Investigation of hydrodynamic characteristics of laminar flow condition around sphere using PIV system

A H Abed,S E Shcheklein

doi:10.1088/1742-6596/1015/3/032001

Abstract

This paper aims to determine the hydrodynamic characteristics of flow around the sphere in unsteady state condition. An experimental test-rig was designed and constructed for this purpose with the application of an adjusted laser optics system. It is based on the technology of pulsed particle visualization of micro tracers in the cross section per unit time interval. Visualization with Particle Image Velocimetry (PIV-system) is used to study the properties of the flow such as its structure. The PIV-system is the most accepted technique allowed one to measure the instantaneous velocity distribution in fluid applications. In this experimental study, o-ring is used to simulate turbulence on the sphere surface and creates very high-level fluctuations, which creates the flow undergoing a laminar-to-turbulent transition. This transition leads to a delay of the separation point of flow from the sphere surface causing a significant reduction in the drag coefficient, reaching 45%. New results obtained can be useful in the development of numerical validation as well as in design processes.

Highlights

Investigation of flow hydrodynamic characteristics around a sphere in a uniform flow such as vortex shedding mechanisms, velocity field, pressure and drag coefficients is necessary in a practical field such as nuclear, chemical and energy fields, but it has a good benchmark to predict the flow characteristics for designing purposes [1]
The results of the drag coefficient are compared with the past studies as shown in figure 3, which show the variation of drag coefficient versus Reynolds number with 8.4%
The drag force is proportionate to the square of the velocity and the increase in velocity at higher Reynolds number is generally more than offsets in the decrease of the drag coefficient as shown in equation (2)

Summary

Introduction

Investigation of flow hydrodynamic characteristics around a sphere in a uniform flow such as vortex shedding mechanisms, velocity field, pressure and drag coefficients is necessary in a practical field such as nuclear, chemical and energy fields, but it has a good benchmark to predict the flow characteristics for designing purposes [1]. There are numerous numerical and experimental studies concentrated on flow characteristics and flow control to reduce the drag coefficients, using a sphere with dimples, roughened, vented spheres and other control methods [2]. In the early studies [3,4,5,6,7], the flow characteristics around a smooth sphere located in a uniform flow and further investigations cited therein were undertaken. In the previous studies of the flow past a sphere, Zhao et al [9] studied the vortex shedding, the drag coefficient and the flow structure of a sphere in the proximity of a flat plate using direct numerical simulation.

Objectives

Results

Conclusion