Affiliation:
1. Mechanical Engineering Department, Indian Institute of Technology Kharagpur , Kharagpur 721302,
Abstract
The fluid dynamics of a bend — an apparently innocuous and abundantly occurring element of a fluid flow network found in engineering applications and in the natural world — is surprisingly complex. The qualitative and quantitative evolution of the primary and secondary flow fields as a fluid progresses through a bend, and its many nuances including the upstream and downstream effects, are documented comprehensively in the present work by invoking the power of high-quality computational fluid dynamics. Large ranges in Reynolds number (100 – 800) and curvature ratio (0.05 – 0.4) are covered, involving 32 separate, three-dimensional computations. The present computations are used to provide extensive new data and to discover substantial amount of new flow physics. As an example, the fluid dynamics of the process of the initiation of the Dean vortices in an initially vortex-free flow field has been established here, for the first time. It is demonstrated through the extensive computations that any two of the three non-dimensional numbers — viz., Reynolds number (Re), curvature ratio (δ), and Dean number (De) — are necessary to characterize the fluid dynamics of a bend; no single non-dimensional number is adequate in this respect. The present paper exposes the hidden consequence of the flow going through a bend on the fluid dynamics and flow loss in subsequent, downstream components.