A numerical study of laminar and turbulent flows in a two‐dimensional bend with or without a guide vane

Abstract

SUMMARYA numerical study of the flow in a two-dimensional 90" circular-arc bend is presented. The study is based on the solution of the governing equations using a finite volume technique. Both laminar and turbulent flows are considered. Particular attention is given to the occurrence and size of the separation regions and, in this respect, the effects of Reynolds number and bend radius to height ratio are discussed. The study includes the effect of a guide vane, placed in the bend, on the flow characteristics. It is shown that the emerging velocity distribution is more uniform than that associated with flow in a bend without a guide vane. The presence of a guide vane is shown to suppress the formation of regions of flow separation. Comparisons are made between the effects on the flow of two different designs of guide vane.

Computational Fluid Dynamics Model for a C-Shaped Sodium Hydroxide Freeze Valve

“…The flow of NaOH in the freeze valve is expected to be laminar due to the very low fluid velocity and the lack of a pressure differential. According to Kotb et al (Kotb et al, 1988), if the ratio of the curvature of the pipe to its diameter is greater than 3.5, which in our case is 4, the flow is fully attached for Reynolds numbers below 10 5 . Additionally, he Grashof number is smaller than 10 5 which is below the threshold of the transition to the turbulent boundary layer (Smith et al, 2013).…”

“…Additionally, he Grashof number is smaller than 10 5 which is below the threshold of the transition to the turbulent boundary layer (Smith et al, 2013). The only driving force for the flow is the natural convection which can be modelled with both laminar and low-Reynolds turbulent models (Kotb et al, 1988;Smith et al, 2013), each yielding similar results for low Grashof numbers. Therefore, due to the higher stability and low computing time, the laminar model was used for all simulations.…”

Optimization Study of Guide Vanes for the Intake Fan-Duct Connection Using CFD

“…Several authors have developed specific studies that guide the design, which have been considered for the development of this research work. The state of the art presents various studies and applications, many of them concluding in the reduction of the shock factor or pressure loss coefficient through the incorporation of guide vanes [2][3][4][5][6][7][8][9]. Within these studies, and by Enayet et al 1982 [10], some incorporate various designs of guide vanes and, therefore, have evaluated the benefits of both the reduction of the shock factor (X) and the distribution of the flow downstream of the elbow, oriented to obtain a less turbulent flow.…”

“…In addition, he emphasizes that an elbow with guide vanes can be 800% more efficient than the same elbow without guide vanes. Kotb and Ward-Smith 1988 [6] point out that the main method to improve the performance of steep curves is to introduce one or more guide vanes, due to two main reasons: the first is to improve the shape of the velocity profile emerging from the elbow, reducing the peak velocities tending to an average; the second is to reduce the pressure gradient at the elbow between high and low pressures to tend to an average. Regarding the latter, its use is recommended only in elbows with high radio of curvature, as it implies the introduction of additional surfaces that can increase speed gradients and shear forces, and by default increases the friction factor.…”