Vorticity and Coherent Structures – Part I

“Big whorls have little whorls that feed on their velocity, and little whorls have lesser whorls and so on to viscosity” – Lewis Fry Richardson Introduction Although this post shall take great advantage of the notion of vorticity to get a glimpse on the small scale organized fluid elements of significant life-time and scale we call …

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Transition to Turbulence Series – Transition Scenarios

Motivation: There are various type of instabilities for a number of flow patterns. The intention of this post is to investigate how these instabilities may trigger laminar-turbulent transition. I shall do my best to classify these routes leading from a stable laminar to a disturbed one flow, and base my path on the mechanisms responsible …

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All About CFD – Mapping the Territory

My name is Tomer (Tom) Avraham. I have been around fluid dynamics, CFD, and Physics in general for the past 20 years. Spent time at workplaces that I can nothing but own great gratitude for (Israeli Aerospace Industry, Elbit, head of engineering in Ansys channel partner, a consultant to STAR-CCM+ channel partner), then enabled myself …

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Nonmodal instability of PDE discretizations  – The Need For Linear Growth Mechanisms – Prolog

Turbulence is the name given to imperfectly understood class of chaotic solutions to the NSE in which many (and denied a spectral gap) degrees of freedom are excited (If we call a dog’s tail a leg than how many legs does a dog have?… It’s still four!) H. Aref 1999. This post serves as somewhat …

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Nonmodal instability of PDE discretizations  – Secondary Instability and Floquet Analysis

Velocity components of the Floquet mode. Introduction The main principle of secondary instability could be described as follows: when disturbances add up to a basic undisturbed flow, they grow such that their amplitude could be described as finite. As a result from the main instability they may achieve saturation characterized in a way as a …

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