlation was proposed as a function of L/D. The predicted values were consistent with both the experimental data and numerical simulation results. Furthermore, this correlation was applied to a fuel assembly with a channel box, it was shown that the drag coefficient can be predicted for a wide range of Reynolds numbers by specifying an appropriate form drag term.

Numerical investigations on drag coefficient of circular cylinder with two free ends in roller bearings

Abstract In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing cavity – that is acting against the roller movement – is usually computed with a two-dimensional model of flow around a cylinder of infinite length. However rollers are of finite length, and the flow is perturbed by the two free ends, the surrounding rings, the cage and other rolling elements. In this article, the Computational Fluid Dynamics (CFD) method is employed to analyze first the flow around one finite-length circular cylinder with two free ends in an open space. Then the model is changed to one finite cylinder and then several in-line circular cylinders sandwiched by two flat walls, which represents a simplified approach. The results indicate that both the flow pattern around the cylinder and its drag coefficient are modified in comparison with the two-dimensional model. Finally a relationship between the drag coefficient and the Reynolds number suitable for circular cylinder in roller bearings is proposed.

Wind-tunnel blockage effect on drag coefficient of circular cylinders

This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti's formula or Maskell's theory with <TEX>${\varepsilon}$</TEX>=0.96. In the super-critical regime, one should prefer using Glauert's formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the flow regimes.

FLUID FORCES ACTING ON MULTIPLE ROWS OF CIRCULAR CYLINDERS IN OPEN-CHANNEL FLOW

Fluid forces acting on a circular cylinder in multiple rows of circular cylinders installed across the whole parts of channel width and partial parts of channel length in an open channel are measured by load cell with three components. Drag coefficient CD of this circular cylinder with large arrangement density λ is larger than the drag coefficient of circular cylinder in uniform flow. Roughness coefficients known as Manning's n for this multiple rows of circular cylinders are evaluated by using these Drag coefficients CD measured. Roughness coefficient of multiple rows of circular cylinders in open channel increases with increase of arrangement density λ and water depth. Profiles of gradually varied flow in multiple rows of circular cylinders are evaluated well by using these Manning's n.

1825 螺旋型スクリューの推進特性の実験

A large scale model is considered for a micro robot imitating the bacterium with a single flagellum such as Vibrio. In order to estimate the driving force exerted to a helical screw propella (flagella propella), we made a floating scale. By use of the floating scale and I-CCD camera, we measured the driving force and the rotation rate for sevral kinds of helical screw propella. The characterstics of driving force was compared to the drag coefficient of circular cylinder in a range of Reynolds number (10)^2&acd;(10)^3.

Remarks about variations in the drag coefficient of circular cylinders moving through water

Numerous flexible underwater structures (towing and mooring lines, trawl lines, oil platform risers, submarine periscopes, etc.) are used in navigation and exploitation of sea resources. Current technologies require a knowledge of the hydrodynamic forces exerted on these structures. All theoretical calculations employ hydrodynamic coefficients, in particular the drag coefficient for which a review of the literature is provided. An original scheme is proposed, based on the influence of transverse velocity, which can account for the apparent increase in the drag coefficient of a submerged cylinder undergoing vibration as a result of hydrodynamic forces. Several applications are presented which show that the use of empiric values for the drag coefficient of a cylinder vibrating on the order of 1.8 is still perfectly justified.