Numerical simulations of buoyancy-driven flows using adaptive mesh refinement: structure and dynamics of a large-scale h
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O R I G I NA L A RT I C L E
Nicholas T. Wimer · Marcus S. Day · Caelan Lapointe · Michael A. Meehan · Amanda S. Makowiecki · Jeffrey F. Glusman · John W. Daily · Gregory B. Rieker · Peter E. Hamlington
Numerical simulations of buoyancy-driven flows using adaptive mesh refinement: structure and dynamics of a large-scale helium plume Received: 20 October 2019 / Accepted: 7 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The physical characteristics and evolution of a large-scale helium plume are examined through a series of numerical simulations with increasing physical resolution using adaptive mesh refinement (AMR). The five simulations each model a 1-m-diameter circular helium plume exiting into a (4 m)3 domain and differ solely with respect to the smallest scales resolved using the AMR, spanning resolutions from 15.6 mm down to 0.976 mm. As the physical resolution becomes finer, the helium–air shear layer and subsequent Kelvin– Helmholtz instability are better resolved, leading to a shift in the observed plume structure and dynamics. In particular, a critical resolution is found between 3.91 and 1.95 mm, below which the mean statistics and frequency content of the plume are altered by the development of a Rayleigh–Taylor (RT) instability near the centerline in close proximity to the plume base. Comparisons are made with prior experimental and computational results, revealing that the presence of the RT instability leads to reduced centerline axial velocities and higher puffing frequencies than when the instability is absent. An analysis of velocity and scalar gradient quantities, and the dynamics of the vorticity in particular, show that gravitational torque associated with the RT instability is responsible for substantial vorticity production in the flow. The grid-converged simulations performed here indicate that very high spatial resolutions are required to accurately capture the near-field structure and dynamics of large-scale plumes, particularly with respect to the development of fundamental flow instabilities. Keywords Helium plume · Adaptive mesh refinement · Buoyancy-driven flow · Kelvin–Helmholtz instability · Rayleigh–Taylor instability
1 Introduction Buoyancy-driven flows are ubiquitous in nature and engineering, spanning natural phenomena as diverse as thermals in the ocean, volcanic plumes, and wildland fires, as well as engineering applications such as flue gas systems and burners for industrial processing. With the growing availability and decreasing cost of high-performance computing resources, numerical simulations are being increasingly used to study these flows, in particular using large eddy (e.g., [1–12]) and direct numerical (e.g., [1,6]) simulations (LES and DNS, respectively). However, prior attempts to reproduce experimental results for larger-scale buoyancydriven flows, particularly in the context of LES for meter-scale plumes and pool fires [13], have proved N. T. Wimer · C. Lapointe · M. A. Meehan · A. S. Makowiecki · J. F. Glusman · J. W. Daily ·
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