Experimental Analysis of Developing Turbulent Flow in a Distorted Elliptical Duct by Laser-Doppler Velocimeter.

Abstract

An experimental study of developing turbulent flow in a distorted ellptical duct was carried out at Reynolds number 0.988×105 by using laser-Doppler velocimeter. In a distorted elliptical duct, the configuration of cross section varies from elliptical to circular and from circular to elliptical along streamwise direction with a constant cross sectional area constant. Three components of velocity and the five of the five stress components were measured at seven different locations to clarify the development of turbulent structure. As a result of this experimental study, it was found that the distributions of streamwise velocity were influenced by the secondary flow and the averaged intensity of the secondary flow over cross section showed the maximum value at midway between inlet and outlet of a distorted duct. Adding to these points, experimental results displayed that the secondary flow of the second kind at inlet section transformed into that of the first kind induced by pressure gradient at a little distance from the inlet and that of the first kind again transformed that of the second kind at the outlet section. The location of the maximum intensity of streamwise normal stress moves gradually from near upper wall to near side wall as the flow develops. The two kinds of shear stress between streamwise fluctuating velocity and cross sectional fluctuating velocity shows distributions different from each other.