Numerical Analysis of Turbulent Flow in a Helically Curved Pipe

Abstract

Numerical analysis has been performed for three-dimensional fully developed turbulent flow in a helically curved pipe by using an algebraic Reynolds stress model. This kind of duct with helical sharp has been applied for passage employed in air conditioner and heat exchanger in many engineering fields. It is interesting point whether the present method can predict correctly the complicated turbulent flow in helically curved pipe, or not. In the numerical calculation, an algebraic Reynolds stress model is introduced to predict correctly anisotropic turbulence. Besides, boundary fitted-coordinate system is used as the method for coordinate transformation to set boundary conditions along complicated shape of helical curved pipe. Three types of helical pipe with different torsion ratio are selected to calculate turbulent flow structure in this research. Calculated results of streamwise mean velocity, secondary flow vectors and turbulence intensity are compared with the experimental data in order to examine the validity of the presented method. As a result of this calculation, it was found that the present method could predict reasonably the streamwise velocity, i.e., the movement of maximum mean velocity from outer wall to inner wall with increasing torsion ratio is reproduced correctly by the presented method. Besides, calculated results of secondary flow are relatively good agreement with the experiment except for the middle point of rotation flow generated by secondary flow in circular cross section. As for the turbulent intensity, the presented method is able to predict characteristic features of its distribution qualitatively but has tendency to underestimate the experimental results. Six components of Reynolds stresses are presented in helical pipe because there is no data to show these distributions. Calculated results suggest that the presented method can predict the turbulent flow in helical pipe.