Wall Y+ approach for dealing with turbulent flow through a constant area duct

The study of flow development in curved ducts has been carried out since the last century. It is of fundamental interest because of its numerous applications in fluid engineering, such as flow through pipeline, in heat exchangers, ventilators, gas turbines, aircraft intakes, gas turbines and centrifugal pumps. The flow development through this type of curved ducts depends on its geometrical and dynamical parameters. In the present paper an approach has been made for dealing with turbulent flows within a curved duct with a rectangular cross-section and the result obtained from the experimental work has been compared and validated through numerical simulation by using Fluent CFD codes. The experiment is carried out at mass average velocity based on the inlet cross section as 40m/s. In the present study using the wall y⁺ as guidance in selecting the appropriate grid configuration and corresponding turbulence models are investigated. The standard k-ϵ, standard k-ω, Reynolds Stress Model (RSM) and Spalart-Almaras (SA) turbulence models are used to solve the closure problem. Their behaviours together with the accompanying near-wall treatments are investigated for wall Y⁺ value less than 5 covering the viscous sub layer and Y⁺ value ranging 5 to 30 in the buffer region. Notably, adopting a wall Y⁺ in the log-law region, where Y⁺ value is greater than 30, has also been taken care during the study. After various trials the optimum results were obtained for the K-ω model with a mesh count of 0.54 millions. In this, the value of Y⁺ was almost within the required range, i.e. 5<y⁺<30. Thus, it was the best mesh that is obtained by wall y+ approach and it has been observed that the K-ω model is also best turbulent model among the four turbulent models mentioned earlier, for predicting the flow through this type of geometry. In the second part of the study an attempt has been made to find out the best model by comparing the computational and experimental results. The mean velocity, static pressure, total pressure and velocity vector distributions at different sections for the 3 models K-ϵ, K-ω, SA and RSM have been presented in the form of contours and in vector plots.