Lift And Drag Forces On A Submerged Circular Cylinder

Abstract

ABSTRACT Correlations for drag coefficients of circular cylinders in a symmetrical flow field have been available in the technical literature for a number of years. However, correlations for drag coefficients on a circular cylinder adjacent to a plane wall are not available in the literature. In addition to the drag forces, the aforementioned geometry of a cylinder adjacent to a plane results in a lift force on the cylinder due to the induced flow. The correlations for this resultant lift coefficient are also unavailable in literature. Investigation of the relationships between the various flow and geometric parameters for the case of a full-size (diameters ranging in size from 6 to 30 in.) circular cylinder submerged in a semi-infinite induced flow stream was undertaken in the U. of Tulsa low speed wind tunnel and the U. of Tulsa-Williams Brothers water tunnel. This was accomplished by placing full-size test cylinders adjacent to a flat plate. Data was recorded for the test cylinders in both the vertical and horizontal position. The depth of the semi-infinite flow field was varied depending on the size of the test cylinder to eliminate the hydraulic jump effects. An empirical correlation of lift coefficients vs Reynolds number and drag coefficients vs Reynolds number were obtained for smooth and rough pipe. INTRODUCTION In the design of'; pipelines which traverse the bed of a flowing stream, hydrodynamic lift and drag forces must be considered. Insufficient strength can result in pipeline rupture due to drag. Insufficient weighting can lead to oscillation and fatigue due to lift forces. Accordingly, an experimental study was undertaken to measure and correlate lift and drag forces. The study was conducted in a water tunnel using pipes ranging in diameter from 6 to 30 in. Pipes were tested in an "as received'; condition and in an artificially roughened condition intended to simulate a concrete jacket. LABORATORY EQUIPMENT Equipment utilized during this investigation included the U. of Tulsa water tunnel. The tunnel circulates water through a test section. In order for flow in deep channels to be simulated and to avoid the difficulties involved in constructing and operating a water tunnel with a very deep test section, a vane is provided in the test section simulating a fluid streamline in very deep flow. The effect of the vane, or solid streamline, is to eliminate free surface effects resultant from the placement of the test object in the shallow test section. The tunnel test section with vane is pictured schematically in Fig. 1. Circulation in the water tunnel is accomplished by means of a stationary propeller driven by an automobile engine. Tunnel velocities are measured by a pitot tube coupled to a mercury inclined manometer. Test object pressures are measured on a water manometer board.